Construction method of deep foundation pit steel sheet pile support structure under complex geological conditions

Abstract

The application discloses a construction method of a deep foundation pit steel sheet pile supporting structure under complex geological conditions, and relates to the field of construction methods of deep foundation pit steel sheet pile supporting structures. The method comprises the following steps: obtaining foundation pit survey data, dividing the foundation pit into multiple geological control sections according to the thickness of soft soil, the buried depth of water-permeable layers, the top boundary buried depth of strongly weathered rock layers, the rock surface fluctuation amplitude and the distance of structures, determining the differentiated construction parameters of each geological control section, including the steel sheet pile type, the pile length, the embedded depth, the pile sinking mode, the lock opening waterproof parameters and the surrounding purlin and internal support arrangement parameters, configuring the steel sheet pile according to the corresponding construction parameters of each section, sinking and setting by using the vibration and static pressure combined pile sinking mode, setting the water-swelling sealing element, the sealing material and the grouting channel at the lock opening to form a triple waterproof structure, collecting monitoring data in the process of layered excavation, and updating the construction parameters of the section and the adjacent sections when the monitoring data exceeds the corresponding threshold value. The application can effectively improve the pile sinking quality and the structural stability of the deep foundation pit steel sheet pile supporting structure under complex geological conditions.

Description

Technical Field

[0001] This invention relates to the field of engineering construction technology, and in particular to a construction method for a steel sheet pile support structure for deep foundation pits under complex geological conditions. Background Technology

[0002] Sheet pile support for deep foundation pits is widely used in foundation pit engineering due to its advantages such as fast construction speed and recyclability. The traditional construction method of sheet pile support usually involves first designing a uniform sheet pile type, pile length and embedment depth based on the overall excavation depth of the foundation pit and preliminary geological survey data. Then, a single pile driving method (such as full-process vibratory hammer driving) is used to drive the sheet piles into the ground to the design elevation. Subsequently, walers and internal supports are installed, and finally the foundation pit soil is excavated in layers. During the excavation process, routine horizontal displacement and settlement monitoring are carried out at a fixed monitoring frequency. However, in complex geological conditions (such as the intermingling of soft soil layers, permeable layers, and strongly weathered rock layers with drastic top undulations), using a uniform and single pile driving method can lead to the following defects: First, when the same sheet pile penetrates the soft soil layer and enters the strongly weathered rock layer, it is very easy to encounter difficulties in driving the pile, pile tilting, or even hammer refusal, making it difficult to drive to the design elevation; Second, using piles of equal length in sections with undulating rock surfaces can result in some piles being insufficiently embedded while others are too long to be driven in, causing abrupt changes in the stiffness of the support structure and uneven stress; Third, the interlocks of the sheet piles are prone to cracking and leakage at the permeable layer and the interface between soft and hard layers due to stratum displacement; Finally, the monitoring data in traditional construction is often only used for post-construction alarms and fails to establish dynamic linkage with the specific construction parameters of each complex section, making it impossible to resolve local stress concentration and seepage risks in a timely manner during excavation through local adjustments (such as internal support pre-stressing, grouting, or dewatering).

[0003] Therefore, the key technical problem of the existing technology is that it is difficult to carry out differentiated support design and construction for complex geological conditions, resulting in poor pile quality, uneven structural stress, and easy leakage and deformation loss of deep foundation pit steel sheet pile support under complex geological conditions. Summary of the Invention

[0004] This invention provides a construction method for deep foundation pit steel sheet pile support structures under complex geological conditions. It enables differentiated support design and construction for complex geological conditions, thereby effectively improving the pile quality and structural stability of deep foundation pit steel sheet pile support under complex geological conditions.

[0005] One embodiment of the present invention provides a construction method for a deep foundation pit steel sheet pile support structure under complex geological conditions, comprising: Obtain the foundation pit investigation data of the foundation pit to be excavated. The foundation pit investigation data includes the stratum distribution parameters, groundwater level, permeability coefficient of each stratum, foundation pit excavation depth, foundation pit boundary position and surrounding structure position. The stratum distribution parameters include the thickness of soft soil layer, the burial depth of permeable layer, the burial depth of the top boundary of strongly weathered rock layer and the undulation amplitude of rock surface. Based on the geological distribution parameters and the distance between the structures determined by the location of the foundation pit edge and the location of the surrounding structures, the foundation pit is divided into multiple geological control sections along the circumference. For each geological control section, the construction parameters for that geological control section are determined by combining the excavation depth of the foundation pit, the stratum distribution parameters, and the permeability coefficient of each stratum. The construction parameters include the sheet pile type, pile length, embedment depth, pile driving method, interlock waterproofing parameters, and waler and internal support arrangement parameters. According to the sheet pile type, pile length and embedment depth corresponding to each geological control section, the sheet piles at each pile position are configured, and each sheet pile is driven into the corresponding design elevation according to the corresponding pile driving method. According to the aforementioned interlock waterproofing parameters, interlock waterproofing nodes are arranged at the corresponding heights of the steel sheet pile interlocks, the permeable layer, and the corner positions of the foundation pit; Install the walers and internal supports according to the waler and internal support layout parameters, and then carry out layered excavation after installation; Monitoring data were collected from various geological control sections during the layered excavation process; When the monitoring data exceeds the corresponding monitoring threshold, the construction parameters of the geological control section to which the monitoring data belongs and its adjacent geological control sections are updated.

[0006] Compared with the prior art, the embodiments of the present invention have the following beneficial effects: This invention, through acquiring multi-dimensional survey data including geological distribution and groundwater level, divides the foundation pit circumferentially into multiple geological control sections. Differentiated construction parameters (including sheet pile type, pile length, driving method, interlock waterproofing parameters, and waler and internal support layout parameters) are determined for each section based on geological conditions and excavation depth. Sheet piles are configured according to these parameters, interlock waterproofing nodes are arranged, and walers and internal supports are installed before layered excavation. Monitoring data for each section is collected during excavation, and when the monitoring data exceeds a threshold, the construction parameters for that section and adjacent sections are updated. This segmented, differentiated design ensures that the support structure of each section matches the geological conditions, avoiding difficulties in pile driving, sudden changes in stiffness, and interlock leakage caused by single pile driving. Dynamic monitoring and parameter updates enable real-time feedback and adjustment during construction, mitigating localized stress concentration and seepage risks. In summary, the embodiments of the present invention, by adopting differentiated support design and construction for complex geological conditions and combining dynamic monitoring and feedback adjustments, can effectively adapt to complex geological conditions, improve the quality of pile formation and the overall stability of the support structure, and avoid uneven stress and uncontrolled deformation of the structure. Attached Figure Description

[0007] Figure 1 This is a schematic flowchart of a construction method for a deep foundation pit steel sheet pile support structure under complex geological conditions, provided by an embodiment of the present invention. Figure 2 This is a schematic diagram of a steel sheet pile support structure for deep foundation pits under complex geological conditions, provided by an embodiment of the present invention. Figure 3 This is a construction schematic diagram of a deep foundation pit steel sheet pile support structure under complex geological conditions provided by an embodiment of the present invention; Figure 4 This is a plan view of the water pumping station foundation pit provided in an embodiment of the present invention; Figure 5 This is an AA cross-sectional view of the water pumping station foundation pit provided in an embodiment of the present invention. Detailed Implementation

[0008] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0009] See Figure 1 and Figure 2 An embodiment of the present invention provides a construction method for a deep foundation pit steel sheet pile support structure under complex geological conditions, comprising: S1, Obtain the foundation pit survey data of the foundation pit to be excavated. The foundation pit survey data includes stratum distribution parameters, groundwater level 950, permeability coefficient of each stratum, foundation pit excavation depth, foundation pit edge position and surrounding structure position. The stratum distribution parameters include soft soil layer thickness 700, permeable layer depth 600, strongly weathered rock layer top boundary depth 900 and rock surface undulation amplitude. S2, based on the geological distribution parameters and the distance between the structures determined by the location of the foundation pit edge and the location of the surrounding structures, the foundation pit is divided into multiple geological control sections along the circumference; S3. For each geological control section, the construction parameters of the geological control section are determined by combining the excavation depth of the foundation pit, the stratum distribution parameters and the permeability coefficient of each stratum at the location of the geological control section. The construction parameters include the steel sheet pile type, pile length, embedment depth, pile driving method, interlock waterproofing parameters and the arrangement parameters of waler 300 and internal support 400. S4, configure the sheet pile support structure 200 at each pile position according to the sheet pile type, pile length and embedment depth corresponding to each geological control section, and drive each sheet pile to the corresponding design elevation according to the corresponding pile driving method; S5. According to the aforementioned interlock waterproofing parameters, interlock waterproofing nodes are arranged at the corresponding heights of the steel sheet pile interlock, the permeable layer 600, and the corner positions of the foundation pit. S6. Install the waler 300 and inner support 400 according to the arrangement parameters of the waler 300 and inner support 400, and then carry out layered excavation after installation; S7. During the layered excavation process, monitoring data of each geological control section is collected. The monitoring data includes the horizontal displacement data of each sheet pile support structure 200, the axial force data of each internal support 400, the settlement data of surrounding structures, and the groundwater level 950. S8. When the monitoring data exceeds the corresponding monitoring threshold, update the construction parameters of the geological control section to which the monitoring data belongs and its adjacent geological control sections.

[0010] Compared with the prior art, the embodiments of the present invention have the following beneficial effects: This invention, through acquiring multi-dimensional survey data including geological distribution and groundwater level, divides the foundation pit circumferentially into multiple geological control sections. Differentiated construction parameters (including sheet pile type, pile length, driving method, interlock waterproofing parameters, and waler and internal support layout parameters) are determined for each section based on geological conditions and excavation depth. Sheet piles are configured according to these parameters, interlock waterproofing nodes are arranged, and walers and internal supports are installed before layered excavation. Monitoring data for each section is collected during excavation, and when the monitoring data exceeds a threshold, the construction parameters for that section and adjacent sections are updated. This segmented, differentiated design ensures that the support structure of each section matches the geological conditions, avoiding difficulties in pile driving, sudden changes in stiffness, and interlock leakage caused by single pile driving. Dynamic monitoring and parameter updates enable real-time feedback and adjustment during construction, mitigating localized stress concentration and seepage risks. In summary, the embodiments of the present invention, by adopting differentiated support design and construction for complex geological conditions and combining dynamic monitoring and feedback adjustments, can effectively adapt to complex geological conditions, improve the quality of pile formation and the overall stability of the support structure, and avoid uneven stress and uncontrolled deformation of the structure.

[0011] As one example, dividing the foundation pit into multiple geological control sections along the circumference includes: The sections between adjacent exploration points along the perimeter of the foundation pit are taken as initial sections, and the control attributes of each initial section are determined according to the geological distribution data and the distance to the structures. Specifically, the initial section with a soft soil layer thickness of 700 mm greater than the preset soft soil thickness value is defined as the soft soil control section; the initial section with a permeable layer depth of 600 mm within the excavation depth range of the foundation pit is defined as the permeable control section; the initial section with a top boundary of the strongly weathered rock layer of 900 mm below the bottom surface of the foundation pit of 110 mm and within the preset embedment influence depth range is defined as the strongly weathered rock control section; the initial section with a height difference between the top boundaries of the strongly weathered rock layer of 900 mm between adjacent exploration points exceeding the preset rock surface undulation value is defined as the soft-hard boundary control section; and the initial section with a distance between the structures less than the preset protection distance is defined as the environmentally sensitive control section.

[0012] In this embodiment, since the strata conditions along the perimeter of the foundation pit often vary, adjacent exploration points are used as initial sections, and their control attributes are determined separately to ensure that each geological control section has relatively uniform strata conditions. In the soft soil control section, sections with thicker soft soil are reinforced with piles of higher bending stiffness and greater embedment depth; in the permeable soil control section, sections where the permeable layer is within the excavation depth range are identified and reinforced with waterproofing; in the strongly weathered rock control section, sections with moderately buried hard rock are reinforced with composite sheet piles; in the soft-hard boundary control section, sections with drastically undulating rock surfaces are reinforced with variable pile lengths to coordinate stiffness differences; and in the environmentally sensitive control section, sections adjacent to surrounding structures are subject to stricter deformation control standards.

[0013] Specifically, in this embodiment, detailed geological survey data of the excavation pit is first obtained. Taking the 620 excavation pit of a sewage treatment plant in a coastal area, which includes a coarse screen and an influent pumping station, as an example, the pit has a planar dimension of approximately 20 meters × 10 meters, and an excavation depth of H. For example, several survey points are arranged along the perimeter of the pit, numbered ZK1 to ZK8. The horizontal distance between adjacent survey points is determined by the site perimeter and the degree of stratum variation. The stratum distribution parameters are obtained at each survey point through drilling sampling and indoor geotechnical tests. The drilling depth is greater than the sum of the excavation depth and the designed embedment depth to ensure penetration of all strata that may affect the stability of the pit.

[0014] For example, the site's strata, from top to bottom, are: plain fill layer 710, silt layer 700, fine sand layer 600, residual sandy clay layer 720, and loose, strongly weathered basalt layer 900. The groundwater level is 950, with a depth determined based on on-site water level observations. There is a three-story brick-concrete residential building (i.e., surrounding structures) within the pre-set protection distance outside the excavation pit boundary. Its foundation is a strip foundation, with a depth determined based on on-site survey data, and it is sensitive to settlement caused by the excavation.

[0015] The section between two adjacent exploration points along the circumference of the foundation pit is taken as an initial section. Taking the section between ZK1 and ZK2 as an example for analysis: the length of this section is determined according to the distance between adjacent exploration points. Reading the profile data from ZK1 and ZK2: Borehole ZK1 revealed a 700mm thick silt layer, which is the first exploration thickness value; borehole ZK2 revealed a 700mm thick silt layer, which is the second exploration thickness value, with an average thickness greater than the preset soft soil thickness value. Borehole ZK1 revealed a 600mm top elevation of the fine sand layer, which is the top and bottom elevation of the first permeable layer; borehole ZK2 revealed a 600mm top elevation of the fine sand layer, which is the top and bottom elevation of the second permeable layer. The bottom elevation of this layer is within the excavation depth range of the foundation pit. Borehole ZK1 revealed a 900mm top boundary depth of the loose, strongly weathered basalt layer, which is the top boundary depth of the first strongly weathered rock layer; borehole ZK2 revealed a 900mm top boundary depth of the loose, strongly weathered basalt layer, which is the top boundary depth of the second strongly weathered rock layer, with an elevation difference exceeding the preset rock surface undulation value. Additionally, there are residential buildings within the preset protection distance outside this section.

[0016] According to the judgment rules: the average thickness of the silt layer at 700 meters in this section is determined to be greater than the preset soft soil thickness value based on the survey results, and is judged as a "soft soil control section"; the bottom elevation of the fine sand layer at 600 meters in this section corresponds to the bottom elevation of the permeable layer within the excavation depth of the foundation pit, and is judged as a "permeable control section"; the top boundary of the loose, strongly weathered basalt layer at 900 meters in this section has an elevation difference between ZK1 and ZK2 that exceeds the preset rock surface undulation value, and is judged as a "soft-hard boundary control section"; the distance between the residential buildings and structures on the outer side of this section is less than the preset protection distance, and is judged as an "environmentally sensitive control section".

[0017] If the top boundary of the 900mm highly weathered rock layer in another section (such as between ZK5 and ZK6) is within the preset embedment influence depth range of 110mm below the bottom of the foundation pit excavation, then this section is only identified as a "highly weathered rock control section". If the 600mm permeable layer between ZK7 and ZK8 is not within the excavation depth range and the 700mm thickness of the soft soil layer is less than the preset soft soil thickness value, the rock surface undulation is less than the preset rock surface undulation value, and the distance between structures is greater than the preset protection distance, then this section will not trigger any special control attributes and will be designed according to conventional support parameters.

[0018] If an initial section simultaneously meets multiple criteria (such as sections ZK1 and ZK2 mentioned above), then the subsequent construction parameters for that section must consider the combined requirements of four control types. For example, the sheet pile type for this section must simultaneously meet the requirements for high bending stiffness in the soft soil control section, high waterproofing level in the permeable control section, variable pile length in the soft-hard boundary control section, and strict displacement control in the environmentally sensitive control section. The most stringent value among the parameters corresponding to each control type will be used as the design basis for that section.

[0019] For example, determining the construction parameters for the geological control section includes: Based on the excavation depth of the foundation pit, the groundwater level of 950, the permeability coefficient of each stratum, and the stratum distribution data of the geological control section, anti-overturning calculation, anti-sliding calculation, pit bottom heave calculation, seepage stability calculation, and displacement limit calculation are performed respectively. The maximum value of the embedment depth obtained from each calculation is determined as the embedment depth of the geological control section, and the sum of the foundation pit excavation depth, the embedment depth, and the pile top construction allowance is determined as the pile length of the geological control section.

[0020] In this embodiment, independent support structure calculations are performed for each geological control section. The maximum embedment depth from each calculation result is taken as the embedment depth of that section to ensure that the section has sufficient safety reserves under all possible failure modes. The overturning resistance calculation ensures that the sheet pile support structure 200 will not rotate and become unstable around the pile bottom; the sliding resistance calculation ensures that overall sliding will not occur; the pit bottom heave resistance calculation ensures that the soft soil at the pit bottom will not heave and fail; the seepage stability calculation ensures that piping or soil erosion will not occur; and the displacement limit calculation ensures that the horizontal displacement is controlled within the allowable range.

[0021] For each identified geological control section, the corresponding excavation depth H of the foundation pit was obtained. The groundwater stability level of 950 mm was determined based on on-site water level observations. The permeability coefficients of each stratum (the permeability coefficient of the fine sand layer at 600 mm was determined based on experimental measurements) and stratum distribution data were also obtained. Deep foundation pit support structure design software was used for segmented calculations, employing an incremental method to simulate the entire process of layered excavation and the installation of 400 mm internal supports.

[0022] 1. Overturning resistance calculation. Based on the excavation depth H of the foundation pit and the soil distribution parameters, calculate the active and passive earth pressures on the inner (foundation pit side) and outer (soil side) sides of the 200mm sheet pile support structure. Active earth pressure coefficient K. a According to Rankine's earth pressure theory: K a =tan²(45°-φ / 2), where φ is the internal friction angle of each soil layer. Passive earth pressure coefficient K p =tan²(45°+φ / 2). For a soft soil layer of 700, the active earth pressure p is calculated using the undrained shear strength parameter: a =γ·z-2·c u passive earth pressure p p =γ·z+2·c u , where c u The undrained shear strength is determined by indoor geotechnical tests or design values. A moment balance equation is established with the bottom 200mm of the sheet pile support structure as the center of rotation: ΣM -ΣM o ≥0, where ΣM ΣM represents the overturning moment of the passive zone earth pressure on the pile bottom. oThe overturning moment of the active earth pressure on the pile bottom. Overturning safety factor K. ot =M / M o K is required ot Not less than the preset overturning safety factor threshold. By testing different embedment depths, the minimum embedment depth D1 that satisfies the safety factor requirement is determined. It is calculated that when the calculated embedment depth value makes K... ot When the preset anti-overturning safety factor threshold is met, the corresponding trial value is determined as D1.

[0023] 2. Sliding resistance calculation. Calculate the total horizontal thrust (resultant force of active earth pressure) acting on the sheet pile support structure 200 mm and the horizontal resistance of the soil at the pile bottom (resultant force of passive earth pressure). Calculate the sliding resistance safety factor K. sl =F / Fd, where F Let Fd be the horizontal resistance and Fd be the horizontal thrust. Then, K is required. sl Not less than the preset anti-slip safety factor threshold. Through trial calculations at different embedment depths, when the calculated embedment depth value makes K... sl When the preset anti-slip safety factor threshold is met, the corresponding trial value is determined as D2.

[0024] 3. Calculation of Heave Resistance at the Pit Bottom. Taking the soft soil below 110mm from the bottom of the excavation pit as the analysis object, calculate the balance between the weight of the superstructure on the soft soil and the heave tendency of the soft soil below 110mm from the bottom of the excavation pit. Heave resistance safety factor K. he =W / F up Where W represents the weight of the soft soil layer above the bottom of the foundation pit (110 kN / m), and F represents the weight of the soft soil layer above the bottom of the foundation pit (kN / m). up The heave force (kN / m) of the soft soil at the bottom of the pit is required to be K. he Not less than the preset anti-heave safety factor threshold. After testing, when the calculated embedment depth value makes K... he When the preset anti-uplift safety factor threshold is met, the corresponding trial value is determined as D3.

[0025] 4. Seepage stability calculation. Determine the water head difference Δh between the inside and outside of the foundation pit. v The Δh v The elevation difference between the bottom of the excavation pit (110m elevation) and the stable groundwater level (950m elevation) is determined. The seepage force J=γ along the most dangerous seepage path is calculated. v ×(Δh v / L se ), where L se γ is the length of the most dangerous seepage path. v The specific gravity of water. Safety factor K for preventing seepage. se =γ′ / J, where γ′ is the effective unit weight of the soil, and K is required. seNot less than the preset seepage resistance safety factor threshold. Through trial calculations, when the calculated embedment depth makes K... se When the preset anti-seepage safety factor threshold is met, the corresponding trial value is determined as D4.

[0026] 5. Displacement Limit Calculation. An incremental method was used for the internal force analysis of the support structure. The excavation process was divided into multiple construction conditions, each set according to the layered excavation depth and the 400mm installation elevation of each internal support. For each condition, the horizontal displacement of the sheet pile support structure was calculated at 200mm. The maximum horizontal displacement δ for each condition was required to be calculated. max ≤βH, where β is the preset horizontal displacement control coefficient. After trial calculation, when the calculated embedment depth makes the maximum horizontal displacement in each working condition meet the displacement limit requirement, the corresponding calculated value is determined as D5.

[0027] After completing the above five verifications, the maximum value among D1, D2, D3, D4, and D5 is taken as the embedment depth D=max(D1,D2,D3,D4,D5) for this geological control section. Finally, based on the excavation depth H, the embedment depth D, and the pile top construction allowance Δh, the length L=H+D+Δh of the 200mm sheet pile support structure for this geological control section is calculated.

[0028] The same method was used to calculate the pile length for other geological control sections: for pure strongly weathered rock control sections and pure soft soil control sections, the embedment depth D was determined according to the verification results of the corresponding geological control sections, and the pile length was determined according to L=H+D+Δh.

[0029] As one example, the configuration of the sheet pile type and the pile length includes at least one of the following configurations: U-shaped steel sheet piles 210 or Z-shaped steel sheet piles are configured in the soft soil control section, combined steel sheet piles are configured in the strongly weathered rock control section, and long pile groups, transition pile groups and short pile groups are configured sequentially along the periphery of the foundation pit in the soft-hard boundary control section, with the pile length of the transition pile group being between the pile length of the long pile group and the pile length of the short pile group.

[0030] In this embodiment, different sheet pile types are configured for different control types to match the mechanical properties of each section with the geological conditions. U-shaped sheet piles 210 are used in the soft soil control section to provide greater bending stiffness to resist lateral earth pressure; composite sheet piles are used in the strongly weathered rock control section to increase the section modulus and the resistance to failure at the embedded ends; and a graded configuration of long pile groups, transition pile groups, and short pile groups is used in the soft-hard boundary control section to ensure that the pile length gradually transitions along the circumference of the foundation pit rather than abruptly, thereby coordinating stiffness differences and avoiding stress concentration.

[0031] Specifically, based on the control type and calculated pile length of each geological control section, the corresponding sheet pile type and length are configured: For soft soil controlled sections (such as the ZK3-ZK4 section), U-shaped steel sheet piles of type 210 (model U-shaped, material determined according to design strength grade, section modulus meeting the bending stiffness requirements of this section) are selected. The pile length is configured according to the calculated value for this section. Upon arrival at the site, the straightness of each steel sheet pile is checked, the curvature is not more than 1‰, the interlocks are undamaged, and a friction-reducing agent (mainly a mixture of asphalt and lubricating grease) is applied to the inside of the interlocks. In soft soil controlled sections, the steel sheet piles are connected by standard interlocking joints without additional welding stiffening components.

[0032] For sections controlled by strongly weathered rock (such as the ZK5-ZK6 section), composite sheet piles are selected. Composite sheet piles consist of U-shaped sheet piles 210 with H-beams welded along their entire length to the outer side of the web to form a composite section member. The H-beams are welded to the centerline of the web of the U-shaped sheet pile 210 using double-sided fillet welds, with the weld height not less than the designed weld height and the weld spacing not exceeding 300mm. The section modulus of the composite sheet pile is approximately 1.8 times that of a single U-shaped sheet pile 210. Upon arrival at the site, the welding quality of the H-beams is inspected; the weld appearance must be full, free of cracks and porosity, and ultrasonic testing is used to randomly check the internal quality of the welds. The pile length is configured according to the calculated value for this section. During installation, ensure that the H-beams of the composite sheet piles face inwards towards the excavation pit to provide additional bending stiffness to resist earth pressure.

[0033] For the soft-hard boundary control section (such as the ZK1-ZK2 section, which simultaneously belongs to the soft soil, permeable, soft-hard boundary, and environmentally sensitive control section), the length of this section is determined based on the spacing between adjacent exploration points, and a variable pile length design is adopted. Specifically, the arrangement is as follows: On the side closer to the soft soil control section ZK2, a group of long piles (several piles, with pile lengths determined according to the calculated values ​​for the long pile group, and pile type 210 U-shaped steel sheet piles) is configured; on the side closer to the strongly weathered rock control section ZK1, a group of short piles (several piles, with pile lengths determined according to the calculated values ​​for the short pile group, and pile type 210 U-shaped steel sheet piles) is configured; between the long and short pile groups, a transition pile group (several piles, with pile lengths between the long and short pile groups, pile type 210 U-shaped steel sheet piles, and the pile length can be taken as the arithmetic mean of the long and short pile group lengths) is configured. The pile length transition from ZK2 to ZK1 is smoothly varied using linear interpolation. All sheet piles use the same U-shaped design, differing only in pile length, to avoid interlocking mismatch issues caused by model variations. The interlocks of transition pile groups require reinforcement; a steel plate of the designed thickness is welded to the outside of the interlock for localized reinforcement, ensuring that the connection strength at the interlocking point between long and short pile groups is not less than the preset axial force control ratio of the standard interlock.

[0034] For permeable control sections (such as the ZK7-ZK8 section), if the section is located in a soft soil area, U-shaped steel sheet piles 210 should be configured as in the soft soil control section, with additional waterproofing reinforcement measures. The cross-section of the water-swellable sealant should be increased from the standard cross-section to an enlarged cross-section, and the spacing of the grout outlets of the grouting channel 520 should be increased from the standard 3m to the design-determined value. If the section is located in a strongly weathered rock area, combined steel sheet piles should be configured as in the strongly weathered rock control section, with additional waterproofing reinforcement measures.

[0035] For environmentally sensitive control sections (such as the ZK1-ZK2 section), the section has been configured with variable pile length design, and deformation control measures have been superimposed. When the waler 300 is installed, the spacing of the densified connection plates is reduced from the standard spacing to a smaller spacing (i.e., densified connection plates are set according to the densified spacing). The internal support 400 is upgraded from the standard steel pipe internal support to a higher stiffness steel pipe internal support to improve the support stiffness.

[0036] As one example, the installation of the waler 300 and inner support 400 according to the arrangement parameters of the waler 300 and inner support 400, followed by layered excavation after installation, includes: In the soft-hard boundary control section, walers 300 are installed at the corresponding positions of the transition pile group and densified connection plates are set. Corner stiffeners 320 are installed at the corner positions of the foundation pit in the soft-hard boundary control section. When installing the inner supports 400, the vertical spacing between two adjacent inner supports 400 in the soft-hard boundary control section is smaller than the vertical spacing between two adjacent inner supports 400 in the soft soil control section. After the installation of each inner support 400 is completed, the next layer of earthwork excavation is carried out.

[0037] In this embodiment, reinforcement measures are taken for the soft-hard boundary control section to address stress concentration caused by abrupt changes in strata. A reinforced connection plate strengthens the connection stiffness between the waler 300 and the transition pile group; corner stiffeners 320 enhance the torsional resistance of the waler 300 at corners; and the spacing of the inner supports 400 is reduced to increase support density and stiffness. These three measures work synergistically to improve the support stiffness of the soft-hard boundary control section.

[0038] The working process of this embodiment is as follows: After the sheet piles in the soft-hard boundary control section are driven, the installation of the walers 300 and the construction of the internal supports 400 begin. The walers 300 use double H-beams (two H-beams welded side by side and connected by connecting plates), and the internal supports 400 use steel pipe internal supports, with the material determined according to the design strength grade.

[0039] First, a reinforced connection plate (not shown in the figure) is installed on the waler 300 at the corresponding position of the transition pile group. The reinforced connection plate is made of steel plate that meets the design strength grade. The thickness and size are determined according to the connection structure between the waler 300 and the sheet pile. It is welded to the web of the waler 300 and the sheet pile along the length of the waler 300 at the designed spacing. The welding of the reinforced connection plate adopts double-sided fillet welds that meet the design weld height requirements. Since the pile length of the transition pile group is between that of the long pile group and the short pile group, the contact conditions between its pile top elevation and the waler 300 are different from those at both ends. The reinforced connection plate can compensate for this difference and ensure that the load transfer path between the waler 300 and all pile tops is continuous and reliable.

[0040] Secondly, corner stiffeners 320 are installed at the four external corners of the foundation pit. The corner stiffeners 320 are triangular Q345B steel plates with a thickness determined by the design, and the length of the right-angled sides is determined by the corner structure dimensions. They are installed on the inner side of the intersection of the double-walled walers 300 at the corner (i.e., the inner area of ​​the included angle of the walers 300), using double-sided fillet welds, with the weld height not less than the designed weld height. The function of the corner stiffeners 320 is to enhance the torsional stiffness and integrity of the walers 300 at the corner, preventing torsional deformation caused by the cross-connection of the walers 300 in two directions at the corner.

[0041] Then, install the internal supports 400, 401, and 402 according to the determined layout parameters of the waler 300 and internal supports 400 for this section. In the soft soil control section, the vertical spacing between two adjacent internal supports 400 is determined according to the support layout parameters for the soft soil control section; in the soft-hard boundary control section, the vertical spacing between two adjacent internal supports 400, 401, and 402 is reduced to less than the support spacing in the soft soil control section to increase the support density. The prestress value of each internal support 400, 401, and 402 is determined sequentially according to the corresponding excavation layer depth, and the pre-set ratio can be increased based on the conventional design value.

[0042] Finally, excavation was carried out in layers according to the principle of "excavating the next layer of earthwork after completing the installation of each 400mm inner support". The specific steps are as follows: First, excavate to the reserved construction height above the design elevation of the first 400mm inner support, install the first 400mm inner support and apply the design prestress; then continue excavating to the reserved construction height above the installation elevation of the next 401mm inner support, install the corresponding 401mm inner support and apply the design prestress; continue this process layer by layer until the reserved construction height above the installation elevation of the last 402mm inner support, install the last 402mm inner support and apply the design prestress; finally, excavate to the design elevation of 110mm at the bottom of the foundation pit. After the installation of each 400mm inner support, prestress monitoring must be carried out within the preset verification time. If the prestress loss exceeds the preset loss ratio of the design value, prestress must be added in a timely manner.

[0043] As an example, the pile driving method includes: Vibratory pile driving is used for the pile segment corresponding to the soft soil layer 700. After forming a guide hole 1050 along the design axis of the steel sheet pile at the pile position corresponding to the strongly weathered rock control section, static pressure pile driving is used. The diameter of the guide hole 1050 is larger than the web width of the corresponding steel sheet pile by a preset diameter margin. The bottom of the guide hole 1050 is lower than the top boundary of the strongly weathered rock layer 900, and the depth of entering the strongly weathered rock layer 900 is 1 / 2 to 2 / 3 of the designed rock layer embedment section length. After forming the guide hole 1050, the bottom of the hole is cleaned and the hole position deviation is checked.

[0044] In this embodiment, different pile driving methods are adopted for different strata. Vibratory pile driving is highly efficient in soft soil layer 700, while static pressure pile driving is highly accurate and causes little disturbance to the strata in hard rock. The guide hole 1050 pre-breaks most of the resistance of the hard rock layer, and the hole diameter is 80mm to 120mm larger than the web width to ensure the introduction space without weakening the embedment effect.

[0045] After the piling equipment arrives on site, different piling methods are adopted according to the control type of the geological control section to which each pile location belongs: For piles located within soft soil control sections, where the entire or majority of the pile body is embedded in the soft soil layer (700mm), vibratory pile driving is employed. The driving equipment selected is a vibratory hammer matched to the sheet pile specifications and the 700mm thickness of the soft soil layer. The excitation force, vibration frequency, and clamping force are determined according to the sheet pile specifications and geological conditions. During construction, the hydraulic clamp of the vibratory hammer is held at the top flange of the sheet pile to ensure effective transmission of vibration energy. After starting the vibratory hammer, it is initially operated at a low frequency to stabilize the pile body, and then gradually increased to the design vibration frequency. Under vibration, the soft soil layer (700mm) around the pile is disturbed, the pile side friction decreases, and the sheet pile sinks into the soil under the combined action of the vibratory hammer's own weight and the vibration force. During vibratory pile driving, the sinking speed is controlled within the design sinking speed range. When the pile depth approaches the design elevation, the excitation force is reduced, and the pile continues to be driven to the design elevation to avoid over-sinking.

[0046] For pile locations within the controlled section of strongly weathered rock, the pile body needs to penetrate 900mm into the strongly weathered rock layer to obtain embedment force. A combination of "guide hole 1050 + static pressure pile driving" is used. The specific operation is as follows: First, a rotary drilling rig is used to drill a guide hole 1050 at the pile location along the design axis of the sheet pile. The diameter of the guide hole 1050 is larger than the width of the corresponding sheet pile web by a predetermined diameter margin. The design depth of the guide hole 1050 is determined based on the design embedment depth of this section. The bottom of the hole is below the top boundary of the strongly weathered rock layer 900mm and penetrates into the strongly weathered rock layer 900mm to a predetermined depth. Mud slurry is used to maintain the stability of the hole wall during drilling. After drilling is completed, the bottom of the hole is cleaned to remove rock powder, rock cuttings, and sediment, ensuring that the thickness of the sediment at the bottom of the hole does not exceed the design allowable value. Then, the hole position deviation is checked. Measuring equipment is used to measure the deviation between the center of the guide hole 1050 and the center of the designed pile position. If the deviation exceeds the design allowable value, the guide hole 1050 is corrected or re-drilled. Finally, the combined steel sheet pile is hoisted into the guide hole 1050, and a hydraulic static pressure pile driver is used to statically drive the steel sheet pile along the guide hole 1050. The pressing force and sinking speed of the static pressure pile driving are determined based on the hardness and embedment depth requirements of the strongly weathered rock layer 900. During the pressing process, the relationship curve between the pressing force and the pile driving depth is recorded in real time. If the pressing force shows a sudden increase or decrease exceeding the preset abnormal threshold, construction must be suspended to investigate the cause before continuing pile driving.

[0047] For pile positions located within the soft-hard boundary control section, the same sheet pile may span a soft soil layer 700 and a strongly weathered rock layer 900. For such pile positions, vibratory pile driving is used in the soft soil layer 700 section. When the pile is driven to the boundary between the soft soil layer 700 and the strongly weathered rock layer 900, it is switched to static pressure pile driving. During the switch, it is necessary to ensure that the vibratory hammer has completely stopped vibrating before starting the static pressure equipment, and the interval between the two should not exceed the preset switching time.

[0048] As one example, driving each sheet pile to the corresponding design elevation according to the corresponding pile driving method includes: For the same sheet pile spanning a soft soil layer 700 and a strongly weathered rock layer 900, inclination data and driving depth data of the sheet pile are collected during the sheet pile driving process. Based on the driving depth data, it is determined whether the sheet pile has been driven to the boundary between the soft soil layer 700 and the strongly weathered rock layer 900. When it is determined that the pile has been driven to the boundary, the process is switched from vibratory pile driving to static pressure pile driving. When the inclination data exceeds the preset inclination control limit, the pile driving is paused and the sheet pile posture is corrected by adjusting the position of the guide frame, reverse traction, or pulling out and re-driving.

[0049] In this embodiment, the boundary between soft and hard strata is determined by pile driving depth data, and the pile driving method is switched in a timely manner to avoid continued vibration in hard rock, which could lead to hammer rejection and tilting. The tilt sensor and depth sensor work together; the depth sensor provides location information for the switching timing, while the tilt sensor provides the basis for attitude correction.

[0050] Specifically, for sheet piles located within the soft-hard boundary control section (ZK1-ZK2 section) with a designed pile length of 17.0m spanning a soft soil layer of 700m and a strongly weathered rock layer of 900m, the depth of the boundary between the soft soil layer of 700m and the strongly weathered rock layer of 900m at the pile location is determined based on geological survey data before pile driving. Based on interpolation of the survey data from ZK1 and ZK2, the depth of the top boundary of the strongly weathered rock layer of 900m at the pile location is -9.0m to the design elevation of 110m from the bottom of the excavation pit (slightly different for different pile locations), with the specific depth determined by the survey data from adjacent pile locations.

[0051] A monitoring system is installed on the pile driving equipment. A MEMS tilt sensor is installed on the vibratory hammer clamp, and the sensor data is transmitted in real time to the monitoring display screen in the cab via a wireless transmission module. A laser depth encoder is installed on the lifting wire rope of the vibratory hammer, and the pile driving depth of the sheet pile is calculated by measuring the length of the released wire rope. The pile driving depth and tilt angle are displayed in real time on the cab display screen using both sets of sensor data.

[0052] The pile driving construction shall be carried out in accordance with the following steps: The first step is to drive the steel sheet piles 100mm down from the ground using vibratory pile driving. Start the vibratory hammer and drive the pile at the designed frequency, monitoring the pile depth data in real time; when the depth approaches the top boundary of the strongly weathered rock layer at 900mm, gradually reduce the excitation force of the vibratory hammer to reduce the inertial impact on the pile body.

[0053] The second step involves the system automatically issuing an audible and visual alarm when the pile driving depth reaches the boundary between the soft soil layer (700mm) and the strongly weathered rock layer (900mm). The operator immediately stops the vibratory hammer operation and, within the preset switching time, removes the vibratory hammer from the pile top, replaces it with a static pressure pile driver, and clamps the pile top with the static pressure pile driver's holder.

[0054] The third step is to start the static pressure pile driver and press the steel sheet pile into the strongly weathered rock layer by 900 with the initial pressing force. When the pressing depth reaches the preset depth and the pressing force does not increase significantly, the pressing force is gradually increased to the design pressing force, and static pressure is continued until the design elevation of the pile top is reached.

[0055] Throughout the entire pile driving process, the tilt data of the sheet pile is monitored in real time. If the tilt exceeds the preset tilt control limit, the display screen will automatically trigger an over-limit alarm and display a correction prompt. The operator will pause the pile driving and take the following corrective measures: (1) Adjust the position of the guide frame: Adjust the horizontal position of the guide frame by using the jacks at the bottom of the guide frame to realign the sheet pile with the design axis; (2) Reverse traction: Hang a steel wire rope on the opposite side of the tilt of the sheet pile and apply reverse traction force through the winch to pull the sheet pile back to the vertical state; (3) Pull out and re-drive: If the tilt exceeds the pull out and re-drive control limit, pull out the sheet pile to the preset height and realign it with the design axis before driving it in again. The number of pull out and re-drive operations shall not exceed the preset number to avoid excessive disturbance to the soil around the pile.

[0056] After the correction is completed, continue driving the piles to the designed elevation at the top of the pile. Immediately after the piles are driven, use a total station to measure the coordinates of the center of the pile top to confirm that the deviation in the plane position does not exceed 50mm. Otherwise, correction measures must be taken (by using jacks to push and adjust or by compensating during the construction of adjacent piles).

[0057] As an example, the waterproof joint of the sheet pile (not shown) includes a water-swellable sealant (not shown) installed inside the sheet pile joint, a joint sealing material (not shown) installed outside the sheet pile joint, and a grouting channel 520 communicating with the sheet pile joint; the grouting channel 520 is arranged vertically along the sheet pile joint, and grout outlets are respectively set at the height corresponding to the permeable layer 600, the junction height of the soft soil layer 700 and the strongly weathered rock layer 900, and the height of the foundation pit corner.

[0058] In this embodiment, triple waterproofing works in stages. The water-swellable sealant fills tiny gaps through physical expansion, the locking sealant forms an elastic barrier through chemical sealing, and the grouting channel 520 seals the leakage channels through pressure grouting. Grout outlets are located at three key heights: the permeable layer 600, the soft-hard interface, and the corner, ensuring that the outlets correspond to the seepage heights. Specifically, grout outlet 521, located at the height corresponding to the permeable layer 600; grout outlet 522, located at the interface between the soft soil layer 700 and the strongly weathered rock layer 900; and grout outlet 523, located at the corner of the foundation pit, each correspond to a specific seepage height.

[0059] Specifically, after the sheet piles are driven, the interlocks between adjacent sheet piles are waterproofed. Each waterproofing node consists of the following three parts: 1. Water-swellable sealing element. Water-swellable rubber waterstop strips are selected. Before driving the sheet piles, the waterstop strips are embedded in the interlock grooves (i.e., the grooves of the C-shaped interlocks) of the first pile driven, arranged along the entire length of the interlock. The waterstop strips are pressed into the bottom of the interlock groove using a special pressing tool (hand-held roller presser), ensuring that the waterstop strip fits tightly against the bottom of the interlock groove without warping or voids. The waterstop strip has a hardness of approximately 60 Shore A in its dry state, possessing a certain degree of elasticity and flexibility to accommodate the deformation of the interlock during pile driving; upon contact with water, it expands in volume, tightly filling the gaps inside the interlock. For the permeable control section, the cross-sectional size of the waterstop strip is increased to 20mm × 25mm to cope with the larger water pressure of the 600mm permeable layer.

[0060] 2. Interlock Sealing Material. A two-component polyurethane sealant is selected. After the sheet piles are driven and the interlocks are clean and dry, the sealant is applied to the outer surface of the interlock using a scraping method. The coating thickness is 3mm, and the coating width covers 50mm on each side of the interlock joint. Before application, the interlock surface must be cleaned with a wire brush and compressed air to remove oil, rust, and moisture, ensuring that the adhesion strength between the sealant and the sheet pile surface is not less than 1.0MPa. After curing, the sealant forms a continuous elastic sealing layer that can accommodate minor deformations of the interlock during use.

[0061] 3. Grouting Channel 520. A grouting pipe meeting the grouting pressure requirements is selected and arranged vertically along the outside of the interlock. The grouting channel 520 is fixed to the outside of the sheet pile web using clips, maintaining the designed distance from the interlock. Grouting outlets 521 are set at the corresponding height of the permeable layer 600mm, 522 at the junction of the soft soil layer 700mm and the strongly weathered rock layer 900mm, and 523 at the corner of the foundation pit. The outlets are circular holes on the sidewall of the grouting pipe, with their diameter and number determined according to the designed grout output. They are temporarily sealed before construction to prevent mud blockage. The top of the grouting channel 520 extends 100mm above the ground as the grouting inlet, and the bottom is closed. For the corner of the foundation pit, the spacing of the outlets 523 is increased according to the waterproofing reinforcement requirements.

[0062] As one example, the waterproofing parameters for the lock joint include grouting location, grouting pressure, and grouting volume; see [link to relevant documentation]. Figure 3 When the groundwater level 950 exceeds the corresponding monitoring threshold or seepage is detected at the steel sheet pile interlock, segmented low-pressure grouting or intermittent grouting is performed through the grout outlets 521, 522, and 523 corresponding to the abnormal groundwater level 950 or seepage location, and the grouting location, grouting pressure, and grouting volume are used as the updated interlock waterproofing parameters for the corresponding geological control section.

[0063] In this embodiment, the grouting location, grouting pressure, and grouting volume are dynamically managed as interlocking waterproofing parameters. Grouting is performed at fixed points 521, 522, and 523 corresponding to abnormal locations, and the parameters are updated in the interlocking waterproofing parameters for that section.

[0064] Specifically, the working process of this embodiment is as follows: During the layered excavation of the foundation pit, the groundwater level at 950 mm and the seepage at the interlocks in each geological control section were continuously monitored. The groundwater level at 950 mm was monitored using automatic water level gauges, installed in observation wells around the foundation pit (one well every 20 m along the pit, 15 m deep). Seepage at the interlocks was detected using a combination of visual inspection and humidity sensors. Grouting for waterproofing was initiated when the daily drop in the groundwater level at 950 mm exceeded the warning threshold of 0.5 m, or when significant seepage was detected at the interlocks of the sheet piles (visible water flow or humidity sensor reading exceeding 90% RH).

[0065] The specific operation process is as follows: During a certain excavation to the design thickness at the elevation, the inspection personnel discovered that turbid water was seeping out from the interlock of the permeable control section (ZK7-ZK8 section, near the 600mm fine sand layer at elevation -5.5m). Simultaneously, the daily drop in water level monitoring well data for this section reached 0.6m, exceeding the 0.5m warning threshold. The construction worker immediately organized grouting. First, the location of the anomaly was determined. Through water level monitoring well data and visual location of the seepage point, the anomaly was determined to be at the interlock between ZK7 and ZK8, at an elevation of approximately -5.3m to -5.8m, corresponding to the top area of ​​the 600mm permeable layer (600mm fine sand layer). Then, the pre-embedded grouting channel 520 at this pile location was located. Based on the construction records, the technicians found the grouting pipe number corresponding to this interlock and determined the grout outlet 521 located within the corresponding height range of the 600mm permeable layer. The grout outlet 521, closest to the center of the seepage, was selected as the main grouting outlet, and an adjacent grout outlet 521 was selected as an auxiliary observation port. Next, the grouting equipment was connected to the 100mm grouting pipe at the ground level. A dual-liquid grouting pump capable of meeting the design grouting pressure and discharge requirements was selected. After connecting the grouting channel 520, a pressure test was conducted to confirm that the grouting channel 520 was unobstructed and unblocked. The grouting material used was a cement-water glass dual-liquid grout. The cement grout water-cement ratio, water glass concentration, volume ratio, and gel time were all determined according to the leakage sealing requirements. Low-pressure grouting was used at the beginning of grouting. When the pressure stabilized and the grouting volume continued to increase, this pressure was maintained and grouting continued. During the grouting process, the grouting situation at the auxiliary outlet 521 was observed. When grout seeped from the auxiliary outlet 521, it indicated that the section of the grouting channel 520 was full, and grouting was paused and intermittent. Multiple grouting cycles could be performed on this hole, and the cumulative grouting volume and peak pressure were used as updated lock-hole waterproofing parameters. After grouting is completed, clean the residual grout in grouting channel 520 (using clean water to rinse), and seal the opening of grouting channel 520. After the grout has cured for 24 hours, check the seepage at this location again to confirm that the seepage has stopped. Record the location of this grouting (lock number ZK7-ZK8, elevation - design thickness grout outlet 521), grouting pressure, and grouting volume, and write them into the construction management file of this permeable control section as updated lock waterproofing parameters.

[0066] As one example, the monitoring data includes horizontal displacement data of each of the sheet pile support structures 200, axial force data of each of the internal supports 400, settlement data of surrounding structures, and groundwater level 950; the monitoring thresholds include horizontal displacement threshold, axial force threshold, settlement threshold, and groundwater level 950 threshold. The construction parameters for updating the geological control section to which the monitoring data belongs and its adjacent geological control sections include: When the horizontal displacement data exceeds the horizontal displacement threshold, reduce the thickness of the subsequent excavation layer or increase the pre-stress of the internal support by 400; when the axial force data exceeds the axial force threshold, adjust the pre-stress of the subsequent internal support by 400 or add temporary supports; when the settlement data exceeds the settlement threshold, reduce the thickness of the subsequent excavation layer or adjust the dewatering parameters; when the groundwater level 950 data exceeds the groundwater level 950 threshold, adjust the grouting position, grouting pressure, or grouting volume in the interlock waterproofing parameters, or adjust the dewatering parameters.

[0067] In this embodiment, different types of monitoring data reflect different engineering problems: horizontal displacement reflects lateral stiffness, axial force reflects support stress, settlement reflects environmental impact, and groundwater stability level 950 reflects seepage risk. Different adjustment measures are then taken accordingly.

[0068] The specific construction process is as follows: This project establishes an automated monitoring system, with monitoring equipment including: inclinometers, axial force gauges, settlement observation points, and water level observation wells. The inclinometers are laid out along the circumference of the foundation pit at preset monitoring intervals, embedded in the soil 200mm outside the sheet pile support structure, with a depth not less than the sum of the excavation depth and the embedment influence depth. Axial force gauges are installed between the end of each 400mm inner support and the 300mm waler, according to the monitoring arrangement requirements for each 400mm inner support. Settlement observation points are located around the surrounding structures and the perimeter of the foundation pit. Water level observation wells are located in the permeable control section and its adjacent sections. The model, range, and accuracy of each monitoring device are determined according to the monitoring and control requirements.

[0069] The monitoring thresholds are set as follows: the horizontal displacement warning value is determined according to the excavation depth of the foundation pit and the preset displacement control ratio; the axial force warning value is determined according to the design bearing capacity of the 400mm internal support and the preset axial force control ratio; the settlement warning value is determined according to the protection level of the surrounding structures; and the groundwater level 950-day drop warning value is determined according to the drainage control requirements.

[0070] The monitoring data is transmitted to the monitoring platform in real time; under normal conditions, data is collected at preset intervals, and when a monitoring data point approaches the warning value, the system automatically shortens the collection interval.

[0071] During actual construction, after excavation reached a certain internal support 400mm condition, the monitoring platform data showed that the horizontal displacement of the top of a certain inclinometer tube in the soft-hard soil boundary control section was close to the corresponding warning value, and the system automatically issued a warning signal. The construction worker analyzed the displacement-time curve and found that the displacement rate was accelerating. Considering that this section was environmentally sensitive, the subsequent construction parameters were immediately adjusted. The thickness of the next excavation layer was reduced from the original set value to the updated smaller value. At the same time, the design prestress of the subsequent internal support 400mm was increased to the updated prestress value, and the prestressing of the internal support 400mm in the adjacent soft soil control section was updated simultaneously to coordinate the stiffness on both sides. After the adjustment, excavation continued, and the displacement growth rate decreased, without triggering a higher-level alarm.

[0072] During subsequent excavation, monitoring data showed that the axial force of a certain internal support (400) exceeded the corresponding warning value, triggering a system alert. The construction workers analyzed the situation and found that this internal support (400) was located at the boundary between a soft-hard rock boundary control section and a strongly weathered rock control section. Due to the difference in stratum stiffness, the internal support (400) experienced concentrated stress. Immediate axial force adjustment measures were implemented: steel wedges were added to both ends of the internal support (400), and temporary steel supports were added adjacent to it with prestressed material applied. After the temporary steel supports were installed, monitoring data showed that the axial force of the original internal support (400) returned to within the control range. Excavation continued until the bottom of the pit was 110mm, at which point the axial force remained stable.

[0073] In monitoring the settlement of surrounding structures, when the settlement approached the warning value but remained within the allowable range, although no warning was triggered, preventative measures were proactively taken considering the increasing trend in settlement rate. These measures included reducing the thickness of subsequent excavation layers and adjusting the dewatering parameters, changing the dewatering depth from the original depth to a new, smaller depth to reduce consolidation settlement of the surrounding soil caused by dewatering. After the adjustment, the settlement rate returned to a lower level.

[0074] During the monitoring of the 950m stable groundwater level, the daily drop in water level at a certain permeable control section exceeded the corresponding warning value for the daily drop of the 950m stable groundwater level, triggering an alert from the system. The construction worker determined that this was due to leakage at the interlock, leading to increased water accumulation in the foundation pit and necessitating increased pumping flow. Waterproofing reinforcement measures were implemented, including preventative grouting of the interlock section. After grouting, the daily drop in water level returned to below the corresponding warning value, resuming normal levels.

[0075] To facilitate understanding of the above embodiments, the following examples are provided: See Figure 4-5This embodiment takes the coarse screen and inlet pumping station 620 foundation pit project of a sewage treatment plant in a coastal area as an example to describe in detail the complete working process of the construction method of the deep foundation pit steel sheet pile support structure 200 under complex geological conditions. The foundation pit has a plan dimension of about 20 meters × 10 meters and an excavation depth of H. The site has complex geological conditions, and the strata from top to bottom are as follows: plain fill layer 710 (thickness determined according to the survey results, loose state), silt layer 700 (thickness determined according to the survey results, fluid plastic state, low bearing capacity, high compressibility), fine sand layer 600 (thickness determined according to the survey results, slightly dense, permeability coefficient determined according to the test value, permeable layer), residual sandy clay layer 720 (thickness determined according to the survey results, plastic), and loose strongly weathered basalt layer 900 (thickness determined according to the survey results, SPT blow count reaches the value of strongly weathered rock). The groundwater level is 950 meters below the design depth. There is a three-story brick-concrete residential building (surrounding structures) within the pre-set protection distance outside the foundation pit edge. Given these complex engineering conditions, the construction process was carried out according to the following steps.

[0076] The first step is to acquire foundation pit survey data and delineate geological control sections. Survey points ZK1 to ZK8 are established along the perimeter of the foundation pit at intervals determined by the site perimeter and the degree of strata variation. Stratigraphic distribution data at each survey point is obtained through drilling sampling and indoor geotechnical tests, including the 700mm thickness of the soft soil layer, the 600mm depth of the permeable layer, the 900mm top boundary depth of the strongly weathered rock layer, and the rock surface undulation. Simultaneously, the groundwater level (950mm), permeability coefficients of each stratum, foundation pit excavation depth, foundation pit boundary location, and the location of surrounding structures are also obtained. Based on the acquired data, the section between adjacent survey points is designated as the initial section. The control attributes of each initial section are determined segment by segment according to the 700mm thickness of the soft soil layer, the 600mm depth of the permeable layer, the 900mm top boundary depth of the strongly weathered rock layer, the rock surface undulation, and the distance between surrounding structures and the foundation pit boundary. Taking the section between ZK1 and ZK2 as an example, the average thickness of the soft soil layer (700mm) (silt layer 700mm) in this section was determined according to the survey results and was identified as a soft soil control section; the bottom elevation of the fine sand layer (600mm) was within the excavation depth range of the foundation pit and was identified as a permeable control section; the top boundary elevation difference of the strongly weathered rock layer (900mm) exceeded the preset rock surface undulation value and was identified as a soft-hard boundary control section; the distance to the residential buildings on the outer side was less than the preset protection distance and was identified as an environmentally sensitive control section. Through the above multi-dimensional segment-by-segment determination, the foundation pit was divided into multiple geological control sections with different control attributes along the circumference: soft soil control section, permeable control section, strongly weathered rock control section, soft-hard boundary control section, and environmentally sensitive control section. Different design parameters and construction measures were adopted for each control section in subsequent construction.

[0077] The second step is to determine the construction parameters for each geological control section. For each identified geological control section, the corresponding excavation depth H, the 950mm burial depth of the groundwater stability level determined by on-site water level observation, the permeability coefficient of each stratum, and the stratum distribution data are obtained. Deep foundation pit support structure design software is used to perform segmented calculations. For each geological control section, anti-overturning calculations, anti-sliding calculations, pit bottom heave calculations, seepage stability calculations, and displacement limit calculations are performed. The maximum value among the embedment depths obtained from each calculation is taken as the embedment depth of that section. The sum of the excavation depth, embedment depth, and pile top construction allowance is then used as the 200mm pile length of the sheet pile support structure for that section. Through this calculation process, the embedment depth and pile length of the soft-hard boundary control section (ZK1-ZK2 section) are determined according to the segmented verification results; the embedment depth of the strongly weathered rock control section is the embedment depth obtained from this verification, and the pile length is 15.8m; the embedment depth and pile length of the pure soft soil control section are determined according to the verification results of this section. In addition to the pile length, the construction parameters for each section also include the steel sheet pile type (U-shaped steel sheet pile 210 is used in the soft soil section, combined steel sheet pile is used in the strongly weathered rock section, and variable pile length design is used in the soft-hard boundary section), the pile driving method (vibratory pile driving in the soft soil section, and static pressure pile driving with guide hole in the strongly weathered rock section), the interlocking waterproof parameters, and the waler 300 and internal support 400 arrangement parameters.

[0078] The third step involves configuring and installing sheet pile support structures 200 according to the construction parameters of each geological control section. In the soft-hard boundary control section (ZK1-ZK2), a variable pile length design is adopted: long pile groups (several piles, with pile lengths determined by the calculated values ​​of the long pile groups) are configured on the side closer to the soft soil control section, short pile groups (several piles, with pile lengths determined by the calculated values ​​of the short pile groups) are configured on the side closer to the strongly weathered rock control section, and transition pile groups (several piles, with pile lengths between the long and short pile groups) are configured in the middle. The pile lengths are smoothly transitioned along the circumference of the foundation pit using linear interpolation to avoid sudden changes in the stiffness of the support structure and stress concentration caused by abrupt changes in pile length. In the strongly weathered rock control section (ZK5-ZK6), composite sheet piles are configured, consisting of U-shaped sheet piles 210 with H-shaped steel welded along their entire length to the outside of their webs to form a composite section member. The section modulus is approximately 1.8 times that of a single U-shaped sheet pile 210. During the installation process, different pile driving methods were adopted for different strata: For piles in soft soil control sections, vibratory pile driving was used, employing a Zoomlion-compatible vibratory hammer (the excitation force and frequency were determined according to the sheet pile specifications and strata conditions) to quickly drive the sheet piles into the ground, with the sinking speed controlled at the designed sinking speed; for piles in strongly weathered rock control sections, a combination of "guide hole + static pressure pile driving" was used. A guide hole was first formed using a rotary drilling rig (the hole diameter was larger than the corresponding sheet pile web width by a pre-set diameter allowance, and the bottom of the hole penetrated within 90mm of the strongly weathered rock layer). After cleaning the hole, the combined steel sheet piles are hoisted in and driven into the ground by a hydraulic static pressure pile driver (the driving force is determined according to the pile driving resistance). In the soft-hard boundary control section, for pile positions that cross the soft soil layer (700mm) and the strongly weathered rock layer (900mm), tilt sensors and depth sensors are installed for real-time monitoring. When the depth data reaches the soft-hard boundary position, an automatic alarm is triggered, and the operator immediately stops the vibratory hammer and switches to the static pressure pile driver within the preset switching time to continue pile driving. At the same time, when the tilt data exceeds the preset tilt control limit, pile driving is paused and the posture is corrected.

[0079] The fourth step is to arrange the waterproof joints of the interlocks and install the walers 300 and the inner supports 400. After the sheet piles are driven, the interlocks between adjacent sheet piles are treated with triple waterproofing: The first layer is a water-swellable sealant (a water-swellable rubber waterstop strip, the cross-section and expansion rate of which are determined according to the interlock gap and waterproofing level), which is embedded in the interlock groove along its length and fills the interlock gap after expanding upon contact with water; the second layer is an interlock sealing material (a two-component polyurethane sealant, the elongation of which meets the requirements for interlock deformation adaptation), which is applied to the outer surface of the interlock and forms an elastic sealing layer after curing; the third layer is a pre-embedded grouting channel 520 (grouting pipe), which is arranged vertically along the interlock, with grout outlets 521 at the corresponding height of the permeable layer 600, grout outlets 522 at the soft-hard interface height, and grout outlets 523 at the corner height of the foundation pit (the hole diameter is determined according to the designed grouting volume). Subsequently, the walers 300 and internal supports 400 were installed: the walers 300 used double H-beams, and the internal supports 400 used steel pipe internal supports. In the soft-hard soil boundary control section, the vertical spacing between adjacent internal supports 400, 401, and 402 was reduced to 2.0m (the thickness was determined by design in the soft soil control section). Densified connection plates were installed at corresponding positions of the transition pile groups, and corner stiffeners 320 were installed at the corners of the foundation pit. The prestress values ​​of each internal support 400, 401, and 402 were determined layer by layer according to the corresponding excavation depth. Layered excavation was carried out layer by layer according to the principle of "excavating the next layer after completing the installation of each internal support 400".

[0080] The fifth step is to establish an automated monitoring system and implement dynamic feedback. Inclinometers (laid out at preset monitoring intervals, with a depth not less than the sum of the excavation depth and the embedment influence depth), axial force gauges (set according to the monitoring arrangement requirement of 400mm for each internal support), settlement observation points (set at the four corners of surrounding structures and around the perimeter of the foundation pit at preset settlement monitoring intervals), and water level observation wells (set at preset water level monitoring intervals) are installed around the foundation pit. Monitoring thresholds are set as follows: horizontal displacement warning value 30mm, axial force warning value determined according to the design bearing capacity and preset axial force control ratio, settlement warning value 18mm, and groundwater stability level 950-day drop warning value 0.5m. All monitoring data are transmitted to the monitoring platform in real time. During construction, when a monitoring data point exceeds its corresponding monitoring threshold, the system not only updates the construction parameters of the geological control section to which the monitoring data belongs, but also simultaneously updates the construction parameters of its adjacent geological control sections. For example, when the horizontal displacement of a certain soft-hard boundary control section approaches the corresponding warning value, the construction parameters of this section are updated to reduce the excavation thickness of the next layer from the original set value to the updated smaller value. At the same time, the prestress of the fifth inner support 402 is increased to the updated prestress value, and the prestress of the inner support 400 of the adjacent soft soil control section is updated simultaneously to coordinate the stiffness on both sides. When the axial force of a certain inner support 400 exceeds the corresponding axial force warning value, the parameters of this section are updated, steel wedges are added, and temporary supports are added. At the same time, the construction parameters of the adjacent strongly weathered rock control section are adjusted to disperse stress. When the settlement rate of surrounding structures shows an increasing trend, the excavation layer thickness of this environmentally sensitive control section and adjacent sections is actively reduced, and the dewatering parameters are adjusted. When the daily drop in water level of a certain permeable control section exceeds the corresponding groundwater stability level 950 daily drop warning value, grouting is carried out at fixed points in this section and adjacent section lock joints through the pre-embedded grouting channel 520 (the grouting pressure and grouting volume are determined according to the degree of leakage and the location of the grout outlets 521, 522, and 523). After all the adjustment measures were implemented, the monitoring data all fell back to the safe range, ensuring that deformation, leakage and stress were controllable throughout the entire foundation pit construction process.

[0081] As one example, during layered excavation, when the horizontal displacement data of a certain geological control section (such as a soft soil control section) exceeds the corresponding monitoring threshold and it is determined that post-grouting reinforcement is required to effectively increase the embedment depth, the system not only triggers reinforcement for the over-limit section itself, but also simultaneously calculates the incremental impact of the redistribution of earth pressure caused by the displacement over-limit and local reinforcement on the stress at the end of the 200mm piles of the sheet pile support structure in adjacent geological control sections (such as adjacent soft-hard boundary control sections or strongly weathered rock control sections), thus achieving preventive and coordinated reinforcement of adjacent sections. Specifically, based on the measured horizontal displacement increment, the system uses the elastic foundation beam m method to invert and calculate the incremental distribution of earth pressure outside the pit in the over-limit section, and then obtains the horizontal stress increment Δσ0 at the end of the 200mm pile of the sheet pile support structure in the over-limit section. Subsequently, the pit soil is regarded as a semi-infinite elastic medium, and the dynamic elastic modulus E of the strata in this area is used as the basis for calculation. aGiven the formation density ρ, calculate the formation stress wave propagation attenuation coefficient α = sqrt(πfρ / (2E)). a Where f is the dominant frequency of soil deformation caused by excavation unloading (determined by inversion from monitoring data). Then, the additional stress increment Δσ at the pile tip of the adjacent geological control section is calculated. =Δσ0×e^( α×L a ), where L a This refers to the horizontal spatial distance from the calculation point of the over-limit section to the end of the pile of the adjacent section.

[0082] When the additional stress increment Δσ After substituting into the overturning resistance calculation formula, the actual overturning resistance safety factor K of the adjacent geological control section is obtained. a Reduced to the preset safety factor threshold K t When the following conditions are met (as determined by design safety reserve requirements), it is determined that there is a risk of deep "kick-toe" instability caused by stress transfer in the adjacent section, and the system immediately updates the construction parameters of the adjacent geological control section. The specific reinforcement measures are as follows: High-pressure jet grouting is performed along the designed embedment depth range 200 mm outside the sheet pile support structure of the adjacent section, at the designed reinforcement spacing, to form a cement-soil enlarged head with a diameter not less than the designed enlarged head diameter. The equivalent embedment depth compensation amount ΔL for jet grouting is... e ΔL is dynamically calculated using the following formula: e =(Δσ ×A p ) / (q s ×π×D e ), where A p q is the cross-sectional area of ​​a single pile. s D represents the standard value of the ultimate lateral resistance between the jet-grouting consolidated body and the surrounding soil and rock layers. e To increase the head diameter, deep jet grouting is actively performed on adjacent sections to expand the base, effectively increasing the actual embedment depth of the adjacent sections to D+ΔL. e It resists the stress increment transmitted from the over-limit section.

[0083] In this embodiment, the additional stress at the pile tip of the over-limit section is calculated and the stress wave is transmitted to the adjacent section. Before the safety factor of the adjacent section decreases, high-pressure jet grouting is used for bottom expansion reinforcement. Because the release of soil pressure during the excavation process has a significant spatial transmission effect, local reinforcement of the over-limit section itself can easily lead to stress transfer to the adjacent relatively weak section and trigger chain deformation. This embodiment uses a stress wave attenuation model to accurately calculate the stress increment of the adjacent section and proactively updates its embedment depth parameters for deep bottom expansion reinforcement before deformation occurs. Therefore, dynamic synergistic compensation of the embedment stiffness of the adjacent section can be achieved, completely blocking the spatial spread of local deformation and achieving proactive defense of the overall stability of the foundation pit.

[0084] As one example, when installing the waler 300 with the parameters specified in the waler and inner support 400 arrangement, a hydraulic variable stiffness servo support device is installed at the support node at the junction of the soft-hard boundary control section and the environmentally sensitive control section. The hydraulic variable stiffness servo support device includes a double-acting hydraulic cylinder, a high-frequency response servo valve, an accumulator, and a pressure sensor, with an equivalent support stiffness K. e Dynamic stepless control can be achieved by adjusting the opening of the servo valve to change the compression volume of the oil in the hydraulic cylinder.

[0085] During the layered excavation process, the system acquires real-time monitoring data from each geological control section and calculates the stratum stiffness ratio K=E1 / E2 between adjacent geological control sections. When the horizontal displacement data of the soft soil control section exceeds the corresponding monitoring threshold due to unloading expansion, the system first calculates the imbalance of the distribution of the support internal forces under the current stratum stiffness ratio η=|F1. F2| / max(F1,F2), where F1 and F2 are the measured axial forces of the inner supports 400 in the two adjacent segments. If the imbalance degree η exceeds the preset imbalance degree threshold, it indicates that the huge expansion thrust on the soft soil side is being rigidly transmitted to the adjacent sensitive side through the waler 300, posing an extremely high risk of nodal shear.

[0086] At this point, the system updates the waler 300 and internal support 400 arrangement parameters for the soft soil control section and its adjacent environmentally sensitive control section, executing a dynamic stiffness adjustment strategy of "one increasing while the other decreases". Specifically, in the soft soil control section, the servo valve opening is reduced to lock the hydraulic cylinder, and the equivalent support stiffness K of the hydraulic variable stiffness servo support device is increased. e1 It actively resists the unloading and expansion of soft soil; at the same time, in the adjacent environmentally sensitive control section, the opening of the servo valve is appropriately increased to reduce the equivalent support stiffness K. e2 This allows the segment to generate displacements within a preset, small, and controllable range to dissipate excess energy. The adjustment amount ΔK of the equivalent support stiffness. e Calculate ΔK using the following formula: e =K e0 ×λ×(δ s δ t ) / δ t K e0 δ is the initial equivalent stiffness, λ is the stiffness adjustment coefficient (determined according to the support stiffness adjustment capability), and δ is the initial equivalent stiffness. s For the measured displacement of the over-limit section, δ t This is the displacement threshold.

[0087] Simultaneously, while reducing the stiffness of the 400mm support within the environmentally sensitive control section to allow for minor displacement, the system also updates the waterproofing parameters of the interlock in this section to prevent tearing of the interlock and settlement of surrounding structures caused by minor deformation. A flexible epoxy resin sealant with a pre-set elongation at break is injected into the grout outlet 523 at the corner height of the foundation pit. After curing, this sealant forms a highly elastic rubber-like isolation layer that absorbs shear displacement deformation at the interlock and maintains a seal.

[0088] In this embodiment, a hydraulic variable stiffness servo support device is installed at the junction of adjacent sections. When the displacement of the soft soil section exceeds the limit, the stiffness ratio on both sides is actively adjusted, supplemented by flexible grouting. Because the excavation and unloading expansion of the soft soil section will generate huge lateral thrust, the traditional equal stiffness internal support 400 will directly transmit this thrust to the adjacent section, causing node damage or settlement of surrounding structures. However, this embodiment uses a hydraulic servo system to achieve reverse guidance of "adding stiffness to resist on the soft soil side and releasing stiffness on the sensitive side". The stiffness adjustment is used to resolve local stress concentration. At the same time, flexible sealing material is injected on the release side to adapt to micro deformation. Therefore, complex stress redistribution can be achieved without increasing the overall support cross-sectional size, ensuring the dual safety of the support structure and waterproofing system under micro deformation.

[0089] As one example, during layered excavation, the system addresses the issue of shear tearing at complex strata boundaries due to differential settlement by employing a differentiated spatial excavation sequence to proactively create a soil arching effect. Specifically, the foundation pit is divided circumferentially into multiple basin-shaped excavation blocks, each with a width determined by the geological control section length and excavation organization. These blocks are then excavated in a stepped, staggered manner, following the sequence of "strongly weathered rock control section → soft-hard boundary control section → soft soil control section," with a height difference of at least one excavation layer thickness maintained between adjacent blocks. Through this specific spatiotemporal sequence, utilizing the displacement trend of the soil in the previously excavated unloading section, a self-stabilizing soil arching effect is formed in the adjacent unexcavated section, thereby reducing the direct earth pressure acting on the sheet pile support structure 200.

[0090] Before each new segment is excavated, the system extracts deep horizontal displacement monitoring data from the geological control sections collected after the previous segment's excavation. Using spatial three-dimensional inclinometer data, the relative shear displacement difference Δδ at the steel sheet pile interlocks at the interface of adjacent segments is calculated. s =δ so t δ ha a When the shear displacement difference Δδ s Exceeding the preset shear threshold Δδ t(Determined according to the requirements for interlock deformation control), but at this time, since the interlock has not been completely torn and no obvious water seepage has been detected at the interlock of the sheet pile, the system determines that the interlock is in the critical tearing stage, immediately updates the interlock waterproofing parameters of the geological control section to which the junction belongs and its adjacent geological control sections, and implements pre-healing grouting.

[0091] The specific update and implementation process is as follows: The system instructs the grouting pump to inject shear-thixotropic grout into the grout outlet 521 at the corresponding height of the permeable layer 600 at the interface. The shear-thixotropic grout is a non-Newtonian fluid that exhibits high-viscosity solid characteristics in a static state (static shear force τ0 and static viscosity η1 meet the lock-sealing requirements); when subjected to lock-sealing shear displacement, its network structure is destroyed, and the viscosity rapidly decreases (the viscosity η2 after shearing meets the grout flow requirements), transforming it into a liquid with good fluidity; when the shearing action stops, it can rapidly restore the network structure within a preset recovery time and eventually solidify. Grouting volume V n Calculated dynamically according to the following formula: V n =V0×(1+γ×Δδ s ), where V0 is the grouting volume for the foundation filling (determined by the filling volume of the interlock foundation), and γ is the shear response coefficient (determined by the shear displacement response test).

[0092] During the grouting process, the grout automatically liquefies when the lock is sheared and deformed, deeply tracking and penetrating into the micro-cracks caused by the displacement; when the deformation tends to stabilize, the grout quickly solidifies and seals the gaps, re-solidifying the lock that might have torn and leaked into a whole.

[0093] In this embodiment, the soil arching effect is utilized for unloading through stepped, staggered excavation, and shear-thixotropic grout is injected in advance when the shear displacement difference of the interlock is detected. Because the settlement and deformation rates of different sections at the junction of complex strata are bound to differ, it is very easy for the interlock of the steel sheet pile to undergo relative shear displacement and tear the water-swellable seal. Traditional water level monitoring or visual inspection often has serious lag. When seepage is detected, a through channel has already formed inside the interlock, making it extremely difficult to seal afterward and prone to grout leakage. However, this embodiment uses the shear displacement difference as a pre-warning indicator and utilizes the intelligent material properties of shear-thixotropic grout that tracks cracks in motion and consolidates in stillness. Therefore, it can achieve adaptive healing before the interlock completely tears and leaks, eliminating the potential for leakage in its infancy and greatly improving the waterproof reliability of the support system under complex stress conditions.

[0094] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A construction method for steel sheet pile support structures for deep foundation pits under complex geological conditions, characterized in that, include: Obtain the foundation pit investigation data of the foundation pit to be excavated. The foundation pit investigation data includes the stratum distribution parameters, groundwater level, permeability coefficient of each stratum, foundation pit excavation depth, foundation pit boundary position and surrounding structure position. The stratum distribution parameters include the thickness of soft soil layer, the burial depth of permeable layer, the burial depth of the top boundary of strongly weathered rock layer and the undulation amplitude of rock surface. Based on the geological distribution parameters and the distance between the structures determined by the location of the foundation pit edge and the location of the surrounding structures, the foundation pit is divided into multiple geological control sections along the circumference. For each geological control section, the construction parameters for that geological control section are determined by combining the excavation depth of the foundation pit, the stratum distribution parameters, and the permeability coefficient of each stratum. The construction parameters include the sheet pile type, pile length, embedment depth, pile driving method, interlock waterproofing parameters, and waler and internal support arrangement parameters. According to the sheet pile type, pile length and embedment depth corresponding to each geological control section, the sheet piles at each pile position are configured, and each sheet pile is driven into the corresponding design elevation according to the corresponding pile driving method. According to the aforementioned interlock waterproofing parameters, interlock waterproofing nodes are arranged at the corresponding heights of the steel sheet pile interlocks, the permeable layer, and the corner positions of the foundation pit; Install the walers and internal supports according to the waler and internal support layout parameters, and then carry out layered excavation after installation; Monitoring data were collected from various geological control sections during the layered excavation process; When the monitoring data exceeds the corresponding monitoring threshold, the construction parameters of the geological control section to which the monitoring data belongs and its adjacent geological control sections are updated.

2. The construction method for deep foundation pit steel sheet pile support structure under complex geological conditions according to claim 1, characterized in that, The division of the foundation pit into multiple geological control sections along its circumference includes: The sections between adjacent exploration points along the perimeter of the foundation pit are taken as initial sections, and the control attributes of each initial section are determined according to the geological distribution parameters and the distance to the structures. Specifically, the initial section with a soft soil layer thickness greater than the preset soft soil thickness value is defined as the soft soil control section; the initial section with a permeable layer depth within the excavation depth range of the foundation pit is defined as the permeable control section; the initial section with the top boundary of the strongly weathered rock layer below the bottom of the foundation pit and within the preset embedment influence depth range is defined as the strongly weathered rock control section; the initial section with a height difference between the top boundaries of the strongly weathered rock layer between adjacent exploration points exceeding the preset rock surface undulation value is defined as the soft-hard boundary control section; and the initial section with the distance between the structures less than the preset protection distance is defined as the environmentally sensitive control section.

3. The construction method for deep foundation pit steel sheet pile support structure under complex geological conditions according to claim 1, characterized in that, The determination of the construction parameters for the geological control section includes: Based on the excavation depth of the foundation pit, groundwater level data, permeability coefficients of each stratum, and the stratum distribution parameters of the geological control section, anti-overturning calculations, anti-sliding calculations, pit bottom heave calculations, seepage stability calculations, and displacement limit calculations are performed respectively. The maximum value among the embedment depths obtained from each calculation is determined as the embedment depth of the geological control section, and the sum of the foundation pit excavation depth, the embedment depth, and the pile top construction allowance is determined as the pile length of the geological control section.

4. The construction method for deep foundation pit steel sheet pile support structure under complex geological conditions according to claim 2, characterized in that, The configuration of the sheet pile type and the pile length includes at least one of the following configuration methods: U-shaped or Z-shaped sheet piles are installed in the soft soil control section, combined sheet piles are installed in the strongly weathered rock control section, and long pile groups, transition pile groups and short pile groups are sequentially installed along the periphery of the foundation pit in the soft-hard boundary control section. The pile length of the transition pile group is between the pile length of the long pile group and the pile length of the short pile group.

5. The construction method for deep foundation pit steel sheet pile support structure under complex geological conditions according to claim 4, characterized in that, The installation of the walers and internal supports according to the waler and internal support arrangement parameters, followed by layered excavation after installation, includes: In the soft-hard boundary control section, walers are installed at the corresponding positions of the transition pile group and densified connection plates are set. Corner stiffeners are installed at the corner positions of the foundation pit in the soft-hard boundary control section. When installing the internal supports, the vertical spacing between two adjacent internal supports in the soft-hard boundary control section is made smaller than the vertical spacing between two adjacent internal supports in the soft soil control section. After the installation of each internal support is completed, the next layer of earthwork excavation is carried out.

6. The construction method for deep foundation pit steel sheet pile support structure under complex geological conditions according to claim 1, characterized in that, The pile driving methods include: Vibratory pile driving is used for the pile section corresponding to the soft soil layer, and static pressure pile driving is used after the guide hole is formed along the design axis of the steel sheet pile at the pile position corresponding to the strongly weathered rock control section. The diameter of the guide hole is 80mm to 120mm larger than the width of the web of the corresponding steel sheet pile. The bottom of the guide hole enters the strongly weathered rock layer, and the bottom of the hole is cleaned and the hole position deviation is checked after the guide hole is formed.

7. The construction method for deep foundation pit steel sheet pile support structure under complex geological conditions according to claim 6, characterized in that, The step of driving each sheet pile to the corresponding design elevation according to the corresponding pile driving method includes: For the same sheet pile crossing a soft soil layer and a strongly weathered rock layer, inclination data and driving depth data of the sheet pile are collected during the pile driving process. Based on the driving depth data, it is determined whether the sheet pile has been driven to the boundary between the soft soil layer and the strongly weathered rock layer. When it is determined that the pile has been driven to the boundary, the pile driving is switched from vibratory pile driving to static pressure pile driving. When the inclination data exceeds 1 / 200, the pile driving is paused and the attitude of the sheet pile is corrected by adjusting the position of the guide frame, reverse traction, or pulling out and re-driving.

8. The construction method for deep foundation pit steel sheet pile support structure under complex geological conditions according to claim 1, characterized in that, The waterproof joint of the sheet pile includes a water-swellable sealant installed inside the sheet pile joint, a joint sealing material installed outside the sheet pile joint, and a grouting channel connected to the sheet pile joint. The grouting channel is arranged vertically along the sheet pile joint, and grout outlets are set at the corresponding height of the permeable layer, the junction height of the soft soil layer and the strongly weathered rock layer, and the corner height of the foundation pit.

9. The construction method for deep foundation pit steel sheet pile support structure under complex geological conditions according to claim 8, characterized in that, The interlock waterproofing parameters include grouting location, grouting pressure, and grouting volume. When the groundwater level exceeds the corresponding monitoring threshold or seepage is detected at the interlock of the sheet pile, segmented low-pressure grouting or intermittent grouting is performed through the grout outlet corresponding to the abnormal groundwater level or seepage location, and the grouting location, grouting pressure, and grouting volume are used as the updated interlock waterproofing parameters for the corresponding geological control section.

10. The construction method for deep foundation pit steel sheet pile support structure under complex geological conditions according to claim 1, characterized in that, The monitoring data includes the horizontal displacement data of each sheet pile, the axial force data of each internal support, the settlement data of surrounding structures, and the groundwater level. The monitoring thresholds include horizontal displacement threshold, axial force threshold, settlement threshold, and groundwater level threshold; The construction parameters for updating the geological control section to which the monitoring data belongs and its adjacent geological control sections include: When the horizontal displacement data exceeds the horizontal displacement threshold, reduce the thickness of the subsequent excavation layer or increase the pre-stress of the internal support. When the axial force data exceeds the axial force threshold, adjust the preload of the subsequent internal support or add temporary support; when the settlement data exceeds the settlement threshold, reduce the thickness of the subsequent excavation layer or adjust the dewatering parameters; when the groundwater level data exceeds the groundwater level threshold, adjust the grouting position, grouting pressure or grouting volume in the interlock waterproofing parameters, or adjust the dewatering parameters.

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