Permanent support structure with reduced embedment depth and increased foundation stiffness and method of construction

Abstract

The present application relates to the technical field of building foundation pit, and proposes a permanent support structure and construction method for reducing embedded depth and strengthening foundation stiffness. The structure comprises optimized support piles arranged along the periphery of the foundation pit and a reinforcing body located at the bottom of the foundation pit. According to the present application, the embedded depth of the support piles is reduced from about one times the depth of the foundation pit in the traditional design to (0.15-0.20)H, wherein the reduced embedded depth is converted into the foundation stiffness. The reinforcing body is a continuous cement-soil consolidation body formed by lateral grooving and rotary jetting solidification of soil and cement slurry, and is arranged in the peripheral area of the embedded end of the support piles. In the construction stage, the reinforcing body and the support piles work together to form an H-shaped reinforced support structure, and in the permanent stage, the reinforcing body participates in the stress as a part of the foundation. The present application not only reduces the pile length and material consumption, reduces the construction cost, improves the overall stiffness and anti-uniform settlement capacity of the foundation, realizes the collaborative combination of support function and foundation structure, and has good engineering applicability.

Description

Technical Field

[0001] This invention relates to the field of building foundation pit technology, specifically to a permanent support structure and construction method that reduces the embedment depth and strengthens the foundation rigidity. Background Technology

[0002] Permanent support structures for deep foundation pits are one of the three directions for high-quality foundation pit engineering and have become an important feature of the new pattern of high-quality foundation pits. They proactively position the foundation pit retaining pile walls as the outer walls of the underground structure, undertaking the function of foundation pit support during the excavation stage, and becoming the outer walls of the main underground structure after the underground structure construction is completed.

[0003] Current foundation pit design theories typically employ retaining pile walls with a length exceeding twice the excavation depth, serving functions such as preventing overturning and uplift during the excavation phase. However, once the foundation becomes the main structure, the underground space becomes a closed enclosure, eliminating the need for excessively deep embedment lengths in the underground structural walls. Therefore, prioritizing the use of the main structure and changing the existing selection and design methods for retaining pile walls to directly utilize the embedment depth as foundation stiffness—saving on foundation investment while simultaneously meeting the support requirements during the excavation phase and avoiding wasted embedment depth—would represent a significant advancement in the theory and technology of permanent support structures.

[0004] Traditional methods for reducing embedment depth, such as increasing pile cross-section, improving material strength, or adding internal supports, typically suffer from problems such as excessive space occupation, interference with the main structure construction, and poor construction convenience, making it difficult to balance safety, economy, and construction efficiency. Furthermore, existing foundation reinforcement methods at the pit bottom often only fulfill single functions such as heave resistance and seepage prevention, failing to effectively match the load-bearing system at the bottom of the support piles and unable to replace the function of deeply embedded pile sections. During foundation pit construction, excessive embedment can also lead to difficulties in ensuring borehole quality, extended construction periods, and increased disturbance to the surrounding soil, further increasing construction risks in complex strata.

[0005] Therefore, under the premise of meeting the strict deformation and safety control requirements of the foundation pit, how to optimize the embedment depth of the support piles, reduce material consumption, improve the overall stiffness of the foundation, and achieve an integrated permanent support scheme in which the support piles and the base reinforcement work together to bear the load has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the problems existing in the background technology, this invention proposes a permanent support structure and construction method that reduces the embedment depth and enhances the stiffness of the foundation. This solution is technically feasible, economical, and convenient to construct. It can effectively optimize the embedment depth of deep foundation pit support piles, improve the stiffness of the foundation, and meet the strict deformation control requirements of the surrounding environment. It has strong engineering applicability and good promotion and application value.

[0007] To achieve the above objectives, the present invention adopts the following solution:

[0008] A permanent support structure that reduces embedment depth and strengthens foundation stiffness includes optimized support piles and a reinforced body. The optimized support piles are arranged around the perimeter of the foundation pit, and their embedment depth is the optimized embedment depth L1, where L1 = (0.15~0.20)H, and H is the excavation depth of the foundation pit. The optimized embedment depth is less than the conventionally designed embedment depth L0. The reinforced body is located within the soil below the bottom of the foundation pit and below the foundation slab of the underground structure, and is arranged around the embedded end of the optimized support pile; the reinforced body is a continuous cement-soil consolidation body formed by lateral trenching and jet spraying of soil and cement grout. The reinforced body extends from the bottom of the self-optimizing support pile into the pit, and its reinforcement depth D satisfies D=(0.10~0.25)H, and its extension width into the pit B satisfies B=(0.05~0.15)H; The reinforced body and the optimized support piles form a synergistic force relationship through the overall reinforcement of the surrounding soil, constituting an H-shaped reinforcement support structure in which the vertical main limb and the horizontal restraint limb work together.

[0009] Optionally, the reinforced body is functionally divided into a pile bottom reinforcement zone, an inner transition zone, and an in-pit extension zone. The pile bottom reinforcement zone is located around the embedded end of the optimized support pile and is used to directly bear the shear force and bending moment transmitted from the bottom of the optimized support pile. The inner transition zone is located outside the pile bottom reinforcement zone and is used to mitigate the abrupt change in stiffness between the optimized support pile and the surrounding strata. The in-pit extension zone extends into the pit of the optimized support pile and is used to provide additional shear resistance, passive resistance, and foundation reinforcement stiffness.

[0010] Optionally, the unconfined compressive strength of the pile bottom reinforcement zone is 2.5~5.0MPa; the unconfined compressive strength of the transition zone is 1.5~3.0MPa; and the unconfined compressive strength of the pit extension zone is 0.8~2.0MPa.

[0011] Optionally, the optimized support pile is a bored pile, a segment of a diaphragm wall, or other vertical load-bearing component capable of bearing lateral loads.

[0012] Optionally, the reinforcement body is arranged along one side of the pit of the optimized support pile, and is arranged in a strip or wall shape.

[0013] Optionally, the equivalent stiffness, shear strength, and bending restraint provided by the reinforced body satisfy the functional substitution for reducing the embedded section of the support pile according to conventional design optimization, specifically satisfying the following equivalent embedded conditions: ; ; ; in, K sThe equivalent stiffness provided to the solidified body; The decrease in embedment stiffness due to the reduction in embedment depth from L0 to L1; V s Shear resistance provided to the solidified body; V d To optimize the design shear force at the bottom of the support piles; M d To optimize the design bending moment at the bottom of the support piles; M s The bending moment provided for the reinforced body.

[0014] Optionally, the shear resistance provided by the reinforced body V s Determined based on the size of the solidified body and the shear strength of the cement-soil: ; in, τ The shear strength of cement-soil; B To reinforce the solidified material, the width of the pit should be extended inwards. D The vertical reinforcement depth of the solidified body.

[0015] Optionally, the reinforcement provides resistance to bending moment. M s Determined by the equivalent stiffness of the reinforced body and the optimized bottom rotation angle of the support pile: Where θ is the bottom rotation angle of the optimized support pile.

[0016] The construction method for permanent support structures that reduce embedment depth and enhance foundation stiffness includes the following steps: Step 1: Based on the excavation depth of the foundation pit, the geological conditions and the requirements of the surrounding environment, determine the optimized embedment depth L1 of the optimized support piles, as well as the planar dimensions of the reinforced body, the vertical reinforcement depth D, the extension width B in the pit, and the strength parameters. Step 2: Construct optimized support piles according to the optimized embedment depth L1, determine the location and axis control points of the optimized support piles, and complete the drilling, reinforcement cage placement and concrete pouring. Step 3: According to the design drawings, conduct surveying and layout in the area adjacent to the embedded end on one side of the optimized support pile pit and in the target area inside the pit to determine the location and range of the pile bottom reinforcement zone, the inner transition zone and the pit extension zone. Step 4: Use a lateral trenching and grouting integrated equipment to perform lateral trenching in the area around the embedded end on one side of the optimized support pile pit. During construction, the biaxial milling rod is lowered along the guide frame to the design depth. The lateral milling angle of the biaxial milling device is adjusted by the angle sensor. The power box drives the biaxial milling device to perform biaxial full-section milling on the in-situ soil. The cutting trajectory of the biaxial milling device is controlled by the stroke sensor and the correction device to cut and form a continuous strip or wall-shaped lateral trench. Step 5: During the lateral trenching process, cement grout is delivered to the bottom grouting pipe through a high-pressure grouting pipeline. Multiple injection holes in the bottom grouting pipe also function as rotary jet nozzles, moving synchronously with the biaxial milling device to spray cement grout onto the bottom of the lateral trench, the trench walls, and the surrounding disturbed soil areas. Under the action of reverse rotation milling and stirring of the biaxial milling rod, the grout mixes and solidifies with the in-situ soil to form a continuous cement-soil consolidation body. By controlling the grouting parameters, a pile bottom reinforcement zone, an inner transition zone, and an in-pit extension zone are formed. Step 6: Curing the reinforced body until its strength meets the design requirements, then excavating the foundation pit. Step 7: After the underground structure foundation slab is completed, optimize the support piles, reinforcement bodies and foundation slab to form a permanent load-bearing system.

[0017] Optionally, the lateral trenching and grouting integrated equipment includes an SJ1000 dual-axis side milling trenching machine. The SJ1000 dual-axis side milling trenching machine is fixed with a high-pressure grouting pipeline and a bottom grouting pipe. The high-pressure grouting pipeline is connected to the bottom grouting pipe. The SJ1000 dual-axis side milling trenching machine includes a dual-axis milling rod, an angle sensor, a power box, a dual-axis milling device, a stroke sensor, and a correction device. The bottom grouting pipe is located at or near the bottom of the dual-axis milling rod and has multiple injection holes along its length.

[0018] The beneficial effects of this invention are as follows: This solution is technically feasible, economically reasonable, and easy to construct. It can effectively optimize the embedment depth of deep foundation pit support piles, achieving functional substitution for reducing the embedment section. Furthermore, it allows the reinforced body to continue functioning as part of the foundation in the permanent stage, improving the overall integrity and long-term stability of the foundation. Moreover, this solution meets the strict deformation control requirements of the surrounding environment, has strong engineering applicability, and possesses good engineering suitability, as detailed below: Firstly, this scheme forms an H-shaped reinforced support structure by setting up a cement-soil reinforced body on the inner side. This reinforced body provides additional shear, displacement, and rotational constraints to the bottom of the support piles, successfully replacing some functions of the traditional deep-embedded section. The optimized support pile embedment depth can be reduced from the conventional design support pile to (0.15~0.20)H, significantly shortening the pile length and directly reducing the amount of concrete and steel reinforcement used, as well as the cost of drilling, thus comprehensively reducing the engineering cost of the foundation pit support. Utilizing the overall soil strengthening effect between the reinforced body and the optimized support piles, a collaborative working mode similar to the vertical main limb and horizontal outward-extending constraint limb in an H-shaped steel structure is constructed. When the optimized support piles undergo bending deformation under lateral earth pressure, the continuous reinforced body on one side of the pit provides passive resistance, shear resistance, and rotational constraints, effectively suppressing horizontal displacement and rotation at the pile bottom, ensuring the safety and deformation control of the foundation pit under the optimized embedment depth conditions. Meanwhile, the reinforced body is divided into a pile bottom reinforcement zone, an inner transition zone, and an in-pit extension zone in terms of functional areas, forming a gradual distribution of stiffness to avoid stress concentration.

[0019] Secondly, the reinforced body is located within the soil below the bottom of the foundation pit and beneath the foundation slab of the underground structure. During the service life of the underground structure, it participates in the stress distribution as a permanent reinforcement component beneath the foundation slab. This improves the overall strength and stiffness of the soil beneath the foundation slab, resulting in more uniform stress distribution and reducing localized deformation and uneven settlement at the edges of the foundation slab, the base of the basement walls, and the vicinity of the support piles. Furthermore, it allows for a reduction in the thickness of the foundation slab above the reinforced body, thus reducing the amount of concrete and steel reinforcement required. When foundation piles are installed at the bottom of the underground structure foundation, the number of piles can be reduced accordingly, or the pile spacing can be increased, thereby reducing the amount of pile foundation work and construction disturbance. This improves the overall stiffness and resistance to uneven settlement of the building foundation, extending the service life of the structure.

[0020] In addition, the reinforced body assumes part of the constraint function of the traditional deep embedded section, which reduces the embedment depth of the conventionally designed support piles, thereby reducing the drilling depth, material consumption, and construction disturbance, and lowering the construction risks in complex strata. Furthermore, the constraint provided by the reinforced body during the excavation of the foundation pit can effectively reduce the deformation of the pit wall and the heave of the pit bottom, reducing the adverse impact on surrounding buildings, pipelines, and roads. Attached Figure Description

[0021] Figure 1 This is a cross-sectional schematic diagram of the H-type reinforced support structure of the present invention; Figure 2 This is a schematic cross-sectional view of the support structure at a conventional embedment depth. Figure 3 This is a cross-sectional schematic diagram of an H-shaped reinforcement support structure with foundation piles in an embodiment of the present invention; Figure 4This is a schematic cross-sectional view of the support structure at the conventional embedment depth when foundation piles are provided in an embodiment of the present invention; Figure 5 This is a schematic diagram comparing the deformation of a conventional support structure and a H-type reinforced support structure in an embodiment of the present invention; Figure 6 This is a schematic diagram comparing the vertical deformation of the surrounding soil between a conventional support structure and a H-shaped reinforced support structure in an embodiment of the present invention. Figure 7 This is a schematic diagram comparing the horizontal deformation of the surrounding soil between a conventional support structure and a H-shaped reinforced support structure in an embodiment of the present invention. Figure 8 This is a construction site diagram of the H-type reinforcement support structure of the present invention used in the simulation embodiment; Figure 9 This is a schematic diagram of the lateral trenching and grouting integrated equipment in this embodiment.

[0022] The following are labels in the diagram: 1. Reinforced body; 2. Optimized support pile; 3. Foundation slab; 4. Foundation pile; 5. High-pressure grouting pipeline; 6. Bottom grouting pipe; 7. SJ1000 dual-axis side milling trenching machine. Detailed Implementation

[0023] To make the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the given embodiments are merely one implementation method and do not represent all embodiments.

[0024] Example 1 Combination Figure 1-2 This embodiment provides a permanent support structure that reduces the embedment depth and enhances the foundation stiffness. Specifically, the structure includes optimized support piles 2 and a reinforced body 1. The optimized support piles 2 are bored piles, segments of diaphragm walls, or other vertical load-bearing components capable of bearing lateral loads. The reinforced body 1 and the optimized support piles 2 form a synergistic force relationship through the overall reinforcement of the surrounding soil, constituting an H-shaped reinforced support structure in which the vertical main limb and the horizontal restraint limb work together.

[0025] The optimized support piles 2 are arranged around the perimeter of the foundation pit, with an embedded depth of optimized embedded depth L1, where L1 = (0.15~0.20)H, and H is the excavation depth of the foundation pit. The optimized embedded depth is less than the conventionally designed embedded depth L0. The reinforcement body 1 is set in the soil below the bottom of the foundation pit and below the foundation slab 3 of the underground structure, and forms a continuous cement-soil consolidation body through lateral trenching and jet grouting. The reinforcement body 1 extends from the lower part of the optimized support piles 2 into the pit, with a reinforcement depth D = (0.10~0.25)H and an extension width B = (0.05~0.15)H within the pit. Furthermore, the reinforcement body 1 is arranged in a strip or wall shape along one side of the optimized support piles 2 within the pit, which can participate in bearing the vertical load transmitted by the foundation slab 3 and improve the overall bearing capacity of the soil below the foundation slab 3, reducing local deformation and uneven settlement below the foundation slab 3.

[0026] The reinforced body 1 is functionally divided into a pile bottom reinforcement zone, an inner transition zone, and an in-pit extension zone to create a gradual stiffness distribution, avoid stress concentration, and enhance the ductility of the system. Specifically, the pile bottom reinforcement zone is located around the embedded end of the optimized support pile 2 and is used to directly bear the shear force and bending moment transmitted from the bottom of the optimized support pile 2; the inner transition zone is located outside the pile bottom reinforcement zone and is used to mitigate the abrupt change in stiffness between the optimized support pile 2 and the surrounding strata; the in-pit extension zone extends into the pit of the optimized support pile 2 and is used to provide additional shear resistance, passive resistance, and foundation stiffness enhancement. Each zone has different unconfined compressive strength design values: the unconfined compressive strength of the pile bottom reinforcement zone is 2.5~5.0 MPa; the unconfined compressive strength of the transition zone is 1.5~3.0 MPa; and the unconfined compressive strength of the in-pit extension zone is 0.8~2.0 MPa.

[0027] The equivalent stiffness, shear strength, and bending restraint provided by the reinforced body 1 satisfy the functional replacement of the reduced embedded section of the conventionally designed optimized support pile 2, and meet the corresponding equivalent embedded conditions: ; ; ; in, K s The equivalent stiffness provided for solid 1; The decrease in embedment stiffness due to the reduction in embedment depth from L0 to L1; V s The shear resistance provided to the solidified body 1; V d To optimize the design shear force at the bottom of support pile 2; M d To optimize the design bending moment at the bottom of support pile 2; M sThe bending moment provided for the solidified body 1.

[0028] Once the foundation slab 3 of the underground structure is completed and reaches its design strength, the reinforced body 1 consolidates with the surrounding soil, improving the overall strength and stiffness of the soil beneath the foundation slab 3. This results in more uniform stress distribution beneath the foundation slab 3, reducing local deformation and uneven settlement. Furthermore, provided that the requirements for foundation bearing capacity, settlement control, stress distribution on the foundation slab 3, and bearing capacity of the foundation piles 4 are met, conditions can be provided for reducing the thickness of the foundation slab 3, decreasing the number of foundation piles 4, or increasing the spacing between foundation piles 4. Specifically, for example... Figure 3-4 As shown, the thickness h1 of the conventional foundation slab 3 without the reinforcement 1 can be optimized to the reduced thickness h0 of the foundation slab 3, where h0 < h1; when the foundation piles 4 are provided at the bottom of the underground structure foundation, the number of conventional piles n1 can be optimized to the reduced number of piles n0, where n0 < n1, based on the effect of the reinforcement 1 on the bearing capacity and deformation coordination of the soil at the bottom of the foundation, or the spacing of the foundation piles 4 can be appropriately increased.

[0029] As one embodiment, when the settlement control requirements are high at the edge of the foundation slab 3 or in the vicinity of the optimized support piles 2, adjustments can be made by increasing the strength of the pile bottom reinforcement zone, increasing the width of the inner transition zone, or increasing the extension width B of the pit extension zone, in order to improve the foundation bearing capacity and deformation coordination capacity of the corresponding area. In specific design, the reinforced body 1 and the surrounding consolidated soil can be considered as the reinforcement range below the foundation slab 3, and its role in foundation bearing capacity, settlement control, and foundation stiffness enhancement can be determined by combining the strength of each zone, the reinforcement area, and the reinforcement depth.

[0030] As one embodiment, taking a deep foundation pit project with an excavation depth of H=18m as an example, the specific application of the H-shaped reinforcement support structure of the support pile-reinforcement body combination described in this invention is illustrated. Figure 8 .

[0031] The surrounding area uses bored piles as the support structure. In the conventional design scheme, according to the elastic foundation beam theory, the embedment depth of the conventional design support piles is L0=17m and the total pile length is 35m, in order to meet the requirements of foundation pit stability and deformation control.

[0032] Using the optimized structure of this invention, the embedment depth of the support pile 2 is reduced to: L1 = 3m (satisfying L1 = (0.15~0.20)H approximately 0.16H), total pile length 21m. Vertical reinforcement depth D = 2m (approximately 0.11H) of reinforced body 1, and extension width within the pit B = 1.5m (approximately 0.08H), both within the dimensional proportions defined in this scheme.

[0033] Specifically, the verification process for the equivalent embedding condition is as follows.

[0034] First, regarding the verification of equivalent stiffness: Based on the calculation results of the PLAXIS 3D numerical model, the internal forces and deformations near the embedded end of the support piles were extracted under the corresponding working conditions, and the following representative values ​​were obtained: .

[0035] The equivalent rotational constraint stiffness provided by the embedded section of the conventionally designed support pile is: .

[0036] According to the principle of equivalent embedment, the embedded section of the retaining pile can be approximated as an elastic foundation beam. Let the horizontal reaction coefficient of the foundation be k, then the equivalent embedment stiffness provided by the embedded section in the conventional design scheme is: .

[0037] The equivalent embedment stiffness provided by the remaining embedded segment is: ,but Substituting L1=3m and L0=17m, we get: .

[0038] The equivalent stiffness reduction of the original embedded section of the support pile is: .

[0039] Since solidification body 1 is a zoned cement-soil solidification body 1, the elastic modulus of the reinforced zone at the pile bottom is taken as: E s1 =500 MPa; the elastic modulus of the inner transition zone is taken as: E s2 =300 MPa; Elastic modulus of the extended zone within the pit is taken as: E s3 =150MPa. Considering that the three zones share the load, the equivalent elastic modulus of each zone is taken as: ; Calculated based on a unit width b=1m, the moment of inertia of the reinforced body section 1 is: Substituting b=1m and D=2m, we get: .

[0040] The bending stiffness of solid 1 is: .

[0041] Considering the interaction between the cement-soil reinforced body 1 and the surrounding soil, construction disturbance, and the influence of boundary constraints, the flexural stiffness reduction factor is taken as follows: η b =0.6, then the equivalent rotational constraint stiffness provided by reinforcement 1 is: ; E eq I s =211239kN m 2 Substituting B=1.5m, we get: ; Take the Poisson's ratio of cement and soil: ; The shear modulus of cement-soil is: ; Substitute E eq =316700kN / m 2 have to: ; The shear area of ​​solid 1 is: A s =bD,A s =1×2=2m 2 ; Take the shear stiffness reduction factor: η s =0.5; The equivalent shear stiffness provided by solid body 1 is: ; Substituting the values ​​into the equation: ; When the bottom of the support pile rotates, the shear stiffness can be supplemented by the extension width B within the pit to form an additional anti-rotation constraint. Its equivalent rotational stiffness can be expressed as: .

[0042] Substituting the values ​​into the equation:

[0043] Therefore, the comprehensive equivalent embedment stiffness that solidification body 1 can provide is:

[0044] The equivalent stiffness condition is: The above 267207 > 206856 meets the requirements.

[0045] This demonstrates that the partitioned cement-soil reinforcement 1 in this embodiment can compensate for the stiffness loss caused by the reduction of the embedment depth of the support pile from 17m to 3m.

[0046] Secondly, the shear condition check includes: In the PLAXIS 3D working condition of this invention, the maximum shear force near the embedded end of the support pile is extracted as: V d =850kN, the widths of the pile bottom reinforcement zone, inner transition zone, and pit extension zone along the pit direction are: B1=0.5m, B2=0.5m, B3=0.5m respectively. The minimum unconfined compressive strengths of the pile bottom reinforcement zone, inner transition zone, and pit extension zone are respectively: q u1 =2.5MPa, q u2 =1.5MPa, qu3 =0.8MPa.

[0047] The shear strength of cement-soil can be estimated using this formula: ; Therefore, the shear strengths of the cement-soil in the pile bottom reinforcement zone, the inner transition zone, and the pit extension zone are respectively: τ 1 = 1.25 MPa τ 2 = 0.75 MPa τ 3 = 0.40 MPa.

[0048] The shear strength provided by solid body 1 is: ; The total shear strength provided by solid body 1 is: ; ; Shear resistance conditions are: The above 2400 > 850 meets the requirements. This indicates that the cement-soil reinforced body 1 in the zone can withstand the shear force transmitted from the embedded end of the support pile.

[0049] Third, the bending condition check includes: In the working condition of this invention in PLAXIS 3D, the maximum bending moment and rotation angle near the embedded end of the support pile are extracted as follows: ; The bending moment of the reinforcement body 1 is calculated according to the stiffness type check: ; The bending resistance condition is: The value of 1068.8 > 960, which meets the bending resistance requirement.

[0050] To more intuitively verify the actual effect of the invention, a collaborative stress analysis model of the foundation pit support structure, foundation soil, and reinforced body was established using the three-dimensional finite element software PLAXIS 3D. The soil was modeled using HSS (Hyperstructure Support System), the support piles were simulated using plate elements, and the reinforced body 1 was modeled using solid elements with corresponding strength and stiffness parameters. The reinforced body 1 was modeled using a linear elastic model, with the elastic modulus of the pile bottom reinforcement zone being 500 MPa, the elastic modulus of the inner transition zone being 300 MPa, and the elastic modulus of the pit extension zone being 150 MPa.

[0051] Two calculation conditions were set up for comparison: Condition 1 (conventional design): conventional embedment depth L0, no reinforced body 1; Condition 2 (the scheme of this invention): embedment depth L1=3m, and the above-mentioned zoned cement-soil reinforced body 1 was set.

[0052] The deformation results after excavation to a depth of 18m from the bottom of the pit are as follows: Figure 5 This reflects the effect of reducing the embedment depth on controlling the lateral deformation of the support piles; Figure 6This reflects the controlling effect of the reinforced body 1 on the bulging of the pit bottom and the deformation of the foundation bottom; Figure 7 This reflects the effect of the reinforced body 1 on the constraint of the passive zone soil inside the pit and the overall deformation coordination.

[0053] Simulation results show that although the proposed solution significantly reduces the embedment depth to 3m (only 17.6% of the conventional solution), the deformation and internal forces of the support piles only increase slightly due to the H-shaped reinforcement structure, still fully meeting the deformation control requirements of relevant codes for the safety level of foundation pits. This strongly demonstrates that the reinforced body 1, by providing multiple constraints of shear resistance, bending resistance, and passive earth pressure at the bottom of the support piles, successfully achieves a structural replacement of the traditional deep embedment section function, while simultaneously improving the overall stiffness of the foundation, realizing the organic combination of temporary support and permanent structure.

[0054] In summary, by setting up a cement-soil reinforcement body 1 on the inner side to form an H-shaped reinforcement support structure, not only is the embedment depth of the deep foundation pit support piles effectively optimized, but it can also directly participate in the foundation stress as an artificial reinforcement layer of the foundation slab 3. This improves the overall stiffness of the building foundation and its resistance to uneven settlement, improves the stress state at the bottom of the support piles, reduces local deformation concentration, and extends the service life of the structure. Simultaneously, the constraint provided by the reinforcement body 1 during the foundation pit excavation process effectively reduces pit wall deformation and pit bottom heave, minimizing adverse impacts on surrounding buildings, pipelines, and roads, and enhancing construction safety. Furthermore, the reinforcement body 1 undertakes some of the constraint functions of the traditional deep embedment section, allowing for a reduction in the embedment depth of the support piles, thereby reducing drilling depth, material consumption, and construction disturbance, and lowering construction risks in complex strata. Therefore, this structural technology is feasible, economical, and convenient to construct, possessing significant potential for widespread application.

[0055] Example 2 This embodiment provides a construction method for a permanent support structure that reduces the embedment depth and strengthens the foundation stiffness, specifically including the following steps: Step 1, Parameter Determination: During the construction preparation stage, based on the excavation depth of the foundation pit, the geological survey report, and the environmental requirements for deformation control from adjacent buildings, a collaborative stress analysis model of the support piles and the reinforced body 1 is established. This model is used to calculate the equivalent embedment conditions required for the support structure during its permanent service phase, comprehensively determining the optimal embedment depth L1 of the support piles, as well as the vertical reinforcement depth D, the pit extension width B, and the planar layout dimensions of the reinforced body 1. Simultaneously, based on the different functional positioning of the pile bottom reinforcement zone, the inner transition zone, and the pit extension zone, the target strength parameters and stiffness requirements for each zone are determined, ensuring that the reinforced body 1 forms a gradually changing stiffness and collaboratively stressed overall constraint system from the bottom of the support piles to the inside of the pit.

[0056] Step 2, Support Pile Construction: The support piles are constructed according to the optimized embedment depth L1 determined in Step 1. First, surveying and setting out are carried out to determine the pile position and axis control points of each support pile. Then, the drilling, reinforcement cage placement, and concrete pouring procedures are completed in sequence, so that the embedment length of the support pile is significantly shorter than that of the conventional design scheme.

[0057] Step 3, reinforcement zone positioning: Before the excavation of the foundation pit, on-site measurement and layout are carried out in the area adjacent to the embedded end on one side of the support pile pit and the target reinforcement area in the pit according to the design drawings. Marking lines are used to mark the plane range and depth limits of the pile bottom reinforcement zone, the inner transition zone and the pit extension zone, so as to provide positioning benchmarks for subsequent construction.

[0058] Step 4, Lateral Trenching: A lateral trenching and grouting integrated equipment is used to create lateral trenches along the area adjacent to the embedded end of the retaining pile within the pit and the target reinforcement area. During construction, the biaxial milling rod is lowered along the guide frame to the designed depth. The lateral milling angle of the biaxial milling device is adjusted using an angle sensor. The power unit drives the biaxial milling device to perform biaxial full-section milling on the in-situ soil. Combined with a stroke sensor and a correction device, the biaxial milling device cuts the soil, achieving quantitative lateral trenching and forming continuous strip-shaped or wall-shaped lateral trenches in the soil. These lateral trenches extend from the bottom of the retaining pile towards the inside of the pit, with their depth and width corresponding to the designed reinforcement range.

[0059] Step 5, Synchronous rotary jet curing: During the lateral trenching process described in Step 4, cement slurry is delivered to the bottom grouting pipe 6 through the high-pressure grouting pipeline 5. The bottom grouting pipe 6 is equipped with multiple injection holes and also serves as a rotary jet nozzle. It moves synchronously with the biaxial milling device, so that the cement slurry is synchronously rotary jet-cured on the bottom, walls and surrounding disturbed soil of the lateral trench through the injection holes. Under the reverse rotation milling and stirring action of the biaxial milling rod, it is mixed with the in-situ soil to form a continuous cement-soil consolidation body.

[0060] During construction, grouting process parameters, including grouting pressure, lifting speed, grout mix ratio, and number of re-grouting operations, were controlled for the pile bottom reinforcement zone, the inner transition zone, and the pit expansion zone. This ensured that the pile bottom reinforcement zone formed a high-strength and high-rigidity cement-soil mass, the inner transition zone formed a medium-strength transition reinforcement zone, and the pit expansion zone formed a reinforcement zone that met the overall reinforcement stiffness and anti-heave requirements. The zones transitioned continuously without interface separation, forming a unified load-bearing reinforced body.

[0061] It is important to understand that the lateral trenching and grouting integrated equipment provided in this embodiment is based on the existing SJ1000 twin-axis side milling trenching machine, with structural improvements and the addition of grouting-related structures to achieve integrated trenching and grouting operations. Specifically, this lateral trenching and grouting integrated equipment includes an SJ1000 twin-axis side milling trenching machine 7, and supporting high-pressure grouting pipeline 5 and bottom grouting pipe 6. Both the high-pressure grouting pipeline 5 and the bottom grouting pipe 6 are fixedly installed on the SJ1000 twin-axis side milling trenching machine 7. The SJ1000 twin-axis side milling trenching machine 7 is an existing mature device. Its standard components include a twin-axis milling rod, an angle sensor, a power box, a twin-axis milling device, a stroke sensor, and a correction device. The specific assembly structure, connection relationship, and inherent working principle of each component are existing technologies in this field and will not be described in detail here. The high-pressure grouting pipeline 5 has one end connected to an external high-pressure grouting device and the other end sealed to the bottom grouting pipe 6 via a flange. A sealing gasket is installed at the connection to prevent grout leakage during high-pressure grouting. The diameter of the high-pressure grouting pipeline 5 is set according to the grouting flow rate requirements and is adapted to the construction parameters of the SJ1000 twin-axis side milling trenching machine.

[0062] The bottom grouting pipe 6 has a length adapted to the bottom length of the biaxial milling rod and is located at or near the bottom of the biaxial milling rod. Multiple injection holes are provided on the bottom grouting pipe 6, and these injection holes are evenly spaced along the length of the bottom grouting pipe 6. The number of injection holes can be adjusted according to the length of the biaxial milling rod and the grouting requirements to ensure that the grouting coverage area matches the trench width and depth.

[0063] Step 6, Earthwork Excavation: The reinforced body 1 is cured until its strength is confirmed to meet design requirements through core sampling or penetration testing. Then, the foundation pit is excavated in layers and sections. During excavation, displacement monitoring points are installed at key locations on the support piles and reinforced body 1 to monitor the horizontal displacement of the support piles, the heave of the pit bottom, and the deformation of reinforced body 1 in real time. If abnormal trends are observed in the monitoring data, measures such as adding temporary supports or localized reinforcement grouting are taken promptly to ensure that reinforced body 1 and support piles are always under coordinated stress.

[0064] Step 7, Permanent Structure Collaboration: After the underground foundation slab 3 is constructed and reaches its design strength, the support piles, the reinforced body 1, and the foundation slab 3 are tightly integrated to form a permanent load-bearing system. The reinforced body 1, as an artificial reinforcement layer below the bottom of the foundation pit, continuously provides shear restraint, bending restraint, and passive earth pressure during the structural service phase. This effectively limits the long-term lateral deformation of the support piles and improves the overall stiffness and resistance to uneven settlement of the building foundation, providing conditions for thinning the foundation slab 3, reducing the number of foundation piles 4, or increasing the spacing between foundation piles 4.

[0065] By using the above construction methods, the embedment depth of the support piles can be significantly reduced, the project investment can be reduced, the construction period can be shortened, and the overall performance of the foundation structure can be improved, all while ensuring the safety of the foundation pit construction and its permanent use function.

[0066] The specific embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A permanent support structure that reduces embedment depth and strengthens foundation stiffness, characterized in that: Includes optimized support piles (2) and reinforced body (1). The optimized support piles (2) are arranged around the perimeter of the foundation pit, and their embedment depth is the optimized embedment depth L1, and L1 = 0.15~0.20H, where H is the excavation depth of the foundation pit. The optimized embedment depth is less than the embedment depth L0 designed according to conventional methods. The reinforcement body (1) is located in the soil below the bottom of the foundation pit and below the foundation slab (3) of the underground structure, and is arranged around the embedded end of the optimized support pile (2); the reinforcement body (1) is a continuous cement-soil solidified body formed by lateral trenching and jet spraying of soil and cement grout. The reinforced body (1) extends into the pit from the lower part of the self-optimizing support pile (2), and its reinforcement depth D satisfies D=0.10~0.25H, and its extension width in the pit B satisfies B=0.05~0.15H; The reinforced body (1) and the optimized support pile (2) form a synergistic force relationship through the overall reinforcement of the surrounding soil, constituting a H-shaped reinforcement support structure in which the vertical main limb and the horizontal restraint limb work together. The reinforced body (1) is divided into a pile bottom reinforcement zone, an inner transition zone and an in-pit expansion zone in terms of functional areas. Each functional zone is formed by controlling the grouting parameters. The pile bottom reinforcement zone is located around the embedded end of the optimized support pile (2) and is used to directly bear the shear force and bending moment transmitted from the bottom of the optimized support pile (2); the inner transition zone is set outside the pile bottom reinforcement zone and is used to mitigate the abrupt change in stiffness between the optimized support pile (2) and the surrounding strata; the pit extension zone extends into the pit of the optimized support pile (2) and is used to provide additional shear resistance, passive resistance and foundation reinforcement stiffness; the unconfined compressive strength of the pile bottom reinforcement zone is 2.5~5.0MPa; the unconfined compressive strength of the inner transition zone is 1.5~3.0MPa; the unconfined compressive strength of the pit extension zone is 0.8~2.0MPa; The equivalent stiffness, shear strength, and bending restraint provided by the solidified body (1) satisfy the functional substitution for reducing the embedded section of the support pile under conventional design, specifically satisfying the following equivalent embedded conditions: ； ； ； in, K s The equivalent stiffness provided to the solid (1); The decrease in embedment stiffness due to the reduction in embedment depth from L0 to L1; V s The shear resistance provided to the solidified body (1); V d To optimize the design shear force at the bottom of the support pile (2); M d To optimize the bottom design bending moment of the support pile (2); M s The bending moment provided for the solidified body (1).

2. The permanent support structure for reducing embedment depth and strengthening foundation stiffness according to claim 1, characterized in that: The optimized support pile (2) is a bored pile, a section of underground continuous wall or other vertical load-bearing component that can bear lateral loads.

3. The permanent support structure for reducing embedment depth and strengthening foundation stiffness according to claim 1, characterized in that: The reinforcement body (1) is arranged along one side of the pit of the optimized support pile (2), and is arranged in a strip or wall shape.

4. The permanent support structure for reducing embedment depth and strengthening foundation stiffness according to claim 1, characterized in that: The shear resistance provided by the solidified body (1) V s Determined based on the dimensions of the solidified body (1) and the shear strength of the cement-soil: ； in, τ The shear strength of cement-soil; B To solidify the soil, (1) extend its width into the pit; D The vertical reinforcement depth of the solid (1) is given.

5. The permanent support structure for reducing embedment depth and strengthening foundation stiffness according to claim 1, characterized in that: The bending moment resistance provided by the solidified body (1) M s Determined by the equivalent stiffness of the reinforced body (1) and the bottom rotation angle of the optimized support pile (2): ； Where θ is the bottom rotation angle of the optimized support pile (2).

6. The construction method for a permanent support structure that reduces embedment depth and strengthens foundation stiffness as described in any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Based on the excavation depth of the foundation pit, the geological conditions and the requirements of the surrounding environment, determine the optimized embedment depth L1 of the optimized support pile (2) and the planar dimensions, vertical reinforcement depth D, pit extension width B and strength parameters of the reinforced body (1); Step 2: Construct optimized support piles (2) according to the optimized embedment depth L1, determine the position and axis control points of optimized support piles (2), and complete hole drilling, reinforcement cage placement and concrete pouring; Step 3: According to the design drawings, conduct surveying and layout in the area adjacent to the embedded end on one side of the optimized support pile (2) pit and the target area in the pit to determine the location and range of the pile bottom reinforcement zone, the inner transition zone and the pit expansion zone; Step 4: Use a lateral trenching and grouting integrated equipment to perform lateral trenching in the area around the embedded end of the optimized support pile (2) pit. During construction, lower the dual-axis milling rod along the guide frame to the design depth, adjust the lateral milling angle of the dual-axis milling device through the angle sensor, and drive the dual-axis milling device to perform dual-axis full-section milling on the in-situ soil by the power box. With the help of the stroke sensor and the correction device, control the cutting trajectory of the dual-axis milling device to cut and form a continuous strip or wall-shaped lateral trench. Step 5: During the lateral trenching process, cement slurry is delivered to the bottom grouting pipe (6) through the high-pressure grouting pipeline (5); the multiple injection holes of the bottom grouting pipe (6) also serve as rotary spray nozzles, and move synchronously with the dual-axis milling device to spray cement slurry to the bottom of the lateral trench, the trench wall and the surrounding disturbed soil area. The slurry is mixed and solidified with the in-situ soil under the action of milling and stirring by the reverse rotation of the biaxial milling rod, forming a continuous cement-soil solidified body; Step 6: Curing the reinforced body (1) until its strength reaches the design requirements, then excavating the foundation pit. Step 7: After the underground structure foundation slab (3) is completed, the support piles (2), the reinforced body (1) and the foundation slab (3) are optimized to form a permanent load-bearing system.

7. The construction method for a permanent support structure that reduces embedment depth and strengthens foundation stiffness according to claim 6, characterized in that: The lateral trenching and grouting integrated equipment includes an SJ1000 dual-axis side milling trenching machine (7), on which a high-pressure grouting pipeline (5) and a bottom grouting pipe (6) are fixed. The high-pressure grouting pipeline (5) is connected to the bottom grouting pipe (6). The SJ1000 dual-axis side milling trenching machine (7) includes a dual-axis milling rod, an angle sensor, a power box, a dual-axis milling device, a stroke sensor, and a correction device. The bottom grouting pipe (6) is located at the bottom of the dual-axis milling rod or near the bottom, and has multiple injection holes along its length.

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