Method for foundation treatment of gravity dam including thick soil layer foundation

Abstract

This disclosure provides a method for treating the foundation of a gravity dam, including a thick soil interlayer, belonging to the field of hydraulic engineering. The method includes: obtaining the foundation parameters of the ground beneath the gravity dam body; the foundation including a thick soil interlayer; based on the foundation parameters, installing cast-in-place piles below the foundation surface of the gravity dam, penetrating the thick soil interlayer and embedded in the underlying bedrock; and performing consolidation grouting treatment on the thick soil interlayer within the dam foundation area to form a grouting structure penetrating the thick soil interlayer and extending into the underlying bedrock. This disclosure can improve the anti-sliding stability of the gravity dam along the thick soil interlayer and control the dam foundation settlement without changing the dam site or completely removing the thick soil interlayer.

Description

Technical Field

[0001] This disclosure relates to the field of hydraulic engineering in water conservancy projects, and in particular to a method for treating gravity dam foundations including thick soil layers. Background Technology

[0002] Gravity dams have strict requirements for foundation conditions, typically needing to be situated on intact bedrock. When a thick layer of soil is present in the dam foundation, this soil layer has low shear strength and a small deformation modulus, making it prone to sliding and settlement along the dam body. Existing technologies mainly involve relocating the dam site or completely removing the thick soil layer, but the former may be limited by dam site resources, while the latter involves a large amount of engineering work and high costs. Therefore, how to provide an economical and reliable method for treating gravity dam foundations without relocating the dam site or completely removing the thick soil layer has become an urgent problem to be solved.

[0003] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0004] This disclosure provides a gravity dam foundation treatment method including a thick soil layer foundation, thereby overcoming, to at least some extent, the problem of high engineering costs caused by the need to change the dam site or completely excavate the thick soil layer in the prior art.

[0005] Other features and advantages of this disclosure will become apparent from the following detailed description, or may be learned in part from practice of this disclosure.

[0006] According to one aspect of this disclosure, a method for treating the foundation of a gravity dam, including a thick soil interlayer, is provided, comprising: obtaining foundation parameters of the foundation below the gravity dam body; the foundation including a thick soil interlayer; based on the foundation parameters, setting cast-in-place piles below the foundation surface of the gravity dam, penetrating the thick soil interlayer and embedded in the underlying bedrock; and performing consolidation grouting treatment on the thick soil interlayer within the dam foundation area to form a grouting structure penetrating the thick soil interlayer and extending into the underlying bedrock.

[0007] In one exemplary embodiment of this disclosure, The exemplary embodiments disclosed herein have the following beneficial effects: The foundation parameters of the ground beneath the gravity dam body are obtained; the foundation includes a thick interlayer of soil. Based on the foundation parameters, cast-in-place piles are installed below the foundation surface of the gravity dam, penetrating the thick interlayer of soil and embedded in the underlying bedrock. The thick interlayer of soil within the dam foundation area is consolidated and grouted to form a grouting structure that penetrates the thick interlayer of soil and extends deep into the underlying bedrock. On one hand, the cast-in-place piles directly transfer the dam load to the underlying bedrock, controlling settlement, and replacing part of the low-strength soil layer with high-shear-strength reinforced concrete, improving the anti-sliding stability along the thick interlayer of soil. On the other hand, the grouting structure formed by consolidation grouting penetrates, splits, and cements the thick interlayer of soil, further improving its shear strength index and compression modulus, working synergistically with the cast-in-place piles to enhance anti-sliding stability and control settlement. Furthermore, this exemplary embodiment can achieve the above effects without changing the dam site or completely excavating the thick interlayer of soil, and has low engineering costs and a short construction period.

[0008] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0009] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0010] Figure 1 The flowchart schematically illustrates a gravity dam foundation treatment method for a thick soil interlayer foundation; Figure 2 A schematic diagram showing the plan layout of the dam foundation piles; Figure 3 A schematic cross-sectional view of the dam foundation treatment method is shown. Figure 4 A schematic longitudinal section view of the dam foundation treatment method is shown. Figure 5 This diagram schematically illustrates a cross-sectional view of the dam foundation in the relevant technology. Among them, 1-1, gravity dam body; 1-2, gravity dam foundation surface; 1-3, transverse joint of gravity dam section; 2, cast-in-place piles; 2-1 lower pile tip of cast-in-place pile; 2-2 top of cast-in-place pile; 3, foundation consolidation grouting; 3-1, bottom line of consolidation grouting; 4, thick interlayer soil; 4-1, boundary line between thick interlayer soil and upper bedrock; 4-2, boundary line between thick interlayer soil and lower bedrock; 5, upper bedrock; 6, lower bedrock; 7, symmetry axis of dam foundation surface; 8, ground line. Detailed Implementation

[0011] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, they are provided so that this disclosure will be more comprehensive and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0012] Exemplary embodiments of this disclosure first provide a method for treating a gravity dam foundation including a thick soil interlayer. The following, in conjunction with the appendix... Figure 1 The exemplary embodiments will be further described as follows: Figure 1 As shown, the above-mentioned gravity dam foundation treatment method including thick soil interlayer foundation may include the following steps S110~S130: Step S110: Obtain the foundation parameters of the ground beneath the gravity dam body; the foundation includes a thick interlayer of soil.

[0013] Gravity dams are water-retaining structures that rely on their own weight to maintain stability, such as concrete gravity dams, roller-compacted concrete gravity dams, or masonry gravity dams. The area below the dam body refers to the soil and rock region below the foundation. The foundation refers to the natural or artificially treated strata that bear the load of the dam and transmits it to deeper rock layers, such as rock foundations, soil foundations, or composite soil-rock foundations.

[0014] Foundation parameters can be indicators or data used to describe the physical and mechanical properties, geometric characteristics, and bearing capacity of the foundation, such as the thickness and burial depth of each soil and rock layer, shear strength indices (including friction coefficient and cohesion), compression modulus, saturated uniaxial compressive strength of rock, and axial compressive strength of concrete. Thick interlayers refer to soil layers located within the dam foundation rock mass that have a certain thickness (usually greater than 0.5 meters) and low shear strength and deformation modulus, such as completely weathered layers, residual soil layers, mudstone interlayers within fault fracture zones, or sedimentary clay interlayers.

[0015] Methods for obtaining foundation parameters may include: conducting indoor geotechnical tests after sampling through geological exploration boreholes; using in-situ tests such as standard penetration tests, static cone penetration tests, or wave velocity tests; making inferences based on geological data from adjacent projects; or using geophysical exploration methods such as seismic reflection and resistivity imaging to obtain the parameters. For example, at a dam site, by arranging five exploration boreholes and taking undisturbed soil samples at the location of thick interlayer soil, the shear friction coefficient was measured to be 0.3 and the cohesion to be 15 kPa. At the same time, the soil compression modulus was obtained by wave velocity testing in the boreholes. Alternatively, empirical values ​​from existing geological parameter databases can be directly accessed by combining regional geological maps and previous exploration reports.

[0016] Step S120: Based on the foundation parameters, cast-in-place piles are installed below the foundation surface of the gravity dam, penetrating the thick interlayer of soil and embedded in the underlying bedrock.

[0017] The foundation surface refers to the bottom surface of a gravity dam that is in direct contact with the foundation, typically the excavated and cleared rock or soil surface. Embedding refers to pressing or casting a portion of the pile into the underlying rock strata to form a fixed connection. Below the foundation surface of a gravity dam refers to the foundation area extending downwards from the foundation surface. The lower bedrock refers to a relatively intact and strong rock layer located below a thick layer of interbedded soil, such as granite, basalt, limestone, or sandstone. A cast-in-place pile is a columnar load-bearing member formed by drilling, placing a reinforcing cage, and pouring concrete. Installing cast-in-place piles that penetrate the thick interbedded soil layer and embed into the lower bedrock can be achieved by arranging several piles under each dam section, allowing the pile body to penetrate the thick interbedded soil layer and the pile tip to penetrate the lower bedrock to a certain depth. This directly transfers the dam load to the lower bedrock and utilizes the shear strength of the pile body to improve the overall shear strength of the thick interbedded soil layer.

[0018] In this exemplary embodiment, the target number and arrangement of cast-in-place piles can be determined first based on the foundation parameters. Then, cast-in-place piles that penetrate the thick interlayer of soil and embed into the underlying bedrock can be installed below the foundation surface of the gravity dam. Specifically, rotary drilling cast-in-place piles, impact drilling cast-in-place piles, or long spiral drilling pressure grouting piles can be used. For example, in the foundation treatment of a gravity dam, after calculation based on geological parameters, drilled cast-in-place piles with a diameter of 1m can be arranged below the foundation surface. After drilling through the 2m thick interlayer of soil, the drilling continues to penetrate 1m into the underlying basalt. Then, the steel cage is lowered and concrete is poured. Alternatively, for cases with thick soft interlayers, post-grouting technology can be used to enhance the pile side resistance, or enlarged-base cast-in-place piles can be used to increase the bearing area at the pile tip.

[0019] Step S130: Consolidation grouting is performed on the thick soil layer within the dam foundation area to form a grouting structure that penetrates the thick soil layer and extends into the underlying bedrock.

[0020] The dam foundation area refers to the region covered by the projected foundation surface of a gravity dam, and may also include a certain width of foundation reinforcement zone upstream and downstream. Consolidation grouting refers to injecting a cementing grout into the soil layer through boreholes, filling pores and fissures and cementing loose particles, thereby improving the integrity, strength, and impermeability of the foundation. The underlying bedrock is defined as above. Grouting structures refer to the network or vein-like reinforced bodies formed after the grout diffuses and solidifies in the soil layer, including grout veins, cement-soil mixtures, and compacted undisturbed soil.

[0021] For the thick soil interlayer within the dam foundation area, consolidation grouting is performed to form a grouting structure that penetrates the thick soil interlayer and extends into the underlying bedrock. Specifically, grouting holes are arranged on the foundation surface, with the hole depth penetrating the thick soil interlayer and extending into the underlying bedrock by no less than 3 meters. Cement grout is then injected using pressure grouting. Under pressure, the grout permeates along the pores, bedding, or fissures of the soil layer. Simultaneously, hydraulic fracturing may occur, forming irregular grout veins. These grout veins, after cementing with the soil, form a three-dimensional network of reinforced body. For example, a quincunx pattern of holes with a hole spacing of 3m and a row spacing of 3m can be used. The grouting pressure is controlled in stages at 0.3MPa, 0.5MPa, and 0.8MPa. P.O42.5 ordinary Portland cement is used as the grout, and the water-cement ratio gradually changes from 2:1 to 0.5:1 until the grout absorption rate is less than 1L / min. Alternatively, for cohesive soil layers with poor permeability, high-pressure jet grouting or deep mixing grouting can be used to directly form cement-soil piles.

[0022] It should be noted that, in order to facilitate construction and prevent temperature cracks, the dam body can be divided into sections along the dam axis (perpendicular to the water flow direction), with transverse joints separating the sections. The length of each section is generally 15 to 25 meters. This exemplary embodiment can process each section of the dam body separately.

[0023] Figure 2 The schematic diagram shows the plan layout of the dam foundation piles, including the gravity dam body, dam foundation surface, transverse joints of the dam section, piles, and the symmetrical axis of the dam foundation surface. The piles are arranged symmetrically along the symmetrical axis of the dam foundation surface. Figure 3 The diagram schematically shows a cross-sectional view of the dam foundation treatment method, also known as the AA cross-section, which shows the gravity dam body, foundation surface, cast-in-place piles, dam foundation consolidation grouting, consolidation grouting bottom line, thick interlayer soil, upper bedrock, lower bedrock, and ground line. The cast-in-place piles penetrate the thick interlayer soil, with the pile tip embedded in the lower bedrock and the pile top extending into the dam body. The consolidation grouting penetrates the thick interlayer soil and extends deep into the lower bedrock. Figure 4 The schematic diagram shows the longitudinal section of the dam foundation treatment method, namely the BB longitudinal section, which shows the cast-in-place piles, dam foundation consolidation grouting, consolidation grouting bottom line, thick interlayer soil, upper bedrock, lower bedrock and ground line, clearly showing the longitudinal layout relationship of the foundation treatment structure. Figure 5 The diagram schematically illustrates a cross-sectional view of a dam foundation in the relevant art, that is, a schematic cross-sectional view of a dam foundation without the treatment of this exemplary embodiment. It shows the gravity dam body, foundation surface, upper bedrock, thick interlayer soil, lower bedrock and ground line, without the installation of cast-in-place piles and consolidation grouting treatment structures.

[0024] Based on the above description, in this exemplary embodiment, the foundation parameters of the ground beneath the gravity dam body are obtained; the foundation includes a thick interlayer of soil; according to the foundation parameters, cast-in-place piles are installed below the foundation surface of the gravity dam, penetrating the thick interlayer of soil and embedded in the underlying bedrock; the thick interlayer of soil within the dam foundation area is consolidated and grouted to form a grouting structure that penetrates the thick interlayer of soil and extends into the underlying bedrock. On the one hand, the cast-in-place piles directly transfer the dam load to the underlying bedrock, controlling settlement, and replacing part of the low-strength soil layer with high-shear-strength reinforced concrete, improving the anti-sliding stability along the thick interlayer of soil; on the other hand, the grouting structure formed by consolidation grouting penetrates, splits, and cements the thick interlayer of soil, further improving its shear strength index and compression modulus, and working synergistically with the cast-in-place piles to enhance anti-sliding stability and control settlement. Furthermore, this exemplary embodiment can achieve the above effects without changing the dam site or completely excavating the thick interlayer of soil, and has low engineering costs and a short construction period.

[0025] In an exemplary embodiment, the aforementioned method of installing cast-in-place piles that penetrate thick soil layers and embed into the underlying bedrock below the foundation surface of a gravity dam, based on foundation parameters, may include: Based on the foundation parameters, determine the target number of cast-in-place piles for each dam section and the corresponding layout for each dam section; According to the layout method, the target number of cast-in-place piles are set under the corresponding dam section; The lower end of each cast-in-place pile is embedded in the hard rock beneath the thick soil layer to a first preset depth, and the top of each cast-in-place pile extends into the gravity dam body to a second preset depth.

[0026] The target number refers to the number of cast-in-place piles required, after verification, to meet the requirements of anti-sliding stability and bearing capacity of the dam body. The arrangement method refers to the planar arrangement of the cast-in-place piles within the foundation surface, such as symmetrical, asymmetrical, staggered, or rectangular grid arrangements. First, based on the foundation parameters, the target number of cast-in-place piles for each dam section is determined, and the corresponding arrangement method for each dam section is also determined. Methods for determining the target number may include iterative calculations using the weighted average method for anti-sliding stability combined with bearing capacity verification; back-calculation of the required number of piles using finite element numerical simulation; or estimation based on empirical formulas from similar projects. Methods for determining the arrangement method may include directly adopting a symmetrical arrangement principle to avoid uneven settlement; adjusting the pile density based on the asymmetry of geological conditions; or arranging according to the minimum spacing required by structural requirements. For example, when the foundation parameters of a certain dam section show that the thick interlayer of soil is inclined downstream and there is an open surface, the target number is calculated to be 28. The arrangement is 14 on each side of the central axis of symmetry of the dam foundation surface, arranged in 4 rows in the direction of water flow. Another example is when the foundation parameters show that the soil layer thickness is uneven, a zoned arrangement can be adopted, with denser arrangement in the thick layer area and sparser arrangement in the thin layer area, but overall symmetry is still maintained.

[0027] Then, according to the layout, the target number of cast-in-place piles are set under the corresponding dam section. The specific construction method for setting up the cast-in-place piles can be as follows: first, the pile positions are measured and marked, then the holes are drilled using a drilling rig. During the drilling process, mud slurry or casing is used to protect the wall to prevent the hole from collapsing. After cleaning the hole, the reinforcing cage is lowered, and finally, concrete is poured. For example, according to the symmetrical layout scheme, a pile position is marked every 3m on both sides of the centerline of the dam section, for a total of 28 holes. A rotary drilling rig is used to drill holes with a diameter of 1.0m. The holes are drilled to the design depth (penetrating the interlayer soil and entering the bedrock 1m). After the sediment thickness at the bottom of the hole is less than 5cm, the reinforcing cage is lowered, and underwater concrete is poured using the tremie method.

[0028] In this design, the lower end of each cast-in-place pile is embedded in the hard rock beneath a thick layer of interbedded soil to a first predetermined depth, and the top of each pile extends into the gravity dam body to a second predetermined depth. The first predetermined depth h1 refers to the length of the lower pile end embedded in the underlying bedrock, for example, 0.5~1.0m, and its function is to ensure the pile end is firmly embedded in the bedrock and prevent pile end slippage. The second predetermined depth h2 refers to the length of the pile top extending into the concrete dam body, for example, 0.5m, and its function is to anchor the pile top to the dam body, allowing the pile and dam body to work together to resist horizontal thrust. This exemplary embodiment allows for controlling the borehole depth to be a first preset depth greater than the bottom of the thick interlayer soil during drilling; during concrete pouring, the pile top elevation is controlled at a second preset depth above the foundation surface, which is then wrapped around the dam body during pouring. For example, in a certain project, the first preset depth is 0.8m, the second preset depth is 0.5m, the drilling depth during construction is 0.8m below the bottom of the interlayer soil, and the pile top elevation is 0.5m above the foundation surface, which is then integrally poured with the dam body concrete later; another example is that when the bedrock has large undulations, grouting at the pile bottom can be used to ensure the rock embedding effect; and the pile top can be reinforced with pre-reserved reinforcing bars to strengthen the connection with the dam body.

[0029] By embedding the pile tip into the bedrock and extending the pile top into the dam body, an integrated anti-sliding and load-bearing structure of "pile-dam" is formed. Compared with simply placing the pile in the soil layer, this significantly improves the pile's pull-out resistance and resistance to horizontal loads, effectively preventing the dam body from sliding along the interlayer of soil and uneven settlement.

[0030] In an exemplary embodiment, the first preset depth is 0.5 meters to 1.0 meters, and the second preset depth is 0.5 meters.

[0031] The first preset depth ensures reliable embedment of the pile tip into the bedrock, preventing slippage or pull-out, while controlling construction costs. The second preset depth ensures integral anchorage between the pile top and the dam body, achieving coordinated load-bearing. Together, these two depths allow the cast-in-place pile to fully utilize its anti-slip and load-bearing functions. It should be noted that the range of values ​​can be adjusted appropriately based on specific geological conditions and dam loads. For example, when the bedrock strength is low, an upper limit of 1.0 meter can be used, while when the bedrock is intact and hard, a lower limit of 0.5 meters can be used.

[0032] In an exemplary embodiment, determining the target number of cast-in-place piles for each dam section based on foundation parameters may include: Obtain the preset number of cast-in-place piles in each dam section, and verify the preset number of cast-in-place piles based on foundation parameters and preset conditions; When the preset number of cast-in-place piles passes verification, the preset number of cast-in-place piles in each dam section will be determined as the target number of cast-in-place piles in each dam section.

[0033] The preset number of cast-in-place piles refers to the number of cast-in-place piles that the designers initially assume need to be installed in a certain dam section, such as a value initially selected based on experience or analogous projects. Preset conditions refer to the criteria for judging whether the preset number is feasible, such as deep anti-sliding stability conditions, bearing capacity conditions, deformation conditions, or economic conditions.

[0034] In this exemplary embodiment, the preset number of cast-in-place piles in each dam section can be obtained first, and then verified based on foundation parameters and preset conditions. Verification methods may include substituting the preset number into a mechanical model to calculate the safety factor or bearing capacity, and then comparing it with the allowable value specified in the code; or performing numerical simulation analysis; or using analytical formulas for calculation, etc. For example, if the preset number for a certain dam section is initially assumed to be 24 piles, and the foundation parameters show low shear strength of the interlayer soil, then the anti-sliding stability condition is first verified: the calculated comprehensive shear friction coefficient is less than the value required by the code, therefore the verification fails; then the preset number is increased to 28 piles for re-verification, and the friction coefficient increases to a value greater than the value required by the code, thus meeting the requirement; alternatively, the preset number can also be directly selected by consulting empirical charts in the design manual, and then verified through bearing capacity conditions; if not met, the number is adjusted and re-verified.

[0035] Once the pre-set number of cast-in-place piles passes verification, the pre-set number of cast-in-place piles in each dam section is determined as the target number of cast-in-place piles for that dam section. The target number is the actual number of piles to be installed during final construction. For example, if 28 piles pass all the pre-set conditions after the above verification, the target number is set at 28 piles; or, if the geological conditions of a certain dam section are good, and the pre-set number of 20 piles passes verification, then the target number is 20 piles; the target number may differ for different dam sections.

[0036] Through the above verification mechanism, the determination of the number of cast-in-place piles can be transformed from experience-based judgment to scientific decision-making based on parameters and conditions, ensuring a balance between the safety and economy of the design, and avoiding waste caused by blindly increasing the number of piles or leaving safety hazards due to insufficient piles.

[0037] In an exemplary embodiment, the aforementioned preset conditions include deep anti-sliding stability conditions; the aforementioned foundation parameters include the shear strength index of concrete, the shear strength index of thick interlayer soil, and the total area of ​​the thick interlayer soil under the dam foundation in each dam section; The above verification of the preset number of cast-in-place piles based on foundation parameters and preset conditions includes: Based on the number of pre-cast piles in each dam section and the cross-sectional area of ​​a single pile, determine the corresponding pre-cast pile cut-off area for each dam section. Based on the pre-set cut-off area of ​​the cast-in-place piles and the total area of ​​the thick interlayer soil under the dam foundation in each dam section, determine the area of ​​the thick interlayer soil not cut off by the cast-in-place piles in each dam section. The comprehensive shear strength index of the thick soil layer is determined based on the shear strength index of concrete, the pre-set cut-off area of ​​cast-in-place piles, the shear strength index of the thick soil layer, and the area of ​​the thick soil layer not cut off by cast-in-place piles. To determine whether the comprehensive shear strength index meets the deep anti-sliding stability conditions, the preset number of cast-in-place piles is verified.

[0038] The shear strength of concrete refers to the shear friction coefficient (f2) and cohesion (c2) of the concrete material used in cast-in-place piles, for example, f2=1.8, c2=3000kPa. The shear strength of the thick soil interlayer refers to the shear friction coefficient (f1) and cohesion (c1) of the natural soil layer, for example, f1=0.3, c1=15kPa. The total area of ​​the thick soil interlayer under the dam foundation within each dam section refers to the horizontally distributed area of ​​the thick soil interlayer within the projected area of ​​the foundation surface of that dam section, denoted as M3. For example, if a dam section is 20m long and 20m wide, then M3=400m².

[0039] In this exemplary embodiment, the number of pre-set cast-in-place piles is verified based on foundation parameters and preset conditions. First, the cross-sectional area of ​​the pre-set cast-in-place piles corresponding to each dam section can be determined based on the number of pre-set cast-in-place piles in each dam section and the cross-sectional area of ​​a single pile. The cross-sectional area of ​​a single pile refers to the cross-sectional area of ​​a single cast-in-place pile. For a circular pile, the area is π×(D / 2)², where D is the pile diameter. The pre-set cross-sectional area M² = pre-set number n × single pile cross-sectional area m. For example, if the pre-set number n = 28 and the pile diameter D = 1.0 m, then m = 0.785 m², and M² = 28 × 0.785 ≈ 22 m². Alternatively, when rectangular piles are used, the cross-sectional area of ​​a single pile is width multiplied by height.

[0040] Then, based on the preset cut-off area M2 of the cast-in-place piles and the total area M3 of the thick interlayer soil beneath the dam foundation in each dam section, the area M1 of the thick interlayer soil not cut off by the cast-in-place piles in each dam section can be determined. The area of ​​the thick interlayer soil not cut off is M1 = M3 - M2. For example, if M3 = 400 m² and M2 = 22 m², then M1 = 378 m². Alternatively, if there is overlap in the pile arrangement or changes in pile diameter, the actual net area can be used for calculation.

[0041] Furthermore, the comprehensive shear strength index of the thick soil interlayer can be determined based on the shear strength index of the concrete, the pre-set cut-off area of ​​the cast-in-place piles, the shear strength index of the thick soil interlayer, and the area of ​​the thick soil interlayer not cut off by the cast-in-place piles. The comprehensive shear strength index can include the comprehensive friction coefficient f3 and the comprehensive cohesion c3. Its physical meaning is the weighted average shear strength of the thick soil interlayer beneath the entire dam foundation surface after considering the replacement effect of the cast-in-place piles. The determination method can be a weighted average method, that is, multiplying the strength index of the concrete by the cut-off area and the strength index of the soil layer by the area not cut off, summing them, and then dividing by the total area. For example, f3=(f1×M1+f2×M2) / M3, c3=(c1×M1+c2×M2) / M3; other combinations can also be used, such as finite element back-calculation considering pile-soil interaction.

[0042] Finally, it is determined whether the comprehensive shear strength index meets the deep anti-sliding stability condition to verify the preset number of cast-in-place piles. When the comprehensive shear strength index meets the deep anti-sliding stability condition, the preset number of cast-in-place piles is verified. The deep anti-sliding stability condition can be the safety factor requirement for dam body sliding along deep soft surfaces as specified in the "Gravity Dam Design Code" or similar standards. In this exemplary embodiment, determining whether the deep anti-sliding stability condition is met can be done by determining whether the anti-sliding stability safety factor K under different working conditions is greater than the allowable value specified for the corresponding working condition. Specifically, the calculated comprehensive shear strength indices f3 and c3 can be processed by deep anti-sliding stability analysis to determine the safety factor K under each working condition. If K ≥ the allowable value [K] specified in the code, the deep anti-sliding stability condition is met, and the preset number of cast-in-place piles is verified. If the verification is not passed, the preset number of cast-in-place piles can be increased, and the above steps can be repeated.

[0043] This exemplary embodiment provides a method for quantitatively determining the number of cast-in-place piles, ensuring the deep anti-sliding stability of the dam body and avoiding over-design or under-design that may result from relying on experience.

[0044] In an exemplary embodiment, determining the comprehensive shear strength index of the thick soil layer based on the shear strength index of concrete, the pre-set cut-off area of ​​the cast-in-place pile, the shear strength index of the thick soil layer, and the area of ​​the thick soil layer not cut off by the cast-in-place pile may include: The comprehensive shear friction coefficient and comprehensive cohesion are obtained by weighting the product of the concrete shear strength index and the pre-set cut-off area of ​​the cast-in-place pile, and the product of the shear strength index of the thick interlayer soil and the area of ​​the thick interlayer soil not cut off by the cast-in-place pile.

[0045] In this exemplary embodiment, the comprehensive shear strength index may include the comprehensive shear friction coefficient and the comprehensive cohesion. The comprehensive shear friction coefficient and comprehensive cohesion can be obtained by weighting the product of the concrete's shear strength index and the pre-defined cross-sectional area of ​​the cast-in-place pile, and the product of the shear strength index of the thick interlayer soil and the area of ​​the thick interlayer soil not cut off by the cast-in-place pile.

[0046] Specifically, firstly, the frictional force and cohesion contributed by the concrete are calculated. The shear friction coefficient f2 of the concrete is multiplied by the cut-off area M2 of the cast-in-place pile to obtain the frictional weight of the concrete portion; the cohesion c2 of the concrete is multiplied by M2 to obtain the cohesion weight of the concrete portion. Simultaneously, the weight contributed by the thick soil layer is calculated. The shear friction coefficient f1 of the thick soil layer is multiplied by the uncut area M1 to obtain the frictional weight of the thick soil layer; the cohesion c1 of the thick soil layer is multiplied by M1 to obtain the cohesion weight of the thick soil layer. Then, the frictional weights of the concrete and the thick soil layer are added together and divided by the total area M3 of the thick soil layer under the dam foundation to obtain the comprehensive shear friction coefficient f3 = (f1 × M1 + f2 × M2) / M3, and the comprehensive cohesion c3 = (c1 × M1 + c2 × M2) / M3.

[0047] Through the above weighted calculation, the shear strength indices of different materials can be combined into a single parameter that reflects the overall anti-slip capability, which facilitates subsequent stability calculations.

[0048] In an exemplary embodiment, the aforementioned preset conditions include preset bearing capacity conditions; the foundation parameters include the total weight of the dam body in each dam section, the axial compressive strength of concrete, and the saturated uniaxial compressive strength of rock; The verification of the preset number of cast-in-place piles based on foundation parameters and preset conditions may include: Calculate the bearing capacity applied to the piles and the underlying bedrock based on the total weight of the dam body and the total cross-sectional area of ​​the cast-in-place piles; To determine whether the bearing capacity meets the preset bearing capacity conditions, so as to verify the preset number of cast-in-place piles; Whether the bearing capacity meets the preset bearing capacity conditions, including whether the bearing capacity is simultaneously less than or equal to the axial compressive strength of concrete and the saturated uniaxial compressive strength of rock.

[0049] The total weight of the dam body refers to the self-weight of the concrete dam body within a single dam section. It can be calculated by multiplying the volume of the dam section by the unit weight of the concrete. For example, a dam section with a volume of approximately 20m × 20m × 35m and a unit weight of 24 kN / m³ would have a total weight of approximately 336,000 kN; or, for a thinner dam section, the total weight would be approximately 151,200 kN. The axial compressive strength of concrete refers to the standard compressive strength of the concrete used in cast-in-place piles. For example, the design value for the axial compressive strength of C30 concrete is 16.7 MPa. The saturated uniaxial compressive strength of rock refers to the uniaxial compressive strength of the underlying bedrock under saturated conditions; for example, basalt can reach 32 MPa.

[0050] In this exemplary embodiment, verifying the preset number of cast-in-place piles based on foundation parameters and preset conditions can also involve determining whether the bearing capacity applied to the cast-in-place piles and the underlying bedrock meets certain conditions. Specifically, the bearing capacity applied to the cast-in-place piles and the underlying bedrock can be calculated first based on the total weight of the dam body and the total cross-sectional area of ​​the cast-in-place piles. The total cross-sectional area of ​​the cast-in-place piles is equal to the preset number multiplied by the cross-sectional area of ​​a single pile, i.e., M2. Bearing capacity (stress) F1 = total weight of dam section G / M2. Then, it is determined whether the bearing capacity meets the preset bearing capacity conditions to verify the preset number of cast-in-place piles. When the bearing capacity meets the preset bearing capacity conditions, the preset number of cast-in-place piles is determined to have passed the verification. The bearing capacity meeting the preset bearing capacity conditions includes the bearing capacity being simultaneously less than or equal to the axial compressive strength f of the concrete. c and the saturated uniaxial compressive strength f of rock r That is, F1 ≤ f c And F1≤f r If F1 is greater than any of these values, it indicates that the preset number of cast-in-place piles may be too small, and the number of piles needs to be increased to reduce the load on a single pile until the condition is met. Alternatively, the bearing capacity condition can also be determined using the pile structure strength verification (considering slenderness ratio and stability coefficient) and the allowable value after correction for bedrock bearing capacity depth.

[0051] Through bearing capacity calculation, this exemplary embodiment ensures that the cast-in-place piles and bedrock will not be crushed or damaged due to excessive compressive stress, thus avoiding foundation failure caused by insufficient pile strength or bedrock yielding.

[0052] In an exemplary embodiment, the ratio of the length to the diameter of the cast-in-place pile is not greater than 60, and the center distance between two adjacent cast-in-place piles is not less than three times the diameter of the cast-in-place pile.

[0053] The pile length H refers to the total length from the pile top (at the second preset depth above the foundation surface) to the pile tip, including the portion embedded in bedrock and the portion penetrating the soil layer. The diameter D refers to the designed diameter of the pile body; in this exemplary embodiment, the diameter D is generally between 0.8m and 1.2m. A length-to-diameter ratio H / D not exceeding 60 is to ensure the lateral stability of the pile and prevent slender piles from bending or becoming unstable under horizontal loads. For example, when the pile length H = 30m and the diameter D = 0.8m, H / D = 37.5 < 60, which meets the requirement; if H = 50m and D = 0.8m, then H / D = 62.5 > 60, and the pile diameter should be increased to 1.0m or more.

[0054] The center-to-center distance between two adjacent piles should not be less than 3D to prevent the overlap of failure modes of the soil between the piles, ensure that each pile can fully utilize its lateral and end resistance, and avoid borehole collapse and cross-hole formation during construction. For example, if the pile diameter is 1.0m, the center-to-center distance should be ≥3m; if the pile diameter is 0.8m, the center-to-center distance should be ≥2.4m.

[0055] In implementation, the spacing can be appropriately increased to 4D~5D according to the actual soil conditions to reduce the group pile effect. Another implementation method: For non-circular piles, the diameter D can be taken as the equivalent diameter (such as the diameter of a circle with the same area). The pile spacing can also be determined through numerical analysis optimization, but it is usually not less than 2.5D.

[0056] Cast-in-place piles that meet the above geometric constraints have reasonable stress distribution and are feasible to construct. They can avoid instability and excessive mutual interference while ensuring bearing capacity, thereby ensuring the foundation treatment effect.

[0057] It should be noted that, in this exemplary embodiment, the number of cast-in-place piles is determined to pass verification when the comprehensive shear strength index meets the deep anti-sliding stability condition, or when the bearing capacity meets the preset bearing capacity condition, or when the comprehensive shear strength index meets the deep anti-sliding stability condition and the bearing capacity meets the preset bearing capacity condition.

[0058] In an exemplary embodiment, the above arrangement includes: the cast-in-place piles are arranged symmetrically along the axis of symmetry of the dam foundation surface.

[0059] The axis of symmetry refers to an axis parallel to the dam axis and passing through the centerline of the dam section. Symmetrical arrangement means that the position, number, diameter, and length of the cast-in-place piles on both sides are completely symmetrical about this axis. For example, if a dam section is 20m wide and the axis of symmetry is located on the centerline (10m from the upstream boundary), and 28 piles are designed, then the 14 piles on the upstream side are symmetrical to the 14 piles on the downstream side about the axis of symmetry; or the 14 piles on the left half are symmetrical to the 14 piles on the right half. The purpose of symmetrical arrangement is to avoid uneven settlement between the upstream and downstream sides or between the left and right sides of the dam, thereby preventing the dam from tilting or cracking. For example, if a symmetrical arrangement is not adopted, with more piles on the upstream side and fewer piles on the downstream side, the settlement on the downstream side will be greater, and the dam may tilt downstream, affecting the opening and closing of the gates and structural safety. This exemplary embodiment can achieve symmetrical arrangement of cast-in-place piles along the axis of symmetry of the dam foundation surface in the following ways: using a mirror symmetric arrangement about the longitudinal centerline of the dam section; or using a central symmetric arrangement about the center point of the dam section; or using a dual-axis symmetric arrangement simultaneously about the longitudinal and transverse axes. The mirror-symmetric layout is achieved by accurately laying out the piles using a total station or GPS with the axis of symmetry as the reference. When the foundation conditions are significantly asymmetrical (e.g., the bedrock on one side is buried at a greater depth), the pile lengths on both sides can be appropriately adjusted to ensure that all pile ends are at the same elevation, while maintaining the geometric symmetry of the pile positions.

[0060] The symmetrical arrangement effectively prevented uneven settlement, ensuring the structural integrity and operational safety of the gravity dam.

[0061] In an exemplary embodiment, the above-described consolidation grouting treatment of the thick soil layer within the dam foundation area may include: Determine the location and parameters of the grouting holes on the foundation surface of the gravity dam; Based on the location and parameters, grouting holes are drilled to penetrate the thick interlayer of soil and extend into the third preset depth in the rock mass below the thick interlayer of soil. Cement grout is injected into the grouting hole to allow the grout to penetrate, split, and cement the thick soil layer, thereby forming a grout vein network that improves the shear strength and compression modulus of the thick soil layer.

[0062] The location refers to the planar coordinates of each grouting hole, and the parameters include hole spacing, row spacing, hole depth, hole diameter, and inclination. Determining the location and parameters of the grouting holes on the foundation surface of the gravity dam can be done according to the recommended quincunx or rectangular grid layout, for example, a hole spacing of 2.5m, a row spacing of 2.5m, and a hole depth penetrating the thick interlayer of soil and extending 3m into the underlying bedrock. Alternatively, adjustments can be made based on the geological characteristics. For example, a larger hole spacing can be used for highly permeable soil layers; for uneven soil layers, the hole spacing can be increased, such as in one project where the hole spacing was adjusted to 3m × 3m based on acoustic wave test results; and for weak lenses present in thick interlayers of soil, the spacing can be locally increased to 1.5m × 1.5m.

[0063] Then, based on the location and parameters, grouting holes are drilled to penetrate the thick interlayer of soil and reach a third predetermined depth within the rock mass below it. Drilling refers to using a geological drilling rig or down-the-hole drill to drill holes at a determined location and angle. The third predetermined depth refers to the depth into the underlying bedrock, typically not less than 3 meters, to ensure the grouting curtain can seal the contact surface between the soil layer and the bedrock. For example, if the hole diameter is determined to be 91 mm, the drilling rig is used to drill to the third predetermined depth (3 meters below the bottom of the thick interlayer of soil), and the borehole is flushed. If the bedrock is fractured, the depth can be increased to 5 meters.

[0064] Finally, cement grout is injected into the grouting holes, allowing the grout to penetrate, fracture, and cement the thick soil interlayer, forming a grout vein network that enhances the shear strength and compression modulus of the thick soil interlayer. Grouting methods can include pure pressure grouting or circulating grouting, with grouting pressure controlled in stages (e.g., pressure increasing gradually), and the water-cement ratio of the grout increasing gradually. Each stage of grouting ends when the grout absorption rate is less than 1 L / min. Under pressure, the grout penetrates along the bedding, fissures, or pores of the soil layer. When the pressure exceeds the tensile strength of the soil, hydraulic fracturing occurs, forming irregular grout veins. These veins solidify to become reinforced structures similar to steel bars. Simultaneously, the grout undergoes ion exchange and cementation reactions with the surrounding soil particles, forming cement-soil that fills the voids in the soil and squeezes out water and air, thus compacting the soil layer. For example, in a certain project, core sampling after grouting revealed a grout vein network with a thickness of 1-5 mm in the soil interlayer. The compressive strength of the core sample increased from 0.5 MPa to 2.5 MPa, and the compression modulus increased threefold. Another implementation method, for cohesive soils with extremely low permeability, is high-pressure jet grouting. This method utilizes a high-pressure jet to cut and mix the soil and inject cement grout, directly forming a cement-soil column with a diameter of approximately 0.6-1.2 m.

[0065] Through the above-mentioned consolidation grouting, the shear strength parameters (friction coefficient and cohesion) and compression modulus of the thick soil layer are significantly improved, thereby further enhancing the anti-sliding stability of the dam body along this layer and reducing settlement deformation.

[0066] In one exemplary embodiment, the third preset depth is not less than 3 meters.

[0067] This ensures that the grouting holes fully penetrate the thick interlayer of soil and reach a certain depth into the underlying bedrock, thus forming a grouting section of sufficient length within the bedrock. If the depth is less than 3 meters, the embedment length between the grouting structure and the bedrock is insufficient, and under horizontal loads, shear failure may occur along the top surface of the bedrock. Simultaneously, the grout cannot adequately seal the surface fissures of the bedrock, significantly reducing the seepage prevention and reinforcement effects. A depth of at least 3 meters ensures reliable anchoring of the grout vein network to the bedrock, integrating the grouting reinforced body with the bedrock as a whole, effectively transferring and dissipating the dam load, and further improving the shear strength and compression modulus of the thick interlayer of soil. It should be noted that 3 meters is the minimum effective depth verified through engineering practice. When geological conditions are complex or bedrock fissures are well-developed, the depth can be appropriately increased to 5 meters or more to further enhance the reinforcement effect. This depth limit complements the rock embedment depth of the cast-in-place piles (first preset depth 0.5~1.0 meters): the cast-in-place piles mainly provide "point" support for anti-sliding and load bearing, while consolidation grouting provides "surface" reinforcement over a large area. The two work together to ensure the stability of the dam body.

[0068] In an exemplary embodiment, the hole spacing of the grouting holes and the row spacing between different rows of grouting holes are 2.5 meters to 3 meters.

[0069] Hole spacing refers to the distance between the centers of two adjacent grouting holes in the same row, while row spacing refers to the vertical distance between two adjacent rows of grouting holes. Considering that a spacing less than 2.5m would increase drilling workload and costs, while a spacing greater than 3m might result in the grout not completely covering the entire dam foundation, leaving unreinforced weak areas, the hole spacing and row spacing between different rows of grouting holes can be set to 2.5m to 3m. For example, for homogeneous thick soil layers, a hole spacing of 3m and a row spacing of 3m are used; for uneven soil layers or soil layers with seepage channels, a hole spacing of 2.5m and a row spacing of 2.5m are used. A rectangular arrangement (hole spacing 3m, row spacing 2.5m) or a staggered arrangement (equivalent spacing 2.8m) can also be used.

[0070] Maintaining the hole spacing and row spacing within the range of 2.5m to 3m ensures the formation of a continuous and uniform grouting reinforcement zone. This avoids unreinforced weak areas due to excessive spacing, while also preventing unnecessary drilling work due to insufficient spacing. This range is an economically reasonable approach proven by engineering practice. The spacing can be equal or unequal, depending on the soil permeability, the degree of fissure development, and the grouting pressure.

[0071] In one exemplary embodiment, the injected cement grout is high-grade silicate cement.

[0072] High-grade silicate cement refers to silicate cement with a strength grade of not less than 42.5, such as P.O42.5 and P.O52.5. This type of cement has high early strength, moderate setting time, high aggregate strength, and good durability, making it suitable for foundation grouting. For example, using P.O42.5 cement with a water-cement ratio of 0.5:1, the compressive strength of the aggregate can reach over 40 MPa after 28 days. Another implementation method is to add appropriate admixtures such as water-reducing agents, bentonite, or fly ash to improve the grout's injectability. For groundwater environments requiring erosion resistance, sulfate-resistant cement can be used.

[0073] Using a hole spacing of 2.5m to 3m and high-grade silicate cement, the project cost can be controlled while ensuring the grouting effect, forming a uniform and continuous reinforcement zone, and the cement stone body has sufficient strength and durability to meet the long-term operation requirements of gravity dams.

[0074] In one exemplary embodiment, the above method may further include: The construction sequence of the controlled cast-in-place pile array is earlier than the construction sequence of the consolidation grouting treatment.

[0075] The construction sequence refers to the chronological arrangement of the main construction steps. "Earlier than" means that the construction of the cast-in-place pile array begins or is completed before the consolidation grouting treatment begins. Specifically, the drilling of all or part of the cast-in-place piles, the placement of the reinforcing cage, and the pouring of concrete should be completed first. Only after the pile concrete reaches a certain strength (e.g., more than 70% of the design strength) should the drilling of grouting holes and pressure grouting begin. This exemplary embodiment, by limiting the construction sequence of piles before grouting, ensures the integrity and strength of the cast-in-place pile concrete, while simultaneously allowing the grout to form a dense network of grout veins around the solidified pile body, further compacting the surrounding soil, thereby fully leveraging the synergistic reinforcement effect of the cast-in-place piles and the grouting structure.

[0076] In one exemplary embodiment, the cast-in-place pile is a reinforced concrete cast-in-place pile, which is used to replace part of the thick interlayer of soil to improve the overall shear strength index of the thick interlayer of soil.

[0077] Among them, reinforced concrete cast-in-place piles refer to piles formed by on-site casting of reinforced concrete cages. Their shear friction coefficient typically reaches 1.0~1.8, and their cohesion reaches 2000~3000 kPa, far exceeding that of natural thick interlayer soil (friction coefficient 0.2~0.4, cohesion 10~30 kPa). Replacing part of the thick interlayer soil does not refer to physically excavating the soil layer, but rather that within the cross-section of the thick interlayer soil, the area occupied by the cast-in-place piles (i.e., the cross-sectional area) replaces the original low-strength soil layer, thereby increasing the weighted average shear strength of the composite strata beneath the entire dam foundation. This exemplary embodiment significantly improves the anti-sliding capacity of the dam foundation along the thick interlayer soil by directly replacing the low-strength soil layer with reinforced concrete cast-in-place piles.

[0078] This exemplary embodiment uses a gravity dam project in a reservoir as an example. The gravity dam has a crest elevation of 500m, a wave wall crest elevation of 501.2m, a maximum dam height of 35m, a crest length of 200m, and a crest width of 6m. It is divided into 10 dam sections, each 20m long. The dam foundation is located on basalt, and a horizontally thick layer of soil, approximately 2m thick, is distributed about 10m below the ground level in the valley dam section. Preliminary calculations indicate that the deep anti-sliding stability of the dam does not meet the specifications, and there are issues with sliding stability and settlement stability, requiring foundation treatment measures.

[0079] Based on the aforementioned method, this embodiment adopts a treatment scheme combining cast-in-place piles and consolidation grouting. First, consolidation grouting is performed on the entire dam foundation area. The grouting holes are arranged in a staggered pattern, with a hole spacing and row spacing of 3.0m. The average designed hole depth is 15.0m, ensuring that the grouting holes penetrate the thick interlayer of soil and reach the underlying bedrock. Second, to prevent settlement of the interlayer of soil under the dam foundation under the dam's gravity load, and to enhance the deep anti-sliding stability of the dam body, cast-in-place piles are installed under each dam section. The pile diameter is 1.0m, with the lower pile end embedded 1.0m into the hard bedrock below the thick interlayer of soil (i.e., the first preset depth is 1.0m), and the top end extending 0.5m into the concrete dam body (i.e., the second preset depth is 0.5m). The center-to-center distance between adjacent piles along the dam direction is 3.0m. A total of four cast-in-place piles are arranged along the water flow direction, two for the upstream foundation and two for the downstream foundation, with a spacing of 3.0m between them. The upstream and downstream cast-in-place piles are symmetrically arranged along the symmetrical axis of the dam foundation.

[0080] Regarding the determination of the number of cast-in-place piles under each dam section, this embodiment verifies the following steps. The basic parameters are as follows: the shear strength index of the thick interlayer soil is taken as f1=0.3, c1=15kPa, and the shear strength index of the concrete is taken as f2=1.8, c2=3000kPa. The total area of ​​the thick interlayer soil under the dam foundation in one dam section is M3=400m². Based on the preset number of cast-in-place piles (28) and the cross-sectional area of ​​a single pile (diameter 1.0m, cross-sectional area of ​​a single pile approximately 0.785m²), the pre-set cut-off area of ​​the cast-in-place piles is calculated as M2=28×0.785≈22m², and the area of ​​the thick interlayer soil not cut off by the cast-in-place piles is M1=400-22=378m². Substituting the values ​​into the weighted average formula, we obtain the comprehensive shear friction coefficient f3 = (f1×M1 + f2×M2) / M3 = (113.4 + 39.6) / 400 = 0.3825, and the comprehensive cohesion c3 = (c1×M1 + c2×M2) / M3 = (5670 + 66000) / 400 = 179.175 kPa. Substituting the comprehensive shear strength index, which includes both the comprehensive shear friction coefficient and the comprehensive cohesion, into the deep anti-slip stability calculation, the results are shown in Table 1 below. Table 1

[0081] Table 1 shows that the safety factor under normal water level conditions increased from 2.12 to 3.49, the safety factor under design flood level conditions increased from 1.94 to 3.21, the safety factor under freezing conditions increased from 2.05 to 3.42, the safety factor under check flood level conditions increased from 1.89 to 3.15, and the safety factor under seismic load conditions increased from 1.83 to 2.65. All conditions meet the requirements of the specifications.

[0082] Simultaneously, bearing capacity calculations were performed: the total weight of the dam body within a dam section, G = 151200 kN, and the total cross-sectional area of ​​the cast-in-place piles, M2 = 22 m². The calculated bearing capacity, F1 = G / M2 = 151200 / 22 ≈ 6872.7 kN / m² ≈ 6.87 MPa (megapascals), is less than both the axial compressive strength of concrete (16.7 MPa) and the saturated uniaxial compressive strength of rock (32 MPa), thus meeting the preset bearing capacity conditions. Based on the above verification, the preset number of cast-in-place piles, 28, passed the verification and was determined as the target number.

[0083] In this embodiment, consolidation grouting, as a safety reserve measure, works in conjunction with cast-in-place piles to effectively improve the anti-sliding stability of the dam foundation along the thick interlayer of soil and control settlement. Implementation results show that, after adopting this method, the deep anti-sliding stability of the dam body changed from not meeting the specifications to meeting them under all five working conditions, and the bearing capacity of the underlying bedrock and concrete also met the design requirements, verifying the effectiveness and reliability of this method.

[0084] It should be understood that this disclosure is not limited to the specific methods, steps, or structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. Those skilled in the art will readily conceive of other embodiments based on the specific implementations provided in this disclosure. Therefore, the specific implementations provided in this disclosure are merely exemplary, and the scope and spirit of this disclosure are indicated by the claims, and should cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary technical means in the art not disclosed in this disclosure.

Claims

1. A method for foundation treatment of a gravity dam including a thick soil layer foundation, characterized by, include: Obtain the foundation parameters of the ground beneath the gravity dam body; the foundation includes a thick soil layer; Based on the foundation parameters, cast-in-place piles that penetrate the thick interlayer of soil and are embedded in the underlying bedrock are installed below the foundation surface of the gravity dam. The thick soil layer within the dam foundation area is consolidated and grouted to form a grouting structure that penetrates the thick soil layer and extends into the underlying bedrock.

2. The method of claim 1, wherein, The method of installing cast-in-place piles that penetrate the thick soil layer and embed into the underlying bedrock below the foundation surface of the gravity dam, based on the foundation parameters, includes: Based on the foundation parameters, determine the target number of cast-in-place piles for each dam section and the corresponding layout for each dam section; According to the aforementioned arrangement, the target number of cast-in-place piles are installed under the corresponding dam section; The lower end of each cast-in-place pile is embedded in the hard rock beneath the thick interlayer of soil to a first preset depth, and the top end of each cast-in-place pile extends into the dam body of the gravity dam to a second preset depth.

3. The method of claim 2, wherein, The determination of the target number of cast-in-place piles for each dam section based on the foundation parameters includes: Obtain the preset number of cast-in-place piles in each dam section, and verify the preset number of cast-in-place piles according to the foundation parameters and preset conditions; When the preset number of cast-in-place piles passes verification, the preset number of cast-in-place piles in each dam section is determined as the target number of cast-in-place piles in each dam section.

4. The method of claim 3, wherein, The preset conditions include deep anti-sliding stability conditions; the foundation parameters include the shear strength index of concrete, the shear strength index of the thick interlayer soil, and the total area of ​​the thick interlayer soil under the dam foundation in each dam section; The verification of the preset number of cast-in-place piles based on the foundation parameters and preset conditions includes: Based on the number of pre-cast piles in each dam section and the cross-sectional area of ​​a single pile, determine the corresponding pre-cast pile cut-off area for each dam section. Based on the preset cut-off area of ​​the cast-in-place piles and the total area of ​​the thick interlayer soil layer under the dam foundation in each dam section, determine the area of ​​the thick interlayer soil layer that is not cut off by the cast-in-place piles in each dam section. Based on the shear strength index of the concrete, the pre-set cut-off area of ​​the cast-in-place pile, the shear strength index of the thick interlayer soil, and the area of ​​the thick interlayer soil not cut off by the cast-in-place pile, the comprehensive shear strength index of the thick interlayer soil is determined. To verify the number of pre-set cast-in-place piles, it is necessary to determine whether the comprehensive shear strength index meets the deep anti-sliding stability condition.

5. The method of claim 4, wherein, The determination of the comprehensive shear strength index of the thick soil layer based on the shear strength index of the concrete, the pre-set cut-off area of ​​the cast-in-place pile, the shear strength index of the thick soil layer, and the area of ​​the thick soil layer not cut off by the cast-in-place pile includes: The comprehensive shear friction coefficient and comprehensive cohesion are obtained by weighted calculation based on the product of the shear strength index of the concrete and the pre-set cut-off area of ​​the cast-in-place pile, and the product of the shear strength index of the thick interlayer soil and the area of ​​the thick interlayer soil not cut off by the cast-in-place pile.

6. The method according to claim 3, characterized in that, The preset conditions include preset bearing capacity conditions; the foundation parameters include the total weight of the dam body in each dam section, the axial compressive strength of concrete, and the saturated uniaxial compressive strength of rock. The verification of the preset number of cast-in-place piles based on the foundation parameters and preset conditions includes: Calculate the bearing capacity applied to the cast-in-place piles and the underlying bedrock based on the total weight of the dam body and the total cross-sectional area of ​​the cast-in-place piles; Determine whether the bearing capacity meets the preset bearing capacity condition in order to verify the preset number of cast-in-place piles; Whether the bearing capacity meets the preset bearing capacity conditions includes whether the bearing capacity is simultaneously less than or equal to the axial compressive strength of concrete and the saturated uniaxial compressive strength of rock.

7. The method according to claim 2, characterized in that, The ratio of the length to the diameter of the cast-in-place pile is not greater than 60, and the center distance between two adjacent cast-in-place piles is not less than three times the diameter of the cast-in-place pile.

8. The method according to claim 2, characterized in that, The arrangement includes: the cast-in-place piles are arranged symmetrically along the axis of symmetry of the dam foundation.

9. The method according to claim 1, characterized in that, The consolidation grouting treatment of the thick soil layer within the dam foundation area includes: The location and parameters of the grouting holes are determined on the foundation surface of the gravity dam; According to the location and parameters, the grouting hole is drilled so that it penetrates the thick interlayer of soil and extends into the rock mass below the thick interlayer of soil to a third preset depth. Cement grout is injected into the grouting hole to allow the grout to penetrate, split, and cement the thick soil layer, thereby forming a grout vein network that improves the shear strength and compression modulus of the thick soil layer.

10. The method according to claim 9, characterized in that, The spacing between the grouting holes and the spacing between different rows of grouting holes are between 2.5 meters and 3 meters.

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