A large cross-section circular anti-slide pile multi-structure comparison pile pushing test method

Abstract

The application discloses a large-section circular anti-slide pile multi-structure comparison pile pushing test method and belongs to the technical field of geotechnical engineering model tests. The method comprises the following steps: a model preparation stage, based on the strict similarity theory, a model pile and a slope body material are designed and prepared, and a self-reducing friction resistance system is installed; an accumulation test stage, single-row pile, multi-type pile comparison, double-row pile and portal frame pile tests are sequentially carried out on the same slope model, and the structure is gradually complicated; and a decrement test stage, single-row cantilever pile test and side friction resistance test are sequentially carried out, and the structure is gradually simplified. The application realizes the system comparison of various anti-slide pile structure forms on one set of model through the closed-loop test logic of "accumulation-decrement", has high test efficiency and strong data comparability, integrates the systematic similarity design, innovative friction resistance reduction and test technology, effectively improves the test precision and authenticity, and provides a comprehensive and reliable test means for the design optimization and theoretical research of the large-section circular anti-slide pile.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering model testing technology, specifically to a model testing method for studying the reinforcement mechanism and performance of large-section circular anti-slide piles, and in particular, a push pile test method that can continuously and systematically compare the anti-slide performance of various structural forms such as single-row piles, double-row piles, multiple types of piles, portal piles, and cantilever piles on a single slope model. Background Technology

[0002] Anti-slide piles are key retaining structures for controlling landslides and reinforcing slopes. Among them, large-section circular anti-slide piles (with a diameter typically greater than or equal to 2 meters) are increasingly widely used in major projects due to their high bending stiffness and mature construction technology. However, the mechanism of their interaction with the surrounding soil and rock is complex, especially in the case of composite structures (such as portal piles with capped beams and double-row piles), where the stress characteristics, failure modes, and group pile effects are still unclear, posing challenges to refined design and safety assessment.

[0003] Model testing is an important means of studying the pile-soil interaction mechanism. Currently, anti-slide pile model tests mostly focus on rectangular cross-section piles or small-scale models, and the test conditions are relatively simple, usually only targeting a single pile type or structural form (such as single-row piles). This type of test method has significant limitations: First, there are few experimental studies on the special pile type of large-section circular piles, and systematic methods for designing scaled-down models and preparing similar materials are lacking; second, there is a lack of effective schemes for conducting continuous and comparative tests on multiple anti-slide pile structural forms (such as independent piles, capped beam piles, anchored piles, double-row piles, portal frame piles, etc.) on the same model, making it difficult to systematically reveal the collaborative working mechanism and performance advantages and disadvantages of different structural forms; third, in conventional tests, the frictional resistance of the model trench sidewalls to the sliding body affects the realism of thrust transmission and distribution, but the degree of its influence is difficult to quantify and eliminate, limiting the accuracy of the test.

[0004] Therefore, developing a high-precision, multi-condition comparative model test method capable of systematically studying the working mechanism of large-section circular anti-slide piles under different structural forms and effectively controlling the influence of sidewall friction is of great significance for deepening the design theory of anti-slide piles and guiding engineering practice. Currently, there are no publicly reported methods that possess the aforementioned "cumulative from simple to complex, decreasing from complex to simple" multi-structure continuous comparative test capabilities, and integrate systematic similarity design, innovative friction reduction, and testing technologies. Summary of the Invention

[0005] To address the lack of a systematic, continuous, and comparable model testing method for various structural forms of large-section circular anti-slide piles in existing technologies, this invention provides a comparative multi-structure push-pile test method for large-section circular anti-slide piles. This method aims to efficiently and continuously conduct tests on various anti-slide pile structures under different working conditions—from simple to complex, and then from complex to simplified—on the same slope model through a logically rigorous "cumulative-decreasing" test procedure. It systematically reveals the reinforcement mechanism, stress characteristics, and failure modes of these structures and provides a solution for quantifying the influence of sidewall friction.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is summarized as follows: A multi-structure comparative test method for large-section circular anti-slide piles includes a model preparation stage, an accumulation test stage, and a decrease test stage, which are executed sequentially.

[0007] First, in the model preparation stage, a system design is conducted based on similarity theory, according to a preset geometric similarity ratio, preferably within the range of 1:4 to 1:10. Large-section circular model piles, simulated sliding bed materials, simulated sliding strip materials, and simulated sliding body materials are prepared. The reinforcement of the model piles is determined according to the principle of equal strength and converted based on the similarity ratio; the mechanical parameters of the model piles, simulated sliding bed, and simulated sliding body materials are all designed and matched according to the similarity theory. In the model test trench, the simulated sliding bed material is sequentially filled and compacted, the simulated sliding strip material is laid, and the simulated sliding body material is filled and compacted to construct a complete slope model. During the model preparation stage, the physical and mechanical parameters of the model pile materials, sliding bed materials, and sliding body materials are rigorously tested. If they do not conform to the similarity theory, the materials are immediately re-prepared. This ensures strict compliance with the similarity theory design. To improve experimental accuracy, a friction-reducing system is installed on the sidewall of the model test trench before filling the slope model. The friction reduction system includes a track parallel to the preset thrust direction, rolling units laid on the track and capable of rolling along the track, and overlapping plates covering the outside of the rolling units. After the slope model is filled and before the pile driving test is carried out, a four-point bending test is performed on the large-section circular model pile to test and obtain its actual bending stiffness parameters.

[0008] Subsequently, the cumulative testing phase commenced. This phase followed the principle of "from simple to complex, cumulative construction," conducting four sets of pile-pushing tests sequentially on the slope model. Each subsequent set of tests was directly implemented based on the slope and pile structure formed in the previous set. The loading system used in the tests was a multi-layer electro-hydraulic servo loading system, capable of applying independently controlled horizontal thrust and displacement to different height layers of the slope model.

[0009] S2.1 Single-row pile test: A single row of large-section circular model piles is implanted in the middle area of ​​the slope model. Horizontal thrust is applied to the slope through the loading system, and data monitoring is carried out simultaneously.

[0010] S2.2 Comparative Test of Multiple Pile Types: Based on the pile structure of the single-row pile test, a comparative test group is formed by modifying the pile tops to include at least two or more types of piles, such as independent piles, capped beam connected piles, and anchored piles. For the anchored piles, the anchor cables are designed according to similarity theory. The elastic coefficient of the model anchor cables is measured through tension tests, and the parameters of the prototype anchor cables are verified by back-calculation. Horizontal thrust is applied and monitored to compare the responses of different types of piles.

[0011] S2.3 Double-row pile test: In the slope model that has completed the multi-type pile comparison test, another row of model piles is added behind the original single-row piles to form a double-row pile structure. Horizontal thrust is applied and monitored to study the pile group effect.

[0012] S2.4 Portal Pile Test: Based on the pile structure of the double-row pile test, a connecting capping beam is added between the tops of the front and rear rows of piles to form a portal pile structure. The connecting capping beam is preferably made of steel components connected by bolts, and a force transmission rod for transmitting horizontal thrust is installed between the corresponding capping beam segments of the front and rear rows of piles. Horizontal thrust is applied and monitored to study the overall collaborative performance.

[0013] Finally, the decreasing test phase is conducted. This phase follows the principle of "simplifying from complex to complex and gradually stripping away" the structure. Based on the complex structure formed in the cumulative test phase, two sets of tests are carried out in sequence by removing or modifying parts of the structure.

[0014] S3.1 Single-row cantilever pile test: Remove the connecting cap beam in the portal pile test and excavate part of the sliding body in front of the rear row of piles in the double-row pile test, so that the rear row of piles is fully exposed and in a cantilever stress state. Apply horizontal thrust and monitor it to study the stress characteristics of the cantilever pile and the influence of anchorage depth.

[0015] S3.2 Side Friction Test: After the single-row cantilever pile test is completed, the soil between the remaining sliding body and the sidewall of the model test trench is further excavated longitudinally to completely separate the sliding body from the sidewall, thereby eliminating sidewall friction. Then, a horizontal thrust is applied to push the sliding body along the sliding surface. By measuring the thrust of the push plate and the displacement of the sliding body, the frictional resistance at the bottom of the sliding body and the frictional resistance of the test trench sidewall are separated and calculated.

[0016] Throughout the entire test, monitoring of each group of tests included, but was not limited to: monitoring pile deformation along depth using a flexible inclinometer; monitoring the distribution of earth pressure before, after, and between piles using earth pressure gauges, wherein the earth pressure gauges were fixedly installed using dedicated test rods or test plates pre-embedded in the soil; monitoring the displacement field on the slope surface using a 3D laser scanner and / or total station; monitoring pile top displacement using an electronic dial gauge; and recording macroscopic deformation phenomena throughout the entire test process using video equipment. At least one group of tests in the cumulative and decreasing test phases included a step of repeatedly loading the same load level to verify the repeatability of the data.

[0017] The present invention has the following beneficial effects: 1. Strong systematicity and comparability: Through the logical sequence of "accumulation" and "decrease", continuous tests on various anti-slide pile structures such as single-row piles, capping piles, anchor piles, double-row piles, portal piles, and cantilever piles are realized in a single model. The test data are from the same source and can be compared, which can systematically reveal the mechanical mechanism, performance advantages and disadvantages, and evolution laws of different structural forms.

[0018] 2. High experimental efficiency and high model utilization: It overcomes the drawback of traditional methods that require separate model preparation for each working condition, greatly saving time, materials and costs, and avoiding data errors caused by model discreteness.

[0019] 3. Highly targeted and innovative: Specifically designed for large-section circular anti-slide piles, it provides a complete model similarity design method (including geometry, materials, reinforcement, anchor cables, etc.). The independently designed friction reduction system and earth pressure testing rods / plates effectively improve test accuracy.

[0020] 4. In-depth understanding of mechanisms: It can not only study the interaction between piles and soil, but also conduct detailed analysis of the group pile effect, the coordinating effect of the capping beam, the contribution of anchor cables and the influence of sidewall friction, providing rich experimental data for theoretical research.

[0021] 5. Clear engineering guidance significance: The test results can be directly used to verify and optimize the design theory of large-section circular anti-slide piles and their combined structures, providing a direct basis for pile type selection, structural optimization and safety assessment in actual engineering. Attached Figure Description

[0022] Figure 1 Schematic diagram of the planar layout of the model test tank.

[0023] Figure 2 Schematic diagram of the cross-sectional structure of the model test tank.

[0024] Figure 3 : Reinforcement cross-section diagram of a large-section circular model pile, unit: mm.

[0025] Figure 4 : Actual photos of the steel cage fabrication process, showing the pre-embedded inclinometer tubes.

[0026] Figure 5 Schematic diagram of the four-point bending stiffness (EI) test device for model piles.

[0027] Figure 6 : Schematic diagram of the self-designed sidewall friction reduction system; a-Planar layout, b-Three-dimensional layout.

[0028] Figure 7 Design drawings of the earth pressure test bar (a) and the earth pressure test plate (b).

[0029] Figure 8 : Layout diagram of single-row circular anti-slide pile push test profile, unit: mm; a: C-1 / C-2 profile, b: C-3 / C-4 profile, c: C-5 / C-6 profile.

[0030] Figure 9 : Plan layout and monitoring component location diagram for single-row circular anti-slide pile pushing test, unit: mm.

[0031] Figure 10 Plan view of the comparative test of multiple types of circular anti-slide piles, unit: mm.

[0032] Figure 11 Comparative test cross-sectional views of various types of circular anti-slide piles, unit: mm; a: C-1 / C-2 cross-section, b: C-3 / C-4 cross-section, c: C-5 / C-6 cross-section.

[0033] Figure 12 : Plan layout and monitoring component location diagram for multi-type circular anti-slide pile pushing test, unit: mm.

[0034] Figure 13 Plan view of the test layout of double-row circular anti-slide piles, unit: mm.

[0035] Figure 14 Cross-sectional view of a double-row circular anti-slide pile pushing test, unit: mm.

[0036] Figure 15 Plan view of test components for double-row circular pile pushing test, unit: mm.

[0037] Figure 16 : Plan layout diagram of the gantry circular pile test, unit: mm.

[0038] Figure 17 : Cross-sectional view of a gantry circular pile test, unit: mm.

[0039] Figure 18Plan view of test components for gantry circular pile pushing test, unit: mm.

[0040] Figure 19 : Plan layout diagram of single-row cantilever circular anti-slide pile test, unit: mm.

[0041] Figure 20 Cross-sectional view of a single-row circular cantilever pile pushing test, unit: mm.

[0042] Figure 21 Plan view of test components for single-row cantilever circular pile pushing test, unit: mm.

[0043] Figure 22 Total friction resistance test layout diagram, unit: mm.

[0044] Figure 23 : Plan view of bottom friction test, unit: mm.

[0045] Figure 24 Total friction resistance test component layout diagram, unit: mm.

[0046] Figure 25 : Planar layout of test components for bottom friction resistance test, unit: mm.

[0047] Figure 26 : Graph of dial gauge test data for stiffness testing of model piles (C-1 to C-12).

[0048] Figure 27 : Flexible inclinometer data curves for stiffness testing of model piles (C-1 to C-11).

[0049] Figure 28 : Deformation distribution curves of piles C-1 to C-6 in single-row pile test, where a: C-1, b: C-2, c: C-3, d: C-4, e: C-5, f: C-6.

[0050] Figure 29 Time history curves of pile top displacement (a) and ground surface displacement (b) in a single-row pile test.

[0051] Figure 30 Representative earth pressure increment distribution curves on the mountain side (af), between piles (h), and river side (im) in single-row pile tests; where a: measuring point T-1, b: measuring point T-2, c: measuring point T-3, d: measuring point T-4, e: measuring point T-5, f: measuring point T-6, g: measuring point T-7, h: measuring point T-8, i: measuring point T-9, j: measuring point T-10, k: measuring point T-11, and l: measuring point T-12.

[0052] Figure 31: Deformation distribution curves of piles C-1 to C-6 in multi-type pile tests, where a: C-1, b: C-2, c: C-3, d: C-4, e: C-5, f: C-6.

[0053] Figure 32 Displacement distribution curves at the top of piles in various types of pile tests.

[0054] Figure 33 : Earth pressure increment distribution curves at various measuring points in multi-type pile tests; where a: measuring point T-1, b: measuring point T-2, c: measuring point T-3, d: measuring point T-4, e: measuring point T-5, f: measuring point T-6, g: measuring point T-7, h: measuring point T-8, i: measuring point T-9, j: measuring point T-10, k: measuring point T-11, l: measuring point T-12.

[0055] Figure 34 Deformation distribution curves of piles C-2(a), C-8(b), C-4(c), C-10(d), C-6(e), and C-12(f) in the double-row pile test.

[0056] Figure 35 Displacement distribution curve at the top of the pile in the double-row pile test.

[0057] Figure 36 Representative earth pressure increment distribution curves on the mountain side (af), between piles (h), and river side (im) during the double-row pile test; where a: measuring point T-1, b: measuring point T-2, c: measuring point T-3, d: measuring point T-4, e: measuring point T-5, f: measuring point T-6, g: measuring point T-7, h: measuring point T-8, i: measuring point T-9, j: measuring point T-10, k: measuring point T-11, and l: measuring point T-12.

[0058] Figure 37 Deformation distribution curves of piles C-1(a), C-4(b), C-6(c), C-7(d), C-10(e), and C-12(f) in the gantry pile test.

[0059] Figure 38 Displacement distribution curve at the top of the gantry pile during the test.

[0060] Figure 39 : Earth pressure increment distribution curves at various measuring points during the portal frame pile test, where a: measuring point T-1, b: measuring point T-2, c: measuring point T-3, d: measuring point T-4, e: measuring point T-5, f: measuring point T-6, g: measuring point T-7, h: measuring point T-8, i: measuring point T-9, j: measuring point T-10, k: measuring point T-11, and l: measuring point T-12.

[0061] Figure 40: Deformation distribution curves of piles C-7 to C-12 in single-row cantilever pile test, where a: C-7, b: C-8, c: C-9, d: C-10, e: C-11, f: C-12.

[0062] Figure 41 Displacement distribution curve at the top of a single-row cantilever pile test.

[0063] Figure 42 : Distribution curves of soil pressure increment on the mountain side (ac) and river side (df) in a single-row cantilever pile test, where a: measuring point T-1, b: measuring point T-2, c: measuring point T-3, d: measuring point T-4, e: measuring point T-5, and f: measuring point T-6.

[0064] Figure 43 Total friction test load-time curves for two push plate tests, where a: first test, b: second test.

[0065] Figure 44 : Bottom friction test load-time curves for two push plate tests, where a: first test, b: second test.

[0066] In the diagram: 1-Rubber rod, 2-Steel pipe, 3-Bamboo plywood, 4-Sliding body, 5-Jack, 6-Thrust plate, 7-Limiting track, 8-Reaction wall. Detailed Implementation

[0067] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. This embodiment is implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following embodiments. Example

[0068] This embodiment uses a large-section circular anti-slide pile (prototype pile diameter 2.0m, pile length 24m, C-35 concrete) in a landslide control project on a highway as the research object. A model test with a scale of 1:5 was conducted to systematically study its anti-slide mechanism. The model test setup is as follows: Figure 1-2 As shown in the figure, the dashed lines represent the concrete blocks that restrict the movement of the slide.

[0069] 1. Experimental preparation and model construction 1.1 Similarity Theory Design and Similarity Ratio Determination This model experiment was designed strictly in accordance with the three similarity theorems. First, the similarity ratio of the three basic independent quantities was determined: C L =5, C γ =1, C g =1; therefore, it is determined that, Specific examples of similarities are shown in Table 1 below: Table 1. Specific similarity ratios of model experiments

[0070] In the table: The geometric similarity ratio between the prototype pile and the model pile; The similarity ratio of the unit weight of the prototype pile and the model pile materials; The similarity ratio of the elastic modulus between the prototype pile and the model pile; The similarity ratio between the Poisson's ratio of the prototype pile and the Poisson's ratio of the model pile; The similarity ratio of the internal friction angles between the prototype slope and the model slope; The load similarity ratio between the prototype pile body and the model pile body; The similarity ratio between the stress in the prototype pile and the stress in the model pile; The similarity ratio between the strain of the prototype pile and the strain of the model pile; The similarity ratio of the area of ​​the prototype pile body to that of the model pile body; The similarity ratio of the bending moments of the prototype pile body and the model pile body; The similarity ratio of the moments of inertia between the prototype pile and the model pile; The shear force similarity ratio between the prototype pile and the model pile; The similarity ratio of the bending stiffness between the prototype pile body and the model pile body; The similarity ratio of the internal friction angles between the prototype slope and the model slope; The similarity ratio of the cohesion between the prototype slope and the model slope; This represents the similarity ratio between the prototype pile anchor cable and the model pile anchor cable.

[0071] 1.2 Model Pile Design and Fabrication Dimensions and Layout: The prototype piles, based on actual engineering designs (such as the Dachao Expressway section), are circular anti-slide piles with a diameter of 2.0m and a spacing of 4.55m. According to the similarity ratio, the model piles adopt an annular cross-section with an outer diameter of 400mm and an inner diameter of 70mm, with a moment of inertia I = 0.001255458m. 4 The piles are 5m long and spaced 0.91m apart. To study the group pile effect and the influence of anchorage depth, 12 model piles were designed and fabricated, numbered C-1 to C-12. In the single-row pile test, three anchorage depths were set: 2.25m for C-1 and C-2, 2.05m for C-3 and C-4, and 1.75m for C-5 and C-6.

[0072] Materials and reinforcement: ① Concrete: Micro-concrete was used for simulation. After mix proportioning tests, the final mix proportion was determined to be (by mass): cement (M32.5): fly ash: steel fiber: water = 1:1:0.13:1.2 (water-cement ratio 0.6). The measured compressive strength was approximately 5.4 MPa, and the elastic modulus was approximately 6.0 GPa, meeting the requirement of a similarity ratio CE=5 (prototype C-35 concrete E≈30 GPa).

[0073] ② Reinforcement: The prototype pile is reinforced with 72 Φ32 HRB400 steel bars on the tension side and 30 Φ32 HRB400 steel bars on the compression side. There are 12 Φ25 stirrups. The stirrups are HPB300; 0-7m uses double-leg stirrups Φ14@200, 7-24m uses double-leg stirrups Φ14@150, and 24-26m uses double-leg stirrups Φ14@150. The concrete grade is C-30.

[0074] The reinforcement ratio of concrete structures is determined according to the principle of equal strength: (1) Among them, A ps A represents the area of ​​the reinforcing steel bars in the prototype structure. pc f is the concrete area of ​​the prototype structure; py,k f is the standard value of the tensile strength of the reinforcing steel bar; pcu,k The standard value of the compressive strength of the concrete cube of the prototype structure; A ms A represents the area of ​​the reinforcing steel bars in the model structure. mc f is the concrete area of ​​the model structure; my,k f is the standard value of the tensile strength of the reinforcing steel bar; mcu,k This represents the standard value of the tensile strength of the reinforcing steel bars in the model structure.

[0075] Therefore: (2) The longitudinal reinforcement of the model test is to be HRB400 Φ10 steel bars, and the stirrups are to be HPB235 Φ3 steel bars. The standard value of the compressive strength of the concrete in the model is 5.4 MPa.

[0076] Therefore, according to calculations, the model pile uses 6Φ10 HRB400 steel bars as the tensile main reinforcement (actual area 471.3mm²). 2 ), 3Φ10 as compression reinforcement (actual area 235.5mm2), 4Φ10 as stirrup reinforcement (actual area 113.04mm2). 2 The stirrups are simulated using Φ2.8mm (No. 12 iron wire) @ 80mm (see...). Figure 3 (Reinforcement section), actual reinforcement area 15.39 mm. 2 .

[0077] ③ Fabrication: Tie the reinforcing cage according to the design, and precisely fix a 70mm inner diameter PVC pipe in the cage core as the inclinometer guide pipe (see...). Figure 4 Layered pouring and thorough compaction with an immersion vibrator were employed, followed by 28 days of curing with a film covering to maintain moisture.

[0078] Actual Measurement of Bending Stiffness (EI): Due to the variability of material properties, the actual stiffness of piles with theoretical mix proportions must be measured and calibrated. The four-point bending method is used (see...). Figure 5 Tests were conducted as follows: A simply supported pile with a span of 4.6m was subjected to simultaneous, graded concentrated loads at two points 1.15m (L / 4) from the support. The load-deflection curves were measured using dial gauges placed at the mid-span and loading points, as well as a continuous flexible inclinometer inside the pile. Based on the formulas of mechanics of materials, the mid-span deflection... (Where P is the total load and a is the distance from the loading point to the support), the actual EI value for each pile is calculated. Measured data shows that the average EI for the first batch of piles (C-1 to C-6) is approximately 13131 kN·m. 2 The average EI of the second batch of piles (C-7 to C-12) is approximately 21468 kN·m. 2 The measured value was directly used for the subsequent inversion analysis of the internal forces of all piles.

[0079] 1.3 Slope Model Filling Materials Design and Preparation: Slide material: Simulating the prototype strongly weathered soft rock, using a mixture of four types of soil. Through heavy compaction tests, its optimum moisture content was determined to be 16.8%, and its maximum dry density was 1.87 g / cm³. 3 .

[0080] Landslide material: Simulated prototype landslide soil, using a 3:7 lime-soil mixture. The optimum moisture content was determined to be 18.8% and the maximum dry density to be 1.81 g / cm³ through heavy compaction tests. 3 .

[0081] Sliding belt material: To form a clear sliding surface, a structure of "double-layer 0.06mm polyethylene plastic cloth sandwiched with 2cm thick high-quality talc powder" is adopted.

[0082] Filling construction and quality control: Slide bed filling: At the bottom of the model trench, mix the four-component soil strictly according to the optimum moisture content and fill it in layers. Each layer is 30cm loosely laid and compacted to a thickness of 22cm (compaction degree ≥0.90) using a mini roller combined with an electric rammer. After every 3-4 layers, take samples on-site using a ring cutter for quick shear tests to ensure that the mean and dispersion of the shear strength indicators (cohesion c, internal friction angle φ) meet the design requirements.

[0083] Slide belt installation: At the designed elevation of the slide, accurately lay the lower layer of plastic sheeting, spread a 2cm thick layer of talcum powder evenly, and then cover it with the upper layer of plastic sheeting to form a flat and continuous weak surface.

[0084] Landslide filling: On top of the slip zone, a 3:7 lime-soil mixture was filled using the same process, controlling the compaction degree to ≥0.90. After the entire slope model was filled, its average physical and mechanical parameters were as follows: slip bed c≈125kPa, φ≈29.5°; landslide body c≈116kPa, φ≈30.8°. These measured values ​​were used as input parameters for numerical simulation comparison.

[0085] 1.4 Installation of the friction reduction system To significantly reduce the constraint of the model groove sidewalls on the sliding body's motion, a rolling friction reduction system was independently designed and installed (see...). Figure 6 ).

[0086] (1) Assembly of the rolling frame: As a rigid rolling unit, a steel pipe 2 with an outer diameter of 48 mm is selected; as a flexible buffer unit, a rubber rod 1 with an outer diameter of 50 mm is selected. In the longitudinal direction of the groove (i.e., parallel to the preset sliding direction), the steel pipes and rubber rods are arranged alternately and closely, while in the transverse direction (perpendicular to the sliding direction), they remain parallel. This staggered arrangement ensures that under the thrust of the sliding body, the elastic deformation of the rubber rods effectively buffers the impact and prevents adjacent steel pipes from directly contacting and squeezing each other, ensuring that the entire frame still maintains a rolling tendency under load.

[0087] (2) Setting of limit rails: like Figure 1 As shown, two parallel channel steels are laid longitudinally as limiting rails 7 directly below the rolling frame. The channel steels are fixed to the pit bottom surface by snap-fit. The ends of all steel pipes and rubber rods are placed within these two rails, serving to provide precise guidance and prevent lateral displacement of the frame.

[0088] (3) Laying of the force transmission plate layer: On top of the installed rolling frame, a force transmission plate layer is laid. In this embodiment, a 15mm thick bamboo plywood 3 is selected. During laying, a "stacked" method is used (e.g., Figure 1 (Illustrative diagram) This means that the lower part of one slab overlaps the upper part of the next slab, and they are laid sequentially from the bottom to the top of the pit. This overlapping method allows relative sliding between the bamboo plywood slabs 3 when the sliding body shifts, without creating resistance due to the ends of the slabs hitting each other. This slab layer completely isolates the backfilled test sliding body (soil) from the rolling frame and evenly transfers the soil pressure to the frame.

[0089] Principle and Effect: When the sliding body tends to move horizontally under thrust, the lateral earth pressure is transmitted to the rolling layer through the bamboo plywood, transforming traditional sliding friction into rolling friction and greatly reducing frictional resistance. Subsequent frictional resistance tests verified that this system can reduce sidewall frictional resistance by approximately 65%, significantly improving the accuracy of thrust transmission.

[0090] 2. Loading and Measurement System Configuration 2.1 Loading the system The system employs a "DGS-6 microcomputer-controlled electro-hydraulic servo geotechnical engineering loading system." This system features three independent rigid push plates (upper CH1, middle CH2, and lower CH3) arranged in front of the reaction frame. Each push plate is synchronously driven by two servo actuators, with a maximum total thrust of 3500 kN (CH1 maximum thrust 900 kN, CH2 maximum thrust 900 kN, CH3 maximum thrust 1800 kN). The control system enables precise loading through displacement and force control, and each layer can operate synchronously or asynchronously, perfectly simulating the distribution of landslide thrust.

[0091] 2.2 Measurement System Earth pressure monitoring: To accurately measure the pile-soil interaction force, an innovative design was developed that allows for pre-embedding of an "earth pressure test rod" and an "earth pressure test plate" (see [reference]). Figure 7 (1) The test rod is a square-section wooden rod with circular holes every 22cm along the axial direction. The BWM28 type (range 1MPa) earth pressure gauge sensor is embedded in the hole with its face facing outward and sealed with silicone. (2) The test plate is a steel plate with earth pressure gauges pasted on its surface. According to the test conditions, the test rod / plate is accurately buried in key positions such as before the pile, after the pile, and between the piles (e.g. Figure 9 , 12 (As shown in Figures 15, 18, and 21). All earth pressure gauge leads converge to the high-speed static data acquisition instrument.

[0092] Pile deformation monitoring: A flexible inclinometer is installed along the entire length of the inclinometer tube of each test pile. The instrument measures the inclination angle of each point on the pile axis in 30cm segments, and the deflection curve of the entire pile is obtained after integration.

[0093] Displacement field monitoring: An electronic dial gauge with a range of 50mm is installed on the top of each pile to monitor the horizontal displacement of the pile top. An array of marker points is set up on the slope surface, and a high-precision total station is used for periodic coordinate measurements. At the same time, a 3D laser scanner is used to obtain a full-field displacement cloud map of the slope surface.

[0094] Process recording: A fixed-position high-definition camera and a drone were used to continuously record the entire test process, capturing macroscopic phenomena such as crack development and soil heave.

[0095] 3. Test Procedures and Operating Conditions The test follows the principle of "cumulative-decreasing" and proceeds with the following six working conditions in sequence, with each subsequent working condition modified based on the previous one.

[0096] 3.1 Working Condition 1: Single-row circular pile pushing test Arrangement: such as Figure 8-9As shown, in the middle of the completed slope, holes were drilled using an electric Luoyang shovel, and the first row of 6 model piles (C-1 to C-6) were inserted. The gaps between the piles were backfilled with micro-concrete grout identical to that of the pile body. All monitoring sensors were then installed.

[0097] Loading and Testing: Loading is performed in stages according to the system outlined in Table 2. Data on earth pressure, pile deformation, and displacement of the pile top and ground surface are collected simultaneously.

[0098] Table 2 Loading regime for single-row circular pile pushing test

[0099]

[0100] result: Pile Deformation: In the single-row circular pile pushing test, the displacement changes of the pile body were measured by setting up flexible inclinometers. One flexible inclinometer was placed every 30cm from the pile top. After the test, the pile deformation curves under various load levels were extracted, such as... Figure 28 As shown in the figure, the overall pile displacement tends to be smooth, exhibiting a gradual decrease from the pile top downwards. Deformation is more pronounced above the slip surface, with a prominent distribution pattern, while deformation is smaller below the slip surface, showing an overall "Y"-shaped distribution. As the external load increases, the pile deformation gradually increases, then gradually decreases during unloading. Finally, after unloading, a small amount of residual deformation remains. Comparing the displacement curves of each pile reveals that the pile displacement under load levels C-5 and C-6 is larger. This is because the anchorage depth of C-5 and C-6 is shallower, resulting in greater overall deformation of the pile under load, thus leading to larger displacement. The pile displacement of C-1, C-2, C-3, and C-4 shows little change.

[0101] Displacement between pile top and ground surface: Figure 29 (a) shows the displacement distribution curves of each pile top. As can be seen from the figure, significant deformation occurs at the pile top after the second level of load is applied. With each increase in load level, the pile top displacement gradually increases, reaching a maximum of 1.3mm to 1.7mm. As the load is gradually unloaded, the pile top displacement gradually decreases. Specifically, piles C-3, C-4, and C-5 show unchanged displacement during the first, second, and third levels of unloading, but decrease gradually after the fourth level. The reason for this is that in the early stages of unloading, the unloading load is relatively small, and the slope deformation still tends to push the piles forward. The piles on both sides undergo more significant displacement deformation during unloading, resulting in obvious displacement deformation for piles C-1, C-2, and C-6. Further comparison of the pile top displacement values ​​shows that C-1 and C-6 have larger values, while C-3, C-4, and C-5 have smaller values. The reason for this is that there is sidewall friction resistance on both sides. Friction reduction treatment was performed on the sidewalls before the experiment, hence the larger displacement values ​​for C-1 and C-6.

[0102] Figure 29 (b) shows the distribution curves of surface displacement at various points. The curves indicate that significant deformation occurred after the second-level load was applied. The deformation at each measuring point remained consistent overall. Further comparison of the displacement values ​​at each measuring point revealed that the surface displacement of the slope gradually decreased from the mountainside to the riverside, and significant plastic deformation still occurred after unloading. The reason for this is that under thrust load, slope deformation occurs from back to front. Under thrust, the soil and rock undergo compressive deformation, thus the slope deformation gradually decreases. Therefore, the surface displacement shows a gradual decrease from the mountainside to the riverside. After unloading, the soil is an elasto-plastic material and will undergo some plastic deformation.

[0103] Earth pressure distribution: such as Figure 30 As shown, the distribution characteristics of earth pressure on the mountainside differ between above and below the sliding surface. Above the sliding surface, the earth pressure is positive, indicating that the soil is under compression, while below the sliding surface, the earth pressure is negative, indicating that the soil is under tension. The reason for this is that above the sliding surface, the thrust of the push plate transmits the soil force, first causing compression, and then to the pile, hence the soil is under compression and the earth pressure is positive. After the pile is subjected to force, it tilts forward as a whole. When the part below the sliding surface tilts forward, the soil does not follow, thus exhibiting tension and a negative earth pressure. Furthermore, above the sliding surface, the distribution exhibits an equilateral triangle pattern increasing from top to bottom, while below the sliding surface, it exhibits an inverted triangle pattern decreasing from top to bottom, with the earth pressure being greatest near the sliding surface. The earth pressure distribution curve between the piles shows an overall tensile distribution. The reason for this is that after the landslide thrust is transmitted to the pile, the pile is subjected to force, but the soil between the piles is not squeezed out. The soil in front of the pile moves forward after being subjected to force, while the soil between the piles does not follow, hence the negative earth pressure between the piles. The earth pressure above the slip surface exhibits a trapezoidal distribution, while the earth pressure below the slip surface shows an inverted triangular distribution, with the greatest earth pressure near the slip surface. The earth pressure on the riverside differs in its characteristics above and below the slip surface: the earth pressure above the slip surface is positive, indicating soil compression, and the earth pressure below the slip surface is also positive, indicating soil compression. The reason for this is that above the slip surface, the thrust of the push plate is transmitted to the pile and further forward, compressing the soil in front of the pile, resulting in a positive earth pressure value. After the pile is subjected to the thrust load, it tilts forward as a whole. When the part below the slip surface tilts forward, it further compresses the soil in front of the pile, so the earth pressure below the slip surface still shows a positive distribution. Simultaneously, on the mountainside, above the slip surface, the earth pressure exhibits an equilateral triangular distribution that increases from top to bottom, while below the slip surface, it exhibits an inverted triangular distribution that decreases from top to bottom, with the greatest earth pressure near the slip surface.

[0104] 3.2 Working Condition 2: Multi-type Circular Pile Pushing Test Implementation process: Structural modifications were carried out on the physical basis of the single-row piles (see appendix). Figure 10-11): ① Connect the tops of piles C-3 and C-4 with a rigid cap beam made of double-layered [20 channel steel to form a "cap beam connection pile"; ② Install a model anchor cable system consisting of steel wire rope, turnbuckle and tension gauge on the tops of piles C-5 and C-6, and tension it in stages to a pre-tension of 7kN to form an "anchored pile"; C-1 and C-2 remain "independent piles".

[0105] The anchor cable of the anchored pile was simulated using an 8mm (7×19) steel wire rope, which was connected to an M18 turnbuckle, a dynamometer, and a [30a channel steel. The [30a channel steel served as the reaction beam for anchoring and was fixed to the test pit. The simulation of the anchor cable considered the free section but not the anchored section. The anchor cable tension of the model pile was set to 7 kN, and a staged tensioning method was adopted, with each stage having a tension load of 2 kN and the final stage having a tension load of 1 kN. One end of the steel wire rope was fixed to the pile head of C-5 and C-6, and the other end was connected to the turnbuckle and the dynamometer. Before the pile pushing test, prestress was applied to the pile head by tightening the turnbuckle. The prestress applied to the pile body could be directly measured using the dynamometer, and the elongation of the steel wire rope could be measured using a vernier caliper.

[0106] The elastic modulus of the prototype anti-slide pile anchor cable is: (3) In the formula: —Prototype pile anchor cable elastic coefficient (unit: N / m); E — Elastic modulus of prototype pile anchor cable (unit: Pa); A —Cross-sectional area of ​​prototype pile anchor cable (unit: m²) 2 ); EA —Tensile stiffness of prototype pile anchor cable (unit: kN); L — Length of the free section of the prototype pile anchor cable (unit: m).

[0107] According to similarity theory, when the geometric similarity ratio is 1:5: (4) In the formula: —Similarity ratio between prototype pile anchor cable and model pile anchor cable; —Elastic coefficient of the prototype pile anchor cable; —Elastic coefficient of the anchor cable in the model pile; When the model pile is tensioned by the anchor cable, the elastic coefficient of the anchor cable in the model test can be obtained by measuring the tension and elongation of the steel wire rope.

[0108] (5) In the formula: —Elastic coefficient of anchor cable for model pile (unit: N / m); —Change in tension of anchor cable in model pile (unit: N); —The elongation of the anchor cable when the tension of the anchor cable changes (unit: m).

[0109] The elastic coefficient of the model was obtained by measuring the displacement during anchor cable tensioning. Tensioning was carried out in stages, with the first stage at 1 kN and each subsequent stage increasing by 1 kN until reaching 7 kN. The elongation of the wire rope under each load stage was recorded to obtain the elastic coefficient of the anchor cable of the model pile.

[0110] During the tensioning of C-5 piles, from the first stage of tensioning to the completion of the seventh stage, the anchor cable displacement elongation is 16.79 mm, corresponding to a tension force change of 6 kN. The elastic coefficient can be calculated to be 357355.37 N / m.

[0111] During the tensioning of C-6 piles, from the first stage of tensioning to the completion of the seventh stage, the anchor cable displacement elongation is 18.47 mm, corresponding to a tension force change of 6 kN. The elastic coefficient can be calculated to be 324851.11 N / m.

[0112] Taking the average of the two yields: =341103.34 N / m, the elastic modulus of the prototype anchor cable was calculated by back-calculation. =8.58×10 6 N / m. The tension of the anchor cable of the model pile is set to 7 kN. According to the similarity ratio of the model test (Table 1), the tension of the anchor cable of the prototype pile is 875 kN. Using 6 anchor cables as the anchor cables of the prototype pile, the free section length of the prototype anchor cable can be calculated as 19.2 m according to the elastic coefficient calculation formula of the prototype anchor cable.

[0113] Loading and Comparison: The same loading system as in Condition 1 is adopted to ensure fair comparison.

[0114] result: Quantitative Comparison of Structural Performance: Pile Top Displacement Results (with appendix) Figure 32The results show that in the different types of circular pile pushing tests, the pile top displacement undergoes significant deformation after the third level of load is applied. With each increase in load, the pile top displacement gradually increases, reaching a maximum of 0.7mm to 1.1mm. As the load is gradually unloaded, the pile top displacement gradually decreases. The displacement changes are relatively small during the first, second, and third levels of unloading, but decrease after the fourth level. This is attributed to the relatively small unloading load in the early stages, where the slope deformation still tends to push the pile forward, resulting in minimal pile rebound deformation. Further comparison of the pile top displacement values ​​reveals that C-1 has the largest value, while C-4 has the smallest. This is attributed to the presence of sidewall friction, which was addressed before the experiment, leading to the larger displacement of C-1. C-6 experienced reduced displacement due to anchor cable tensioning, while C-4, connected to the C-3 capping beam, exhibited smaller pile top deformation.

[0115] Differences in working mechanisms: From the pile deformation curve (attached) Figure 31 As you can see, the capping beam connection causes the deformation curves of piles C-3 and C-4 to highly overlap, achieving coordinated deformation. The curves of anchored piles C-5 and C-6 show that the pile body undergoes backward deformation in the early stage of loading, and the displacement of the pile top is firmly restricted by the anchor cable. Its maximum bending moment point is about 0.5m lower than that of the independent pile, indicating that the anchor cable changes the cantilever force mode of the pile body by providing reverse tension, making it closer to a beam simply supported at one end.

[0116] Earth pressure distribution: From Figure 12 As can be seen, the earth pressure gauges are arranged in five rows: two rows on the mountainside, one row between piles, and two rows on the riverside. The following are the earth pressure increment distribution curves under various load levels, and the earth pressure distribution is shown in the appendix. Figure 33The graph shows three distribution patterns of earth pressure on the mountainside, between piles, and along the riverbank, with the piles as the boundary. The distribution of earth pressure on the mountainside differs between the area above and below the slip surface. Above the slip surface, the earth pressure is positive, indicating compression, while below, it is negative, indicating tension. This is because above the slip surface, the thrust of the push plate transmits the pressure to the soil, causing compression before it is transferred to the pile, resulting in positive earth pressure. When the pile is stressed, it tilts forward as a whole. Below the slip surface, the soil does not follow the tilt, thus exhibiting tension and negative earth pressure. Furthermore, the earth pressure distribution above the slip surface on the mountainside shows an equilateral triangle pattern increasing from top to bottom, while below, it shows an inverted triangle pattern decreasing from top to bottom, with the highest earth pressure near the slip surface. The earth pressure distribution curve between piles shows an overall tensile distribution. The reasons for this are as follows: After the landslide thrust is transmitted to the pile, the pile is stressed, but the soil between the piles is not squeezed out. The soil in front of the pile moves forward under stress, but the soil between the piles does not follow, so the soil pressure between the piles is negative. The soil pressure above the sliding surface shows a trapezoidal distribution, while the soil pressure below the sliding surface shows an inverted triangular distribution, with the soil pressure near the sliding surface being the greatest. The soil pressure on the river side has different characteristics above and below the sliding surface. The soil pressure above the sliding surface is positive, indicating that the soil is under pressure, and the soil pressure below the sliding surface is also positive, indicating that the soil is under pressure. The reason for this is that the thrust of the push plate above the sliding surface is transmitted to the pile and further forward, causing the soil in front of the pile to be under pressure, resulting in a positive soil pressure. After the pile is subjected to thrust load, it tilts forward as a whole. When the part below the sliding surface tilts forward, it further compresses the soil in front of the pile, so the soil pressure in front of the pile still shows a positive distribution below the sliding surface. Meanwhile, the distribution pattern above the slip surface on the mountainside exhibits an equilateral triangle pattern that increases from top to bottom, while the distribution pattern below the slip surface exhibits an inverted triangle pattern that decreases from top to bottom, with the greatest soil pressure near the slip surface.

[0117] 3.3 Working Condition 3: Test of Double-Row Pile Group Effect Implementation process: After removing the cap beam and anchor cables, a second row of 6 model piles (C-7 to C-12) was installed 0.88m behind the original single-row piles (now defined as the "front row piles") (on the mountainside), forming a double-row pile system, as shown in the attached diagram. Figure 13 Appendix Figure 14 As shown. Inclinometers were arranged correspondingly for the front row of piles (C-2, C-4, C-6) and the newly added rear row of piles (C-8, C-10, C-12), as follows. Figure 15 As shown.

[0118] Loading process: A higher load level was applied, as shown in Table 3. The total thrust of the seventh stage reached approximately 2962 kN, in order to explore its ultimate collaborative working capability.

[0119] Table 3 Loading regime for double-row circular pile pushing test

[0120] Results and Mechanism Analysis: Load sharing and shielding effect between front and rear rows: pile deformation curve ( Figure 34 The comparison shows that, under the same thrust, the displacement and curvature of the rear piles (such as C-8) are generally greater than those of the corresponding front piles (such as C-2). For example, the displacement of pile C-8 at the slip surface is 57% greater than that of pile C-2. This intuitively proves that the landslide thrust is mainly borne by the rear piles, while the front piles play a role in "blocking" and unloading the soil behind them.

[0121] Deformation asynchrony: Pile top displacement curve ( Figure 35 The data shows that the displacement development curves of the front and rear rows of piles are separate. The displacement group of the front row of piles (about 0.3-0.6 mm) is smaller than that of the rear row of piles (about 0.7-1.1 mm), and the change patterns are not completely synchronized. This indicates that when the double rows of piles are not connected, they work together as two independent anti-slip structures, rather than as a whole.

[0122] Strengthening of soil arching effect between piles: Earth pressure distribution ( Figure 36 This indicates that the soil pressure between the two rows of piles is significantly higher than that behind a single row of piles, forming a strong "pile arch" that effectively transfers some of the thrust to the front row of piles, thus confirming the force transmission mechanism of the soil between rows.

[0123] 3.4 Working Condition 4: Portal Frame Circular Pile Pushing Test Implementation process: Install an integral steel gantry cap beam spanning the front and rear of the double-row piles (see...). Figure 16-18 To address the issue of inconsistent deformation between the front and rear rows during initial testing, a rigid force transmission rod capable of transmitting horizontal thrust was innovatively added to the cap beam.

[0124] Loading and Testing: Load to a higher level according to the system specified in Table 4 to test its ultimate bearing capacity and integrity.

[0125] Table 4 Loading regime for gantry circular pile pushing test

[0126] Results and Mechanism Analysis: Excellent overall performance: The optimized gantry structure demonstrates significant improvement. (Pile deformation curve attached) Figure 37The results show that the deformation curves of the mountain-side piles and the river-side piles have basically the same distribution characteristics. The displacement curves of both piles are relatively smooth, with more obvious deformation above the slip surface and a prominent distribution characteristic. The push pile curve exhibits a curved distribution characteristic, which is also quite obvious. The deformation below the slip surface is smaller, and the overall distribution characteristic is "Y". This also indicates that the capping beam design in this gantry pile test is reasonable, and the mountain-side piles and river-side piles exhibit the same deformation characteristics. In this gantry pile capping beam design, a force transmission rod is added between the two piles, which effectively transfers the deformation and thrust of the mountain-side pile to the river-side pile. Therefore, the deformation characteristics of the mountain-side piles and the river-side piles are the same. Further comparison of the pile displacements on the mountainside and riverside reveals that the displacement of the mountainside piles is slightly greater than that of the riverside piles. The reason for this is that the mountainside piles are the rear row, while the riverside piles are the front row. The rear row of piles experiences greater stress than the front row. Furthermore, when dowel bars are used to transmit the stress and deformation of the mountainside piles, the dowel bars also undergo corresponding compressive deformation. Therefore, the displacements of the piles on the mountainside and riverside are inconsistent, with the mountainside piles exhibiting a larger displacement. In addition, the pile displacement curves of the gantry piles also show that the pile deformation gradually increases with increasing external load, then gradually decreases during unloading, and finally, after unloading, a small amount of residual deformation remains.

[0127] Pile top displacement curve (attached) Figure 38 The results show that significant deformation occurred at the pile top after the second level of load was applied. The pile top displacement gradually increased with each increase in load, reaching a maximum of 0.5mm to 0.9mm. As the load was gradually unloaded, the pile top displacement gradually decreased. Comparing the pile top displacements of the piles on the mountain side and the piles on the river side, their displacements tended to be consistent, further demonstrating the rationality of the capping beam design in the gantry pile pushing model test. The pile top displacements on both sides of the same row of piles were not completely consistent, still showing a distribution characteristic of larger displacements on the mountain side and smaller displacements on the river side. The reason for this is that the capping beam and its added dowel bars in the model test underwent some compressive deformation under the thrust of the mountain side piles, thus causing the pile top displacements on both sides of the mountain and river to not completely converge.

[0128] Earth pressure distribution optimization: such as Figure 39As shown in the figure, the earth pressure on the mountainside piles, the earth pressure between pile rows on both sides of the mountain and river, the earth pressure between pile rows on the riverside, and the earth pressure on the riverside piles exhibit three overall distribution patterns, with the riverside piles serving as the boundary. The earth pressure on the mountainside piles and the earth pressure between pile rows on both sides of the mountain and river show different distribution characteristics above and below the slip surface. The earth pressure above the slip surface is positive, indicating that the soil is under compression, while the earth pressure below the slip surface is negative, indicating that the soil is under tension. The reason for this is that above the slip surface, the thrust of the push plate first causes compression in the soil before it is transmitted to the mountainside piles. The mountainside piles then compress the soil between the pile rows on both sides of the mountain and river before transmitting the thrust to the riverside piles. Therefore, the soil above the slip surface is under compression, and the earth pressure is positive. After being subjected to force, the mountainside piles and riverside piles will tilt forward as a whole. When the part below the slip surface tilts forward, the soil does not follow suit, thus exhibiting the characteristic of tensile soil and negative earth pressure. The soil pressure distribution above the slip surface on the mountainside piles generally exhibits an equilateral triangle pattern, increasing from top to bottom, while below the slip surface, it shows an inverted triangle pattern, decreasing from top to bottom, with the greatest soil pressure near the slip surface. Furthermore, the soil pressure between the pile rows on both sides of the river generally exhibits a trapezoidal pattern above the slip surface, increasing from top to bottom, while below the slip surface, it shows an inverted triangle pattern, decreasing from top to bottom, with the greatest soil pressure near the slip surface. The soil pressure distribution curve between the piles fluctuates around zero, indicating that the soil pressure between the piles on the riverside remains essentially unchanged. This is because the double-row piles have strong anti-slip capabilities, resulting in a smaller thrust transmitted to the riverside piles. The soil between the riverside piles experiences minimal stress, thus the soil pressure between them tends to be zero. The soil pressure on the riverside piles exhibits similar characteristics above and below the slip surface: positive soil pressure above the slip surface indicates soil compression, and positive soil pressure below the slip surface also indicates soil compression. The reason for this is that the thrust force from the push plate above the slip surface is transmitted to the pile on the riverside and then further forward, compressing the soil in front of the pile, resulting in a positive earth pressure. After being subjected to the thrust load, the pile on the riverside tilts forward as a whole. When the portion below the slip surface tilts forward, it further compresses the soil in front of the pile. Therefore, the earth pressure in front of the pile below the slip surface still exhibits a positive distribution. The overall earth pressure shows a triangular distribution pattern that increases from top to bottom above the slip surface, and an inverted triangular distribution pattern that decreases from top to bottom below the slip surface. The earth pressure is also greatest near the slip surface.

[0129] 3.5 Working Condition 5: Single-row cantilever circular pile pushing test Implementation process: Remove the gantry cap beam, then carefully excavate all the sliding body in front of piles C-7 to C-12, placing it in a cantilevered stress state, as shown in the attached diagram. Figures 19-20 As shown.

[0130] Loading and testing: Loading was performed according to the conditions in Table 5 to study the pile performance under cantilever conditions.

[0131] Table 5 Loading regime for single-row cantilever pile pushing test

[0132] result: Pile displacement: such as Figure 40 As shown in the figure, the overall pile displacement tends to be smooth, exhibiting a gradual decrease from the pile top downwards. Deformation is more pronounced above the slip surface, with a prominent distribution pattern, while deformation below the slip surface is smaller, showing an overall "Y"-shaped linear distribution. With increasing external load, pile deformation gradually increases, then gradually decreases during unloading, ultimately leaving a small amount of residual deformation after unloading. Comparing the pile displacement curves, it can be found that the pile displacement under loads C-11 and C-12 is the largest, followed by C-10 and C-9, while C-7 and C-8 have the smallest displacement. This is because the anchorage depth of C-11 and C-12 is shallower, resulting in greater overall deformation and thus larger displacement after the pile is subjected to force. The anchorage depth of C-10 and C-9 is the second deepest, hence the smaller displacement, while C-7 and C-8 have the largest anchorage depth and therefore the smallest displacement.

[0133] Pile top displacement: such as Figure 41 As shown in the figure, the pile top displacement undergoes significant deformation after the second level of load is applied. With each increase in load, the pile top displacement gradually increases, reaching a maximum of 5mm to 6.5mm. As the load is gradually unloaded, the pile top displacement gradually decreases. The displacement decreases slightly during the unloading of the first level of load, but significantly decreases after the unloading of the second level. This is because the unloading amount during the first level of load is relatively small, resulting in a smaller displacement of the pile. Further comparison of the pile top displacement values ​​shows that C-12 and C-11 have the largest values, followed by C-10 and C-9, while C-7 and C-8 have the smallest values. The reason for this is that the anchorage depth of the six piles is divided into three groups. C-12 and C-11 have the smallest anchorage depth, followed by C-10 and C-9, while C-7 and C-8 have the largest anchorage depth. The greater the anchorage depth, the stronger the anti-sliding ability of the pile. Therefore, C-12 and C-11 have larger displacement values, C-10 and C-9 have the next larger displacement values, and C-7 and C-8 have the smallest displacement values.

[0134] Earth pressure distribution: such as Figure 42As shown in the figure, the earth pressure distribution on the mountainside and the riverside exhibit two different patterns, with the pile as the boundary. The distribution characteristics of the earth pressure on the mountainside differ between the area above and below the sliding surface. Above the sliding surface, the earth pressure is positive, indicating compression, while below, it is negative, indicating tension. The reason for this is that above the sliding surface, the thrust of the push plate transmits the soil pressure first to the pile, resulting in positive earth pressure. After the pile is subjected to force, it tilts forward as a whole. When the area below the sliding surface tilts forward, the soil does not follow suit, thus exhibiting tension and negative earth pressure. Furthermore, the earth pressure distribution above the sliding surface on the mountainside shows an equilateral triangle pattern increasing from top to bottom, while below the sliding surface, it shows an inverted triangle pattern decreasing from top to bottom, with the earth pressure being greatest near the sliding surface. The earth pressure distribution curve between the piles shows an overall tensile distribution. The reasons for this are as follows: After the landslide thrust is transmitted to the pile, the pile is stressed, but the soil between the piles is not squeezed out. The soil in front of the pile moves forward under stress, but the soil between the piles does not follow, so the soil pressure between the piles is negative. The soil pressure above the sliding surface generally exhibits a trapezoidal distribution, while the soil pressure below the sliding surface exhibits an inverted triangular distribution. The soil pressure near the sliding surface is also the largest. The soil pressure on the river side has basically the same properties above and below the sliding surface, with a smaller value close to zero. The reason for this is that in the single-row cantilever pile pushing test, the soil pressure gauge is on the outside of the soil cantilever, and there is no point of application under the thrust. The soil pressure gauge moves forward with the soil under the thrust, so the soil pressure value is close to zero.

[0135] 3.6 Operating Condition Six: Separation and Quantification Test of Sidewall Friction Total friction test: After excavating the piles, test the total friction force required to push the remaining sliding body in the soil (see layout). Figure 22 , 24 The test curve is shown below. Figure 43 The results are shown in Table 6.

[0136] Table 6. Total friction resistance test results

[0137] The total frictional force of the remaining sliding body after the pile was calculated based on the average of the two tests, which was 710.78 kN.

[0138] Bottom friction test: Further excavate both sides of the sliding body to test the pure bottom friction force (see layout). Figure 23 , 25 The test curve is shown below. Figure 44 The results are shown in Table 7.

[0139] Table 7 Results of Bottom Friction Resistance Test

[0140] The total frictional force of the remaining sliding body after the pile was calculated based on the average of the two tests to be 423.13 kN.

[0141] Calculation results: Side wall friction = Total friction - Bottom friction = 710.78 kN - 423.13 kN = 287.65 kN. The calculation results can be directly used for experimental data analysis.

[0142] In summary, this invention, through a logically rigorous and interconnected "cumulative-decreasing" closed-loop test procedure, efficiently and systematically completed a comparative study of six anti-slide pile structural forms on a single slope model. The experiments not only revealed the working mechanism and performance evolution laws from single piles to complex combined structures, but also quantified the influence of boundary conditions through innovative testing techniques. All working conditions are supported by detailed raw data (load, displacement, earth pressure) and intuitive result curves, ensuring strong data comparability and reliable conclusions. This invention provides a comprehensive, refined, and reliable experimental methodology for the theoretical research and engineering optimization design of large-section circular anti-slide piles.

Claims

1. A large cross-section circular anti-slide pile multi-structure contrast pushing pile test method, characterized in that, Includes the following steps: S1. Model preparation stage: Based on the preset similarity ratio, prepare large-section circular model piles, simulated sliding bed material, simulated sliding strip material and simulated sliding body material; in the model test trench, fill and compact the simulated sliding bed material, lay the simulated sliding strip material and fill and compact the simulated sliding body material in sequence to construct the slope model; S2. Cumulative Test Phase: In the slope model, the following sets of pile pushing tests are conducted sequentially, with each subsequent set of tests based on the slope and pile structure formed by the previous set of tests: S2.1 Single-row pile test: A single row of large-section circular model piles was implanted in the middle of the slope model. Horizontal thrust was applied to the slope through a loading system, and the pile-soil system response was monitored. S2.2 Multi-type pile comparison test: Based on the pile structure that has completed the single-row pile test, modify it to form a comparison group that includes at least two or more types of piles, including independent piles, cap beam connecting piles and anchor piles, apply horizontal thrust and monitor it; S2.3 Double-row pile test: In the slope model that has completed the multi-type pile comparison test, another row of model piles is added after the original single-row piles to form a double-row pile structure. Horizontal thrust is applied and monitored. S2.4 Portal pile test: Based on the pile structure of the double-row pile test, a connecting cap beam is added to the top of the front and rear rows of piles to form a portal pile structure. Horizontal thrust is applied and monitored. The monitoring includes at least one of the following: monitoring pile deformation using a flexible inclinometer; monitoring the distribution of soil pressure before, after, and between piles using an earth pressure gauge, wherein the earth pressure gauge is fixed by a test rod or test plate pre-embedded in the soil; monitoring slope surface displacement using a three-dimensional laser scanner and / or total station; monitoring pile top displacement using an electronic dial gauge; and recording the macroscopic deformation process of the test using video equipment. S3. Decreasing Test Phase: Based on the structure that has completed the portal frame pile test, the following sets of tests are carried out in sequence, with each subsequent set of tests achieved by removing or modifying parts of the structure from the previous set of tests: S3.1 Single-row cantilever pile test: Remove the connecting cap beam and excavate part of the sliding body in front of the rear row of piles in the double row of piles, so that the rear row of piles is exposed as a cantilever pile, apply horizontal thrust and monitor it; S3.2 Side friction test: After the single-row cantilever pile test, the soil between the rear row of piles and the side wall of the model test trench is further removed longitudinally to separate the remaining sliding body from the side wall of the model test trench. Then, a horizontal thrust is applied, and the bottom friction and side wall friction of the sliding body are separated and calculated by measuring the thrust of the push plate and the displacement of the sliding body.

2. The multi-structure comparative pile pushing test method for large-section circular anti-slide piles according to claim 1, characterized in that, In the cumulative test phase S2 and the decreasing test phase S3, each test group includes loading, load monitoring, and unloading steps, and in at least one test group, repeated loading tests of the same load level are conducted.

3. The multi-structure comparative pile pushing test method for large-section circular anti-slide piles according to claim 1 or 2, characterized in that, The similarity ratio is a geometric similarity ratio, which ranges from 1:4 to 1:10; The reinforcement of the model pile is determined according to the principle of equal strength and the similarity ratio; the mechanical parameters of the model pile, the simulated sliding bed and the simulated sliding body are determined according to the similarity theory.

4. The multi-structure comparative pile pushing test method for large-section circular anti-slide piles according to claim 1, characterized in that, In step S2.2, the anchor cable similarity design method for the anchor pile is as follows: determine the target elastic coefficient of the model anchor cable according to the similarity ratio; measure the elastic coefficient of the model anchor cable through a tension test, and calculate the parameters of the prototype anchor cable accordingly.

5. The multi-structure comparative pile pushing test method for large-section circular anti-slide piles according to claim 1, characterized in that, In step S2.4, the connecting crown beam is made of steel components connected by bolts, and a force transmission rod capable of transmitting horizontal force is set between the corresponding crown beam segments of the front and rear rows of piles.

6. The multi-structure comparative push-pile test method for large-section circular anti-slide piles according to claim 1, characterized in that, The loading system is a multi-layer electro-hydraulic servo loading system, which can apply independently controlled horizontal loads with thrust and displacement to different heights of the slope.

7. The multi-structure comparative push-pile test method for large-section circular anti-slide piles according to claim 1, characterized in that, After the model preparation stage S1 and before the cumulative test stage S2, the bending stiffness of the large cross-section circular model pile is tested; its flexural deformation under vertical load is tested by the "four-point bending" method, and the bending stiffness of the model pile is calculated based on the flexural deformation diagram.

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