A lateral friction reduction device and method for a trench model test

Abstract

The application discloses a lateral friction reduction device and method for a pit slot model test. The device comprises a composite friction reduction layer arranged between a pit slot sidewall and a test sliding body. The composite layer is formed by a rolling framework formed by rigid rolling units and flexible buffer units arranged longitudinally and alternately next to the sidewall, a force transmission plate layer arranged on the framework in a shingle type, and a limiting track arranged at the bottom of the framework. The method comprises the following steps: after a main test is completed, keeping the system in place, releasing the constraint behind the pile, directly measuring the remaining total friction and the bottom friction after the system is reduced by applying a pushing force and monitoring data, and obtaining the lateral friction by subtracting the bottom friction from the total friction. The application converts the sliding friction which is difficult to control into the rolling and flexible deformation friction which is controllable in the system, significantly reduces the sidewall friction interference, realizes the quantification of the remaining friction, and effectively improves the precision and reliability of the pit slot model test.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering physical model testing technology, specifically to a device and method for reducing lateral friction in pit model testing. Background Technology

[0002] In geotechnical engineering, conducting large-scale physical model tests using pits (such as pile-soil interaction tests for anti-slide piles) is an important method for studying the stress mechanism of structures. However, a long-standing technical problem in such tests remains unresolved: a huge lateral skin friction is generated between the test sliding body and the concrete sidewalls of the pit. This skin friction, though not the subject of the test, acts as a significant interference force, severely contaminating the test data and failing to accurately reflect the pile-soil interaction force, thus significantly reducing the accuracy and reliability of the test results.

[0003] Currently, the industry has tried passive friction reduction methods such as applying lubricants and laying smooth plastic films, but these methods have limited effectiveness, are unstable, cannot be quantitatively evaluated, and are difficult to withstand the high pressure and shear of large-scale soil masses. Therefore, how to actively, effectively, and quantitatively reduce lateral friction in pit model tests has become a key bottleneck in improving the scientific rigor and accuracy of such tests. Summary of the Invention

[0004] To address the shortcomings of the aforementioned background technology, this invention aims to provide a lateral friction reduction device and method for pit model tests. This method can actively isolate and significantly reduce sidewall friction, and can achieve accurate quantification of remaining friction, thereby significantly improving the data accuracy of pit model tests.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] First, the method of the present invention includes a lateral friction reduction device, through which lateral friction is reduced.

[0007] The device is laid between the sidewall of the pit and the test slide, and its core component is a composite friction-reducing layer. This composite friction-reducing layer mainly consists of three functional parts:

[0008] Rolling skeleton: Located adjacent to the sidewall of the pit, it consists of multiple rigid rolling units and flexible buffer units arranged alternately along the longitudinal direction of the model (i.e., the expected sliding direction). This alternating structural design ensures that when subjected to the thrust of the sliding body, the rigid units provide the main rolling support, while the flexible units buffer uneven force through deformation and prevent adjacent rigid units from jamming together, thus ensuring that the overall skeleton maintains a smooth rolling trend under stress.

[0009] Force transmission plate layer: This layer is laid between the rolling frame and the test sliding body. Its function is to evenly and smoothly transfer the soil pressure generated by the test sliding body to the rolling frame below, avoiding stress concentration. Simultaneously, it acts as an insulating interface, preventing soil particles from intruding into the gaps between the rolling frame. Preferably, this force transmission plate layer is laid in an overlapping manner using multiple sheets (such as bamboo plywood). This structure allows for relative slippage between the sheets during large displacements of the sliding body, without creating new sources of resistance due to their own rigid constraints.

[0010] Limiting rail: Located at the bottom of the rolling frame, it provides physical guidance and constraint for the movement of the rolling frame, ensuring that its rolling direction is consistent with the sliding direction designed in the experiment, and preventing deflection.

[0011] Secondly, the present invention provides a method for testing lateral friction resistance using the above-described system.

[0012] This method enables direct and quantitative measurement of the remaining frictional resistance after system reduction. The steps are as follows:

[0013] Test preparation: After completing the main test items such as pile-soil interaction, the friction reduction system was kept in its original state.

[0014] Releasing constraints: Locally excavate the obstruction at the contact point between the pile and the sliding body behind it, so that the sliding body is only constrained by the side wall friction, restoring its potential conditions for sliding along the friction reduction system.

[0015] Thrust test: Apply a horizontal thrust to the sliding body to push it to slide along the friction reduction system.

[0016] Further remove all side constraints: remove all friction reduction systems on the sides of the sliding body, so that the sliding body only has mechanical connection with the soil on the bottom surface.

[0017] Applying thrust and monitoring data: Hydraulic jacks are used to push the sliding body through a rigid force transmission plate. High-precision force sensors are installed between the jacks and the reaction wall to monitor the thrust (load) in real time. Simultaneously, displacement gauges are placed on the push plate and at the top and bottom of the sliding body slope to monitor displacement.

[0018] Test Procedure and Data Acquisition: A thrust was slowly applied, propelling the sliding body a short distance along the anti-friction system. The relationship between thrust and time, and displacement and time, was continuously recorded throughout the process. Two independent tests were also conducted.

[0019] Data acquisition and calculation: Simultaneously monitor and record the applied thrust and the displacement data of the sliding body. By analyzing the thrust-displacement (or thrust-time) curves, the maximum total static friction required to initiate the sliding body and the total sliding friction required to maintain the sliding can be determined.

[0020] The remaining lateral frictional resistance can be obtained by subtracting the remaining bottom frictional resistance from the remaining total frictional resistance in the test data. This value is the objectively existing and precisely quantifiable lateral frictional resistance under the test conditions after effective reduction by the system of this invention.

[0021] Finally, the present invention also provides a method for improving the accuracy of pit model tests.

[0022] The core of this method lies in actively constructing a controllable frictional interface, and its steps include:

[0023] Between the sidewall of the pit model and the test sliding body, a composite friction-reducing layer as described above is constructed. Through this specific intermediate layer, the direct sliding friction, which is originally difficult to control and has huge values ​​between the soil and the concrete sidewall, is transformed into a controllable friction form within the composite friction-reducing layer, mainly consisting of rolling friction and flexible material deformation friction. This fundamental transformation not only actively reduces most of the interfering frictional resistance, but also makes the remaining frictional resistance stable, isolated, and measurable, thus achieving an integrated solution for the "reduction, isolation, and quantification" of lateral frictional resistance interference.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] By employing a composite friction-reducing layer consisting of a rolling frame, force-transmitting plates, and limiting tracks, the uncontrollable sliding friction between the pit sidewalls and the sliding body can be effectively transformed into controllable rolling and flexible deformation friction within the system, thus significantly reducing experimental interference. This system not only drastically reduces lateral friction but also makes the remaining friction stable and measurable, providing a reliable basis for accurate analysis of experimental data. Furthermore, its rigid-flexible structural design avoids jamming or excessive deformation; the overlapping plates accommodate large displacements; the overall structure is robust and reliable; it can be manufactured using conventional materials; installation is simple; and it is reusable, effectively balancing experimental accuracy and economy. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the planar layout of the friction reduction system provided in an embodiment of the present invention.

[0027] Figure 2 This is a three-dimensional structural diagram of the friction reduction system provided in an embodiment of the present invention.

[0028] Figure 3 This is a plan view of the total friction test of the sliding body in an embodiment of the present invention.

[0029] Figure 4 This is a cross-sectional schematic diagram of a total friction or bottom friction test performed on a sliding body in an embodiment of the present invention.

[0030] Figure 5This is a plan view of the components (dial gauge) used to conduct a total friction resistance test on the sliding body in an embodiment of the present invention.

[0031] Figure 6 This is a curve showing the load-time relationship of the push plate during the first total friction resistance test in this embodiment of the invention.

[0032] Figure 7 This is a curve showing the load-time relationship of the push plate in the second total friction resistance test in this embodiment of the invention.

[0033] Figure 8 This is a graph showing the displacement-time relationship of the push plate during the first total friction resistance test in an embodiment of the present invention.

[0034] Figure 9 This is a graph showing the displacement-time relationship of the push plate during the second total friction resistance test in this embodiment of the invention.

[0035] Figure 10 This is a curve showing the displacement-time relationship at the top of the slope during the first total friction resistance test in an embodiment of the present invention.

[0036] Figure 11 This is a curve showing the displacement-time relationship at the top of the slope during the second total friction resistance test in this embodiment of the invention.

[0037] Figure 12 This is a curve showing the displacement-time relationship at the bottom of the slope during the first total friction resistance test in an embodiment of the present invention.

[0038] Figure 13 This is a curve showing the displacement-time relationship at the bottom of the slope during the second total friction resistance test in this embodiment of the invention.

[0039] Figure 14 This is a plan view of the sliding body for bottom friction resistance testing in an embodiment of the present invention.

[0040] Figure 15 This is a plan view of the components (dial gauge) used to conduct a bottom friction resistance test on the sliding body in an embodiment of the present invention.

[0041] Figure 16 This is a curve showing the load-time relationship of the push plate during the first bottom friction resistance test in an embodiment of the present invention.

[0042] Figure 17 This is a curve showing the load-time relationship of the push plate in the second bottom friction resistance test in this embodiment of the invention.

[0043] Figure 18 This is a graph showing the displacement-time relationship of the push plate during the first bottom friction resistance test in an embodiment of the present invention.

[0044] Figure 19This is a graph showing the displacement-time relationship of the push plate during the second bottom friction resistance test in an embodiment of the present invention.

[0045] Figure 20 This is a curve showing the displacement-time relationship at the top of the slope during the first bottom friction resistance test in an embodiment of the present invention.

[0046] Figure 21 This is a curve showing the displacement-time relationship at the top of the slope during the second bottom friction resistance test in an embodiment of the present invention.

[0047] Figure 22 This is a curve showing the displacement-time relationship at the bottom of the slope during the first bottom friction resistance test in an embodiment of the present invention.

[0048] Figure 23 This is a curve showing the displacement-time relationship at the bottom of the slope during the second bottom friction resistance test in an embodiment of the present invention.

[0049] Figure 1-5 In 14-16: 1-rubber rod, 2-steel pipe, 3-bamboo plywood, 4-sliding body, 5-jack, 6-thrust plate, 7-limiting track, 8-reaction wall, 9-sliding bed, 10-sliding surface, 11-limiting concrete block. Detailed Implementation

[0050] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can fully understand and implement the present invention. The following description is merely exemplary and is not intended to limit the present invention.

[0051] Example: Lateral friction reduction and testing in anti-slide pile trench model test

[0052] This embodiment uses a large-scale anti-slide pile-soil interaction pit model test as an application scenario to explain the implementation process of the present invention in detail.

[0053] 1. Fabrication and installation of friction reduction devices

[0054] like Figures 1 to 2 As shown, the lateral friction reduction device is first constructed in the test pit.

[0055] (1) Assembly of the rolling frame:

[0056] 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 2 and rubber rods 1 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.

[0057] (2) Setting of limit rails:

[0058] 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.

[0059] (3) Laying of the force transmission plate layer:

[0060] 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.

[0061] 2. Conduct of the main experiment

[0062] After the friction reduction system was installed, the soil was backfilled according to the test design to form the test sliding body, and the anti-slide pile model was poured. Subsequently, a conventional pile-soil interaction loading test (main test) was conducted. During this process, the force exerted by the sliding body on the sidewall of the pit was mainly converted into internal rolling friction and flexible deformation friction through this system, and the interference of sidewall friction on the main test data was effectively suppressed and isolated.

[0063] 3. Test of total lateral frictional resistance

[0064] (3.1) Total friction resistance test

[0065] This test aims to determine the total frictional resistance of the sliding body under the combined constraints of the sidewall system and the bottom surface. The test plan layout and cross-sectional diagram are shown below. Figure 3 and Figure 4 As shown, the planar layout of the monitoring components is shown in the figure. Figure 5 .in Figure 3 and Figure 4 The dashed line represents the limiting concrete block 11 that limits the slide 9. It is used to fix the slide and prevent it from moving with the slide body during friction testing. This is common knowledge in the field of pit model testing.

[0066] Release the pile constraint: At a predetermined position behind the pile, locally excavate the contact area between the pile and the sliding body to cut off the direct mechanical constraint of the pile on the sliding body, so that the sliding body is mechanically connected only to the pit sidewall through the friction reduction system and to the bottom of the pit through the bottom soil.

[0067] Test Implementation and Data Acquisition: A "DGS-6 Microcomputer-Controlled Electro-hydraulic Servo Geotechnical Engineering Loading System" was used to apply horizontal thrust to the sliding body. This system has three independent rigid push plates arranged in front of the reaction frame, from top to bottom: CH1, CH2, and CH3 (see [link to test implementation]). Figure 4 Each push plate is synchronously driven by two servo actuators, and the maximum total thrust of the system is 3500kN. During the test, the hydraulic jack pushes the sliding body through the rigid push plates of the system. A high-precision force sensor is installed between the jack and the reaction wall to monitor the thrust in real time. Simultaneously, displacement monitoring components are arranged at the top and bottom of the slopes of the push plates and the sliding body (see [reference to measurement point layout]). Figure 5 The displacement changes were monitored. A thrust was slowly applied, propelling the sliding body along the anti-friction system for a distance. Thrust-time and displacement-time data were continuously recorded throughout the process. Two independent tests were conducted in this embodiment.

[0068] Test Results: The load-time curve, displacement-time curve, slope top displacement-time curve, and slope bottom displacement-time curve obtained from the first total friction resistance test are shown below. Figure 6 , Figure 8 , Figure 10 , Figure 12 As shown. The corresponding curves for the second test are respectively as follows. Figure 7 , Figure 9 , Figure 11 , Figure 13 As shown. By analyzing the thrust-displacement curves, the maximum static friction required to initiate the sliding body and the sliding friction required to maintain sliding can be determined.

[0069] (3.2) Bottom friction resistance test

[0070] This test aims to determine the bottom skin friction generated solely by the interaction between the sliding body and the soil at the bottom of the pit after the sidewall system has been removed. The test setup is as follows: Figure 4 (profile), Figure 14 (Plane) and Figure 15 (Component layout) is shown.

[0071] Remove sidewall constraints: Remove the entire friction reduction system (rolling skeleton, force transmission plate layer, etc.) on the side of the sliding body, so that the sliding body maintains mechanical connection only with the bottom soil.

[0072] Test Implementation and Data Acquisition: The same "DGS-6 Microcomputer-Controlled Electro-hydraulic Servo Geotechnical Engineering Loading System" and monitoring method as the total friction resistance test were used (see the layout of push plates CH1, CH2, and CH3 for details). Figure 4 A horizontal thrust was applied to the sliding body, and the thrust and displacement data were recorded. Two independent tests were also conducted.

[0073] Test results: The curves obtained from the first bottom friction resistance test are as follows: Figure 16 , Figure 18 , Figure 20 , Figure 22 As shown. The corresponding curves for the second test are respectively as follows. Figure 17 , Figure 19 , Figure 21 , Figure 23 As shown.

[0074] Results Analysis: Based on the load-time curve, the peak force is the maximum static friction force, and the average force during the steady-state phase is the sliding friction force. Combining the data from two tests, the average total frictional resistance of the remaining sliding body behind the pile is approximately 710.78 kN (see Table 1), and the average bottom frictional resistance is approximately 423.12 kN (see Table 2). Therefore, the lateral frictional resistance of the remaining sliding body is 287.66 kN (710.78 - 423.12 = 287.66 kN). This value represents the actual, precisely quantifiable lateral disturbance force present in the experiment under the system of this invention.

[0075] Table 1. Total frictional resistance test results

[0076]

[0077] Table 2 Results of Bottom Friction Resistance Test

[0078]

Claims

1. A lateral friction reduction device for pit model tests, characterized in that, This includes a composite friction-reducing layer laid between the sidewalls of the pit and the test slide body; The composite friction-reducing layer includes: A rolling frame is provided adjacent to the sidewall of the pit, and the rolling frame is composed of multiple rigid rolling units and flexible buffer units arranged alternately in the longitudinal direction; A force transmission plate layer is laid between the rolling frame and the test sliding body. The force transmission plate layer is made of multiple bamboo plywoods laid in a tile-like manner, and is used to uniformly transmit soil pressure to the rolling frame. A limiting track is provided at the bottom of the rolling frame to constrain the rolling direction of the rolling frame; The composite friction-reducing layer transforms the sliding friction between the pit sidewall and the test slide into the rolling friction of the rolling skeleton and the deformation friction of the flexible buffer unit.

2. The lateral friction reduction device for a pit model test according to claim 1, characterized in that, The rigid rolling unit is a steel pipe, and the flexible buffer unit is a rubber rod; the steel pipe and the rubber rod are arranged in parallel in the transverse direction and alternately arranged in the longitudinal direction.

3. The lateral friction reduction device for a pit model test according to claim 2, characterized in that, The outer diameter of the steel pipe is 48mm, and the outer diameter of the rubber rod is 50mm.

4. The lateral friction reduction device for a pit model test according to claim 1, characterized in that, The limiting track is made of channel steel.

5. A method for reducing lateral friction in a pit model test, characterized in that, The lateral friction resistance test is performed using the apparatus described in any one of claims 1 to 4, and the specific steps are as follows: S1: After completing the main test of pile-soil interaction, keep the lateral friction reduction device in place; S2: Release the constraint of the pile on the sliding body, so that the sliding body can slide along the lateral friction reduction device; S3: Apply a horizontal thrust to the sliding body and monitor the thrust and displacement data to determine the remaining total frictional resistance after being reduced by the lateral friction reduction device; S4: Release the lateral friction reduction device on the side of the sliding body; S5: Apply a horizontal thrust to the sliding body and monitor the thrust and displacement data to determine the remaining bottom friction. S6: Calculate the remaining lateral friction resistance based on the remaining total friction resistance and the remaining bottom friction resistance.

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