Model test determination method for potential fracture surface of reinforced earth retaining wall

Abstract

The invention belongs to the field of retaining wall engineering, and particularly relates to a model test determination method for a potential fracture surface of a reinforced soil retaining wall, which comprises the following steps: erecting a reinforced concrete model box; reinforced soil is laid; geogrids are fully laid in the longitudinal direction, twist nails are arranged in the longitudinal direction of the geogrids at intervals, drainage blind pipes are fixed, the length from the twist nails to the rear wall is measured, and then plain fill is filled; carrying out a loading test on the top of the reinforced soil retaining wall, measuring the distance between each twist nail and the rear wall of the model box as well as the distance between the corresponding rib material mark point and the rear wall of the model box to obtain final positions, and subtracting the position changes of the twist nails and the corresponding rib material mark point to obtain the relative displacement of rib soil; and the twisted nails with the relative displacement peak value in each layer of reinforced soil in the side face of the reinforced soil retaining wall are marked, a smooth curve for connecting the twisted nails marked in each layer of reinforced soil is drawn, and the actual potential fracture face of the reinforced soil retaining wall can be obtained. The method does not need a large number of tests, is low in cost, simple and easy to implement, rapid and effective, and can reflect the reinforced soil retaining wall damage mechanism more truly.

Description

Technical Field

[0001] This invention belongs to the field of retaining wall engineering, and in particular, it is a model test method for determining the potential fracture surface of a reinforced soil retaining wall. Background Technology

[0002] Reinforced soil retaining walls are widely used in infrastructure projects such as highways, railways, and waterway revetments due to their advantages of low cost, convenient construction, and space saving. As a flexible retaining structure, its reinforcement principle relies on soil deformation to induce frictional resistance between the reinforcement and the soil. In this process, the spatial distribution of the potential fracture surface directly determines the effective anchorage length of the reinforcement: if the reinforcement is too short, the anchorage section outside the fracture surface will be insufficient, leading to insufficient pull-out resistance, reduced overall stability, or even complex failure; while if the reinforcement is too long, it will result in material waste and increased project costs. Therefore, accurately determining the potential fracture surface is not only crucial to the safety and economy of reinforced soil retaining walls, but also a core issue that continues to be a focus of current academic research and engineering practice.

[0003] However, current methods for determining potential fracture surfaces primarily rely on flexible displacement gauges or strain gauges to monitor reinforcement deformation and thus determine the fracture surface morphology. This method carries significant engineering risks. Flexible displacement gauges are relatively large, typically around 30 cm, and only a small number can be installed per layer of reinforcement, often only testing the deformation at the ends of the reinforcement. Strain gauges, on the other hand, have limited strain range, are expensive, and have a high failure rate, sometimes exceeding 50%. These limitations in the number, performance, and placement of sensors directly lead to significant differences in the potential fracture surface morphology obtained from different studies and practices, affecting the reliability and consistency of design data. Furthermore, the reinforcement function of the reinforcement is that when there is relative shear deformation and shear stress at the soil-reinforcement interface, the frictional and passive resistance between the soil and reinforcement can prevent relative displacement between the reinforcement and soil, thereby reducing lateral soil displacement. The internal stability failure of reinforced soil retaining walls mainly manifests as tensile or pull-out failure of the reinforcement. Therefore, determining the potential fracture surface based on the connection of the peak values ​​of the relative displacement between reinforcement and soil better reflects the true mechanical mechanism of the structure.

[0004] There is no unified standard in my country for using the relative displacement of reinforced soil to determine the potential fracture surface of reinforced soil retaining walls, and there are few related engineering practices. As a result, this important topic is still in the research and exploration stage and has not yet formed a systematic and scalable technical system. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a model test method for determining the potential fracture surface of reinforced soil retaining walls, which can more accurately locate the potential fracture surface of reinforced soil retaining walls.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A model test method for determining the potential fracture surface of a reinforced soil retaining wall, comprising the following steps:

[0008] Step 1: Construct a reinforced concrete model box with three walls, with the direction between the two side walls being horizontal and the direction facing the back wall being vertical;

[0009] Step 2: Lay the first layer of reinforced soil;

[0010] A geogrid is laid across the ground longitudinally, and twisted nails are spaced apart along the geogrid in one longitudinal direction. The twisted nails pass through the geogrid and are driven into the soil. A drainage pipe is fixed to the side of the geogrid away from the back wall. The length of each twisted nail from the back wall is measured. Plain fill soil is placed in the reinforced concrete model box area inside the drainage blind pipe to form the first layer of reinforced soil.

[0011] Step 3: Lay multiple layers of reinforced soil above the second layer of reinforced soil;

[0012] A geogrid is laid longitudinally on the first layer of reinforced soil, and twisted nails are spaced apart along the same longitudinal direction as the first layer of reinforced soil (forming a twisted nail arrangement surface). The twisted nails pass through the geogrid and are driven into the first layer of reinforced soil. A drainage pipe is fixed to the side of the geogrid away from the back wall, forming a panel wall with the drainage pipes of the upper and lower reinforced soil layers. The length of each twisted nail from the back wall is measured. Plain fill soil in the area of ​​the reinforced concrete model box inside the drainage blind pipe to form this layer of reinforced soil; repeat this arrangement at least five times to complete the arrangement of the reinforced soil retaining wall.

[0013] Step 4: Conduct a loading test on the top of the reinforced soil retaining wall. After the test, dismantle the reinforced concrete model box and measure the distance between each twisted nail and the back wall of the model box. And the distance between the ribs of the geogrid adjacent to the twisted nail and the rear wall of the model box. To measure the relative displacement of the reinforcement and soil ;

[0014] Step 5: Mark the relative displacement of each layer of reinforced soil on the side of the reinforced soil retaining wall. By plotting the relative displacement of each layer of reinforced soil with respect to the panel using the peak value of the spiral nails, and drawing a smooth curve connecting the marked spiral nails in each layer of reinforced soil, the actual potential fracture surface of the reinforced soil retaining wall can be obtained.

[0015] As a further preferred option, in step one, Vaseline is applied to the inner wall of the reinforced concrete model box and a plastic film is laid on it, and a layer of clay and gravel is laid at the bottom of the model box as the lower cushion layer.

[0016] As a further preferred option, in steps two and three, the drainage blind pipe is wrapped in reverse using a geogrid, and then a connecting rod is inserted through the bottom of the drainage blind pipe to fix it in place.

[0017] As a further preferred option, in steps two and three, the length of the geogrid in each layer of reinforced soil is 1m-1.5m in the longitudinal direction of the reinforced soil.

[0018] As a further preferred option, in step four, The solution relation is:

[0019] .

[0020] As a further preferred option, the reinforced concrete model box is 2 m high, 3 m wide laterally, and 2 m deep longitudinally, with each layer of reinforced soil being 0.4 m high and having two drainage blind pipes.

[0021] As a further preferred option, in steps two and three, the geogrid grid is arranged longitudinally along its length direction, and two twisted nails are arranged in a geogrid grid, one of which abuts against the ribs of the geogrid, and the other is located near the center of the grid; the geogrid includes multiple parallel ribs, with several connecting strips between the ribs, and the long strip area between two connecting strips is the grid.

[0022] As a further preferred option, the spacing between two adjacent spiral studs in the longitudinal direction of a layer of reinforced soil is 12 cm, and the length of one grid of the geogrid is 24 cm.

[0023] As a further preferred option, in steps two and three, at least three spiral nail arrangement surfaces are arranged on the reinforced soil retaining wall.

[0024] As a further preferred option, step four involves a loading test in which wooden planks are laid on top of the reinforced soil retaining wall and a vertical load of 5 kPa to 15 kPa is applied using sandbags.

[0025] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0026] The initial positions of the twist nail and corresponding reinforcement marking points were determined. Final position and To calculate the relative displacement of the reinforced soil This avoids the limitations of flexible displacement gauges and strain gauges in terms of size, durability, and number of measuring points, significantly improving the measurement accuracy of potential fracture surfaces in reinforced soil retaining walls and ensuring project safety.

[0027] Meanwhile, this invention requires no extensive testing, is low-cost, simple and easy to implement, and fast and effective. It more realistically reflects the failure mechanism of reinforced soil retaining walls, and has no limitations on panels, reinforcement materials and loading types. It can be widely used in the field of retaining wall engineering and has excellent practicality. Attached Figure Description

[0028] Figure 1 This is a flowchart of the method for determining the potential fracture surface of a reinforced soil retaining wall model provided in an embodiment of the present invention;

[0029] Figure 2 This is an overall view of the reinforced soil retaining wall model provided in this invention example;

[0030] Figure 3 It is a diagram of the arrangement of twisted nails and ribs, where (a) is the arrangement of twisted nails and ribs (unit: mm), and (b) is the actual arrangement of twisted nails and ribs;

[0031] Figure 4 This is a diagram showing the positional relationship between the twisted nails and ribs before loading;

[0032] Figure 5 This is a diagram of the loading device for the model test;

[0033] Figure 6 This is a diagram showing the positional relationship between the twisted nails and the ribs after loading;

[0034] Figure 7 It is the potential fracture surface of the reinforced soil retaining wall determined by the relative displacement of the reinforced soil. Detailed Implementation

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0036] This invention provides a model test method for determining the potential fracture surface of a reinforced soil retaining wall, comprising the following steps:

[0037] 1) Use the layered filling method to build a reinforced soil retaining wall model in a reinforced concrete model box. Mark the position of the reinforcement every 12 cm and nail a twisted nail directly below it.

[0038] 2) Use a steel tape measure to measure the distance between the twisted nail and the back wall of the model box to obtain the initial position of the twisted nail and the corresponding reinforcement mark point. ;

[0039] 3) Conduct a loading test. After the test, disassemble the reinforced soil retaining wall model and use a steel tape measure to measure the distance between the spiral nails and the corresponding reinforcement markings and the rear wall of the model box to obtain their final positions. and ;

[0040] 4) The relative displacement between the reinforcement and soil can be measured by subtracting the positional changes of the twisted nail from the corresponding reinforcement marker. ;

[0041] 5) Draw a diagram showing the relationship between the relative displacement of each layer of reinforced soil and the distance to the panel, and connect the peak values ​​of the relative displacement of each layer of reinforced soil into a smooth curve to obtain the actual potential fracture surface of the reinforced soil retaining wall.

[0042] This invention can accurately and easily determine the location of the potential fracture surface of a reinforced soil retaining wall based on model tests.

[0043] like Figure 1 As shown, a reinforced concrete model box with three walls is constructed. The direction between the two side walls is horizontal, and the direction facing the back wall is vertical. Vaseline is applied to the inner wall of the concrete model box and a plastic film is laid on it. A layer of clay and gravel is laid at the bottom of the model box as the lower layer.

[0044] like Figure 2 As shown, this reinforced soil retaining wall uses drainage blind pipes as flexible panels and geogrids as reinforcement materials. The model is 2 m high, 3 m wide on the left and right, and 2 m deep in the front and back. In one case, three sections AA', BB' and CC' are arranged on one side of the model. Each section has 5 layers, each layer is 0.4 m high, and two drainage blind pipes are arranged in each section and wrapped with geogrids. Geogrid connecting rods are then used to connect them to form an organic whole. The geogrid reinforcement length and wrapping length at each height are designed according to the "Technical Specification for Application of Geosynthetics" (GB / T 50290-2014) as shown in Table 1.

[0045] Table 1. Reinforcement Length at Various Heights

[0046] Reinforcing bar installation height (m) Reinforcement length (m) Length of reverse wrapping (m) 1.6 1.1 0.3 1.2 1.3 0.4 0.8 1.4 0.5 0.4 1.3 0.5 0.0 1.1 0.6

[0047] like Figure 3 As shown, since the geogrid is spaced 24 cm apart, the position of the reinforcement is marked every 12 cm and a twisted nail is driven directly below it. Therefore, twisted nails are driven into the soil directly below the geogrid ribs and the middle part of the ribs at three sections of each layer. The geogrid ribs and the middle part serve as reinforcement marking points.

[0048] like Figure 4 As shown, the initial positions of the twisted nails and ribs were obtained by measuring the distance between the twisted nails and the back wall of the model box using a steel tape measure. ;

[0049] Plain fill was constructed using a layered filling method and compacted with a two-way plate compactor. The moisture content of each layer was determined using the ring cutter method according to the "Technical Specification for Application of Geosynthetics" (GB / T 50290-2014). Its unit is dimensionless, moisture content The test shall be conducted in accordance with the Chinese standard GB / T50123-2019 "Standard for Geotechnical Testing Methods" to ensure that the moisture content is at the optimum.

[0050] Geogrid connectors are used to connect and fix adjacent drainage blind pipes, and steel bars are driven in to ensure the integrity of the model.

[0051] like Figure 5 As shown, wooden boards were laid on top of the reinforced soil retaining wall model and a vertical load of 5 kPa / level was applied by sandbags, with a maximum load of 15 kPa.

[0052] like Figure 6 As shown, after the settlement stabilized, the reinforced soil retaining wall model was dismantled. A steel tape measure was used to measure the distance between the spiral nails and the grid ribs and the rear wall of the model box. and The relative displacement of the reinforcement and soil can be measured by subtracting the positional changes of the twisted nails and the ribs. The relationship is as follows:

[0053]

[0054] By plotting the relative displacement between the reinforced soil layers and the panel in each layer of the model, and connecting the peak values ​​of the relative displacement between the reinforced soil layers into a smooth curve, the actual potential fracture surface of the reinforced soil retaining wall can be obtained; that is, as shown in the figure. Figure 7 As shown in the diagram, the left Y-axis represents the height of the reinforced soil retaining wall model, the right Y-axis is a scale for the relative displacement between the reinforced soil and the wall, and the X-axis represents the distance from the drainage blind pipe panel. By plotting the relative displacement data points of the reinforced soil and the wall within the corresponding height range for each layer, and connecting the peak points to form a smooth curve, the actual potential fracture surface of the reinforced soil retaining wall can be obtained. This potential fracture surface is located at "0.32H" at the top of the revetment composite structure model and at a distance of 0.12H from the panel at the bottom of the model, where H refers to the height of the reinforced soil retaining wall.

[0055] By determining the initial positions of the twist nails and grating ribs Final position and To calculate the relative displacement of the reinforced soil This avoids the limitations of flexible displacement gauges and strain gauges in terms of size, durability, and the number of measuring points.

[0056] Meanwhile, this invention requires no extensive testing, is low-cost, simple and easy to implement, fast and effective, and more realistically reflects the failure mechanism of reinforced soil retaining walls. It can be widely applied in the field of retaining wall engineering and has excellent practicality.

[0057] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A model test method for determining the potential fracture surface of a reinforced soil retaining wall, characterized in that, Includes the following steps: Step 1: Construct a reinforced concrete model box with three walls, with the direction between the two side walls being horizontal and the direction facing the back wall being vertical; Step 2: Lay the first layer of reinforced soil; A geogrid is laid across the ground longitudinally, and twisted nails are spaced apart along the geogrid in one longitudinal direction. The twisted nails pass through the geogrid and are driven into the soil. A drainage pipe is fixed to the side of the geogrid away from the back wall. The length of each twisted nail from the back wall is measured. Plain fill soil is placed in the reinforced concrete model box area inside the drainage blind pipe to form the first layer of reinforced soil. Step 3: Lay multiple layers of reinforced soil above the second layer of reinforced soil; Geogrid is laid longitudinally on the first layer of reinforced soil, and twisted nails are spaced apart along the same longitudinal direction of the geogrid to form a twisted nail arrangement surface. The twisted nails pass through the geogrid and are driven into the first layer of reinforced soil. A drainage pipe is fixed to the side of the geogrid away from the back wall, forming a panel wall with the drainage pipes of the upper and lower reinforced soil layers. The length of each twisted nail from the back wall is measured. Plain fill soil in the area of ​​the reinforced concrete model box inside the drainage blind pipe to form this layer of reinforced soil; repeat this arrangement at least five times to complete the arrangement of the reinforced soil retaining wall. Step 4: Conduct a loading test on the top of the reinforced soil retaining wall. After the test, dismantle the reinforced concrete model box and measure the distance between each twisted nail and the back wall of the model box. And the distance between the ribs of the geogrid adjacent to the twisted nail and the rear wall of the model box. To measure the relative displacement of the reinforcement and soil ; Step 5: Mark the relative displacement of each layer of reinforced soil on the side of the reinforced soil retaining wall. By plotting the relative displacement of each layer of reinforced soil with respect to the panel using the peak value of the spiral nails, and drawing a smooth curve connecting the marked spiral nails in each layer of reinforced soil, the actual potential fracture surface of the reinforced soil retaining wall can be obtained.

2. The method for determining the potential fracture surface of a reinforced soil retaining wall by model test according to claim 1, characterized in that: In step one, Vaseline is applied to the inner wall of the reinforced concrete model box and a plastic film is laid on it. A layer of clay and gravel is laid at the bottom of the model box as the lower cushion layer.

3. The method for determining the potential fracture surface of a reinforced soil retaining wall by model test according to claim 1, characterized in that: In steps two and three, the drainage blind pipe is wrapped in reverse using geogrid, and then a connecting rod is inserted through the bottom of the drainage blind pipe to fix it in place.

4. The method for determining the potential fracture surface of a reinforced soil retaining wall through model tests according to claim 1, characterized in that: In steps two and three, the length of the geogrid in each layer of reinforced soil is 1m-1.5m in the longitudinal direction.

5. The method for determining the potential fracture surface of a reinforced soil retaining wall by model test according to claim 1, characterized in that: In step four, The solution relation is: 。 6. The method for determining the potential fracture surface of a reinforced soil retaining wall by model test according to claim 1, characterized in that: The reinforced concrete model box is 2 m high, 3 m wide laterally, and 2 m deep longitudinally. Each layer of reinforced soil is 0.4 m high and has two drainage blind pipes.

7. The method for determining the potential fracture surface of a reinforced soil retaining wall by model test according to claim 1, characterized in that: In steps two and three, the geogrid mesh is arranged longitudinally along its length. Two twisted nails are arranged in a geogrid mesh, one of which is against the rib of the geogrid, and the other is near the center of the mesh.

8. The method for determining the potential fracture surface of a reinforced soil retaining wall through model tests according to claim 7, characterized in that: The spacing between two adjacent spiral nails in the longitudinal direction of a layer of reinforced soil is 12cm, and the length of one grid of the geogrid is 24cm.

9. The method for determining the potential fracture surface of a reinforced soil retaining wall through model tests according to claim 1, characterized in that: In steps two and three, at least three spiral nail placement surfaces are arranged on the reinforced soil retaining wall.

10. The method for determining the potential fracture surface of a reinforced soil retaining wall by model test according to claim 1, characterized in that: In step four, the loading test includes laying wooden planks on top of the reinforced soil retaining wall and applying a vertical load of 5 kPa-15 kPa using sandbags.

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