A model test method for judging arching effect of soil between piles

Abstract

The application discloses a model test discrimination method for arching effect of soil between piles, which can utilize the soil pressure distribution law measured by pressure sensors installed in different soil bodies far and near between two adjacent piles, and simultaneously combine the apparent shape formed after stress displacement of the fine sand layer with different colors laid on the surface of the model soil body, and comprehensively research and judge the soil pressure characteristics and the apparent shape, if the discrimination results of the two are greater than the center distance of the two piles, then it is judged as invalid, otherwise, the discrimination result of the pressure box is used as the criterion, so that the effect of improving the discrimination reliability is achieved.

Description

Technical Field

[0001] This invention patent belongs to the field of underground geotechnical engineering, specifically relating to a model test method for determining the arching effect of soil between piles. Background Technology

[0002] Numerous field measurements and model tests show that the earth pressure borne by pile structures differs to varying degrees from theoretical calculations (Coulomb earth pressure, Rankine earth pressure). While many factors contribute to this discrepancy, the most significant is the soil arching effect caused by pile-soil interaction. This effect occurs when soil (sand) particles form an arch, which, under external loads (horizontal loads for pile structures), compresses the particles to form an arched force chain, transferring the load. The soil arching effect alters the direction of load transfer and provides stress shielding; for example, the soil between two piles, within the soil arching effect, experiences significantly less pressure than the soil outside the arch. The microscopic mechanism of the soil arching effect and its coordination and interaction with geotechnical structures are highly complex. The formation, development, and failure of the soil arching effect are influenced by many factors, such as soil and rock mechanics parameters, pile spacing, pile cross-sectional shape, and dimensions. Determining whether an effective soil arching effect has formed is crucial for engineering structural design.

[0003] Currently, in model tests, the determination of soil arching effect (contact force chain between granular media in a generalized sense) mainly adopts photoelastic testing, that is, using a photoelastic instrument to detect particle contact stress. However, this method requires high optical sensitivity and transparency of the granular material, especially for the thickness along the light incident direction, which cannot be too large. Therefore, it is difficult to adapt to the determination of soil arching effect in pile model tests.

[0004] To address the aforementioned issues, this invention proposes a model test method for determining the arching effect of soil between piles. Summary of the Invention

[0005] To achieve the above-mentioned technical effects, the present invention is implemented through the following technical solution: a model test method for determining the arching effect of soil between piles, specifically including the following steps:

[0006] S1. In the model test, eight rows of pressure sensors were arranged along the centerline of any two adjacent piles, from the line connecting the closest piles to the furthest piles, at intervals of 1 / 2 pile diameter. To reduce random interference, three layers of pressure sensors were arranged at equal intervals along the depth direction.

[0007] S2, and spread several strips of fine sand of different colors on the surface of the soil; apply a uniformly distributed horizontal load to the left on the right side of the model;

[0008] S3. Read the pressure sensor data and average the values ​​of the three pressure sensors at the same distance from the pile connection line.

[0009] S4. Plot the curve of earth pressure variation along the direction of incoming pressure, with the distance from the line connecting the piles as the horizontal axis and the average value calculated in S3 as the vertical axis.

[0010] S5. Based on the stress shielding effect of the soil arch effect, the first peak of the curve drawn in S4 is determined to be the inner boundary of the soil arch.

[0011] S6. Compare and analyze the judgment result of S5 with the apparent shape formed by the colored fine sand layer on the soil surface after loading: if the difference between the two judgment results is greater than the center distance between the two piles, it is judged as invalid; otherwise, the judgment result of the pressure cell shall prevail.

[0012] Furthermore, the model in S1 also includes model piles and pressure sensors, with the pressure sensors installed on the model piles.

[0013] Furthermore, in S1, eight pressure sensors are installed in each row.

[0014] Furthermore, S3 reads the force values ​​of the sensors in the soil along the centerline of two adjacent piles through pressure sensors. To improve accuracy, the average values ​​F1 to F8 of the pressure sensors at their respective distances from the upper, middle, and lower layers are taken.

[0015] Furthermore, S4 specifically includes plotting eight pressure values ​​between two adjacent piles in the middle into an arched curve.

[0016] The beneficial effects of this invention are:

[0017] This invention utilizes the earth pressure distribution patterns measured by pressure sensors installed at different distances between two adjacent piles. It also combines this with the apparent shapes formed by the displacement of fine sand particles of different colors on the model soil surface under stress. By comprehensively analyzing both the earth pressure characteristics and the apparent shapes, if the difference between the two determinations exceeds the center-to-center distance between the two piles, the result is deemed invalid; otherwise, the pressure sensor determination result prevails. This improves the reliability of the identification process. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A schematic axonometric view of the model structure provided in an embodiment of the present invention;

[0020] Figure 2 This is a top view of the model structure provided in an embodiment of the present invention;

[0021] Figure 3 A schematic diagram of the mechanical model provided in an embodiment of the present invention;

[0022] Figure 4 This is a schematic diagram of the earth pressure arch curve between every two adjacent arches provided in an embodiment of the present invention;

[0023] The attached diagram lists the components represented by each number as follows:

[0024] Model pile 1, pressure sensor 2. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1

[0027] A model test method for identifying the arching effect of soil between piles includes the following steps:

[0028] S1, such as Figure 1 As shown, model pile 1 is placed in the soil, and pressure sensors 2 are installed in three layers (eight sensors per layer) at equal intervals along the centerline of every two adjacent piles; Figure 2 As shown, different colored sand grains are laid in strips on the surface of the model soil.

[0029] S2, such as Figure 3 As shown, a uniformly distributed horizontal load to the left is applied to the right side of the model;

[0030] S3, such as Figure 4 As shown, the force values ​​of the sensors in the soil along the centerline of two adjacent piles are read by pressure sensor 2. To improve accuracy, the average values ​​F1, F2, F3, ..., F8 of the pressure sensors 2 at their respective distances from the upper, middle and lower layers are taken.

[0031] S4. Plot the eight pressure values ​​between two adjacent piles into an arched curve;

[0032] S5. Compare the arched curve (mechanical arch) fitted by earth pressure with the "rainbow arch" (phenomenal arch) formed by the displacement of sand particles on the upper surface of the model due to force for joint identification.

[0033] The number of sensors in step 1) can be appropriately increased to reduce the error.

[0034] In step 2), the length of the different colored stripes of sand can be appropriately reduced, so that the "rainbow arch" formed by the displacement of the sand particles on the surface can be more obvious.

[0035] The horizontal axis of the arched curve drawn in step 4) is "distance from soil pressure sensor 2 to pile", and the vertical axis is "stress in soil".

[0036] Step 5) essentially involves a comprehensive analysis of earth pressure characteristics (mechanical arch) and apparent deformation (phenomenal arch), which complement and corroborate each other to improve the reliability of the identification.

[0037] As described above, this invention utilizes the soil pressure distribution pattern measured by pressure sensors installed at different distances between two adjacent piles (i.e., a rapid increase in pressure from the closest pressure cell to the farthest pressure cell, with the first peak value being the inner boundary of the soil arching effect). This is combined with the apparent shape formed by the displacement of fine sand particles of different colors on the model soil surface under stress. The soil pressure characteristics (mechanical arch) and the apparent shape (phenomenal arch) are then comprehensively evaluated. If the difference between the two evaluation results is greater than the center-to-center distance between the two piles, the result is deemed invalid; otherwise, the pressure cell evaluation result is taken as the standard. This improves the reliability of the identification.

[0038] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not describe all details exhaustively, nor do they limit the invention to the specific implementations described.

Claims

1. A model test method for determining the arching effect of soil between piles, characterized in that, Specifically, the following steps are included: S1. In the model test, eight rows of pressure sensors were arranged along the centerline of any two adjacent piles, from the line connecting the closest piles to the furthest piles, at intervals of 1 / 2 pile diameter. To reduce random interference, three layers of pressure sensors were arranged at equal intervals along the depth direction. S2, and spread several strips of fine sand of different colors on the surface of the soil; apply a uniformly distributed horizontal load to the left on the right side of the model; S3. Read the pressure sensor data and average the values ​​of the three pressure sensors at the same distance from the pile connection line. S4. Plot the curve of earth pressure variation along the direction of incoming pressure, with the distance from the line connecting the piles as the horizontal axis and the average value calculated in S3 as the vertical axis. S5. Based on the stress shielding effect of the soil arch effect, the first peak of the curve drawn in S4 is determined to be the inner boundary of the soil arch. S6. Compare and analyze the judgment result of S5 with the apparent shape formed by the colored fine sand layer on the soil surface after loading: if the difference between the two judgment results is greater than the center distance between the two piles, it is judged as invalid; otherwise, the judgment result of the pressure cell shall prevail.

2. The model test method for the arching effect of soil between piles according to claim 1, characterized in that: The model in S1 also includes model piles and pressure sensors, with the pressure sensors installed on the model piles.

3. The model test method for the arching effect of soil between piles according to claim 1, characterized in that: In S1, eight pressure sensors are installed in each row.

4. The model test method for the arching effect of soil between piles according to claim 1, characterized in that: The S3 reads the force value of the sensor in the soil on the centerline of two adjacent piles through the pressure sensor. In order to improve the accuracy, the average values ​​F1 to F8 of the pressure sensors at the upper, middle and lower distances are taken respectively.

5. The model test method for the arching effect of soil between piles according to claim 1, characterized in that: Specifically, S4 involves plotting eight pressure values ​​between two adjacent piles in the middle into an arched curve.

Images