A testing device and testing method for in-situ static lateral earth pressure

Abstract

The application discloses a kind of in situ static lateral earth pressure testing device and testing method, testing device includes: test pile, up and down push rod, conical wedge, sensor push rod, earth pressure cell, step screw and handle, hollow column that can determine test position is equipped in test pile, up and down push rod is arranged in hollow column, conical wedge is arranged between two up and down push rod, one end of sensor push rod is connected with earth pressure cell, the other end passes through hollow column, earth pressure cell is arranged in the side of test pile, handle is connected with up and down push rod and step screw.Handle rotates, make step screw synchronous up and down movement, simultaneously drive up and down push rod up and down movement, make conical wedge on up and down push rod extrude sensor push rod, sensor push rod moves outward and pushes earth pressure cell into cohesive soil, to meet the demand of testing soil static lateral pressure.

Description

Technical Field

[0001] This invention relates to the technical field of geotechnical engineering testing, and in particular to a testing device and method for in-situ static lateral earth pressure. Background Technology

[0002] Current standards for calculating earth pressure on foundation pits and retaining walls are based on Rankine and Coulomb's active and passive earth pressure calculation theories. The active and passive earth pressure coefficients are related to the internal friction angle in the soil shear strength parameters. The magnitude of earth pressure stress depends not only on the depth of the calculation point but also on the soil's shear strength parameters. Currently, surveying units primarily use borehole sampling to obtain soil shear strength indices through laboratory geotechnical testing equipment. While shear strength indices can be obtained using appropriate experimental methods based on the actual engineering conditions, numerous influencing factors mean that, regardless of the advanced indoor testing equipment used, the experimental values ​​obtained from soil samples in the laboratory cannot accurately reflect the actual situation. The best method for assessing the soil pressure stress along the pile sides of retaining piles in foundation pit support is to set up as many soil pressure stress measuring points as possible along the pile sides to obtain as much static soil pressure stress as possible. This in-situ testing value best reflects the actual load-bearing conditions of the retaining structure. If in-situ static lateral pressure tests can be conducted during each engineering survey process, and the test results provided to the design unit in the report, it will not only provide design references but also help to refine the shear strength indices through analysis of a large amount of measured data, further improving the earth pressure calculation theory.

[0003] Static lateral earth pressure is rarely obtained directly through in-situ measurement using stress sensors embedded in the field, but the in-situ horizontal stress σ can be directly measured through a pressuremeter test. h The principle is that when the elastic membrane of the pressure-spotting device begins to expand and the borehole wall just begins to produce radial strain, the pressure on the outside of the membrane sleeve is the in-situ horizontal stress σ of the soil. h Because the pressuremeter test requires sophisticated operational procedures and yields highly dispersed static lateral pressure values, its application is limited. In engineering, to facilitate the calculation of lateral earth pressure at various points, the lateral earth pressure at rest is usually not expressed in the form of pressure at a single point, but rather using the lateral earth pressure coefficient of each soil layer. This is achieved by dividing the measured lateral stress by the vertical stress σ at that point. v The ratio of these two values ​​is the static lateral pressure coefficient k0. The physical meaning of the static earth pressure coefficient k0 is that, under conditions where lateral deformation is not allowed, an increase in axial pressure Δσ1 on a soil sample will cause a corresponding increase in lateral pressure Δσ3, and their ratio is... It is called the lateral pressure coefficient ξ of the soil or the static earth pressure coefficient k0.

[0004]

[0005] The methods for testing the static lateral pressure coefficient k0 of soil are divided into laboratory tests and in-situ tests, but the commonly used method is the in-situ test using a flat-blade dilatometer. Because the probe is statically inserted into the soil, it compresses the surrounding soil, so the initial in-situ lateral stress cannot be directly determined by the flat-blade test. Therefore, the static lateral pressure coefficient cannot be measured or directly calculated. It requires graphical processing to obtain the static lateral pressure coefficient. An empirical relationship between the static lateral pressure coefficient k0 and the horizontal stress exponent k is established. D The empirical formulas provided are for designers to use, but their accuracy is not high.

[0006] The coefficient of lateral pressure at rest reflects the changes in horizontal stress in the foundation, and can be used to directly calculate the pressure distribution and safety factor acting on retaining structures. As a fundamental parameter in geotechnical engineering design, the coefficient of earth pressure at rest (k0) is widely used in the design of foundation pits, retaining walls, dams, mines, soil deformation, tunnels, and other practical engineering projects. Its accurate determination directly impacts engineering design, cost, and safety, and has received increasing attention from the civil engineering and geotechnical engineering communities in recent years. Because national and local standards and regulations do not provide specifications for the coefficient of earth pressure at rest, most surveying and design institutes only provide laboratory shear strength test results for soil samples from relevant soil layers. Providing only one value for a single soil layer without reflecting the influence of soil depth is inaccurate.

[0007] The main indoor testing methods include the empirical formula method, the compression tester method, and the triaxial compression tester method. The lateral pressure tester method requires that the specimen not undergo lateral deformation after applying vertical pressure; that is, the vertical strain and volumetric strain must be equal. Under this condition, the ratio of the pressure on the specimen's side to the vertical stress is the static lateral pressure coefficient. The sidewall of this method is a rubber membrane water bladder. The triaxial compression tester method uses a lateral deformation indicator installed on the side of the specimen wrapped in a rubber membrane to indicate whether lateral deformation will occur when axial pressure is applied. If there is a tendency for lateral deformation, the lateral pressure is immediately increased or the axial pressure is decreased to prevent lateral deformation of the specimen during axial compression.

[0008] The empirical formula method calculates the value of k0 from the effective internal friction angle, using the formula given by Jaky:

[0009]

[0010]

[0011] In the formula: The effective internal friction angle of the soil.

[0012] In summary, the lateral dilatation test using a flat shovel cannot directly determine the static lateral pressure coefficient k0. The empirical formulas and related parameters for calculating k0 are numerous and difficult to select appropriately. The soil structure and physical and mechanical properties of construction sites vary greatly, thus the calculation formulas and methods for determining k0 lack universality. Existing survey and design standards do not require the provision of the static lateral pressure coefficient; survey results generally only provide shear strength indices for relevant soil layers, failing to reflect the influence of soil depth on shear strength. To improve the reliability of foundation pit design, it is necessary to provide experimental values ​​of the in-situ static lateral pressure coefficient, hence this invention. Summary of the Invention

[0013] The purpose of this invention is to overcome the shortcomings of the prior art and provide an in-situ lateral earth pressure testing device that can be used for in-situ testing after borehole sampling during engineering surveys.

[0014] To achieve the above objectives, the solution of the present invention is:

[0015] An in-situ static lateral earth pressure testing device includes: at least one test pile, at least two upper and lower push rods, at least one conical wedge, at least one sensor push rod, at least one earth pressure box, at least one step screw, and a throttle.

[0016] The test pile is equipped with a hollow column, and the side of the test pile is provided with at least one trough for accommodating the earth pressure cell. The hollow column is used to determine the measurement position. The hollow column is provided with a through hole connecting to the trough. Both ends of the hollow column protrude out of the test pile.

[0017] The upper and lower push rods are installed inside the hollow column, with the upper and lower push rods at the top protruding from the top of the hollow column;

[0018] The conical wedge is positioned between the two upper and lower push rods, and its installation position is close to the through hole of the hollow column.

[0019] One end of the sensor push rod is connected to the earth pressure box, and the other end passes through the through hole of the hollow column and faces the center of the hollow column.

[0020] The earth pressure cell is placed in the groove of the test pile, with the front of the earth pressure cell facing the outside of the test pile and the back of the earth pressure cell connected to the sensor push rod.

[0021] The stepping screw is located at the top of the hollow column;

[0022] The throttle connects the topmost up and down push rods and the topmost stepping screw.

[0023] Furthermore, the test pile is configured with multiple sections, with a conical drill bit installed at the bottom of the lowest test pile.

[0024] Furthermore, multiple troughs are installed at different heights of the test pile.

[0025] Furthermore, the test pile has multiple sets of partitions longitudinally spaced around the outer periphery of the hollow column. Each set of partitions includes two ribs, and the distance between the two ribs corresponds to the width of the earth pressure cell. Two rings of plates are installed at intervals at the location where the earth pressure cell needs to be installed, and the groove is formed between the two rings of plates and the two ribs.

[0026] Furthermore, the test pile is provided in multiple sections. The bottom of the hollow column in the upper section of the test pile is provided with a stud, and the top of the hollow column in the lower section of the test pile is provided with a corresponding stud connector. The bottom of the upper and lower push rods of the upper section are connected to the top of the upper and lower push rods of the lower section, so that the upper and lower push rods move synchronously.

[0027] Another objective of this invention is to overcome the shortcomings of the prior art and provide a method for testing in-situ lateral earth pressure that can be performed after borehole sampling during engineering surveys.

[0028] A method for testing lateral earth pressure using the aforementioned in-situ static lateral earth pressure testing device includes the following steps:

[0029] Step A: Develop an exploration plan and determine the boreholes where the static lateral pressure stress of the soil layer needs to be tested;

[0030] Step B: At the borehole location where the static lateral pressure stress of the soil layer needs to be tested, normal borehole sampling should be carried out first;

[0031] Step C: Based on the soil conditions and drilling depth, select the test pile segment length of the testing device, and perform debugging work on each component and earth pressure cell in test pile 1;

[0032] Step D: Insert the test piles in sections, connect the cable joints of the upper and lower earth pressure boxes, and take waterproof sealing measures for the cables;

[0033] Step E: Determine the location (depth or elevation) of the earth pressure cell in the soil layer and make initial records including the initial earth pressure stress;

[0034] Step F: Rotate the handle to press the earth pressure cell into the clay of the borehole wall, and record the earth pressure stress after each earth pressure cell is in place.

[0035] Step G: Continuously test the pressure changes of the earth pressure cell, and determine the test interval based on the changes in earth pressure stress;

[0036] Step H: After the soil pressure stress stabilizes after several tests, terminate the test. This stable soil pressure stress value is the static lateral soil pressure stress value of the soil layer at that depth.

[0037] Step 1: Extract the test device in sections and continue drilling downwards;

[0038] Repeat steps B through I until all soil layers required for testing are completed, then terminate the test.

[0039] After adopting the above scheme, the tumbler of the in-situ static lateral earth pressure testing device of the present invention rotates, which can make the stepping screw move up and down synchronously along the hollow column, and at the same time drive the upper and lower push rods to move up and down, so that the conical wedges set on the upper and lower push rods squeeze the sensor push rod, the sensor push rod moves outward, and pushes the earth pressure box into the cohesive soil. The test method of testing lateral earth pressure using the in-situ static lateral earth pressure testing device of the present invention can be used to test the lateral pressure of the soil layer in situ after drilling and sampling during the engineering survey process. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the structure of the testing device of the present invention. Figure 1 .

[0041] Figure 2 This is a schematic diagram of the structure of the testing device of the present invention. Figure 2 A drill bit is installed at the bottom of the test pile.

[0042] Figure 3 This is a schematic diagram of the structure of the multi-section test pile of the present invention.

[0043] Figure 4 This is a cross-sectional view of the present invention.

[0044] Figure 5 This is a schematic diagram of the throttle mechanism of the present invention. Detailed Implementation

[0045] To further explain the technical solution of the present invention, the present invention will be described in detail below through specific embodiments.

[0046] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "X," "Y," and "Z," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0047] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0048] like Figures 1 to 5 As shown, the present invention discloses a testing device for in-situ static lateral earth pressure, which includes at least one test pile 1, at least two upper and lower push rods 3, at least one conical wedge 4, at least one sensor push rod 5, at least one earth pressure box 6, at least one step screw 7, and a throttle 8.

[0049] The test pile 1 is provided with a hollow column 2. The side of the test pile 1 is provided with at least one trough 11 for accommodating the earth pressure box 6. The hollow column 2 is used to determine the measurement position. The hollow column 2 is provided with a through hole 21 that connects to the trough 11. Both ends of the hollow column 2 protrude out of the test pile 1.

[0050] The upper and lower push rods 3 are installed inside the hollow column 2, with the upper and lower push rods 3 at the top protruding from the top of the hollow column 2.

[0051] The conical wedge 4 is positioned between the two upper and lower push rods 3, and the installation position of the conical wedge 4 is close to the through hole 21 of the hollow column 2.

[0052] One end of the sensor push rod 5 is connected to the earth pressure box 6, and the other end passes through the through hole 21 of the hollow column 2 toward the center of the hollow column 2.

[0053] The earth pressure cell 6 is placed in the trough 11 of the test pile 1, with the front of the earth pressure cell 6 facing the outside of the test pile 1, and the back of the earth pressure cell 6 connected to the sensor push rod 5.

[0054] The stepping screw 7 is installed at the top of the hollow column 2;

[0055] The throttle 8 is connected to the top upper and lower push rods 3 and the top stepping screw 7.

[0056] The working principle of the in-situ static lateral earth pressure testing device of the present invention is as follows: rotating the handle 8 clockwise causes the stepping screw 7 to move up and down synchronously along the hollow column 2, which in turn drives the upper and lower push rods 3 to move up and down. This causes the conical wedge 4 set on the upper and lower push rods 3 to squeeze the sensor push rod 5, and the sensor push rod 5 to move outward, pushing the earth pressure box 6 into the cohesive soil, thereby meeting the requirements for testing the static lateral earth pressure of the soil.

[0057] Depending on the required testing depth, the test pile 1 can be configured with multiple sections. A conical drill bit 12 can be installed at the bottom end of the lowest test pile 1 to facilitate insertion of the test pile 1 into the borehole. Multiple receiving slots 11 can be installed at different heights of the test pile 1 to facilitate simultaneous measurement of the static lateral pressure of the soil at different depths. The structure of the test pile 1 can vary. In this embodiment, multiple sets of partitions are longitudinally spaced around the hollow column 2 of the test pile 1. Each set of partitions includes two ribs 13, the distance between which corresponds to the width of the earth pressure cell 6. Two spaced rings of plates 14 are installed at the locations where the earth pressure cell 6 needs to be installed. The receiving slots 11 are formed between the two rings of plates 14 and the two ribs 13. Figure 4 As shown in this embodiment, the test pile 1 has two upper and lower troughs 11 in each of its four directions. The four troughs 11 at the same height allow for the simultaneous installation of four earth pressure cells 6. A fan-shaped empty area 15 is formed between the adjacent two ribs 13 and the ring plate 14 between the two sets of partitions. A cable protection pipe 16 can be installed in the empty area 15 to protect the cable. The number and location of the earth pressure cells 6 can be determined according to actual needs. A more accurate value can be obtained by taking the average value after multiple earth pressure cells 6 simultaneously test the static lateral pressure of the same soil layer.

[0058] like Figure 3 As shown, when multiple test piles 1 are connected, a stud 21 is provided on the outer periphery of the bottom of the hollow column 2 in the upper test pile 1, and a connector 23 corresponding to the stud 21 is provided on the top of the hollow column 2 in the lower test pile. During installation, the upper and lower test piles 1 are connected together by the stud 21 and the connector 23. The bottom of the upper and lower push rods 3 of the upper section is connected to the top of the upper and lower push rods 3 of the lower section, so that the upper and lower push rods 3 move synchronously.

[0059] This invention also discloses a testing method for testing lateral earth pressure using the above-mentioned in-situ static lateral earth pressure testing device, which includes the following steps:

[0060] Step A: Develop an exploration plan and determine the boreholes where the static lateral pressure stress of the soil layer needs to be tested;

[0061] Step B: At the borehole location where the static lateral pressure stress of the soil layer needs to be tested, normal borehole sampling should be carried out first;

[0062] Step C: Based on the soil conditions and drilling depth, select the test pile segment length of the testing device, and perform debugging work on each component and earth pressure cell in test pile 1;

[0063] Step D: Insert the test piles in sections and connect the cable joints of the upper and lower sections of the earth pressure box 6, and take waterproof sealing measures for the cables;

[0064] Step E: Determine the location (depth or elevation) of the earth pressure cell 6 in the soil layer and make initial records including the initial earth pressure stress;

[0065] Step F: Rotate the handle 8 to press the earth pressure box 6 into the clay of the borehole wall, and record the earth pressure stress after each earth pressure box is in place.

[0066] Step G: Continuously test the pressure changes of the earth pressure cell, and determine the test interval based on the changes in earth pressure stress;

[0067] Step H: After the soil pressure stress stabilizes after several tests, terminate the test. This stable soil pressure stress value is the static lateral soil pressure stress value of the soil layer at that depth.

[0068] Step 1: Extract the test device in sections and continue drilling downwards;

[0069] Repeat steps B through I until all soil layers required for testing are completed, then terminate the test.

[0070] The above embodiments and illustrations are not intended to limit the product form and style of the present invention. Any appropriate changes or modifications made by those skilled in the art should be considered as not departing from the patent scope of the present invention.

Claims

1. A device for testing the lateral earth pressure at rest in situ, characterized in that, The utility model relates to a kind of in-situ static lateral earth pressure testing device, including: At least one test pile, at least two upper and lower push rods, at least one tapered wedge, at least one sensor push rod, at least one earth pressure cell, at least one step screw rod and a rotating handle; The test pile is provided with a hollow column, and the side of the test pile is provided with at least one container groove for accommodating the earth pressure cell. The hollow column is used to determine the measurement position. The hollow column is provided with a through hole communicating with the container groove. The two ends of the hollow column protrude outside the test pile. The upper and lower push rods are arranged in the hollow column. The uppermost upper and lower push rods protrude out of the top end of the hollow column. The tapered wedge is arranged between the two upper and lower push rods, and the installation position of the tapered wedge is close to the through hole of the hollow column. One end of the sensor push rod is connected to the earth pressure cell, and the other end passes through the through hole of the hollow column and faces the center of the hollow column. The earth pressure cell is placed in the container groove of the test pile, and the front of the earth pressure cell faces the outside of the test pile. The back of the earth pressure cell is connected to the sensor push rod. The step screw rod is arranged at the top of the hollow column. The rotating handle is connected to the uppermost upper and lower push rod and the uppermost step screw rod.

2. A device for testing the lateral earth pressure at rest in situ as claimed in claim 1, characterized in that: The test pile is provided with multiple sections. The bottom end of the bottommost test pile is provided with a tapered drill bit.

3. A device for testing the lateral earth pressure at rest in situ as claimed in claim 1, characterized in that: Multiple container grooves are arranged at different heights of the test pile.

4. A device for testing the lateral earth pressure at rest in situ as claimed in claim 1, characterized in that: Multiple sets of partition plates are longitudinally arranged on the outer periphery of the hollow column. Each set of partition plates includes two rib plates. The distance between the two rib plates corresponds to the width of the earth pressure cell. Two circle plates are arranged at the position where the earth pressure cell is needed to be installed. The two circle plates and the two rib plates form the container groove.

5. A device for testing the lateral earth pressure at rest in situ as claimed in claim 1, characterized in that: The test pile is provided with multiple sections. The bottom end of the hollow column in the upper section of the test pile is provided with a threaded stud. The top end of the hollow column in the lower section of the test pile is provided with a connecting head corresponding to the threaded stud. The bottom end of the upper and lower push rod in the upper section is connected to the top end of the upper and lower push rod in the lower section, so that the upper and lower push rods move synchronously.

6. A test method for testing lateral earth pressure using the in-situ static lateral earth pressure testing device according to any one of claims 1-5, comprising the following steps: Step A: Prepare a survey plan to determine the drill hole where the static lateral earth pressure of the soil layer needs to be tested. Step B: In the drill hole where the static lateral earth pressure of the soil layer needs to be tested, first perform normal drilling sampling. Step C: According to the soil layer condition and the drilling depth, select the section length of the test pile of the testing device, and prepare for the debugging of each element in the test pile and the earth pressure cell. Step D: Put in the test pile section by section, connect the cable connectors of the earth pressure cells in the upper and lower sections, and take waterproof sealing measures for the cable. Step E: Determine the position of the earth pressure cell in the soil layer and make initial records including the initial earth pressure. Step F: Rotate the rotating handle to press the earth pressure cell into the clay of the hole wall, and record the earth pressure of each earth pressure cell after it is in place. Step G: Continuously test the pressure change of the earth pressure cell, and determine the interval test time according to the change of the earth pressure. Step H: When the earth pressure of the previous and subsequent times is stable and does not change, terminate the test. The stable earth pressure value is the static lateral earth pressure value of the soil layer at that depth. Step I: Extract the testing device section by section, and continue drilling downward. Repeat steps B - step I until each soil layer required for the test is completed, and terminate the test.

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