Method for measuring in-situ shear strength parameter of expansive soil

Abstract

The invention belongs to the technical field of expansive soil shear strength detection, discloses an expansive soil in-situ shear strength parameter determination method, and aims to solve the problem that the difference between the shear strength and the actual shear strength is large when the shear strength is calculated after c and phi in a reconnaissance stage are adopted for reduction during retaining design. The method comprises the following steps: (1) obtaining shear strength parameters c and phi of the undisturbed expansive soil under different water contents omega, and obtaining functional relational expressions c = f1 (omega) and phi = f2 (omega) between c and phi and the water contents omega; (2) acquiring the water content omega of the expansive soil by using an in-situ measurement mechanism; (3) substituting the obtained water content omega into the function relation in the step (1): c = f1 (omega); and phi = f2 (omega), so that the shear strength parameters c and phi can be obtained, the actual shear strength of the expansive soil can be obtained, and the designed support is safer and more reliable.

Description

Technical Field

[0001] The invention belongs to the technical field of expansive soil shear strength detection, and in particular relates to an in-situ shear strength parameter determination method for expansive soil. Background Art

[0002] Expansive soil is a kind of highly plastic clay widely distributed in various regions of the world. The clay particles in the soil are mainly composed of hydrophilic minerals, and have significant water absorption and expansion and water loss and shrinkage deformation characteristics. When the water content in the expansive soil changes, it is very easy to cause the expansive soil slope to slide gently, shallow sliding, expansive soil foundation pit collapse and other hazards, causing serious economic and property losses.

[0003] In order to ensure the safety of expansive soil slopes and foundation pits, they need to be supported, and the shear strength parameters c (cohesion) and φ (internal friction angle) of the soil are important parameters for support design. However, the shear strength parameters c and φ of expansive soil are not constants, but change continuously with the expansion and contraction of the soil.

[0004] Among them, the shear strength is expressed by the following formula: shear strength = c + σtanφ, σ is the normal pressure on the shear surface.

[0005] In the existing retaining design, the shear strength parameters provided in the survey stage are often used and reduced. However, the selection of the reduction coefficient depends entirely on the experience of engineering and technical personnel, without any theoretical basis, and cannot provide reliable data support for retaining design. In addition, the survey stage to the design stage usually takes a long time. During this process, due to climate changes such as rainfall or exposure, the moisture in the expansive soil changes and causes expansion or contraction, which in turn affects the shear strength of the expansive soil. That is to say, c1 and φ1 at this time are no longer c0 and φ0 in the survey stage. If c0 and φ0 in the survey stage are used for retaining design, there will be major safety hazards. Summary of the invention

[0006] In order to solve the problem that the shear strength is calculated by reducing the cohesion (c) and the internal friction angle (φ) during the survey during support design, resulting in a large difference between the shear strength and the actual shear strength, the present invention provides an in-situ shear strength parameter determination method for expansive soil. The in-situ measurement method is used to obtain the actual shear strength of the expansive soil, so that the calculated shear strength is closer to the actual shear strength of the expansive body, thereby providing reliable data support for support design.

[0007] In order to solve the technical problem, the technical solution adopted by the present invention is:

[0008] A method for determining in-situ shear strength parameters of expansive soil, characterized by comprising:

[0009] (1) Obtain the shear strength parameters c and φ of the original expansive soil at different water contents ω, and obtain the functional relationship between c and φ and the water content ω: c = f1(ω), φ = f2(ω);

[0010] (2) The in-situ measuring device is inserted into the specified depth of the expansive soil, and the moisture content ω of the expansive soil is obtained by using the in-situ measuring device;

[0011] (3) Substituting the moisture content ω obtained in step (2) into the functional relationship in step (1): c = f1(ω); φ = f2(ω), the shear strength parameters c and φ can be obtained, and the shear strength calculation formula can be used to obtain the shear strength of the expansive soil at this time.

[0012] In some embodiments, after the in-situ measurement mechanism is penetrated into the designated depth of the expansive soil, the in-situ measurement mechanism should be left stationary for a period of time to allow the groundwater to fully react with the quicklime in the in-situ measurement mechanism.

[0013] In some embodiments, the in-situ measurement mechanism includes a first sleeve and a second sleeve, the second sleeve is sleeved inside the first sleeve and forms a accommodating cavity between the first sleeve, the second sleeve has a second cavity inside, the inner wall of the second cavity is sleeved with a second permeable membrane bag for water to pass through, the first sleeve is provided with a first cavity, the first cavity is sleeved with a first permeable membrane bag for water to pass through, the first permeable membrane bag and the second permeable membrane bag are used to load quicklime, a plurality of through holes interconnected with the second cavity are opened on the circumferential wall of the second sleeve, a plurality of through holes interconnected with the first cavity are opened on the inner wall of the first sleeve; the first permeable membrane bag and the second permeable membrane bag are equipped with electronic scales for weighing.

[0014] In some embodiments, the first cavity and the second cavity are respectively provided with pressure rings for pressing in the first permeable membrane bag and the second permeable membrane bag.

[0015] In some embodiments, the bottom end of the first sleeve extends out of the bottom end of the second sleeve, the bottom of the first cavity of the first sleeve is flush with the lower end of the second sleeve, the bottom end of the second sleeve is pointed, the bottom end of the first sleeve extends outward and forms an upwardly tilted crown, and a groove is formed between the crown and the outer wall of the first sleeve.

[0016] In some embodiments, the tops of the first sleeve and the second sleeve are connected via an end cover, a movable ring is provided in the accommodating cavity, the movable ring can slide along the inner wall of the first sleeve and the outer wall of the second sleeve, a through hole is provided on the end cover in an area corresponding to the accommodating cavity, at least two pull rods are connected to the movable ring, and the pull rods pass through the end cover and are connected to the connecting ring.

[0017] In some embodiments, the top of the second sleeve extends out of the first sleeve and is provided with an end cap.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention firstly tests the original expansive soil in the slope engineering or foundation pit engineering site during the survey stage, performs a dry-wet cycle test indoors, measures the shear strength parameters c and φ of the expansive soil with different moisture contents ω, and then obtains the functional relationship between the shear strength parameters c, φ and the moisture content ω of the expansive soil in the region c=f1(ω) and φ=f2(ω) through mathematical and statistical analysis. When designing the retaining wall, the in-situ measuring mechanism penetrates into the specified depth of the expansive soil and obtains the moisture content ω of the expansive soil at this time, thereby obtaining the shear strength parameters c and φ using the obtained functional relationship, and finally calculating the shear strength using the shear strength parameters c and φ, and designing the retaining wall based on the calculated shear strength. Compared with the prior art that uses the shear strength parameters in the survey stage for reduction, the present invention can provide more reliable design parameters (i.e., shear strength) for retaining wall design, thereby making the designed retaining wall safer and more reliable.

[0020] The present invention utilizes the structural design of the first sleeve and the second sleeve, on the one hand, utilizes the accommodation cavity between the first sleeve and the second sleeve to obtain the volume of the expansive soil during the measurement, and then utilizes the data obtained in the survey stage (wherein the density, water content, relative density and other data of the expansive soil are obtained in the survey stage) to calculate the weight of the expansive soil in the accommodation space, and utilizes the electronic scale and the weight of the quicklime added to calculate the weight of the water participating in the reaction in the permeable membrane bag (the first permeable membrane bag and the second permeable membrane bag), and finally obtains the water content ω of the expansive soil. The outer wall of the first sleeve is utilized to form the first protective layer, and the structural design of the first sleeve and the second sleeve is utilized to greatly increase the contact area, so that the expansive soil in the accommodation cavity can be synchronously and quickly entered from the inside and the outside and react with the water in the permeable membrane bag to reduce the measurement time. Therefore, the present invention can carry out in-situ measurement of the water content of the expansive soil, and compared with the prior art method of taking samples back to the laboratory for measurement, the water content of the expansive soil can be quickly obtained.

[0021] The present invention adopts an in-situ measuring mechanism to measure the expansive soil in-situ. Compared with the prior art method of taking samples back to the laboratory for testing, it can not only improve the measurement efficiency, but also greatly reduce the disturbance to the original expansive soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of an embodiment of an in-situ measurement mechanism of the present invention;

[0023] Figure 2 for Figure 1A schematic diagram of a partial enlarged view of the center A;

[0024] Figure 3 for Figure 1 Schematic diagram of the local enlarged view of point B in the middle.

[0025] Markings in the figure: 1. first sleeve, 101. first cavity, 102. first permeable membrane bag, 103. through hole, 2. second sleeve, 201. second cavity, 202. second permeable membrane bag, 203. accommodating cavity, 3. crown, 301. groove, 4. end cover, 5. movable ring, 6. pull rod, 7. connecting ring, 8. pressure ring, 9. end cap. DETAILED DESCRIPTION

[0026] The present invention is further described below in conjunction with embodiments, which are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, other embodiments obtained by ordinary technicians in the field without creative work are all within the scope of protection of the present invention.

[0027] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention; the terms "first", "second", and "third" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance; in addition, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0028] In conjunction with the accompanying drawings, the method for determining the in-situ shear strength parameters of expansive soil of the present invention comprises:

[0029] (1) Obtain the shear strength parameters c and φ of the original expansive soil at different water contents ω, and obtain the functional relationship between c and φ and the water content ω: c = f1(ω), φ = f2(ω);

[0030] (2) the in-situ measuring device is inserted into the specified depth of the expansive soil, and the water content ω of the expansive soil at that time is obtained by using the in-situ measuring device;

[0031] (3) Substituting the moisture content ω obtained in step (2) into the functional relationship in step (1): c = f1(ω); φ = f2(ω), the shear strength parameters c and φ can be obtained, and the shear strength calculation formula can be used to obtain the shear strength of the expansive soil at this time.

[0032] Wherein, shear strength=c+σtanφ, σ is the normal pressure on the shear surface, which can be understood by those skilled in the art and will not be elaborated here.

[0033] Specifically, the functional relationship between the shear strength parameters c, φ and the water content ω: c = f1(ω), φ = f2(ω) can be obtained in advance, and those skilled in the art can understand and comprehend it. Specifically, during the survey stage, the original expansive soil test is conducted in the slope engineering or foundation pit functional site, and a dry-wet cycle test is conducted indoors to measure the shear strength parameters c, φ of the expansive soil with different water contents ω. Through mathematical and statistical analysis, the water content relationship between the shear strength parameters of the expansive soil in the area and the water content ω is obtained: c = f1(ω) and φ = f2(ω).

[0034] For example, c = a1-b1ω and φ = a2-b2ω, c = a1e -b1 and φ = a2e -b2 In the specific implementation process, the technicians in this field can obtain the shear strength parameters c and φ under different moisture contents ω through step (1), and through mathematical and statistical analysis, they can obtain the functional relationship between the moisture content ω and the shear strength parameters c and φ.

[0035] In the prior art, when designing retaining walls for projects such as slopes and foundation pits, the shear strength parameters c and φ obtained during the survey phase are used as retaining wall design parameters. However, there is a long time interval between the geological survey phase and the retaining wall design phase. With the constant change of weather, the actual shear strength parameters c and φ of the expansive soil will change greatly, resulting in a large difference between the shear strength parameters c and φ used in the retaining wall design and the actual shear strength parameters c and φ of the expansive soil, which causes a great safety hazard in the designed retaining walls.

[0036] The present invention firstly tests the original expansive soil in the slope engineering or foundation pit engineering site during the survey stage, performs a dry-wet cycle test indoors, measures the shear strength parameters c and φ of the expansive soil with different moisture contents ω, and then obtains the functional relationship between the shear strength parameters c, φ and the moisture content ω of the expansive soil in the region c=f1(ω) and φ=f2(ω) through mathematical and statistical analysis. When designing the retaining wall, the in-situ measuring mechanism penetrates into the specified depth of the expansive soil and obtains the moisture content ω of the expansive soil at this time, thereby obtaining the shear strength parameters c and φ using the obtained functional relationship, and finally calculating the shear strength using the shear strength parameters c and φ, and designing the retaining wall based on the calculated shear strength. Compared with the prior art that uses the shear strength parameters in the survey stage for reduction, the present invention can provide more reliable design parameters (i.e., shear strength) for retaining wall design, thereby making the designed retaining wall safer and more reliable.

[0037] Furthermore, the in-situ measuring mechanism of the present invention measures the water content ω in-situ, and thus can provide more reliable design parameters for the retaining design at that location. Compared with the prior art which uses the shear strength in one area during retaining design (i.e., one shear strength is used in a larger area), the present invention can conveniently test the water content of the expansive soil at each retaining design location, thereby further improving the reliability and scientificity of the retaining design.

[0038] In some embodiments, after the in-situ measuring mechanism is penetrated to a specified depth of the expansive soil, the in-situ measuring mechanism should be left stationary for a period of time to allow the groundwater to fully react with the quicklime in the in-situ measuring mechanism. Among them, although the quicklime in the in-situ measuring mechanism reacts with water very quickly, it takes a certain amount of time for the groundwater to leach out of the expansive soil. Therefore, it is necessary to leave the in-situ measuring mechanism stationary for a period of time after penetration.

[0039] The specific static time can be determined based on the time it takes for the thickness of the expansive soil (ie, the width of the accommodating cavity between the first sleeve and the second sleeve) to leach out groundwater.

[0040] In some embodiments, the in-situ measurement mechanism includes a first sleeve 1 and a second sleeve 2, the second sleeve 2 is sleeved inside the first sleeve 1 and forms a receiving cavity 203 between the first sleeve, the second sleeve 2 has a second cavity 201 inside, the inner wall of the second cavity 201 is sleeved with a second permeable membrane bag 202 for water to pass through, the first sleeve 1 is provided with a first cavity 101, the first cavity 101 is sleeved with a first permeable membrane bag 102 for water to pass through, the first permeable membrane bag 102 and the second permeable membrane bag 202 are used to load quicklime, the circumferential wall of the second sleeve 2 is provided with a plurality of through holes 103 interconnected with the second cavity 201, the inner wall of the first sleeve 1 (i.e., the inner wall closer to the second sleeve side) is provided with a plurality of through holes 103 interconnected with the first cavity 101; the first permeable membrane bag 102 and the second permeable membrane bag 202 are equipped with an electronic scale for weighing. After the reaction is completed, the first permeable membrane bag and the second permeable membrane bag can be taken out and weighed using an electronic scale. Alternatively, the first permeable membrane bag and the second permeable membrane bag may be suspended in the first cavity and the second cavity and then weighed, but the first permeable membrane bag and the second permeable membrane bag should be prevented from contacting the inner walls of the first cavity and the second cavity respectively during the suspension process. The first permeable membrane bag and the second permeable membrane bag, which can only allow water to pass through, are prior art products. For example, a common reverse osmosis membrane used for water purification can be used to make a bag shape, thereby obtaining the first permeable membrane bag and the second permeable membrane bag.

[0041] In the specific implementation process, the maximum moisture content of the expansive soil is estimated based on the survey data in the survey stage, so as to further estimate the initial mass of quicklime that undergoes a full chemical reaction (CaO+H2O=Ca(OH)2) with the water corresponding to the maximum moisture content, and the quicklime with the calculated weight is placed in a permeable membrane bag (wherein the mass of the permeable membrane bag can be weighed before the quicklime is added, so as to know the weight of the permeable membrane bag itself), and the infiltrated water in the expansive soil enters the permeable membrane bag to undergo a full chemical reaction with the quicklime, and then the mass of the quicklime after the full reaction is measured minus the initial mass, so as to obtain the mass of the infiltrated water, and thus the moisture content ω of the expansive soil at this time is calculated.

[0042] Among them, quicklime reacts with water very quickly, and the water in the expansive soil will be quickly absorbed by the quicklime. Due to the small size of the casing (the outer diameter of the first casing is 30-50mm), the water absorbed by the quicklime will not cause a significant hydraulic gradient in the expansive soil. Only under a larger hydraulic gradient will the water in the distant expansive soil penetrate into the nearby expansive soil.

[0043] The present invention utilizes the structural design of the first sleeve 1 and the second sleeve 2, on the one hand, utilizes the accommodation cavity between the first sleeve and the second sleeve to obtain the volume of the expansive soil during the measurement, and then utilizes the data obtained in the survey stage (wherein the density, water content, relative density and other data of the expansive soil are obtained in the survey stage) to calculate the weight of the expansive soil in the accommodation space, and utilizes the electronic scale and the weight of the quicklime added to calculate the weight of the water participating in the reaction in the permeable membrane bag (the first permeable membrane bag and the second permeable membrane bag), and finally obtains the water content ω of the expansive soil. The first protective layer is formed by utilizing the outer wall of the first sleeve, and the structural design of the first sleeve and the second sleeve is utilized to greatly increase the contact area, so that the expansive soil in the accommodation cavity can be synchronously and quickly entered from the inside and the outside and react with the water in the permeable membrane bag to reduce the measurement time. Therefore, the present invention can carry out in-situ measurement of the water content of the expansive soil, and compared with the prior art, the water content of the expansive soil can be quickly obtained by taking samples back to the laboratory for measurement.

[0044] In actual practice, in addition to the commonly used weight method (drying method), the methods for determining soil moisture content mainly include the following methods.

[0045] The neutron method is mainly used to measure the moisture in deeper soil layers, but is not suitable for soil surface and soil with organic matter, because the hydrogen in organic matter will affect the results of moisture determination. At the same time, the equipment is expensive and there is a certain radiation risk to the operator.

[0046] The γ-ray method uses the attenuation of γ-rays emitted by radioactive isotopes when penetrating the soil to measure soil moisture content. As the wet bulk density of the soil increases, the attenuation of γ-rays increases, thereby inferring the soil moisture content. This method is non-contact and non-destructive, but it also has the problem of radiation risk and high equipment cost.

[0047] The tensiometer method (negative pressure gauge method) indirectly calculates the soil moisture content by measuring the soil water suction. When the clay head is inserted into the soil, the soil moisture content can be determined by measuring the suction value when the free water in the tube and the soil water reach water potential equilibrium, combined with the soil water characteristic curve, which is suitable for fixed-point continuous observation. However, due to the narrow range of the tensiometer method, it can generally only measure the soil water suction below 80-85KPa, and it will fail if it exceeds this range. However, due to its own properties, the water absorption of expansive soil varies greatly at different water contents, and the water suction range of expansive soil is much greater than the suction value of the tensiometer method. Therefore, the tensiometer method is not suitable for expansive soil.

[0048] The resistance method is a method that uses the relationship between the resistance of certain porous materials (such as gypsum, nylon, and glass fiber) and their water content. When the block components embedded with motors are placed in moist soil, they absorb soil moisture until they reach equilibrium. The resistance of the block components is determined by their moisture content, which in turn is determined by the moisture tension or suction of the nearby soil. However, in actual situations, factors such as soil structure and temperature will also affect the measurement results. Therefore, in complex environments, the accuracy and reliability are relatively poor. Moreover, the water suction of expansive soils at different moisture contents varies greatly, which further reduces the accuracy when testing expansive soils, and ultimately leads to the resistance method not being used for expansive soils.

[0049] FDR method and TDR method. The principle of TDR method is that the waveform on an unmatched transmission line will be emitted, and the waveform at any point on the transmission line is the superposition of the original waveform and the emitted waveform, but the equipment of TDR method is expensive.

[0050] The principle of the FDR method (also known as the high-frequency vibration method) is similar to that of the TDR method. It uses the working principle of electromagnetic pulses. The FDR method measures the apparent dielectric constant of the soil according to the frequency of electromagnetic waves propagating in the medium to obtain the volumetric moisture content of the soil. When electromagnetic waves propagate in dry soil, the propagation speed of electromagnetic waves is relatively fast due to the friction and damping between soil particles. When there is moisture in the soil, the presence of moisture will increase the dielectric constant of the soil, thereby reducing the propagation speed of electromagnetic waves. Therefore, by measuring the speed at which electromagnetic waves propagate in the soil, the moisture content in the soil can be inferred. However, since the current calibration method can hardly obtain uniform sample parameters covering all moisture ranges of the soil under natural conditions, the unreasonable secondary calibration parameters are the fundamental reason for poor data reliability. Especially for expansive soil, its dielectric constant will also change under different moisture contents. More importantly, the electrodes of the sensor method (TDR method and FDR method) are short and cannot be extended to the required depth, and are easily affected by soil salinity.

[0051] Based on the above reasons, the moisture content test for expansive soil is mainly based on the weight method. Although the weight method (drying method) has accurate numerical values, it needs to be sampled in the laboratory for operation, which is very time-consuming; sampling in several areas further increases the measurement time. At the same time, sampling will increase the disturbance to the original expansive soil, while the present invention uses an in-situ measurement mechanism to measure the expansive soil in situ, which can greatly reduce the disturbance to the original expansive soil.

[0052] In the specific implementation process, the outer diameter of the first sleeve is controlled between 30-50mm, and the outer diameter of the second sleeve is 20-40mm, so that the first sleeve and the second sleeve have sufficient mechanical strength to be able to penetrate into the expansive soil. The spacing between the first sleeve and the second sleeve (i.e., the length of the cavity) is controlled between 3-6mm. Within this range, the spacing between the first sleeve and the second sleeve can facilitate the entry of the expansive soil, and at the same time, the time for groundwater to seep out of the expansive soil can be relatively short, so that the chemical reaction with quicklime can be completed in a short time, thereby obtaining the moisture content of the expansive soil, and using the obtained functional relationship to obtain the shear strength parameter, the shear strength of the expansive soil is calculated based on the calculated shear strength parameters c and φ, and used as the design parameters of the retaining design.

[0053] In some embodiments, the first cavity 101 and the second cavity 201 are provided with a pressure ring 8, the pressure ring 8 in the first cavity 101 is adapted to the first cavity 101, and the pressure ring 8 in the second cavity 201 is adapted to the second cavity 201. The pressure ring 8 can play a certain supporting and pressing role on the first permeable membrane bag 102 and the second permeable membrane bag 202, so as to facilitate the first permeable membrane bag 102 and the second permeable membrane bag 202 to be respectively sleeved in the first cavity 101 and the second cavity 201. That is to say, the pressure ring 8 is respectively loaded into the first permeable membrane bag 102 and the second permeable membrane bag 202, and the weight of the pressure ring 8 is used to drive the first permeable membrane bag and the second permeable membrane bag to enter the first cavity 101 and the second cavity 201 respectively. Among them, when the pressure ring is used to press the first permeable membrane bag and the second permeable membrane bag, the weight of the pressure ring should be discharged to avoid affecting the quality of the groundwater adsorbed by quicklime.

[0054] In some embodiments, the bottom end of the first sleeve 1 extends out of the bottom end of the second sleeve 2, the position of the through hole 103 at the lowest end of the first sleeve 1 is flush with the lower end of the second sleeve 2, the bottom end of the second sleeve 2 is pointed, the bottom end of the first sleeve 1 extends outward and forms an upwardly tilted crown 3, and a groove 301 is formed between the crown 3 and the outer wall of the first sleeve 1. In the specific implementation process, since the bottom of the first sleeve is lower than the bottom of the second sleeve and the bottom of the first sleeve extends outward to form an upwardly tilted crown, on the one hand, the crown is used to cut the soil to facilitate penetration into the soil, and on the other hand, the groove formed between the crown and the outer wall of the first sleeve can also prevent groundwater outside the first sleeve from entering the accommodating cavity between the first sleeve and the second sleeve, thereby improving the reliability of the data. At the same time, since the through hole at the lowest end of the first sleeve is flush with the bottom of the second sleeve, the groundwater that penetrates downward to the bottom surface of the second sleeve is adsorbed by the first permeable membrane bag in the first cavity and will not be unable to be adsorbed due to the crown extending downward from the bottom end of the second sleeve.

[0055] During the specific implementation process, the lower end of the crown is also pointed to facilitate penetration into the expansive soil.

[0056] In some embodiments, the through hole 103 at the lowest end of the first sleeve 1 is flush with the bottom of the second cavity 201, so that the parallel through holes 103 (i.e., the through hole 103 at the lowest end of the first sleeve) can be used to drain the groundwater seeping from the expansive soil between the first sleeve 1 and the second sleeve 2 into the first cavity 101 and react chemically with the quicklime in the first permeable membrane bag 102.

[0057] The through holes 103 at other positions on the first sleeve 1 (i.e., the through holes except the through hole at the lowermost end of the first sleeve) and the through holes 103 on the second sleeve 2 are designed to be inclined upward to prevent the through holes from being blocked by expansion soil during penetration.

[0058] In some embodiments, the tops of the first sleeve 1 and the second sleeve 2 are connected via an end cap 4, a movable ring 5 is sleeved in the accommodating cavity 203, the movable ring 5 can slide along the inner wall of the first sleeve 1 and the outer wall of the second sleeve 2, a through hole is opened on the end cap 4 corresponding to the area of ​​the accommodating cavity, and at least two pull rods 6 are connected to the movable ring 5, and the pull rods 6 pass through the end cap 4 and are connected to a connecting ring 7. Among them, the movable ring 5 can be used to judge whether the first sleeve 1 and the second sleeve 2 have penetrated to a specified depth; at the same time, when the in-situ measuring mechanism is pulled out after the measurement is completed, the movable ring 5 can also be used to apply a reverse force to squeeze the expansive soil, so as to facilitate the rapid pulling out of the entire in-situ measuring mechanism, and also use the squeezing effect of the movable ring 5 to prevent the expansive soil from being pulled out, so as to minimize the disturbance of the expansive soil. In the specific implementation process, the connecting ring 7 cannot affect the penetration operation of the entire in-situ measuring mechanism.

[0059] In some embodiments, the top of the second sleeve 2 extends out of the first sleeve 1 and is provided with an end cap 9. The end cap 9 facilitates placement into the expansive soil. In the specific implementation process, the end cap 9 extends outward to form a whole with the end cover 4, thereby improving the strength of the entire in-situ measurement mechanism. In some embodiments, a pull ring is provided on the end cap 9 through a pin shaft, and the pull ring is used to facilitate pulling the entire in-situ measurement mechanism out of the expansive soil.

Claims

1. A method for determining in-situ shear strength parameters of expansive soil, characterized in that: include: (1) Obtain the shear strength parameters c and φ of the original expansive soil at different water contents ω, and obtain the functional relationship between c and φ and the water content ω: c = f1(ω), φ = f2(ω); (2) The in-situ measuring device is inserted into the specified depth of the expansive soil, and the moisture content ω of the expansive soil is obtained by using the in-situ measuring device; (3) Substituting the moisture content ω obtained in step (2) into the functional relationship in step (1): c = f1(ω); φ = f2(ω), the shear strength parameters c and φ can be obtained, and the shear strength calculation formula can be used to obtain the shear strength of the expansive soil at this time.

2. The method for determining the in-situ shear strength parameters of expansive soil according to claim 1, characterized in that: In step (2), after the in-situ measuring mechanism is penetrated to a specified depth in the expansive soil, the in-situ measuring mechanism should be left stationary for a period of time to allow the groundwater to fully react with the quicklime in the in-situ measuring mechanism.

3. The method for determining the in-situ shear strength parameters of expansive soil according to claim 1 or 2, characterized in that: The in-situ measurement mechanism comprises a first sleeve (1) and a second sleeve (2); the second sleeve (2) is sleeved inside the first sleeve (1) and forms a receiving cavity (203) with the first sleeve (1); the second sleeve (2) has a second cavity (201) inside, the inner wall of the second cavity (201) is sleeved with a second permeable membrane bag (202) for water to pass through; the first sleeve (1) is provided with a first cavity (101), the first cavity (101) is sleeved with a second permeable membrane bag (202) for water to pass through; A first permeable membrane bag (102) through which water passes; the first permeable membrane bag (102) and the second permeable membrane bag (202) are used to contain quicklime; a plurality of through holes (103) interconnected with the second cavity (201) are provided on the circumferential wall of the second sleeve (2); a plurality of through holes (103) interconnected with the first cavity (101) are provided on the inner wall of the first sleeve (1); the first permeable membrane bag (102) and the second permeable membrane bag (202) are equipped with electronic scales for weighing.

4. The method for determining the in-situ shear strength parameters of expansive soil according to claim 3, characterized in that: The first cavity (101) and the second cavity (201) are respectively provided with pressure rings (8) for pressing in the first permeable membrane bag (102) and the second permeable membrane bag (202).

5. The method for determining in-situ shear strength parameters of expansive soil according to claim 3 or 4, characterized in that: The bottom end of the first sleeve (1) extends outward from the bottom end of the second sleeve (2); the through hole (103) at the bottom end of the first sleeve (1) is flush with the bottom end of the second sleeve (2); the bottom end of the second sleeve (2) is pointed; the bottom end of the first sleeve (1) extends outward and forms an upwardly tilted crown (3); a groove (301) is formed between the crown (3) and the outer wall of the first sleeve (1).

6. The method for determining in-situ shear strength parameters of expansive soil according to claim 3, characterized in that: The tops of the first sleeve (1) and the second sleeve (2) are connected via an end cover (4); a movable ring (5) is sleeved in the accommodating cavity (203); the movable ring (5) is capable of sliding along the inner wall of the first sleeve (1) and the outer wall of the second sleeve (2); a through hole is provided on the end cover (4) in an area corresponding to the accommodating cavity (203); at least two pull rods (6) are connected to the movable ring (5); the pull rods (6) pass through the end cover (4) and are connected to a connecting ring (7).

7. The method for determining in-situ shear strength parameters of expansive soil according to claim 6, characterized in that: The top of the second sleeve (2) extends out of the first sleeve (1) and is provided with an end cap (9).

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