A rock and soil static lateral pressure simulation device and effective stress calculation method

Abstract

The present invention discloses a rock and soil static side pressure simulation device and an effective stress calculation method, wherein the rock and soil static side pressure simulation device includes a metering cylinder, a liquid inlet box, a test cylinder, a liquid outlet box and a metering cylinder; a support structure is provided on the top of the liquid inlet box, the support structure includes a hydraulic oil cylinder and an axial force gauge, the axial force gauge is provided on the top of the liquid inlet box, and the hydraulic rod of the hydraulic oil cylinder is pressed against the axial force gauge; a plurality of pressure sensors are provided on the side of the test cylinder. The present invention provides a rock and soil static side pressure simulation device and an effective stress calculation method, which can directly measure the rock and soil static side pressure of reshaped soil or original soil taken on site, directly simulate the actual situation of the rock and soil on the foundation pit side, and make the foundation pit static side pressure test results more accurate. At the same time, it breaks through the traditional concept of Terzaghi's effective stress and proposes a new effective stress calculation formula to provide support for the development of theoretical soil mechanics.

Description

Technical Field

[0001] The present invention relates to the technical field of geotechnical test measurement, and in particular to a rock and soil static lateral pressure simulation device and an effective stress calculation method. Background Art

[0002] Natural rock and soil are divided into saturated rock and soil and unsaturated rock and soil. The current methods for calculating the lateral pressure of foundation pit support include separate calculation of soil and water and combined calculation of soil and water. The accuracy of the calculation mainly depends on the static lateral pressure coefficient k0 of the soil skeleton. The static lateral pressure coefficient k0 of the soil skeleton varies under different rock and soil bond strengths, different free water pressures, different soil skeleton stresses, or different water supply conditions. This leads to inaccurate calculations of the total static lateral pressure of rock and soil using the static lateral pressure coefficient k0 of the soil skeleton. At the same time, there is still debate about the correctness of separate calculation of soil and water and combined calculation of soil and water. Some geotechnical experts have also questioned whether Terzaghi's effective stress calculation is applicable to combined calculation of soil and water.

[0003] If the safety factor for the static lateral pressure coefficient k0 used in design calculations is too small, it can easily lead to insufficient foundation pit support and serious safety accidents. Conversely, if the safety factor for the static lateral pressure coefficient k0 used in design calculations is too large, it will cause unnecessary waste. Therefore, it is urgent to find a simulation device that can accurately measure the static lateral pressure of geotechnical materials and correctly analyze the relationship between static lateral pressure and effective stress in geotechnical materials to ensure foundation pit support safety and reduce construction costs.

[0004] Patent application CN113049473A discloses a device and method for measuring the water content and permeability of rock and soil (hereinafter referred to as Prior Art 1). Prior Art 1 discloses a device and method capable of simulating on-site gravity water pressure conditions through a test device and accurately calculating the water content and permeability under different water pressures. However, it cannot measure the static pressure of rock and soil, and its structure and functionality require improvement. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of existing technologies by providing a device for simulating the static lateral pressure of rock and soil and a method for calculating effective stress. This device simulates actual rock and soil in situ using remolded soil or undisturbed soil sampled on site. It can directly measure the actual free water pressure and static lateral pressure of rock and soil under soil skeleton stress conditions in the simulated remolded soil or undisturbed soil sampled on site, providing an accurate reference for calculating foundation pit support forces.

[0006] The object of the present invention is achieved through the following technical solutions: a method for calculating effective stress in rock and soil. Effective stress is the average stress of the total cross-section on which the soil particles on the cross-section are subjected to the force. The effective stress is proportional to the bearing capacity. The effective stress calculation formula is as follows:

[0007] σ′=(σ-μu w)(1-n) / (1-μ)

[0008] Where:

[0009] σ′—effective stress, (kPa);

[0010] σ—total vertical stress on the total cross section, (kPa);

[0011] u w —pore water pressure (kPa);

[0012] μ – water supply degree;

[0013] n – porosity.

[0014] A rock and soil static lateral pressure simulation device comprises a first metering cylinder, a liquid inlet box, a test cylinder, a liquid outlet box and a second metering cylinder;

[0015] A liquid inlet pipeline is provided between the first metering cylinder and the liquid inlet tank. The liquid inlet pipeline includes a low-position pipe section and a high-position pipe section. A quantitative delivery pump is installed on the low-position pipe section, and a first pressure gauge and a first flow sensor are provided on the high-position pipe section. The liquid inlet pipeline is also connected to an overflow pipeline, and a first pressure regulating overflow valve is installed on the overflow pipeline.

[0016] The experimental cylinder is arranged between the liquid inlet box and the liquid outlet box, an upper filter plate is arranged between the liquid inlet box and the experimental cylinder, and a lower filter plate is arranged between the experimental cylinder and the liquid outlet box; a liquid outlet pipeline is arranged between the liquid outlet box and the second metering cylinder, and a second flow sensor, a second pressure gauge and a second pressure regulating overflow valve are installed on the liquid outlet pipeline;

[0017] A supporting structure is set on the top of the liquid inlet tank. The supporting structure includes a hydraulic cylinder and an axial force meter. The axial force meter is set on the top of the liquid inlet tank, and the hydraulic rod of the hydraulic cylinder is pressed against the axial force meter. Several pressure sensors are set on the side of the test cylinder.

[0018] Preferably, a first water filter cloth is positioned below the upper filter plate, and the first water filter cloth and the upper filter plate form an upper filter assembly. Preferably, a second water filter cloth is positioned above the lower filter plate, and the second water filter cloth and the lower filter plate form a lower filter assembly. Preferably, a first fixed support frame is positioned below metering cylinder 1; a second fixed support frame is positioned below the liquid outlet box; and a third fixed support frame is positioned below metering cylinder 2.

[0019] Preferably, a hoisting platform is provided on the second fixed support frame, and the hydraulic cylinder is fixed in an inverted manner on the hoisting platform. Preferably, the upper filter plate is provided with a plurality of upper water passages, and the cross-sectional area of ​​the upper water passages is not less than 40% of the cross-sectional area of ​​the upper filter plate.

[0020] Preferably, the lower filter plate is provided with a plurality of lower water passages, and the cross-sectional area of ​​the lower water passages is not less than 40% of the cross-sectional area of ​​the lower filter plate.

[0021] Preferably, an elastic rubber pad is provided on the stress-bearing surface of the pressure sensor, and the pressure sensor is mounted to the side of the test cylinder by bolts. After the pressure sensor is mounted, the elastic rubber pad is located between the pressure sensor and the test cylinder.

[0022] Preferably, a first regulating valve is also provided on the low-level pipe section; a third regulating valve is installed on the high-level pipe section of the liquid inlet pipeline; the low-level pipe section of the liquid inlet pipeline is connected to the first liquid discharge pipeline, and a second regulating valve is installed on the first liquid discharge pipeline; a fourth regulating valve is also installed on the liquid outlet pipeline.

[0023] Preferably, the installation position of the liquid outlet box is higher than that of the second metering cylinder; one end of the liquid outlet pipeline is connected to the bottom of the liquid outlet box, and the other end of the liquid outlet pipe is arranged above the second metering cylinder.

[0024] The present invention provides a geotechnical static lateral pressure simulation device and effective stress calculation method. These devices can directly measure the geotechnical static lateral pressure of remolded soil or undisturbed soil sampled on-site, simulating the actual geotechnical conditions at the side of a foundation pit and improving the accuracy of pit static lateral pressure test results. Furthermore, this invention breaks through the traditional concept of effective stress defined by Terzaghi and proposes a new effective stress calculation formula, providing support for the development of theoretical soil mechanics. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 This is a schematic diagram of a rock and soil static side pressure simulation device;

[0027] In the figure, 1-first fixed support frame, 2-metering cylinder 1, 3-quantitative delivery pump, 4-first regulating valve, 5-second regulating valve, 6-first pressure regulating overflow valve, 7-first pressure gauge, 8-first flow sensor, 9-third regulating valve, 10-liquid inlet box, 11-upper filter plate, 12-first water filter cloth, 13-experimental cylinder, 14-lower filter plate, 15-liquid outlet box, 16-fourth regulating valve, 17-second flow sensor, 18-second pressure gauge, 19-second pressure regulating overflow valve, 20-metering cylinder 2, 21-fifth regulating valve, 22-second fixed support frame, 23-third fixed support frame, 24-bolt, 25-elastic rubber pad, 26-pressure sensor, 27-second water filter cloth, 28-hydraulic cylinder, 29-axial force meter, 30-pad, 31-hydraulic system. DETAILED DESCRIPTION

[0028] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings, but the protection scope of the present invention is not limited to the following.

[0029] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention.

[0030] In the description of the present invention, it should be understood that the terms indicating orientation or positional relationships are based on the orientation or positional relationships shown in the accompanying drawings and are only used to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, they cannot be understood as limiting the present invention.

[0031] Example 1

[0032] A method for calculating effective stress in geotechnical environments:

[0033] In theoretical soil mechanics calculations, the static lateral pressure of rock and soil has always been linked to the effective stress, which is now analyzed.

[0034] (1) The relationship between Terzaghi's effective stress principle and soil and water separation

[0035] Terzaghi established the effective stress principle formula through experimental observation:

[0036] σ = σ′ + u w (1)

[0037] σ1 = k0σ′ + u w (2)

[0038] In formula (1-2):

[0039] σ—total vertical stress on the cross section, (kPa);

[0040] σ′--effective stress (average stress of soil skeleton force on horizontal section), (kPa);

[0041] u w —neutralization stress (pore water pressure), (kPa);

[0042] σ1—static lateral pressure of rock and soil, (kPa);

[0043] k0—static lateral pressure coefficient of soil skeleton.

[0044] Through experimental observation, Terzaghi established the effective stress principle formula (1). The static lateral pressure of rock and soil is obtained by multiplying the soil skeleton stress by the static lateral pressure coefficient based on the effective stress principle. Although this calculation formula is not theoretically derived, Terzaghi defines the effective stress as the average stress on the total cross section of the difference between the gravity of the soil skeleton and the buoyancy of the same volume of water on the soil skeleton, resulting in the theoretical equivalence of formula (1). However, in practical applications, it was found that this formula is not applicable to clay soil, which has led to some experts and scholars raising doubts. If it is also applicable to clay soil, then no one would question it. There are many methods for calculating the static lateral pressure of rock and soil today, and no unified opinion has been formed. Therefore, the present invention directly measures the static lateral pressure of rock and soil by simulating the actual situation on site, and the obtained value will be more accurate.

[0045] (2) Derivation of effective stress

[0046] Terzaghi believed that effective stress can produce a noticeable effect on the soil or increase the shear strength of the soil. That is to say, when there is an additional load, the soil will deform. After the deformation stabilizes, the effective stress increases. The increased effective stress should be equal to the average stress of the additional load. After the effective stress increases, the shear strength of the soil will also increase. For saturated soil, when the load increases and the soil deforms, the water in the soil will be squeezed out, the area of ​​soil particles on the cross section will increase, and the shear strength will increase at the same time; for unsaturated soil, when the load increases and the soil deforms, the soil skeleton will become denser, the area of ​​soil particles on the cross section will increase, and the shear strength will increase at the same time. The increase in additional load (effective force) directly leads to an increase in the area of ​​soil particles on the cross section, and both effective stress and shear strength increase. Through the above analysis, the present invention proposes that effective stress is the average stress of the force borne by the soil particles on the cross section on the total cross section. The effective stress is proportional to the bearing capacity. The greater the effective stress, the greater the bearing capacity. When the porosity of the soil is 0, the effective stress is the largest and the bearing capacity is also the largest. The effective stress calculation formula is as follows:

[0047] σ′=(σ -μu w )(1-n) / (1-μ) (3)

[0048] In formula (3):

[0049] σ′—effective stress (average stress on the total cross section of soil particles subjected to the force), (kPa);

[0050] σ—total vertical stress on the total cross section, (kPa);

[0051] u w —pore water pressure (kPa);

[0052] μ – water supply degree;

[0053] n – porosity.

[0054] From formula (3), we can know that:

[0055] When n = μ, σ′ = σ - μu w , which is the calculation formula for the effective stress of sandy soil without weakly bound water.

[0056] When μ=0, σ′=σ(1-n), which is the calculation formula for the effective stress of clay soil with no water supply.

[0057] When n=0, μ=0, σ′=σ, which is the effective stress calculation formula for saturated soil with no porosity. At this time, the effective stress is the largest.

[0058] Effective stress change analysis: When σ, u w , μ remain unchanged, as n increases, σ′ becomes smaller; when σ, u w When n remains unchanged, σ′ increases as μ increases.

[0059] Formula (3) can clearly explain why the bearing capacity of clay soil is lower than that of sandy soil, and why the bearing capacity of loose soil of the same type is lower than that of dense soil.

[0060] Therefore, the static lateral pressure of rock and soil is a combination of the isotropic properties of free water and the anisotropic properties of the soil skeleton, and the effective stress is the average stress of the force borne by the soil particles on the cross section on the total cross section, and there is no direct connection.

[0061] Whether it is the static side pressure, water content or permeability coefficient of geotechnical materials, the static side pressure, water content and permeability coefficient will be different under different types of soil, different free water pressure (or different head pressure difference) and different soil skeleton stress conditions. In indoor tests, it is necessary to use original soil samples to simulate the on-site water pressure and soil skeleton stress conditions to the maximum extent, measure and calculate the accurate static side pressure, water content and permeability coefficient multiple times, and provide strong support for geotechnical calculations. In summary, based on indoor tests on original soil samples, the static side pressure, water content and permeability coefficient under original soil conditions can be accurately calculated, and the effective stress can be accurately calculated using the new effective stress formula.

[0062] This embodiment breaks through the traditional Terzaghi concept of effective stress, breaks the traditional thinking, combines the actual situation, proposes a new effective stress calculation formula, and proposes that the calculation of rock and soil static lateral pressure has no direct connection with the calculation of effective stress, providing support for the development of theoretical soil mechanics.

[0063] Example 2

[0064] like Figure 1As shown, a rock and soil static side pressure simulation device includes a metering cylinder 2, a liquid inlet box 10, a test cylinder 13, a liquid outlet box 15 and a metering cylinder 20;

[0065] A liquid inlet pipeline is provided between the metering cylinder 2 and the liquid inlet box 10. The liquid inlet pipeline includes a low-level pipe section and a high-level pipe section. A quantitative delivery pump 3 is installed on the low-level pipe section, and a first pressure gauge 7 and a first flow sensor 8 are provided on the high-level pipe section. The liquid inlet pipeline is also connected to an overflow pipeline, and a first pressure regulating overflow valve 6 is installed on the overflow pipeline.

[0066] The experimental cylinder 13 is arranged between the liquid inlet box 10 and the liquid outlet box 15. An upper filter plate 11 is arranged between the liquid inlet box 10 and the experimental cylinder 13, and a lower filter plate 14 is arranged between the experimental cylinder 13 and the liquid outlet box 15. A liquid outlet pipeline is arranged between the liquid outlet box 15 and the second metering cylinder 20. A second flow sensor 17, a second pressure gauge 18, and a second pressure regulating relief valve 19 are installed on the liquid outlet pipeline.

[0067] A supporting structure is provided on the top of the liquid inlet tank 10. The supporting structure includes a hydraulic cylinder 28 and an axial force gauge 29. The axial force gauge 29 is provided on the top of the liquid inlet tank 10 (a cushion block 30 may be provided between the axial force gauge 29 and the liquid inlet tank 10). The hydraulic rod of the hydraulic cylinder 28 is supported on the axial force gauge 29. A plurality of pressure sensors 26 are provided on the side of the test cylinder 13. The side of the test cylinder 13 is opened, and the pressure sensors 26 are provided at the opening.

[0068] This embodiment provides a technical solution for measuring the lateral pressure of the test tube 13. This not only measures the water content and permeability of rock and soil in any state, but also directly measures the static lateral pressure of remolded soil or undisturbed soil sampled on-site. This directly simulates the actual conditions of the rock and soil at the side of the foundation pit, resulting in more accurate static lateral pressure test results. This measurement device is suitable for measuring water content and permeability in all soil types and under different water pressure conditions, and is worthy of global promotion and application.

[0069] Example 3

[0070] Different from the second embodiment, a first water filter cloth 12 is provided below the upper filter plate 11 of this embodiment, and the first water filter cloth 12 and the upper filter plate 11 form an upper filter assembly.

[0071] A second water filter cloth 27 is disposed above the lower filter plate 14 , and the second water filter cloth 27 and the lower filter plate 14 form a lower filter assembly.

[0072] The upper filter plate 11 is provided with a plurality of upper water passages, and the cross-sectional area of ​​the upper water passages is not less than 40% of the cross-sectional area of ​​the upper filter plate 11 .

[0073] The lower filter plate 14 is provided with a plurality of lower water passages, and the cross-sectional area of ​​the lower water passages is not less than 40% of the cross-sectional area of ​​the lower filter plate 14 .

[0074] This embodiment proposes that the water passage area is not less than 40% of the total area (the rock and soil water passage area generally does not exceed 40%), and the filter cloth soil particles cannot pass through, and can only pass water or hydraulic oil.

[0075] Example 4

[0076] In order to ensure the height of the installation components, a first fixed support frame 1 is provided under the metering cylinder 1 2; a second fixed support frame 22 is provided under the liquid outlet box 15 (the liquid outlet box 15 is in the middle part of the bracket); and a third fixed support frame 23 is provided under the metering cylinder 2 20.

[0077] A hoisting platform is provided on the second fixed support frame 22, and the hydraulic oil cylinder 28 is fixed upside down on the hoisting platform. The extension, retraction and adjustment of the hydraulic oil pressure of the hydraulic oil cylinder 28 are realized by the hydraulic system 31.

[0078] The force displayed by the axial force meter 29 is added to the required supporting force. The required supporting force can be calculated by taking into account the gravity of each component, the cross-sectional area of ​​the test cylinder 13, and the total pressure value of the formation to calculate the required supporting force of the hydraulic cylinder 28. The calculation method of the required supporting force is not discussed in this embodiment. In short, the supporting force applied to the top of the test cylinder 13 can be observed through the axial force meter 29. The simulated soil sample is consistent with the free water pressure and soil skeleton stress on site. The pressure of each pressure sensor 26 is directly recorded and the average value is taken (if there is only one pressure sensor 26, the pressure value of the pressure sensor 26 is directly recorded). This average value is the static side pressure value of the saturated soil of the simulated formation.

[0079] Example 5

[0080] An elastic rubber pad 25 is attached to the load-bearing surface of the pressure sensor 26. The pressure sensor 26 is mounted to the side of the test cylinder 13 via bolts 24. After the pressure sensor 26 is installed, the elastic rubber pad 25 is located between the pressure sensor 26 and the test cylinder 13. Two or four pressure sensors 26 are provided, all arranged circumferentially around the test cylinder 13, and all installed at the same height.

[0081] In order to directly measure the static side pressure of rock and soil, several pressure sensors 26 (such as 2 or 4) are designed on the side of the test cylinder 13. The pressure sensors 26 are fixed to the test cylinder 13 by bolts 24, and elastic rubber pads 25 are pasted on the stress-bearing surfaces of the pressure sensors 26.

[0082] Example 6

[0083] To improve the piping system, this embodiment also features a first regulating valve 4 on the lower section of the pipe; a third regulating valve 9 on the higher section of the liquid inlet pipe; the lower section of the liquid inlet pipe connects to the first liquid discharge pipe, which is equipped with a second regulating valve 5; and a fourth regulating valve 16 on the liquid discharge pipe. These valves facilitate control of various functions, making pipeline control more convenient and safer.

[0084] Example 7

[0085] In this embodiment, the installation position of the liquid outlet box 15 is higher than that of the second metering cylinder 20. The installation height of the liquid outlet box 15 is based on ensuring that the liquid in the liquid outlet box 15 can flow smoothly into the second metering cylinder 20. One end of the liquid outlet pipe is connected to the bottom of the liquid outlet box 15, and the other end of the liquid outlet pipe is arranged above the second metering cylinder 20 to facilitate liquid discharge.

[0086] Example 8

[0087] The liquid inlet box 10, the experimental cylinder 13 and the liquid outlet box 15 are all circular transparent cylinders and can bear the required pressure.

[0088] Example 9

[0089] The bottom of the liquid inlet tank 10 is connected to a second liquid discharge line, which is equipped with a shutoff valve. The bottom of the second metering cylinder 20 is connected to a third liquid discharge line, which is equipped with a fifth regulating valve 21. These changes solve many control issues of the entire device, such as enabling the shutoff of related pipelines through the shutoff valve. The liquid discharge line allows for more efficient liquid drainage, making the entire device easier to maintain.

[0090] Example 10

[0091] This embodiment provides an operation or application method of a device for measuring the water content and permeability of rock and soil (for details, please refer to the utility model patent "A device for measuring the water content and permeability of rock and soil", patent number: ZL 2021 20695146.8). The soil sample simulation is basically the same as the operation in the present invention):

[0092] Soil Sample Installation: Adjust bolts 24 so that the bearing surface of the elastic rubber pad 25 is slightly outward from the inside of the test tube 13 (the bearing surface of the elastic rubber pad 25 can be flush with the inside of the test tube 13 or slightly away from the center of the test tube 13, but generally should not extend beyond the outside of the test tube 13). Adjust the second pressure-regulating relief valve 19 to a certain pressure, and fill the liquid outlet tank 15 with water. Above the liquid outlet tank 15 is the lower filter plate 14, and above this, a second water filter cloth 27 is installed. Then, place the soil sample (original soil sample or remolded soil sample collected on-site) into the test tube 13. Ensure that the test tube 13 is completely filled, with no gaps between the soil sample and the wall of the test tube 13. Adjust bolts 24 so that the bearing surface of the elastic rubber pad 25 is against the soil sample. (The use of the elastic rubber pad 25 can realistically simulate the forces exerted on the pressure sensor 26 by both the water pressure of the pore water channel area and the stress of the soil skeleton area, resulting in more accurate pressure measurements.) Install the first water filter cloth 12 , the upper filter plate 11 , the liquid inlet cylinder, the pad 30 , the axial force gauge 29 , and the related pipelines, and lightly press the hydraulic cylinder 28 against the axial force gauge 29 .

[0093] Simulation of actual on-site conditions of soil samples and direct measurement of static lateral pressure:

[0094] (1) Simulation of saturated soil samples

[0095] For saturated soil, the metering pump 3 is activated, pumping the water in the metering cylinder 2 to the inlet tank 10, fully saturating the soil sample and filling the inlet tank 10 with water. The first and second pressure-regulating relief valves 6 and 19 adjust the relief pressure to the simulated formation water pressure. The metering pump 3 is then shut down, and the first regulating valve 4 is closed. The hydraulic system 31 is activated, forcing the hydraulic cylinder 28 downward. As pressure increases, the hydraulic cylinder 28 rod, axial force gauge 29, spacer 30, inlet tank 10, upper filter plate 11, and first filter cloth 12 move downward, compressing the saturated soil sample and forcing the water in the sample into the inlet tank 10 and outlet tank 15. Simultaneously, the water pressure increases. When the water pressure reaches the simulated formation water pressure, the first and second pressure-regulating relief valves 6 and 19 overflow, ensuring that the water pressure in the soil sample remains at the simulated formation water pressure. Taking into account the gravity of the axial force gauge 29, spacer 30, inlet tank 10, and upper filter plate 11, the soil sample is pressurized to the simulated total vertical pressure of the formation. The required support force of the hydraulic cylinder 28 is calculated based on the gravity of each component, the cross-sectional area of ​​the test tube 13, and the total formation pressure. The force indicated by the axial force gauge 29 is then applied until the required support force is reached. At this point, the simulated soil sample matches the on-site free water pressure and soil skeleton stress. The pressures of each pressure sensor 26 are directly recorded and averaged. This average value represents the saturated soil static pressure of the simulated formation.

[0096] (2) Simulation of unsaturated soil samples

[0097] For unsaturated soil, the hydraulic system 31 is directly activated, forcing the hydraulic cylinder 28 downward. As pressure increases, the hydraulic cylinder 28 rod, axial force gauge 29, spacer 30, inlet tank 10, upper filter plate 11, and first water filter cloth 12 move downward, compressing the unsaturated soil sample and pressurizing it to the simulated total formation pressure. The required supporting force of the hydraulic cylinder 28 is calculated based on the gravity of each component, the cross-sectional area of ​​the test tube 13, and the total formation pressure. The force indicated by the axial force gauge 29 is then increased to the required supporting force. At this point, the simulated soil sample matches the unsaturated soil pressure at site, directly indicating the pressure of each pressure sensor 26 and taking the average value. This average value represents the static side pressure of the unsaturated soil in the simulated formation.

[0098] The measurement process and calculation method of water supply degree: water is filled in the metering cylinder 2, and the quantitative delivery pump 3 is started. The water in the metering cylinder 2 passes through the first regulating valve 4, the quantitative delivery pump 3, the first pressure gauge 7, the first flow sensor 8, and the third regulating valve 9, enters the liquid inlet box 10, passes through the water filter cloth and the upper filter plate 11, penetrates into the soil sample, and permeates downwards;

[0099] The water that permeates the soil sample enters the liquid outlet box 15 through the water filter cloth and the lower filter plate 14. When the water pressure in the liquid outlet box 15 exceeds the overflow pressure of the second pressure regulating overflow valve 19, the water overflows into the second metering cylinder 20 through the fourth regulating valve 16, the second flow sensor 17, the second pressure gauge 18, and the second pressure regulating overflow valve 19.

[0100] The relief pressures of the first pressure regulating relief valve 6 and the second pressure regulating relief valve 19 are both adjusted to the gravity water pressure required by the soil sample (the pressure values ​​are read by the first pressure gauge 7 and the second pressure gauge 18), and the soil sample is fully saturated. After the soil sample is fully saturated, the third regulating valve 9 and the fourth regulating valve 16 are closed;

[0101] Clean the water in metering cylinder 1 2 and metering cylinder 2 20. Fill metering cylinder 1 2 with hydraulic oil, then start the quantitative delivery pump 3, open the closed third regulating valve 9 and fourth regulating valve 16, increase the overflow pressure of the first pressure regulating relief valve 6 (the increase range is 0.01-0.02Mpa), and the hydraulic oil enters the soil sample to squeeze out the gravity water. The water in the liquid inlet tank 10, soil sample, and liquid outlet tank 15 overflows into metering cylinder 2 20. After the gravity water in the liquid inlet tank 10, soil sample, and liquid outlet tank 15 has been replaced by the hydraulic oil, stop the quantitative delivery pump 3. Since water and hydraulic oil are immiscible, the water volume in metering cylinder 2 20 can be directly read.

[0102] A method for calculating rock and soil water supply degree, assuming that the volume of the liquid inlet tank 10 is V 进 , the volume of the liquid outlet tank 15 is V 出 , the volume of the experimental tube 13 is V 实 The volume of gravity water in the measuring cylinder 20 is V 水 , the water supply degree is μ. According to the definition of water supply degree, the rock and soil water supply degree under this water pressure condition can be calculated:

[0103] μ=(V 水 -V 进 -V 出 ) / V 实 .

[0104] A method for calculating the rock and soil permeability coefficient adopts a water-saturated soil sample according to the measurement process method of the water supply degree, and closes the third regulating valve 9 and the fourth regulating valve 16 after the soil sample is fully saturated;

[0105] Clean the water in the metering cylinder 20. Then start the quantitative delivery pump 3, open the closed third regulating valve 9 and the fifth regulating valve 21, slowly adjust the overflow pressure of the first pressure regulating relief valve 6 to the upper head pressure, and slowly adjust the overflow pressure of the second pressure regulating relief valve 19 to the lower head pressure to form an upper and lower head difference (the head difference is not less than 0.1Mpa). The head pressure is read by the first pressure gauge 7 and the second pressure gauge 18. Wait until the water flow rate per unit time of the first flow sensor 8 and the second flow sensor 17 is basically equal (the difference does not exceed 0.001m 3 After the flow stabilizes, record the upper and lower head pressures and flow rate values. You can use different head differences to record the flow rate multiple times to calculate the average permeability coefficient of the soil sample. After the flow stabilizes, record the upper and lower head pressures and two flow rate values. You can use different head differences to record the flow rate multiple times to calculate the average permeability coefficient of the soil sample. If you need to calculate the seepage flow rate under specific working conditions, you can also use this working condition to directly measure the permeability coefficient, thereby more accurately calculating the seepage flow rate.

[0106] Assume that the water head pressure of the first pressure regulating relief valve 6 is h, the water head pressure of the second pressure regulating relief valve 19 is h, the length of the test tube 13 is L, the water flow rate per unit time (flow sensor value) is Q, the permeability coefficient in Darcy's law is K, and the circular area of ​​the test tube 13 is A;

[0107] According to Darcy's law formula:

[0108] Q=KA(h2-h1) / L,

[0109] However, the area in this formula is not the area of ​​the gravity water channel, but the cross-sectional area of ​​the soil sample and the gravity water, which should be optimized. The area of ​​the gravity water channel in the circular area of ​​the experimental cylinder 13 is μA, and the permeability coefficient in the optimized Darcy's law is K1;

[0110] The optimized Darcy's law formula should be:

[0111] Q=K1μA(h2-h1) / L,

[0112] At this point, the permeability coefficient can be calculated:

[0113] K1 = QL / (μA(h2-h1)).

[0114] Example 11

[0115] A device for measuring soil water content and permeability mainly includes a metering cylinder 1 (2), a quantitative delivery pump (3), a first pressure-regulating relief valve (6), a first pressure gauge (7), a first flow sensor (8), a liquid inlet tank (10), an upper filter plate (11), a test cylinder (13), a lower filter plate (14), a liquid outlet tank (15), a second flow sensor (17), a second pressure gauge (18), a second pressure-regulating relief valve (19), a metering cylinder 2 (20), a shut-off valve, and related pipelines. To control the flow between components and the pipelines, a first regulating valve (4), a second regulating valve (5), a third regulating valve (9), a first water filter cloth (12), a fourth regulating valve (16), and a fifth regulating valve (21) are provided. To ensure the height of the installed components, a first fixed support frame (1) (mounted below metering cylinder 1 (2), a second fixed support frame (22) (mounted below the liquid outlet tank (15), and a third fixed support frame (23) (mounted below metering cylinder 2 (20)) are provided. The liquid inlet tank (10), the test cylinder (13), and the liquid outlet tank (15) are all round, transparent cylinders capable of bearing the required pressure. Water filter cloths are provided above the upper filter plate 11 and the lower filter plate 14. The water filter cloths cannot allow soil particles to pass through, but can only allow water or hydraulic oil to pass through.

[0116] Soil Sample Installation: Adjust bolts 24 so that the bearing surface of the elastic rubber pad 25 is slightly outward from the inside of the test tube 13 (the bearing surface of the elastic rubber pad 25 can be flush with the inside of the test tube 13 or slightly away from the center of the test tube 13, but generally should not extend beyond the outside of the test tube 13). Adjust the second pressure-regulating relief valve 19 to a certain pressure, and fill the liquid outlet tank 15 with water. Above the liquid outlet tank 15 is the lower filter plate 14, and above this, a second water filter cloth 27 is installed. Then, place the soil sample (original soil sample or remolded soil sample collected on-site) into the test tube 13. Ensure that the test tube 13 is completely filled, with no gaps between the soil sample and the wall of the test tube 13. Adjust bolts 24 so that the bearing surface of the elastic rubber pad 25 is against the soil sample. (The use of the elastic rubber pad 25 can realistically simulate the forces exerted on the pressure sensor 26 by both the water pressure of the pore water channel area and the stress of the soil skeleton area, resulting in more accurate pressure measurements.) Install the first water filter cloth 12 , the upper filter plate 11 , the liquid inlet cylinder, the pad 30 , the axial force gauge 29 , and the related pipelines, and lightly press the hydraulic cylinder 28 against the axial force gauge 29 .

[0117] Simulation of actual on-site conditions of soil samples and direct measurement of static lateral pressure:

[0118] (1) Simulation of saturated soil samples

[0119] For saturated soil, the metering pump 3 is activated, pumping the water in the metering cylinder 2 to the inlet tank 10, fully saturating the soil sample and filling the inlet tank 10 with water. The first and second pressure-regulating relief valves 6 and 19 adjust the relief pressure to the simulated formation water pressure. The metering pump 3 is then shut down, and the first regulating valve 4 is closed. The hydraulic system 31 is activated, forcing the hydraulic cylinder 28 downward. As pressure increases, the hydraulic cylinder 28 rod, axial force gauge 29, spacer 30, inlet tank 10, upper filter plate 11, and first filter cloth 12 move downward, compressing the saturated soil sample and forcing the water in the sample into the inlet tank 10 and outlet tank 15. Simultaneously, the water pressure increases. When the water pressure reaches the simulated formation water pressure, the first and second pressure-regulating relief valves 6 and 19 overflow, ensuring that the water pressure in the soil sample remains at the simulated formation water pressure. Taking into account the gravity of the axial force gauge 29, spacer 30, inlet tank 10, and upper filter plate 11, the soil sample is pressurized to the simulated total vertical pressure of the formation. The required support force of the hydraulic cylinder 28 is calculated based on the gravity of each component, the cross-sectional area of ​​the test tube 13, and the total formation pressure. The force indicated by the axial force gauge 29 is then applied until the required support force is reached. At this point, the simulated soil sample matches the on-site free water pressure and soil skeleton stress. The pressures of each pressure sensor 26 are directly recorded and averaged. This average value represents the saturated soil static pressure of the simulated formation.

[0120] (2) Simulation of unsaturated soil samples

[0121] For unsaturated soil, the hydraulic system 31 is directly activated, forcing the hydraulic cylinder 28 downward. As pressure increases, the hydraulic cylinder 28 rod, axial force gauge 29, spacer 30, inlet tank 10, upper filter plate 11, and first water filter cloth 12 move downward, compressing the unsaturated soil sample and pressurizing it to the simulated total formation pressure. The required supporting force of the hydraulic cylinder 28 is calculated based on the gravity of each component, the cross-sectional area of ​​the test tube 13, and the total formation pressure. The force indicated by the axial force gauge 29 is then increased to the required supporting force. At this point, the simulated soil sample matches the unsaturated soil pressure at site, directly indicating the pressure of each pressure sensor 26 and taking the average value. This average value represents the static side pressure of the unsaturated soil in the simulated formation.

[0122] The measurement process and calculation method of water supply degree: water is filled in the metering cylinder 2, and the quantitative delivery pump 3 is started. The water in the metering cylinder 2 passes through the first regulating valve 4, the quantitative delivery pump 3, the first pressure gauge 7, the first flow sensor 8, and the third regulating valve 9, enters the liquid inlet box 10, passes through the water filter cloth and the upper filter plate 11, penetrates into the soil sample, and penetrates downward.

[0123] The water that permeates the soil sample enters the liquid outlet box 15 through the water filter cloth and the lower filter plate 14. When the water pressure in the liquid outlet box 15 exceeds the overflow pressure of the second pressure regulating overflow valve 19, the water overflows into the second metering cylinder 20 through the fourth regulating valve 16, the second flow sensor 17, the second pressure gauge 18, and the second pressure regulating overflow valve 19.

[0124] The overflow pressures of the first pressure-regulating relief valve 6 and the second pressure-regulating relief valve 19 are both adjusted to the gravity water pressure required by the soil sample (the pressure values ​​are read by the first pressure gauge 7 and the second pressure gauge 18), fully saturating the soil sample. After the soil sample is fully saturated, the third regulating valve 9 and the fourth regulating valve 16 are closed.

[0125] Clean out the water in metering cylinder 1 2 and metering cylinder 2 20. Fill metering cylinder 1 2 with hydraulic oil, then start the quantitative delivery pump 3. Open the closed third regulating valve 9 and fourth regulating valve 16, and slightly increase the relief pressure of the first pressure-regulating relief valve 6. The hydraulic oil enters the soil sample and displaces the gravity water. The water in the liquid inlet tank 10, soil sample, and liquid outlet tank 15 overflows into metering cylinder 2 20. After the gravity water in the liquid inlet tank 10, soil sample, and liquid outlet tank 15 has been completely replaced by hydraulic oil, stop the quantitative delivery pump 3. Since water and hydraulic oil are immiscible, the water volume in metering cylinder 2 20 can be directly read.

[0126] Assume the volume of the liquid inlet tank 10 is V 进 , the volume of the liquid outlet tank 15 is V 出 , the volume of the experimental tube 13 is V 实 The volume of gravity water in the measuring cylinder 20 is V 水 , the water supply degree is μ. According to the definition of water supply degree, the rock and soil water supply degree under this water pressure condition can be calculated:

[0127] μ=(V 水 -V 进 -V 出 ) / V 实

[0128] The measurement process and calculation method of the permeability coefficient: Use a water-saturated soil sample according to the measurement process of the water supply degree. After the soil sample is fully saturated, close the third regulating valve 9 and the fourth regulating valve 16. Clean the water in the metering cylinder 20. Then start the quantitative delivery pump 3, open the closed third regulating valve 9 and the fifth regulating valve 21, slowly increase the overflow pressure of the first pressure regulating relief valve 6, and slowly lower the overflow pressure of the second pressure regulating relief valve 19 to form an upper and lower water head difference. The water head pressure can be read by the first pressure gauge 7 and the second pressure gauge 18. Wait until the water flow rate per unit time of the first flow sensor 8 and the second flow sensor 17 is basically equal. After the flow rate stabilizes, record the upper and lower water head pressures and flow values. The water flow value can be recorded multiple times with different head differences to calculate the average permeability coefficient of this soil sample.

[0129] Assume that the water head pressure of the first pressure regulating relief valve 6 is h, the water head pressure of the second pressure regulating relief valve 19 is h, the length of the experimental cylinder 13 is L, the water flow rate per unit time (flow sensor value) is Q, the permeability coefficient in Darcy's law is K, and the circular area of ​​the experimental cylinder 13 is A.

[0130] According to Darcy's law formula:

[0131] Q=KA(h2-h1) / L,

[0132] However, the area in this formula is not the area of ​​the gravity water channel, but the cross-sectional area between the soil sample and the gravity water, which should be optimized. According to Wang Guoyi's paper, the area of ​​the gravity water channel in the circular area of ​​the experimental cylinder 13 is μA. Let the permeability coefficient in the optimized Darcy's law be K1.

[0133] The optimized Darcy's law formula should be:

[0134] Q=K1μA(h2-h1) / L,

[0135] At this point, the permeability coefficient can be calculated (optimized Darcy's law formula permeability coefficient):

[0136] K1 = QL / (μA(h2-h1)).

[0137] Since the water content of fine-grained clay and dense soil is extremely low, it takes a long time to completely replace the gravity water in the soil sample when measuring the water content.

[0138] Whether it is water content or permeability, the water content and permeability will be different under different types of soil and different gravity water pressure (or different head pressure difference) conditions. In indoor tests, it is necessary to use original soil samples to simulate the on-site water pressure conditions to the maximum extent possible, measure and calculate the accurate water content and permeability multiple times, and provide strong support for the calculation of water-soil pressure and water seepage flow in saturated soil. In summary, based on indoor tests on original soil samples, the water content and permeability under original soil conditions can be accurately calculated, and the optimized Darcy's law formula can help accurately calculate the water seepage flow in saturated soil.

[0139] The above description is merely a diagram illustrating some principles and functions of a rock and soil static side pressure simulation device and an effective stress calculation method of the present invention, and is not intended to limit the present invention to the specific structure and applicable scope shown and described. Therefore, all corresponding modifications and equivalents that may be utilized fall within the scope of the patent applied for by the present invention.

[0140] Although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they become aware of the basic inventive concepts. Therefore, the appended claims are intended to be interpreted as covering the preferred embodiments and all changes and modifications that fall within the scope of the invention. The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A method for calculating effective stress in rock and soil, characterized by: The formula for calculating effective stress is as follows: σ′=(σ -μu w )(1-n) / (1-μ) Where: σ′—effective stress, (kPa); σ—total vertical stress on the total cross section, (kPa); u w —pore water pressure (kPa); μ – water supply degree; n – porosity.

2. A rock and soil static lateral pressure simulation device, based on the rock and soil effective stress calculation method according to claim 1, comprising a first metering cylinder, a liquid inlet box, a test cylinder, a liquid outlet box and a second metering cylinder; A liquid inlet pipeline is provided between the first metering cylinder and the liquid inlet tank. The liquid inlet pipeline includes a low-position pipe section and a high-position pipe section. A quantitative delivery pump is installed on the low-position pipe section, and a first pressure gauge and a first flow sensor are provided on the high-position pipe section. The liquid inlet pipeline is also connected to an overflow pipeline, and a first pressure regulating overflow valve is installed on the overflow pipeline. The experimental cylinder is arranged between the liquid inlet box and the liquid outlet box, an upper filter plate is arranged between the liquid inlet box and the experimental cylinder, and a lower filter plate is arranged between the experimental cylinder and the liquid outlet box; a liquid outlet pipeline is arranged between the liquid outlet box and the second metering cylinder, and a second flow sensor, a second pressure gauge and a second pressure regulating overflow valve are installed on the liquid outlet pipeline; Its characteristics are: A supporting structure is set on the top of the liquid inlet tank. The supporting structure includes a hydraulic cylinder and an axial force meter. The axial force meter is set on the top of the liquid inlet tank, and the hydraulic rod of the hydraulic cylinder is pressed against the axial force meter. Several pressure sensors are set on the side of the test cylinder.

3. The rock and soil static side pressure simulation device according to claim 2, characterized in that: A first water filter cloth is arranged below the upper filter plate, and the first water filter cloth and the upper filter plate form an upper filter assembly.

4. A rock and soil static side pressure simulation device according to claim 2 or 3, characterized in that: A second water filter cloth is arranged above the lower filter plate, and the second water filter cloth and the lower filter plate form a lower filter assembly.

5. The rock and soil static side pressure simulation device according to claim 2, characterized in that: A first fixed support frame is arranged below the first metering cylinder; a second fixed support frame is arranged below the liquid outlet box; and a third fixed support frame is arranged below the second metering cylinder.

6. The rock and soil static side pressure simulation device according to claim 2, characterized in that: A hoisting platform is provided on the second fixed support frame, and the hydraulic cylinder is fixed in an inverted manner on the hoisting platform.

7. The rock and soil static side pressure simulation device according to claim 2, characterized in that: The upper filter plate is provided with a plurality of upper water passages, and the cross-sectional area of ​​the upper water passages is not less than 40% of the cross-sectional area of ​​the upper filter plate.

8. The rock and soil static side pressure simulation device according to claim 2, characterized in that: The lower filter plate is provided with a plurality of lower water passages, and the cross-sectional area of ​​the lower water passages is not less than 40% of the cross-sectional area of ​​the lower filter plate.

9. The rock and soil static side pressure simulation device according to claim 2, characterized in that: An elastic rubber pad is provided on the stress-bearing surface of the pressure sensor, and the pressure sensor is mounted to the side of the test cylinder through bolts. After the pressure sensor is mounted, the elastic rubber pad is located between the pressure sensor and the test cylinder.

10. The rock and soil static side pressure simulation device according to claim 2, characterized in that: A first regulating valve is also provided on the low-level pipe section; a third regulating valve is installed on the high-level pipe section of the liquid inlet pipeline; the low-level pipe section of the liquid inlet pipeline is connected to the first liquid discharge pipeline, and a second regulating valve is installed on the first liquid discharge pipeline; a fourth regulating valve is also installed on the liquid discharge pipeline.

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