Field test device and method for free expansion rate and permeability coefficient of expansive soil

Abstract

The invention discloses an expansive soil free expansion rate and permeability coefficient field test device and method, relates to the technical field of expansive soil tests, and aims to solve the problems that in the prior art, expansive soil expansion potential judgment standards are not unified, and test data discreteness is large. Comprising a cutting ring assembly, a moisture content measuring assembly, a displacement measuring assembly and a water supply assembly. The cutting ring assembly is used for fixing a test soil body; the moisture content measuring assembly monitors the moisture content of the soil body in real time; the displacement measuring assembly records soil surface and deep displacement; the water supply assembly controls water injection. The test method comprises a test method and a numerical analysis method, the permeability coefficient and the free expansion rate of the soil body are calculated by injecting water and monitoring the moisture content and the displacement change of the test soil body, a moisture content curve is fitted by combining numerical analysis, the expansion coefficient and the saturated moisture content are solved, and the free expansion rate of the soil body is finally determined. The free expansion rate and the permeability coefficient of the expansive soil are rapidly and accurately measured on site, the expansion potential is judged, and a reliable basis is provided for engineering application.

Description

Technical Field

[0001] The present invention relates to the technical field of expansive soil tests, and particularly relates to a field test device and method for the free swelling ratio and permeability coefficient of expansive soil. Background Art

[0002] Expansive soil is a highly plastic clay. In its natural state, the physical and mechanical strength of expansive soil is generally high, and its compressibility is low, so it is easily mistaken for a good building foundation. The clay particles in expansive soil are mainly composed of hydrophilic minerals, and it has two significant deformation characteristics of water absorption expansion and water loss shrinkage. Moreover, it expands and shrinks repeatedly, and its strength decays rapidly after soaking in water. Due to its significant swelling and shrinkage characteristics, it often causes serious problems in engineering applications, such as road cracks, uneven settlement and cracking of buildings, slope instability, etc. In the engineering construction in expansive soil areas, the free swelling ratio and permeability coefficient of expansive soil are the basis for formulating engineering measures that are safe, applicable, technically advanced, and economically reasonable. The free swelling ratio is one of the important bases for distinguishing expansive soil from non-expansive soil, and it is also a key index for the classification of expansive soil. Different grades of expansive soil require different measures to be considered in engineering design and construction. In slope engineering, the permeability coefficient of expansive soil can analyze the infiltration speed and range of rainwater in the soil mass, and then analyze the relationship between rainfall and slope stability, providing an important basis for the stability evaluation and protection design of slopes; for foundation and foundation engineering, the permeability coefficient can evaluate the swelling and shrinkage deformation of foundation soil when the groundwater level changes.

[0003] The current national standard "Technical Code for Building in Expansive Soil Regions" proposes to obtain the montmorillonite content, cation exchange capacity, free swelling ratio, swelling ratio under different pressures, and swelling force of expansive soil through laboratory tests, and determine the bearing capacity of the expansive soil foundation and the swelling deformation amount during immersion through in-situ soaking load tests; "Geotechnical Test Methods and Standards" proposes to determine the permeability coefficient of foundation soil through laboratory tests and in-situ permeability tests. However, the following problems exist in the process of expansive soil tests: 1. The indoor geotechnical tests are affected by the non-uniformity of the foundation soil and the representativeness of the test soil samples. The test data are discrete. A sufficient number of sample numbers are required for mathematical statistics to judge the swelling potential of expansive soil, which is costly and inefficient. 2. The determination results obtained from the free swelling ratio, montmorillonite content, and cation exchange capacity in the indoor tests of expansive soil in some regions are contradictory. For example, in a certain project in Yunnan Province, judged by the standard of free swelling ratio, 70% - 80% of the foundation soil is non-expansive, with a small amount of weakly expansive, and very little medium-strongly expansive; judged by the montmorillonite content, there is almost no non-expansive, and basically all have weak, medium, and strong swelling potential. The results guided by different discrimination standards are contradictory, and there is a controversy in the discrimination standard of the swelling potential of expansive soil. 3. There are size effects and sample representativeness problems in indoor permeability tests. The sample size of indoor permeability tests is usually small, which is quite different from the soil layer thickness and range in actual projects, and cannot fully reflect the characteristics of the entire soil layer. The small-sized samples may ignore the influence of large pores, fissures, etc. existing in the soil layer on permeability, resulting in the test results not conforming to the actual situation; the disturbance of undisturbed soil samples will damage the soil structure and affect its permeability. 4. The operation process of in-situ permeability tests is relatively complex. For example, in the water injection test, factors such as the water injection speed, water volume, and time need to be controlled to ensure the accuracy and reliability of the test. At the same time, parameters such as the water level and water volume need to be monitored and recorded in real time during the test, which requires high operation skills for the test personnel. Summary of the Invention

[0004] To solve the above problems, the present invention provides an in-situ test device and method for the free swelling ratio and permeability coefficient of expansive soil.

[0005] The technical solution adopted by the present invention is as follows:

[0006] An in-situ test device for the free swelling ratio and permeability coefficient of expansive soil, the in-situ test device for the free swelling ratio and permeability coefficient of expansive soil includes a cutting ring assembly, a water content measurement assembly, a displacement measurement assembly, and a water supply assembly;

[0007] The ring knife assembly includes a large ring knife with a cylindrical structure. The bottom of the large ring knife is open and the top is closed, and its bottom is inserted into the expansive soil mass. The moisture content measurement assembly includes a probe inserted into the expansive soil mass, and a number of moisture meters are arranged at equal intervals on the probe. The moisture meters are connected to a moisture display installed on the large ring knife through internal wiring of the probe. The displacement measurement assembly includes a Bluetooth digital display micrometer for measuring the displacement data of the soil surface and a Bluetooth digital display micrometer for measuring the displacement data of the soil mass at a fixed depth of the expansive soil. A set of Bluetooth digital display micrometers are all installed on the large ring knife. The water supply assembly includes a water bucket and a load cell located at the bottom of the water bucket. A water pipe extending to the inside of the large ring knife is installed on one side of the water bucket, and a float valve is installed at the water outlet.

[0008] Further, a snap ring is installed on the large ring knife, and a protective ring is installed through the snap ring. The protective ring is an annular plate body and is located on the surface of the expansive soil. A number of through holes are arranged circumferentially on the protective ring, and screw nails inserted into the expansive soil are installed through the through holes.

[0009] A field test method for the free swelling ratio and permeability coefficient of expansive soil. This field test method for the free swelling ratio and permeability coefficient of expansive soil is based on the above-mentioned field test device for the free swelling ratio and permeability coefficient of expansive soil, and this field test method for the free swelling ratio and permeability coefficient of expansive soil can determine the free swelling ratio and permeability coefficient of expansive soil;

[0010] The steps are as follows:

[0011] Step 1, site preparation and ring knife installation: Select a dry expansive soil foundation, remove the loose soil layer on the surface and level it. Take a sample of the expansive soil and calculate the natural density of the soil mass. Vertically press the large ring knife into the soil mass, install the protective ring and screw in the screw nails to ensure that the ring knife does not float due to soil expansion.

[0012] Step 2, installation of the moisture content measurement assembly: Number the moisture meters and install them at equal intervals on the probe. Insert the probe into the center of the soil mass. The first moisture meter is located at a certain depth below the soil surface, and record the moisture content at each depth.

[0013] Step 3, installation of the displacement measurement assembly: Use a thin-wall soil sampling tube to insert into the soil mass at a certain depth at a certain position away from the probe. After vertically pulling out the soil sampling tube, measure the depth from the bottom of the hole to the soil surface. Remove the soil sample in the soil sampling tube, insert it into the soil hole and then install the first Bluetooth digital display micrometer. The probe of the first Bluetooth digital display micrometer is located at the bottom of the soil hole, and record the displacement data at a certain soil depth during the water injection process. Install the second Bluetooth digital display micrometer at a symmetric position on the other side of the probe. The probe of the second Bluetooth digital display micrometer is located on the soil surface, and record the displacement data of the soil surface.

[0014] Step 4, measurement data: Turn on the moisture meter and the displacement measurement assembly and record the data.

[0015] Step 5, Water injection and data recording: Adjust the height of the float valve from the soil surface, inject water into the large ring cutter through the water supply component, control the water surface to be at a certain height above the soil surface through the ball valve, measure the water depth above the soil surface, and record the water injection mass at different times.

[0016] When the water contents measured by the first water content meter to the third water content meter are the same, record the mass of the water bucket and the time; when the water contents measured by the first water content meter to the fourth water content meter are the same, record the mass of the water bucket, the time and the water depth data in the thin-wall soil sampler, and calculate the permeability coefficient accordingly.

[0017] When the water contents measured by the first water content meter to the fourth water content meter are the same, it is considered that the swelling deformation of the soil body from the soil surface to the bottom of the thin-wall soil sampler is stable, and calculate the free swelling ratio.

[0018] Step 6, Test termination: After the data collection and analysis are completed, stop the test and dismantle the device.

[0019] Furthermore, in Step 5, the calculation formula for the permeability coefficient is:

[0020]

[0021] In the formula, k is the permeability coefficient of the soil body; m 1 is the mass of the water bucket recorded when the water contents measured by the first water content meter to the third water content meter are the same; m 2 is the mass of the water bucket recorded when the water contents measured by the first water content meter to the fourth water content meter are the same; ρ w is the density of water; t 1 is the time recorded when the water contents measured by the first water content meter to the third water content meter are the same; t 2 is the time recorded when the water contents measured by the first water content meter to the fourth water content meter are the same; h 0 is the depth from the bottom of the hole measured through the thin-wall soil sampler to the soil surface; A is the inner area of the large ring cutter; h w0 is the water depth above the soil surface; h w is the water depth data in the thin-wall soil sampler recorded when the water contents measured by the first water content meter to the fourth water content meter are the same.

[0022] Furthermore, in Step 5, the calculation formula for the free swelling ratio is:

[0023]

[0024] In the formula, δ ef is the free swelling ratio, h 1 is the displacement data during the water injection process recorded by the first Bluetooth digital display micrometer; h 2 is the soil surface displacement data recorded by the second Bluetooth digital display micrometer.

[0025] Further, the in-situ test method for the free swelling ratio and permeability coefficient of expansive soil calculates the free swelling ratio of expansive soil (numerical analysis method) by recording the water content of soil at different depths, the surface displacement of the soil, and the water injection volume;

[0026] The steps are as follows:

[0027] Step 1, Site preparation and installation of the core cutter: Select a dry expansive soil foundation, remove the loose soil layer on the surface and level it; Take samples of the expansive soil and calculate the natural density of the soil; Vertically press the large core cutter into the soil, install the protective ring and screw in the screw to ensure that the core cutter does not float due to soil expansion;

[0028] Step 2, Installation of the water content measurement component: Number the water meters and install them at equal intervals on the probe. Insert the probe into the center of the soil. The first water meter is located at a certain depth below the soil surface, and record the water content at each depth;

[0029] Step 3, Installation of the displacement measurement component, install a Bluetooth digital display micrometer. The probe of the Bluetooth digital display micrometer is located on the soil surface, and record the soil surface displacement data;

[0030] Step 4, Measuring data: Turn on the water meter and the displacement measurement component, and record the data; At time t 0 , record the initial water content of the soil at different depths, and fit the quintic function of water content and different depths; Solve the quintic function according to the depth of each water meter and the measured initial water content to obtain the relationship curve between the initial water content and the depth;

[0031] Step 5, Water injection and data recording: Uniformly inject water into the core cutter, keep the water surface at a certain height above the soil surface, stop injecting water after injecting a certain mass of water. The amount of water injection should ensure that the water does not seep down to the lowest water meter, that is, the measured water content of the soil at the lowest water meter does not change; At this time, record the water injection mass and the water content of the soil at different depths;

[0032] When the expansion deformation of the test soil is completed, that is, the reading of the digital display dial gauge remains unchanged, record the expansion deformation amount and the water content of the soil at different depths, and fit the quintic function of water content and depth at time t 1 ; Solve the quintic function according to the depth of each water meter and the measured water content at time t 1 to obtain the relationship curve between water content and depth at time t 1 ;

[0033] Verify the water content curve at time t fitted by the water injection mass and the increase in water content of the test soil; If the verification is successful, proceed to the next step, otherwise refit the quintic function of water content and depth at time t 1 ; 1 Solve for t

[0034] Solve for t 1Coefficient of time dilation; Repeatedly fit the univariate fifth-degree function of water content and depth at other times, solve the dilation coefficients at different times, and calculate the average dilation coefficient;

[0035] When the water contents measured by the first water content meter and the second water content meter at different times during the water injection process do not change, it is considered that the soil body reaches saturation. Take the average value as the saturated water content of the soil body and calculate the free swelling rate of the soil body;

[0036] Step six, test termination: After the data collection and analysis are completed, stop the test and remove the device.

[0037] Furthermore, in step four, at time t 0 , record the initial water content ω(h) of the soil body at different depths t0 , and fit the univariate fifth-degree function of water content ω and depth h:

[0038] ω(h)t 0 =ah 5 +bh 4 +ch 3 +dh 2 +eh+f

[0039] In the formula, a, b, c, d, e, and f are the coefficients of the fitted univariate fifth-degree polynomial function, which are used to describe the variation relationship of water content ω(h)t 0 with depth h; f is the constant term, indicating the initial water content at time t 0 when h = 0, that is, at the soil surface;

[0040] Solve the coefficients a, b, c, d, e, and f according to the depths of each water content meter and the measured initial water content:

[0041] a, b, c, d, e, f, and obtain the relationship curve between the initial water content ω(h)t 0 and depth h;

[0042] In step five, when the swelling deformation of the test soil body is completed, that is, the reading of the digital display dial gauge remains unchanged, record the swelling deformation amount s(t 1 ) and the water content ω(h)t 1 , and fit the univariate fifth-degree function of water content and depth at time t 1 :

[0043] ω(h)t 1 =a 1 h 5 +b 1 h 4 +c 1 h 3 +d 1 h 2 +e 1 h+f 1 Equation 5

[0044] According to the depth of each water content meter and the measured water content at time t 1 to solve the coefficients: a 1 , b 1 , c 1 , d 1 , e 1 , f 1 , and obtain the relationship curve between the water content ω(h)t 1 at time t 1 and the depth h;

[0045] Verify the water content curve of the fitted t 1 at time t through the injection water mass and the increase in the water content of the test soil mass:

[0046]

[0047] In the formula, m(t 1 ) represents the total mass of water injected into the test soil mass at time t 1 ; represents the definite integral from the depth h = 0 to the depth h = h n ; ρ d represents the dry density of the soil mass; A is the inner area of the large ring cutter; dh represents the infinitesimal of the depth h;

[0048] If equation 6 holds, then proceed to the next step; otherwise, refit equation 5;

[0049] Solve the swelling coefficient at time t 1 from equation 7

[0050]

[0051] In the formula, s(t 1 ) represents the total swelling deformation of the test soil mass at time t 1 ;

[0052] Solve the swelling coefficients at different times t n ; Solve the average swelling coefficient λ p from equation 8:

[0053]

[0054] In the formula, represents the swelling coefficients of the soil mass measured at different times t 1 , t 2 ,... t n ; n represents the number of tests or the total number of measurement times.

[0055] Further, in step five, when the water contents ω 1 and ω 2 measured by the first water content meter and the second water content meter at different times do not change, it is considered that the soil mass reaches saturation, and the average value is taken as the saturated water content ω sat of the soil mass. The free swelling ratio of the soil mass is calculated by the following formula;

[0056] δ ef =λ p ·ω sat Formula 9

[0057] In the formula, δ ef represents the free swelling ratio of the soil mass; λ p represents the swelling coefficient of the soil mass; ω sat represents the saturated water content of the soil mass.

[0058] The beneficial effects of the present invention are as follows:

[0059] 1. Improve the test accuracy and reliability:

[0060] By directly measuring the free swelling ratio and permeability coefficient of expansive soil through the on-site test device, the problems of insufficient representativeness of soil samples and data dispersion in laboratory tests are avoided, and the accuracy and reliability of test results are significantly improved.

[0061] 2. Unify the discrimination criteria:

[0062] By using on-site test data combined with numerical analysis methods, the free swelling ratio of expansive soil can be more accurately discriminated, and the problem of inconsistent discrimination results of different indicators in national standards and local standards is solved, providing a unified discrimination basis for engineering applications.

[0063] 3. Reduce the test cost and improve the efficiency:

[0064] The on-site test device and method reduce the demand for a large number of laboratory test samples, reduce the test cost, and at the same time, through real-time monitoring and data collection, the test efficiency is significantly improved.

[0065] 4. Comprehensively measure multiple parameters:

[0066] The device integrates a water content measurement system, a displacement measurement system and a water supply system, and can simultaneously measure the water content, displacement change, permeability coefficient and swelling coefficient of the soil mass, providing comprehensive data support for engineering design and construction.

[0067] 5. Strong adaptability:

[0068] The device is flexibly designed and applicable to expansive soil tests under different geological conditions, and can effectively cope with the test problems brought by the non-uniformity of foundation soil.

[0069] 6. Real-time data monitoring and recording:

[0070] The test data is monitored and recorded in real time through a micro moisture meter and a digital display dial indicator, ensuring the continuity and accuracy of the data and providing a reliable basis for subsequent analysis.

[0071] 7. Application of numerical analysis method:

[0072] Combined with the numerical analysis method, by fitting the moisture content curve and calculating the swelling coefficient, the swelling characteristics of expansive soil can be evaluated more scientifically, providing a scientific basis for engineering decision-making.

[0073] In summary, the in-situ test device and test method for the free swelling ratio and permeability coefficient of expansive soil provided by the present invention have significant advantages such as high precision, low cost, high efficiency, and strong adaptability, providing reliable technical support for engineering construction in expansive soil areas. Description of the drawings

[0074] Figure 1 It is a schematic diagram of the overall structure of the in-situ test device for the free swelling ratio and permeability coefficient of expansive soil of the present invention;

[0075] In the figure, 1 - large ring cutter, 2 - retaining ring, 3 - protecting ring, 4 - screw, 5 - first Bluetooth digital display micrometer, 6 - second Bluetooth digital display micrometer, 7 - moisture display, 8 - probe, 9 - moisture meter, 10 - load cell, 11 - water bucket, 12 - ball valve. Detailed implementation manners

[0076] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings of the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0077] For ease of explanation, spatial relative terms such as "upper", "lower", "left", "right", etc. can be used here to describe the relationship between one element or feature shown in the figure and another element or feature. It should be understood that in addition to the orientation shown in the figure, the spatial terms are intended to include different orientations during the use or operation of the device. For example, if the device in the figure is inverted, the element described as being "below" other elements or features will be located "above" other elements or features. Therefore, the exemplary term "lower" can include both the upper and lower orientations. The device can be positioned in other ways, and the spatial relative descriptions used here can be interpreted accordingly.

[0078] Embodiment 1

[0079] In view of the problems existing in the process of swelling soil tests, this embodiment proposes an in-situ test device for the free swelling ratio and permeability coefficient of swelling soil. As Figure 1 shown, the in-situ test device for the free swelling ratio and permeability coefficient of swelling soil includes a cutting ring assembly, a water content measurement assembly, a displacement measurement assembly, and a water supply assembly.

[0080] Among them, the cutting ring assembly includes a large cutting ring 1 with a cylindrical structure. The large cutting ring 1 has a diameter of 10 cm and a height of 30 cm. The bottom of the large cutting ring 1 is open and the top is closed. Its bottom is inserted into the swelling soil mass. The large cutting ring 1 serves as the main container for the test soil mass and is vertically pressed into the soil mass to fix the test soil mass and prevent lateral deformation when the soil mass swells. Further, in order to ensure the stability of the large cutting ring 1 inserted into the swelling soil mass, as Figure 1 shown, in this embodiment, a snap ring 2 is installed 5 cm below the top plate of the outer wall of the cutting ring. The snap ring 2 is 2 cm wide and is provided with a slot on it, and a protective ring 3 is installed through the slot. The protective ring 3 is an annular plate body with an inner diameter of 10.5 cm and an outer diameter of 20 cm. Four through holes are arranged on the circumference of the protective ring 3, and screw nails 4 inserted into the swelling soil are installed through the through holes and fixed in the soil mass through the screw nails 4 to prevent the cutting ring from floating up due to the vertical swelling of the soil mass and ensure the stability of the cutting ring during the test process.

[0081] As Figure 1 shown, the water content measurement assembly in this embodiment includes a probe 8 inserted into the swelling soil mass. The probe 8 is 30 cm to 35 cm long. Moisture meters 9 are arranged at equal intervals of 5 cm on the probe 8, and a total of 6 moisture meters 9 are installed. The moisture meters 9 are connected to a moisture display 7 installed on the large cutting ring 1 through the internal wiring of the probe 8. The probe 8 is inserted into the center of the soil mass to fix the micro moisture meters 9 and ensure their accurate positioning at different depths. The moisture meters 9 monitor and store in real time the changes in the water content of the soil mass at different depths during the test process and provide the water distribution data during the water absorption and swelling process of the soil mass.

[0082] As Figure 1 shown, the displacement measurement assembly in this embodiment includes a Bluetooth digital display micrometer for measuring the displacement data on the surface of the test soil mass and a Bluetooth digital display micrometer for measuring the displacement data of the soil mass at a fixed depth of the swelling soil. A set of Bluetooth digital display micrometers are all installed on the large cutting ring 1. The probe of the first Bluetooth digital display micrometer 5 is located at the bottom of the soil hole and is used to record the displacement data at a certain soil depth during the water injection process, reflecting the swelling deformation situation inside the soil mass. The probe of the second Bluetooth digital display micrometer 6 is located on the surface of the soil mass and is used to record the displacement data on the surface of the soil mass, reflecting the swelling deformation situation on the surface of the soil mass. By recording the displacement changes on the surface and inside of the soil mass, the free swelling ratio and swelling deformation amount of the soil mass can be calculated.

[0083] As Figure 1As shown in the figure, the water supply component in this embodiment includes a water bucket 11 and a weighing sensor 10 located at the bottom of the water bucket 11. A water pipe extending into the large ring cutter 1 is installed on one side of the water bucket 11. A float valve 12 with adjustable height is installed at the water outlet of the water pipe. The water bucket 11 is used to uniformly inject water into the ring cutter to simulate the process of soil water absorption and expansion. The float valve 12 is used to control the water surface height in the large ring cutter. The weighing sensor 10 records the water injection mass in real time to ensure the accurate control of the water injection volume and provide data support for calculating the permeability coefficient.

[0084] The in-situ test device for the free swelling ratio and permeability coefficient of expansive soil fixes the test soil body through the ring cutter assembly to ensure the stability of the soil body and the accuracy of the test data during the test. The moisture content measuring component monitors the change of the soil moisture content in real time to provide key data for analyzing the soil water absorption and expansion process. The displacement measuring component records the displacement changes on the surface and inside of the soil body to calculate the swelling deformation amount and free swelling ratio of the soil body. The water supply component accurately controls the water surface height and water injection volume in the large ring cutter to simulate the soil water absorption and expansion process and provide basic data for calculating the permeability coefficient and swelling coefficient. Each component works together to achieve the accurate determination of the free swelling ratio and permeability coefficient of expansive soil and provides reliable technical support for engineering applications.

[0085] It should be noted that the Bluetooth digital display micrometer, moisture display, moisture meter, weighing sensor, and ball valve in this embodiment are commercially available finished equipment.

[0086] Embodiment 2

[0087] Based on the in-situ test device for the free swelling ratio and permeability coefficient of expansive soil provided in Embodiment 1, this embodiment also proposes an in-situ test method for the free swelling ratio and permeability coefficient of expansive soil, that is: the test method; this in-situ test method for the free swelling ratio and permeability coefficient of expansive soil can determine the free swelling ratio and permeability coefficient of expansive soil.

[0088] The specific steps are as follows:

[0089] Step 1, Site preparation and ring cutter installation:

[0090] Select the foundation soil body on the expansive soil site that is not affected by the groundwater level. The soil is dry and is approximately considered to be in the air-dried state. Remove the loose soil on the surface and level the test range. Take samples of the expansive soil and calculate the natural density ρ of the soil 0 ; Apply a thin layer of lubricating oil to the inner and outer walls of the large ring cutter, vertically press it into the soil by 25 cm, place the retaining ring, and screw the screw into the soil from the round hole of the retaining ring. The retaining ring is closely attached to the soil outside the ring cutter to ensure that the ring cutter does not float due to the vertical expansion of the soil.

[0091] Step 2, Installation of the moisture content measuring component:

[0092] Six moisture meters are numbered and installed on the probe at equal intervals. The probe is inserted into the center of the test soil body at a uniform speed. The first moisture meter is located 0.5 cm to 1 cm below the soil surface, and the water content ω at different depths is recorded. 1 ~ω 6 。

[0093] Step 3, Installation of displacement measurement components:

[0094] A thin-walled soil sampling tube with a diameter of 1 cm and a length of about 15 cm is inserted 10 cm into the soil body 3 cm away from the probe. After the soil sampling tube is vertically pulled out, the depth h from the bottom of the hole to the soil surface is measured with a vernier caliper. 0 ; Remove the soil sample in the soil sampling tube, insert it into the soil hole, and then install the first Bluetooth digital display micrometer. The probe of the first Bluetooth digital display micrometer is located at the bottom of the soil hole, and the displacement data h at a certain soil depth h during the water injection process is recorded. 0 ; Install the second Bluetooth digital display micrometer at a symmetric position on the other side of the probe. The probe of the second Bluetooth digital display micrometer is located on the soil surface, and the displacement data h of the soil surface is recorded. 1 。 2 。

[0095] Step 4, Measurement data:

[0096] Turn on the moisture meter and the displacement measurement components, and record the data.

[0097] Step 5, Water injection and data recording:

[0098] Uniformly inject water into the large ring cutter through the water supply component, and adjust the height of the float valve to keep the water surface at a certain height h above the soil surface. w0 , and record the water injection mass at different times;

[0099] When the water contents measured by the first moisture meter to the third moisture meter are the same, that is, ω 1 =ω 2 =ω 3 , record the mass m of the water bucket 1 and the time t 1 ;

[0100] When the water contents measured by the first moisture meter to the fourth moisture meter are the same, that is, ω 1 =ω 2 =ω 3 =ω 4 , record the mass m of the water bucket 2 , the time t 2 and the water depth data h in the thin-walled soil sampling tube. w , and the permeability coefficient k of the soil body from the soil surface to the third moisture meter section can be calculated;

[0101] The calculation formula for the permeability coefficient is:

[0102]

[0103] In the formula, k is the permeability coefficient of the soil mass; m 1 is the mass of the water bucket recorded when the water contents measured by the first water content meter to the third water content meter are the same; m 2 is the mass of the water bucket recorded when the water contents measured by the first water content meter to the fourth water content meter are the same; ρ w is the density of water; t 1 is the time recorded when the water contents measured by the first water content meter to the third water content meter are the same; t 2 is the time recorded when the water contents measured by the first water content meter to the fourth water content meter are the same; h 0 is the depth from the bottom of the hole measured by the thin-wall soil sampler to the soil surface; A is the inner area of the large ring cutter; h w0 is the depth from the water surface in the large ring cutter to the soil surface; h w is the water depth data in the thin-wall soil sampler measured when the water contents measured by the first water content meter to the fourth water content meter are the same.

[0104] When the water contents measured by the first water content meter to the fourth water content meter are the same, that is, ω 1 = ω 2 = ω 3 = ω 4 = ω 0 , it can be considered that the soil mass expansion deformation within the range from the soil surface to the depth h ef is stable, and the free swelling ratio δ

[0105] of the soil mass can be calculated according to the displacement data of the digital display dial gauge;

[0106]

[0107] In the formula, δ ef is the free swelling ratio, h 1 is the displacement data during the water injection process recorded by the first Bluetooth digital display micrometer; h 2 is the soil surface displacement data recorded by the second Bluetooth digital display micrometer.

[0108] Step Six, test termination: After the data collection and analysis are completed, stop the test and remove the device.

[0109] Furthermore, the in-situ test method for the free swelling ratio and permeability coefficient of expansive soil can calculate the free swelling ratio of expansive soil through numerical analysis, that is, the numerical analysis method;

[0110] The steps are as follows:

[0111] Step One, site preparation and installation of the ring cutter:

[0112] Select the foundation soil mass that is not affected by the groundwater level on the expansive soil site. The soil mass is dry and is approximately considered to be in the air-dried state. Remove the loose soil mass on the surface and level the test range; take samples of the expansive soil and calculate the natural density ρ of the soil mass. 0 Apply a thin layer of lubricating oil to the inner and outer walls of the large ring cutter, vertically press it into the soil mass by 25 cm, place the retaining ring, and screw the screw into the soil mass from the round hole of the retaining ring. Ensure that the retaining ring is in close contact with the soil mass outside the ring cutter to prevent the ring cutter from floating up due to the vertical expansion of the soil mass.

[0113] Step 2: Installation of the moisture content measurement component:

[0114] Number the six moisture meters and install them at equal intervals on the probe. Insert the probe into the center of the test soil mass at a constant speed. The first moisture meter is located 0.5 cm to 1 cm below the soil surface, and record the moisture content ω 1 ~ω 6 .

[0115] Step 3: Installation of the displacement measurement component:

[0116] Install a Bluetooth digital display micrometer. The probe of the Bluetooth digital display micrometer is located on the soil surface, and record the displacement data h(t) of the soil surface.

[0117] Step 4: Measurement data:

[0118] Turn on the moisture meter and the displacement measurement component, and record the data;

[0119] t 0 At the moment, record the initial moisture content ω(h) t0 of the soil mass at different depths, and fit the quintic function of the moisture content ω and the depth h;

[0120] ω(h)t 0 =ah 5 +bh 4 +ch 3 +dh 2 +eh + f Equation 4

[0121] In the formula, a, b, c, d, e, and f are the coefficients of the fitted quintic polynomial function, which are used to describe the variation relationship of the moisture content ω(h)t 0 with the depth h; the constant term f represents the initial moisture content when h = 0, that is, at the soil surface;

[0122] Solve the coefficients:

[0123] a, b, c, d, e, and f according to the depths of each moisture meter and the measured initial moisture content, and obtain the relationship curve between the initial moisture content ω(h)t 0 and the depth h.

[0124] Step 5: Water injection and data recording:

[0125] Uniformly pour water into the ring knife, keeping the water surface 1 mm to 3 mm above the soil surface. Stop pouring water after injecting a certain mass of water. The amount of water injected should ensure that the water does not seep down to the sixth moisture meter, that is, the measured water content of the soil at the sixth moisture meter does not change. At this time, record the mass of the injected water \(m_t\). 1 and the maximum water content of the moisture meters at different depths;

[0126] When the swelling deformation of the test soil is completed, that is, the reading of the digital display dial gauge remains unchanged, record the swelling deformation amount \(s(t)\) 1 and the water content \(\omega(h)_t\). 1 , fit the quintic function of the water content \(\omega\) and the depth \(h\) at time \(t\); 1 \(\omega(h)_t\)

[0127] \(= a\) 1 \(h^5\) 1 \(+ b\) 5 \(h^4\) 1 \(+ c\) 4 \(h^3\) 1 \(+ d\) 3 \(h^2\) 1 \(+ e\) 2 \(h + f\) 1 Equation 5 1 Equation 5

[0128] Solve for the coefficients according to the depths and measured water contents of each moisture meter at time \(t\): 1 \(a\),

[0129] \(a\), 1 \(b\), 1 \(c\), 1 \(d\), 1 \(e\), 1 \(f\), 1 , and obtain the relationship curve between the water content \(\omega(h)_t\) 1 at time \(t\) and the depth \(h\). 1 Check the fitted water content curve at time \(t\) by the mass of the injected water and the increase in the water content of the test soil;

[0130] In the formula, \(m(t)\) 1 represents the total mass of the water injected into the test soil at time \(t\);

[0131]

[0132] 1 1 represents the definite integral from the depth \(h = 0\) to the depth \(h = h\); \(\rho\) n d represents the dry density of the soil; \(A\) is the area inside the large ring knife; \(dh\) represents the differential of the depth \(h\); n d d represents the dry density of the soil; \(A\) is the area inside the large ring knife; \(dh\) represents the differential of the depth \(h\);

[0133] If Equation 6 holds, proceed to the next step; otherwise, refit Equation 5.

[0134] Solve for t from Equation 7 1 Time dilation coefficient

[0135]

[0136] where s(t 1 ) represents the total swelling deformation of the test soil mass at time t 1 ;

[0137] Repeat fitting the unary fifth-order function of water content and depth at other times, and solve for the swelling coefficient at different times t n ; Solve for the average swelling coefficient λ from Equation 8 p :

[0138]

[0139] where represents the swelling coefficient of the soil mass measured at different times t 1 , t 2 ,... t n ; n represents the number of tests or the total number of measurement times.

[0140] When the water contents ω 1 and ω 2 measured by the first and second water content gauges at different times do not change, it is considered that the soil mass has reached saturation, and the average value is taken as the saturated water content ω sat of the soil mass. Calculate the free swelling ratio of the soil mass through the following formula;

[0141] δ ef = λ p · ω sat Equation 3

[0142] where δ ef represents the free swelling ratio of the soil mass; λ p represents the swelling coefficient of the soil mass; ω sat represents the saturated water content of the soil mass.

[0143] Step Six, Test Termination: After data collection and analysis are completed, stop the test and remove the device.

[0144] It should be noted that according to the national standard "Technical Code for Building in Expansive Soil Regions", the shrinkage coefficient λ s of expansive soil is the ratio of the difference Δδ s in the vertical linear shrinkage rate during the linear change stage of the water loss shrinkage process to the corresponding difference Δω in water content; similarly, assume that the swelling coefficient λ pIt is the difference in the vertical linear expansion rate Δδ p The ratio to the corresponding difference in water content Δω, and the free expansion rate is the expansion coefficient λ p Multiplied by the saturated water content ω sat That is, Equation 3.

[0145] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A field test device for free expansion rate and permeability coefficient of expansive soil, characterized by: The expansive soil free expansion rate and permeability coefficient field test device comprises a ring cutter assembly, a moisture content measurement assembly, a displacement measurement assembly, and a water supply assembly; The ring cutter assembly comprises a large ring cutter in a cylindrical structure, the bottom of the large ring cutter is open and the top is closed, and the bottom of the large ring cutter is inserted into the expansive soil body; The moisture content measurement assembly comprises a probe inserted into the expansive soil body, a plurality of moisture meters are arranged at equal intervals on the probe, and the moisture meters are connected to the moisture display installed on the large ring knife through the internal wiring of the probe; The displacement measurement assembly includes a Bluetooth digital display micrometer for measuring soil surface displacement data and a Bluetooth digital display micrometer for measuring soil displacement data at a fixed depth of expansive soil, and a set of Bluetooth digital display micrometers are installed on the large ring cutter; The water supply assembly comprises a water bucket and a weighing sensor located at the bottom of the water bucket; a water pipe extending to the inside of the large ring knife is installed on one side of the water bucket, and a float valve is installed at the water outlet.

2. The on-site testing device for free expansion rate and permeability coefficient of expansive soil according to claim 1, characterized in that: The large ring cutter is provided with a clamping ring, through which a guard ring is provided. The guard ring is an annular plate body and is located on the surface of the expansive soil. A plurality of through holes are arranged on the circumference of the guard ring, through which spiral nails inserted into the expansive soil are provided.

3. A method for testing the free expansion rate and permeability coefficient of expansive soil (test method), the method for testing the free expansion rate and permeability coefficient of expansive soil is based on the device for testing the free expansion rate and permeability coefficient of expansive soil according to any one of claims 1 to 2, characterized in that: The free expansion rate and permeability coefficient field test method of expansive soil can determine the free expansion rate and permeability coefficient of expansive soil; Here are the steps: Step 1: Site preparation and ring cutter installation: Select a dry expansive soil foundation, remove the loose soil on the surface and level it; sample the expansive soil and calculate the natural density of the soil; press the large ring cutter vertically into the soil, install the guard ring and screw in the screw to ensure that the ring cutter does not float up due to soil expansion; Step 2: Install the moisture content measurement component: number the moisture meters and install them on the probes at equal intervals. Insert the probe into the center of the soil. The first moisture meter is located at a certain depth below the soil surface. Record the moisture content at each depth. Step three, installation of displacement measurement components: insert a thin-walled soil sampling tube into the soil at a certain distance from the probe to a certain depth, pull out the soil sampling tube vertically and measure the depth from the bottom of the hole to the surface of the soil; remove the soil sample in the soil sampling tube, insert it into the soil hole and install the first Bluetooth digital display dial gauge, the first Bluetooth digital display dial gauge probe is located at the bottom of the soil hole, and records the displacement data at a certain soil depth during the water injection process; install the second Bluetooth digital display dial gauge at a symmetrical position on the other side of the probe, the second Bluetooth digital display dial gauge probe is located on the soil surface, and records the displacement data on the soil surface; Step 4: Measure data: Turn on the moisture meter and displacement measurement components and record the data; Step 5: Water injection and data recording: adjust the height of the float valve from the soil surface, inject water evenly into the large ring knife through the water supply component, control the water surface to a certain height above the soil surface through the ball valve, measure the water depth above the soil surface, and record the water injection quality at different times; When the moisture content measured by the first moisture meter to the third moisture meter is the same, record the mass of the bucket and the time; when the moisture content measured by the first moisture meter to the fourth moisture meter is the same, record the mass of the bucket, the time and the water depth data in the thin-walled soil sampling pipe to calculate the permeability coefficient; When the moisture contents measured by the first to fourth moisture meters are the same, it is considered that the expansion and deformation of the soil from the soil surface to the bottom of the thin-walled soil sampling pipe is stable, and the free expansion rate is calculated; Step 6, test termination: After data collection and analysis are completed, stop the test and dismantle the device.

4. The method for testing the free expansion rate and permeability coefficient of expansive soil according to claim 3, characterized in that: In step 5, the calculation formula of the permeability coefficient is: Where k is the soil permeability coefficient; m1 is the mass of the bucket recorded when the moisture content measured by the first moisture meter to the third moisture meter is the same; m2 is the mass of the bucket recorded when the moisture content measured by the first moisture meter to the fourth moisture meter is the same; ρ w is the density of water; t1 is the time recorded when the moisture content measured by the first moisture meter to the third moisture meter is the same; t2 is the time recorded when the moisture content measured by the first moisture meter to the fourth moisture meter is the same; h0 is the depth from the bottom of the hole to the soil surface measured by the thin-walled soil sampling tube; A is the inner area of ​​the large ring cutter; h w0 h is the water depth above the soil surface; w The water depth data in the thin-walled soil sampling pipe is recorded when the moisture contents measured by the first to fourth moisture meters are the same.

5. The method for testing the free expansion rate and permeability coefficient of expansive soil according to claim 3, characterized in that: In step 5, the free expansion rate is calculated as: In the formula, δ ef is the free expansion rate, h1 is the displacement data during the water injection process recorded by the first Bluetooth digital display micrometer; h2 is the soil surface displacement data recorded by the second Bluetooth digital display micrometer.

6. The method for testing the free expansion rate of expansive soil according to claim 3, characterized in that: The free expansion rate field test method of expansive soil can quickly determine the free expansion rate of expansive soil and determine the expansion potential; Here are the steps: Step 1: Site preparation and ring cutter installation: Select a dry expansive soil foundation, remove the loose soil on the surface and level it; sample the expansive soil and calculate the natural density of the soil; press the large ring cutter vertically into the soil, install the retaining ring and screw in the screw to ensure that the ring cutter does not float up due to soil expansion; Step 2: Install the moisture content measurement component: number the moisture meters and install them on the probes at equal intervals. Insert the probe into the center of the soil. The first moisture meter is located at a certain depth below the soil surface. Record the moisture content at each depth. Step 3: Installation of displacement measurement components: Install a Bluetooth digital display micrometer, with the Bluetooth digital display micrometer probe located on the soil surface to record the displacement data of the soil surface; Step 4, measuring data: turn on the moisture meter and displacement measurement component, and record the data; at time t0, record the initial moisture content of the soil at different depths, and fit the one-variable quintic function of moisture content and different depths; solve the one-variable quintic function according to the depth of each moisture meter and the measured initial moisture content, and obtain the relationship curve between the initial moisture content and the depth; Step 5: Water injection and data recording: water is injected evenly into the cutter ring, and the water surface is kept at a certain height above the soil surface. After a certain mass of water is injected, water injection is stopped. The amount of water injected must ensure that the water does not infiltrate to the moisture meter at the bottom, that is, the measured soil moisture content at the moisture meter at the bottom does not change. At this time, record the water injection mass and the soil moisture content at different depths. When the expansion and deformation of the test soil is completed, that is, the reading of the digital display dial gauge remains unchanged, the expansion and deformation amount and the soil moisture content at different depths are recorded, and a one-dimensional quintic function of moisture content and depth at time t1 is fitted; the one-dimensional quintic function is solved according to the depth of each moisture meter at time t1 and the measured moisture content, and the relationship curve between moisture content and depth at time t1 is obtained; The fitted moisture content curve at time t1 is checked by the water injection quality and the increase in moisture content of the test soil; if the check is successful, proceed to the next step, otherwise, the one-variable quintic function of moisture content and depth at time t1 is refitted; Solve the expansion coefficient at time t1; repeat fitting the quintic function of water content and depth at other times, and solve the expansion coefficient at different times, and calculate the average expansion coefficient; When the moisture content measured by the first moisture meter and the second moisture meter at different times during the water injection process does not change, the soil is considered to be saturated, and the average value is taken as the saturated moisture content of the soil, and the free expansion rate of the soil is calculated; Step 6, test termination: After data collection and analysis are completed, stop the test and dismantle the device.

7. The field test method for free expansion coefficient of expansive soil according to claim 6, characterized in that: In step 4, at time t0, record the initial soil moisture content ω(h) at different depths. t0 , fitting the quintic function of water content ω and depth h: ω(h)t0 = ah 5 + bh 4 + ch 3 + dh 2 + eh + f Equation 4 In the formula, a, b, c, d, e, and f are the coefficients of the fitted univariate quintic polynomial function, which are used to describe the relationship between the moisture content ω(h)t0 and the depth h; f is a constant term, which represents the initial moisture content at time t0 when h = 0, i.e., the soil surface; According to the depth of each moisture meter and the measured initial moisture content, the coefficients a, b, c, d, e, and f are solved to obtain the relationship curve between the initial moisture content ω(h)t0 and the depth h; In step 5, when the expansion and deformation of the test soil is completed, that is, the reading of the digital dial indicator remains unchanged, the expansion deformation s(t1) and the moisture content ω(h)t1 are recorded, and the univariate quintic function of moisture content and depth at time t1 is fitted: ω(h)t1 = a1h 5 + b1h 4 + c1h 3 + d1h 2 + e1h + f1 Equation 5 The coefficient is solved according to the depth of each moisture meter at time t1 and the measured moisture content: a1, b1, c1, d1, e1, f1, and the relationship curve between the water content ω(h)t1 and the depth h at time t1 are obtained; The moisture content curve at time t1 is fitted by checking the injection quality and the increase in moisture content of the test soil: In the formula, m(t1) represents the total mass of water injected into the test soil at time t1; Denotes the distance from depth h = 0 to depth h = h n The definite integral of d represents the dry density of the soil; A is the area inside the large ring cutter; dh represents the microelement of the depth h; If equation 6 holds true, proceed to the next step, otherwise refit equation 5; The expansion coefficient λ at time t1 is solved by equation 7 p1 : In the formula, s(t1) represents the total expansion deformation of the test soil at time t1; Solve for different times t n The expansion coefficient λ pn , the average expansion coefficient λ is solved by formula 8 p : In the formula, λ p1 ,λ p2 , …, λ pn Indicates at different times t1, t2, ..., t n The measured soil expansion coefficient; n represents the total number of tests or measurement moments.

8. The method for testing the free expansion rate and permeability coefficient of expansive soil according to claim 6, characterized in that: In step 5, when the moisture contents ω1 and ω2 measured by the first moisture meter and the second moisture meter at different times do not change, the soil is considered to be saturated, and the average value is taken as the saturated moisture content ω of the soil. sat , the free expansion rate of soil is calculated by the following formula; d ef =λ p ·oh sat formula 9 In the formula, δ ef Represents the free expansion rate of soil; p Represents the expansion coefficient of soil; ω sat It represents the saturated moisture content of soil.

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