A device and method for testing the free expansion rate and permeability coefficient of an expansive soil in situ

Abstract

The application discloses an expansive soil free expansion rate and permeability coefficient field test device and method, relates to the technical field of expansive soil test, and aims to solve the problems of non-uniform expansive soil expansion potential discrimination standards and large test data discreteness in the prior art. The device comprises a ring cutter assembly, a water content measuring assembly, a displacement measuring assembly and a water supply assembly. The ring cutter assembly is used for fixing a test soil body; the water content measuring assembly is used for monitoring the water content of the soil body in real time; the displacement measuring assembly is used for recording the surface and deep displacement of the soil body; and the water supply assembly is used for controlling water injection. The test method comprises a test method and a numerical analysis method. The water content and displacement changes of the test soil body are monitored through water injection, the permeability coefficient and the free expansion rate of the soil body are calculated, the water content curve is fitted in combination with numerical analysis, the expansion coefficient and the saturated water content are solved, and finally, the free expansion rate of the soil body is determined, so that the free expansion rate and the permeability coefficient of the expansive soil are rapidly and accurately determined on site, the expansion potential is determined, and a reliable basis is provided for engineering application.

Description

Technical Field

[0001] This invention relates to the field of expansive soil testing technology, and in particular to a field testing device and method for the free swelling rate and permeability coefficient of expansive soil. Background Technology

[0002] Expansive soil is a type of highly plastic clay. In its natural state, expansive soil generally has high physical and mechanical strength and low compressibility, which can easily lead to it being mistakenly considered a good foundation material for buildings. The clay particles in expansive soil are mainly composed of hydrophilic minerals, exhibiting significant swelling upon water absorption and shrinkage upon water loss. Its strength decreases sharply after repeated swelling and shrinkage and immersion 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, and slope instability. In engineering construction in expansive soil areas, the free swelling rate and permeability coefficient of expansive soil are fundamental to developing safe, applicable, technologically advanced, and economically reasonable engineering measures. The free swelling rate is one of the important criteria for distinguishing between expansive and non-expansive soils and is also a key indicator for expansive soil classification. Different grades of expansive soil require different considerations in engineering design and construction. In slope engineering, the permeability coefficient of expansive soil can be used to analyze the infiltration rate and range of rainwater in the soil, and then to analyze the relationship between rainfall and slope stability, providing an important basis for slope stability assessment and protection design. For foundation engineering, the permeability coefficient can be used to assess the expansion and contraction deformation of foundation soil when the groundwater level changes.

[0003] The current national standard, "Technical Code for Construction in Expansive Soil Areas," proposes obtaining montmorillonite content, cation exchange capacity, free swelling rate, swelling rate under different pressures, and swelling force of expansive soil through indoor tests, and determining the bearing capacity and swelling deformation of expansive soil foundations during immersion through field immersion load tests. The "Geotechnical Testing Methods and Standards" proposes determining the permeability coefficient of foundation soil through indoor tests and field permeability tests. However, the following problems exist in the testing process for expansive soil: 1. Indoor geotechnical tests are affected by the heterogeneity of the foundation soil and the representativeness of the test samples, resulting in discrete test data. A sufficiently large sample size is required for statistical analysis to determine the swelling potential of expansive soil, which is costly and inefficient. 2. In some areas, the results obtained from indoor tests of expansive soil based on free swelling rate, montmorillonite content, and cation exchange capacity are contradictory. For example, in a project in Yunnan Province, judging by the standard of free expansion rate, 70%–80% of the foundation soil was non-expanding, a small amount was weakly expansive, and very little was moderately or strongly expansive. However, using montmorillonite content as the criterion, almost no non-expanding soil was found, and most soil exhibited weak, moderate, or strong expansive potential. Different criteria lead to contradictory results, and the criteria for determining the expansive potential of expansive soil are controversial. 3. Indoor permeability tests suffer from size effects and sample representativeness issues. The sample size in indoor permeability tests is usually small, differing significantly from the thickness and range of soil layers in actual projects. This makes it impossible to fully reflect the characteristics of the entire soil layer. Small-sized samples may overlook the influence of large pores and fissures in the soil layer on permeability, leading to test results that do not match reality. Disturbing undisturbed soil samples can damage the soil structure and affect its permeability. 4. The operation process of field permeability tests is relatively complex. For example, in water injection tests, it is necessary to control factors such as injection speed, water volume, and time to ensure the accuracy and reliability of the test. Simultaneously, parameters such as water level and water volume need to be monitored and recorded in real time during the test, which requires a high level of operational skill from the test personnel. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a field testing device and method for the free swelling rate and permeability coefficient of expansive soil.

[0005] The technical solution adopted in this invention is as follows:

[0006] A field test device for free swelling rate and permeability coefficient of expansive soil, comprising a ring sampler assembly, a moisture content measurement assembly, a displacement measurement assembly, and a water supply assembly;

[0007] The ring cutter assembly includes a large ring cutter with a cylindrical structure, open at the bottom and closed at the top, with its bottom inserted into the expansive soil. The moisture content measurement assembly includes a probe inserted into the expansive soil, with several moisture meters evenly spaced on the probe. The moisture meters are connected to a moisture display mounted on the large ring cutter via internal wiring. The displacement measurement assembly includes a Bluetooth digital dial indicator for measuring soil surface displacement and a Bluetooth digital dial indicator for measuring soil displacement at a fixed depth. A set of Bluetooth digital dial indicators are mounted on the large ring cutter. The water supply assembly includes a water bucket and a weighing sensor located at the bottom of the water bucket. A water pipe extending into the large ring cutter is installed on one side of the water bucket, and a float valve is installed at the water outlet.

[0008] Furthermore, a retaining ring is installed on the large ring cutter, and a retaining ring is installed through the retaining ring. The retaining ring is an annular plate located on the surface of the expansive soil. Several through holes are provided around the circumference of the retaining ring, and spiral nails that are inserted into the expansive soil are installed through the through holes.

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

[0010] The steps are as follows:

[0011] Step 1, Site preparation and ring cutter installation: Select a dry expansive soil foundation, remove the loose surface soil and level it; take samples of the expansive soil and calculate the natural density of the soil; press the large ring cutter vertically into the soil, install the protective ring and screw in the spiral nail to ensure that the ring cutter does not float up due to soil expansion;

[0012] Step 2, Installation of moisture content measurement components: Number the moisture meters and install them on the probe 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.

[0013] Step 3, Installation of Displacement Measurement Components: Insert a thin-walled soil sampling tube into the soil at a certain depth at a certain distance from the probe. After vertically pulling out the sampling tube, measure the depth from the bottom of the hole to the soil surface. Remove the soil sample from the sampling tube, insert it into the soil hole, and install the first Bluetooth digital display dial gauge. The probe of the first Bluetooth digital display dial gauge is located at the bottom of the soil hole, and the displacement data at a certain soil depth is recorded during water injection. Install the second Bluetooth digital display dial gauge at a symmetrical position on the other side of the probe. The probe of the second Bluetooth digital display dial gauge is located at the soil surface, and the displacement data of the soil surface is recorded.

[0014] Step 4, Data Measurement: Turn on the moisture meter and displacement measurement unit, 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 assembly, control the water surface to be 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;

[0016] When the moisture content measured by the first 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 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 tube, and use this to calculate the permeability coefficient.

[0017] When the moisture content measured by the first to the fourth moisture meters is the same, it is assumed that the soil expansion deformation from the soil surface to the bottom of the thin-walled soil sampling tube is stable, and the free expansion rate is calculated.

[0018] Step Six, Test Termination: After data acquisition and analysis are completed, stop the test and dismantle the device.

[0019] Furthermore, in step 5, the formula for calculating the permeability coefficient is:

[0020]

[0021] In the formula, k is the soil permeability coefficient; The mass of the bucket recorded when the moisture content measured by the first to third moisture meters is the same; The mass of the water bucket is recorded when the moisture content measured by the first to fourth moisture meters is the same. The density of water; The time recorded when the moisture content measured by the first to the third moisture meter is the same; The time recorded when the moisture content measured by the first to fourth moisture meters is the same; A is the depth from the bottom of the borehole to the soil surface measured through the thin-walled soil sampling tube; A is the inner area of ​​the large ring cutter. The water depth above the soil surface; The water depth data in the thin-walled soil sampling tube is recorded when the moisture content measured by the first to fourth moisture meters is the same.

[0022] Furthermore, in step 5, the formula for calculating the free expansion rate is:

[0023]

[0024] In the formula, For free expansion rate, The displacement data during the water injection process is recorded by the first Bluetooth digital display dial gauge; The data represents the soil surface displacement recorded by the second Bluetooth digital dial indicator.

[0025] Furthermore, the field test method for free swelling rate and permeability coefficient of expansive soil calculates the free swelling rate of expansive soil by recording the soil moisture content, soil surface displacement and water injection volume at different depths (numerical analysis method).

[0026] The steps are as follows:

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

[0028] Step 2, Installation of moisture content measurement components: Number the moisture meters and install them on the probe 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.

[0029] Step 3: Install the displacement measurement component. Install the Bluetooth digital display dial gauge, place the Bluetooth digital display dial gauge probe on the soil surface, and record the displacement data of the soil surface.

[0030] Step 4, Data Measurement: Turn on the moisture meter and displacement measurement unit, and record the data; At any given time, the initial moisture content of the soil at different depths is recorded, and a quintic function of moisture content and different depths is fitted. Based on the depth of each moisture meter and the measured initial moisture content, the quintic function is solved to obtain the relationship curve between initial moisture content and depth.

[0031] Step 5, Water Injection and Data Recording: Inject water evenly into the ring cutter, keeping the water level at a certain height above the soil surface. Stop injecting water after injecting a certain mass of water. The amount of water injected must ensure that the water does not seep down to the lowest moisture meter, that is, the measured soil moisture content at the lowest moisture meter does not change. At this time, record the water injection mass and the soil moisture content at different depths.

[0032] Once the soil expansion and deformation is complete (i.e., the digital dial gauge reading remains constant), record the amount of expansion and deformation and the soil moisture content at different depths, and then fit the data. A quintic function of water content and depth at any given time; according to Solving the quintic function based on the depth of the moisture meter at each time point and the measured moisture content yields the following result: Moisture content versus depth curve at any given time;

[0033] The fit was verified by comparing the injection quality with the increase in soil moisture content. The moisture content curve is obtained at any given time; if the verification is successful, proceed to the next step; otherwise, refit the curve. A quintic function of water content and depth at any given moment;

[0034] Solve The expansion coefficient at different times is calculated; the quintic function of water content and depth at other times is repeatedly fitted, and the expansion coefficient at different times is solved to calculate the average expansion coefficient;

[0035] If the moisture content measured by the first and second moisture meters does not change at different times during the water injection process, the soil is considered to be saturated. The average value is taken as the saturated moisture content of the soil, and the free expansion rate of the soil is calculated.

[0036] Step Six, Test Termination: After data acquisition and analysis are completed, stop the test and dismantle the device.

[0037] Furthermore, in step four, Record the initial moisture content of the soil at different depths at various times. Fitting moisture content With depth A quintic function in one variable:

[0038]

[0039] In the formula, These are the coefficients of a univariate fifth-degree polynomial function, used to describe the moisture content. With depth The relationship between the changes; f is a constant term, representing the change at time t0. That is, the initial moisture content at the soil surface;

[0040] The coefficients are calculated based on the depth of each moisture meter and the measured initial moisture content:

[0041] The initial moisture content was obtained. With depth Relationship curve;

[0042] In step five, once the expansion and deformation of the test soil is complete, i.e., the digital dial gauge reading remains unchanged, record the amount of expansion and deformation. and moisture content , fitting A quintic function of water content and depth at any given time:

[0043] Formula 5

[0044] according to Depth of moisture meter at each time point and coefficients for calculating measured moisture content: ,get Moisture content at any time With depth Relationship curve;

[0045] The fit was verified by comparing the injection quality with the increase in soil moisture content. Moisture content curve at different times:

[0046] Formula 6

[0047] In the formula, Indicates in At any given moment, the total mass of water injected into the test soil; Indicates from depth To depth The definite integral; The dry density of the soil is represented by A; A is the inner area of ​​the large ring cutter. Indicates depth The infinitesimal element;

[0048] If Equation 6 holds true, proceed to the next step; otherwise, refit Equation 5.

[0049] Solve from Equation 7 Time-based expansion coefficient :

[0050] Formula 7

[0051] In the formula, Indicates in At any given moment, the total expansion deformation of the test soil;

[0052] Solving at different times coefficient of thermal expansion The average expansion coefficient can be solved using Equation 8. :

[0053] Formula 8

[0054] In the formula, Indicates different times The measured soil expansion coefficient; n represents the total number of tests or measurement times.

[0055] Furthermore, in step five, the moisture content measured by the first and second moisture meters at different times... and If no change occurs, the soil is considered saturated, and its average value is taken as the saturated water content of the soil. The free expansion rate of the soil is calculated using the following formula;

[0056] Formula 9

[0057] In the formula, This represents the free expansion rate of the soil. Indicates the coefficient of soil expansion; This indicates the saturated water content of the soil.

[0058] The beneficial effects of this invention are:

[0059] 1. Improve test accuracy and reliability:

[0060] The free swelling rate and permeability coefficient of expansive soil are directly measured by field testing equipment, avoiding the problems of insufficient soil sample representativeness and data dispersion in indoor tests, and significantly improving the accuracy and reliability of test results.

[0061] 2. Unified judgment criteria:

[0062] By combining field test data with numerical analysis, the free expansion rate of expansive soil can be determined more accurately, which solves the problem of inconsistent judgment results for different indicators in national and local standards, and provides a unified judgment basis for engineering applications.

[0063] 3. Reduce testing costs and improve efficiency:

[0064] Field testing equipment and methods reduce the need for a large number of indoor test samples, lower testing costs, and significantly improve testing efficiency through real-time monitoring and data acquisition.

[0065] 4. Comprehensive measurement of multiple parameters:

[0066] The device integrates a moisture content measurement system, a displacement measurement system, and a water supply system, enabling it to simultaneously measure the soil's moisture content, displacement change, permeability coefficient, and expansion coefficient, providing comprehensive data support for engineering design and construction.

[0067] 5. Highly adaptable:

[0068] The device is flexibly designed and suitable for expansive soil tests under different geological conditions, effectively addressing the testing challenges caused by the heterogeneity of foundation soil.

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

[0070] The experimental data was monitored and recorded in real time using a miniature moisture meter and a digital dial gauge, ensuring the continuity and accuracy of the data and providing a reliable basis for subsequent analysis.

[0071] 7. Application of numerical analysis methods:

[0072] By combining numerical analysis methods, fitting moisture content curves, and calculating the expansion coefficient, the expansion characteristics of expansive soil can be evaluated more scientifically, providing a scientific basis for engineering decisions.

[0073] In summary, the field test device and method for free swelling rate and permeability coefficient of expansive soil provided by this 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. Attached Figure Description

[0074] Figure 1 This is a schematic diagram of the overall structure of the field test device for the free swelling rate and permeability coefficient of expansive soil.

[0075] In the diagram, 1—large ring cutter, 2—clamping ring, 3—protective ring, 4—spiral nail, 5—first Bluetooth digital display dial indicator, 6—second Bluetooth digital display dial indicator, 7—moisture display, 8—probe, 9—moisture meter, 10—weighing sensor, 11—water bucket, 12—ball valve. Detailed Implementation

[0076] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0077] For ease of explanation, spatial relative terms such as “above,” “below,” “left,” and “right” may be used herein to describe the relationship of one element or feature shown in the figure relative to another element or feature. It should be understood that, in addition to dealing with the orientation shown in the figure, spatial terms are intended to include different orientations of the device in use or operation. For example, if the device in the figure is inverted, an element described as being “below” other elements or features would be defined as being “above” other elements or features. Therefore, the exemplary term “below” can encompass both above and below. The device may be positioned in other ways, and the spatial relative descriptions used herein can be interpreted accordingly.

[0078] Example 1

[0079] To address the problems encountered in expansive soil testing, this embodiment proposes a field testing device for the free swelling rate and permeability coefficient of expansive soil. For example... Figure 1 As shown, the field test device for the free swelling rate and permeability coefficient of expansive soil includes a ring cutter assembly, a moisture content measurement assembly, a displacement measurement assembly, and a water supply assembly.

[0080] The ring sampler assembly includes a large cylindrical ring sampler 1, 10 cm in diameter and 30 cm high. The large ring sampler 1 has an open bottom and a closed top, with its bottom inserted into the expansive soil. The large ring sampler 1 serves as the main container for the test soil, vertically pressed into the soil to fix it and prevent lateral deformation during soil expansion. Furthermore, to ensure the stability of the large ring sampler 1 inserted into the expansive soil, such as… Figure 1As shown, in this embodiment, a retaining ring 2 is installed 5cm below the top plate of the outer wall of the ring cutter. The retaining ring 2 is 2cm wide and has a retaining groove, through which a protective ring 3 is installed. The protective ring 3 is an annular plate with an inner diameter of 10.5cm and an outer diameter of 20cm. Four through holes are provided on the circumference of the protective ring 3. Spiral nails 4, which are inserted into the expansive soil, are installed through the through holes and fixed in the soil by the spiral nails 4 to prevent the ring cutter from floating due to the vertical expansion of the soil and to ensure the stability of the ring cutter during the test.

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

[0082] like Figure 1 As shown, the displacement measurement component in this embodiment includes a Bluetooth digital dial indicator for measuring surface displacement data of the soil and a Bluetooth digital dial indicator for measuring soil displacement data at a fixed depth in expansive soil. A set of Bluetooth digital dial indicators is mounted on the large ring cutter 1. The probe of the first Bluetooth digital dial indicator 5 is located at the bottom of the soil hole and is used to record displacement data at a certain soil depth during water injection, reflecting the expansion and deformation of the soil. The probe of the second Bluetooth digital dial indicator 6 is located on the soil surface and is used to record surface displacement data, reflecting the expansion and deformation of the soil surface. By recording the displacement changes on the soil surface and inside, the free expansion rate and expansion deformation of the soil can be calculated.

[0083] like Figure 1 As shown, the water supply assembly in this embodiment includes a water tank 11 and a weighing sensor 10 located at the bottom of the water tank 11. A water pipe extending into the large ring cutter 1 is installed on one side of the water tank 11. An adjustable float valve 12 is installed at the outlet of the water pipe. The water tank 11 is used to uniformly inject water into the ring cutter, simulating the process of soil absorbing water and expanding. The float valve 12 is used to control the water level inside the large ring cutter. The weighing sensor 10 records the water injection mass in real time to ensure accurate control of the water injection volume and provide data support for calculating the permeability coefficient.

[0084] This field testing device for the free swelling rate and permeability coefficient of expansive soil uses a ring cutter assembly to fix the test soil, ensuring soil stability and data accuracy during the test. A moisture content measurement assembly monitors real-time changes in soil moisture content, providing crucial data for analyzing the soil's water absorption and swelling process. A displacement measurement assembly records surface and internal displacement changes, calculating the soil's swelling deformation and free swelling rate. A water supply assembly precisely controls the water level and injection volume within the large ring cutter, simulating the soil's water absorption and swelling process, providing fundamental data for calculating the permeability and swelling coefficients. The coordinated operation of these components enables accurate determination of the free swelling rate and permeability coefficient of expansive soil, providing reliable technical support for engineering applications.

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

[0086] Example 2

[0087] Based on the field test device for free swelling rate and permeability coefficient of expansive soil provided in Example 1, this example also proposes a field test method for free swelling rate and permeability coefficient of expansive soil, namely: test method; this field test method for free swelling rate and permeability coefficient of expansive soil can determine the free swelling rate and permeability coefficient of expansive soil;

[0088] The specific steps are as follows:

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

[0090] On the expansive soil site, select foundation soil unaffected by the groundwater level. The soil should be dry, approximately considered to be in an air-dried state. Remove the loose topsoil and level the test area. Take samples of the expansive soil and calculate its natural density. Apply a thin layer of lubricating oil to the inner and outer walls of the large ring cutter, press it vertically into the soil for 25cm, insert the retaining ring, and screw the spiral nail into the soil through the round hole of the retaining ring. The retaining ring should be in close contact with the soil outside the ring cutter to ensure that the ring cutter does not float up due to the vertical expansion of the soil.

[0091] Step 2, Installation of moisture content measurement components:

[0092] Six moisture meters were numbered and installed at equal intervals on the probe. The probe was inserted into the center of the test soil at a uniform speed, with the first moisture meter positioned 0.5 cm to 1 cm below the soil surface. The moisture content at different depths was recorded. ~ .

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

[0094] Using a thin-walled soil sampling tube with a diameter of 1 cm and a length of approximately 15 cm, insert it 10 cm into the soil at a distance of 3 cm from the probe. After vertically withdrawing the sampling tube, use a vernier caliper to measure the depth from the bottom of the hole to the soil surface. Remove the soil sample from the sampling tube, insert it into the soil hole, and install the first Bluetooth digital dial indicator. The probe of the first Bluetooth digital dial indicator is located at the bottom of the soil hole to record a certain soil depth during the water injection process. Displacement data A second Bluetooth digital dial indicator is installed at a symmetrical position on the other side of the probe. The probe of the second Bluetooth digital dial indicator is positioned on the soil surface to record the displacement data of the soil surface. .

[0095] Step 4, Measurement Data:

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

[0097] Step 5, Water Injection and Data Recording:

[0098] Water is evenly injected into the large cutter head through the water supply assembly, and the float valve height is adjusted to maintain the water level at a certain height h above the soil surface. w0 Record the water injection quality at different times;

[0099] When the moisture content measured by the first to the third moisture meter is the same, that is... = = Record the weight of the bucket at that time. and time ;

[0100] When the moisture content measured by the first to the fourth moisture meters is the same, that is... = = = Record the weight of the bucket at that time. ,time and water depth data in thin-walled soil sampling pipes It can calculate the permeability coefficient k of the soil from the soil surface to the third moisture meter section over time;

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

[0102]

[0103] In the formula, k is the soil permeability coefficient; The mass of the bucket recorded when the moisture content measured by the first to third moisture meters is the same; The mass of the water bucket is recorded when the moisture content measured by the first to fourth moisture meters is the same. The density of water; The time recorded when the moisture content measured by the first to the third moisture meter is the same; The time recorded when the moisture content measured by the first to fourth moisture meters is the same; A is the depth from the bottom of the borehole to the soil surface measured through a thin-walled sampling tube; A is the inner area of ​​the large ring cutter; h w0 The depth from the water surface to the soil surface inside the large ring cutter; The water depth data in the thin-walled soil sampling tube is measured when the moisture content measured by the first to fourth moisture meters is the same.

[0104] When the moisture content measured by the first to the fourth moisture meters is the same, that is... = = = At that time, the top surface of the soil can be considered to be to a depth of Within a certain range, the soil expansion deformation is stable. The free expansion rate of the soil can be calculated based on the displacement data from the digital dial gauge. ;

[0105] The formula for calculating the free expansion rate is:

[0106]

[0107] In the formula, For free expansion rate, The displacement data during the water injection process is recorded by the first Bluetooth digital display dial gauge; The data represents the soil surface displacement recorded by the second Bluetooth digital dial indicator.

[0108] Step Six, Test Termination: After data acquisition and analysis are completed, stop the test and dismantle the device.

[0109] Furthermore, this field test method for the free swelling rate and permeability coefficient of expansive soil can calculate the free swelling rate of expansive soil through numerical analysis, i.e., the numerical analysis method.

[0110] The steps are as follows:

[0111] Step 1, Site preparation and ring cutter installation:

[0112] On the expansive soil site, select foundation soil unaffected by the groundwater level. The soil should be dry, approximately considered to be in an air-dried state. Remove the loose topsoil and level the test area. Take samples of the expansive soil and calculate its natural density. Apply a thin layer of lubricating oil to the inner and outer walls of the large ring cutter, press it vertically into the soil for 25cm, insert the retaining ring, and screw the spiral nail into the soil through the round hole of the retaining ring. The retaining ring should be in close contact with the soil outside the ring cutter to ensure that the ring cutter does not float up due to the vertical expansion of the soil.

[0113] Step 2, Installation of moisture content measurement components:

[0114] Six moisture meters were numbered and installed at equal intervals on the probe. The probe was inserted into the center of the test soil at a uniform speed, with the first moisture meter positioned 0.5 cm to 1 cm below the soil surface. The moisture content at different depths was recorded. ~ .

[0115] Step 3, Installation of displacement measurement components:

[0116] Install a Bluetooth digital dial indicator, with the probe positioned on the soil surface to record soil surface displacement data. .

[0117] Step 4, Measurement Data:

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

[0119] Record the initial moisture content of the soil at different depths at various times. Fitting moisture content With depth A quintic function in one variable;

[0120] Formula 4

[0121] In the formula, These are the coefficients of a univariate fifth-degree polynomial function, used to describe the moisture content. With depth The changing relationship; The constant term represents when That is, the initial moisture content at the soil surface;

[0122] The coefficients are calculated based on the depth of each moisture meter and the measured initial moisture content:

[0123] The initial moisture content was obtained. With depth Relationship curve.

[0124] Step 5, Water Injection and Data Recording:

[0125] Evenly inject water into the ring cutter, maintaining the water level 1mm~3mm below the soil surface. After injecting a certain amount of water, stop injecting. The amount of water injected must ensure that no water seeps down to the sixth moisture meter, meaning that the soil moisture content measured by the sixth moisture meter has not changed. Record the water injection mass at this point. And the maximum moisture content at different depths;

[0126] Once the soil expansion and deformation is complete, i.e. the digital dial gauge reading remains constant, record the amount of expansion and deformation. and moisture content , fitting Moisture content at any time With depth A quintic function in one variable;

[0127] Formula 5

[0128] according to Depth of moisture meter at each time point and coefficients for calculating measured moisture content:

[0129] ,get Moisture content at any time With depth Relationship curve.

[0130] The fit was verified by comparing the injection quality with the increase in soil moisture content. Moisture content curve at any given time;

[0131] Formula 6

[0132] In the formula, Indicates in At any given moment, the total mass of water injected into the test soil; Indicates from depth To depth The definite integral; The dry density of the soil is represented by A; A is the inner area of ​​the large ring cutter. Indicates depth The infinitesimal element;

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

[0134] Solve from Equation 7 Time-based expansion coefficient :

[0135] Formula 7

[0136] In the formula, Indicates in At any given moment, the total expansion deformation of the test soil;

[0137] Repeatedly fit a univariate quintic function of water content versus depth at other times, and solve for the different times. coefficient of thermal expansion The average expansion coefficient can be solved using Equation 8. :

[0138] Formula 8

[0139] In the formula, Indicates different times The measured soil expansion coefficient; n represents the total number of tests or measurement times.

[0140] The moisture content measured by the first and second moisture meters at different times and If no change occurs, the soil is considered saturated, and its average value is taken as the saturated water content of the soil. The free expansion rate of the soil is calculated using the following formula;

[0141] Formula 3

[0142] In the formula, This represents the free expansion rate of the soil. Indicates the coefficient of soil expansion; This indicates the saturated water content of the soil.

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

[0144] It should be noted that, according to the national standard "Technical Specification for Construction in Expansive Soil Areas", the shrinkage coefficient of expansive soil is... The difference in vertical linear shrinkage rate during the linear change phase of the water loss shrinkage process. Difference from corresponding moisture content Ratio; similarly, assume the expansion coefficient during the water absorption and expansion process of expansive soil. The difference in vertical linear expansion rate Difference from corresponding moisture content The ratio indicates that the free expansion rate is the expansion coefficient. With saturated moisture content The product of , i.e., Equation 3.

[0145] The foregoing has shown and described 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 to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for testing the free swelling rate and the permeability coefficient of an expansive soil in situ, characterized in that: The free swelling rate and permeability coefficient field test method of the expansive soil is based on an expansive soil free swelling rate and permeability coefficient field test device, which comprises a ring cutter assembly, a water content measuring assembly, a displacement measuring 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, the top is closed, and the bottom is inserted into the expansive soil body; The water content measuring assembly comprises a probe inserted into the expansive soil body, a plurality of moisture meters are arranged on the probe at equal intervals, and the moisture meters are connected with a moisture display installed on the large ring cutter through internal wiring of the probe; The displacement measuring assembly comprises a Bluetooth digital display micrometer for measuring the displacement data of the surface of the soil body and a Bluetooth digital display micrometer for measuring the displacement data of the soil body at a fixed depth of the expansive soil, and a group of Bluetooth digital display micrometers are installed on the large ring cutter; The water supply assembly comprises a water bucket and a weighing sensor at the bottom of the water bucket; a water pipe extending into the inside of the large ring cutter is installed on one side of the water bucket, and a float valve is installed at the water outlet. The free swelling rate field test method of the expansive soil can quickly determine the free swelling rate of the expansive soil and determine the swelling potential; The steps are as follows: Step one, site preparation and ring cutter installation: select a dry expansive soil foundation, remove the loose surface soil and level it; sample the expansive soil, calculate the natural density of the soil body; vertically press the large ring cutter into the soil body, install the retaining ring and screw in the spiral screw, and ensure that the ring cutter does not float due to soil swelling; Step two, installation of the water content measuring assembly: number the moisture meters and install them on the probe at equal intervals, insert the probe into the center of the soil body, and the first moisture meter is located at a certain depth below the surface of the soil body, and record the water content at each depth; Step three, installation of the displacement measuring assembly: install the Bluetooth digital display micrometer, and the probe of the Bluetooth digital display micrometer is located on the surface of the soil body to record the displacement data of the surface of the soil body; Step four, measurement data: turn on the moisture meter and displacement measurement assembly, record data; At this time, record the initial water content of the soil at different depths, and fit a quintic function of water content and depth. According to the depth of each moisture meter and the measured initial water content, the quintic function is solved to obtain the relationship curve between the initial water content and the depth. Step five, water injection and data recording: uniformly inject water into the ring cutter, keep the water surface at a certain height above the soil surface, stop injecting water after injecting a certain amount of water, and ensure that the water does not infiltrate to the lowermost moisture meter, that is, the measured water content of the soil at the lowermost moisture meter does not change; at this time, record the water injection quality and the water content of the soil at different depths; When the swelling deformation of the test soil body is completed, i.e. the reading of the digital dial gauge is unchanged, the swelling deformation and the water content of the soil body at different depths are recorded, and a quintic function of the water content and the depth at the moment is fitted According to the depth and the measured water content of each moisture meter at the moment, the quintic function is solved to obtain the relationship curve between the water content and the depth at the moment According to the depth and the measured water content of each moisture meter at the moment, the quintic function is solved to obtain the relationship curve between the water content and the depth at the moment According to the depth and the measured water content of each moisture meter at the moment, the quintic function is solved to obtain the relationship curve between the water content and the depth at the moment The fitted water content curve at time t1; if the check is passed, the next step is performed, otherwise the monomial quintic function of water content and depth at time t1 is refitted; Solve the swelling coefficient at t1; repeat the fitting of the monadic quintic function of the water content and the depth at other times, and solve the swelling coefficients at different times to calculate the average swelling coefficient; When the water contents measured by the first moisture meter and the second moisture meter at different times during the water injection process do not change, it is considered that the soil reaches saturation, and the average value is taken as the saturated water content of the soil to calculate the free swelling rate of the soil; Step six, termination of the test: after the data collection and analysis are completed, stop the test and remove the device; In step four, At this moment, record the initial water content of the soil at different depths , fit a quintic function of water content ω and depth h: Formula 4 wherein is the coefficient of a fitted quintic polynomial function describing the change of water content with depth ; is a constant term representing the initial water content at the moment when the surface of the soil body Solving the coefficient according to the depth of each moisture meter and the measured initial moisture content: , the initial moisture content and the depth relationship curve; In step five, when the swelling deformation of the test soil body is completed, i.e. the reading of the digital dial gauge is unchanged, the swelling deformation is recorded and the moisture content , a quintic function of the moisture content and the depth at the moment is fitted ​ Formula 5 According to Depth and measured moisture content of each moisture meter at the time of solving the coefficient: , obtaining moisture content depth relationship curve; The fitting is checked by the water injection quality and the moisture content increase of the test soil The moisture content curve at the moment: Formula 6 where m(t1) represents the total mass of water injected into the test soil body at time t1; represents the definite integral from depth h = 0 to depth h = h n represents the dry density of the soil body; A is the inner area of the ring knife; d represents the infinitesimal of depth h ;​​ If equation 6 is established, proceed to the next step, otherwise, re-fit equation 5; Solving for the expansion coefficient λ at time t1 from equation 7 p1 : Formula 7 In the formula, represents the total expansion deformation of the test soil at t1. Solve for the expansion coefficient λ n at different times t pn Solve for the average expansion coefficient λ p from equation 8: Formula 8 where λ p1 , λ p2 , …, λ pn represent the measured swelling coefficients of the soil at different times t1, t2, …, t n n represents the number of tests or the total number of measurement times.

2. The method for measuring the free swelling ratio and permeability coefficient of expansive soil according to claim 1, characterized in that: The large ring cutter is provided with a snap ring, the retaining ring is installed on the snap ring, the retaining ring is an annular plate body, and the retaining ring is located on the surface of the expansive soil; a plurality of through holes are arranged on the circumference of the retaining ring, and the spiral screw inserted into the expansive soil is installed through the through holes.

3. The method for measuring free swelling ratio and permeability coefficient of expansive soil according to claim 1, wherein: In step five, the soil is considered saturated when the moisture content measured by the first and second moisture meters at different times and do not change, and the average of these values is taken as the saturated moisture content of the soil The free swell rate of the soil is calculated by the following equation; Formula 9 In the formula, represents the free expansion rate of the soil body; represents the expansion coefficient of the soil body; represents the saturated water content of the soil body.

4. The method for measuring free swelling ratio and permeability coefficient of expansive soil according to claim 1, wherein: The free swelling rate and permeability coefficient field test method of the expansive soil can determine the free swelling rate and permeability coefficient of the expansive soil; The steps are as follows: Step 1, site preparation and ring installation: select dry swelling soil foundation, remove the surface loose soil and flatten; sample the swelling soil, calculate the natural density of the soil; vertically press the large ring into the soil, install the ring and screw into the screw, ensure that the ring does not float due to soil swelling; Step 2, installation of moisture content measurement assembly: number the moisture meter and install it on the probe at equal intervals, insert the probe into the center of the soil, and 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 assembly: insert the thin-walled soil sampling pipe into the soil at a certain position from the probe, measure the depth from the bottom of the hole to the soil surface after pulling out the soil sampling pipe vertically; remove the soil sample in the soil sampling pipe, insert it into the soil hole, and install the first Bluetooth digital dial gauge. The probe of the first Bluetooth digital dial gauge is located at the bottom of the soil hole, and the displacement data at a certain depth of the soil during water injection is recorded. Install the second Bluetooth digital dial gauge at the symmetrical position on the other side of the probe, and the probe of the second Bluetooth digital dial gauge is located at the surface of the soil. Record the surface displacement data of the soil; Step 4, data measurement: turn on the moisture meter and displacement measurement assembly and record the data; Step 5, water injection and data recording: adjust the height of the float ball valve above the soil surface, uniformly inject water into the large ring through the water supply assembly, control the water surface above the soil surface through the ball valve, measure the water depth above the soil surface, and record the water quality at different times; When the moisture contents measured by the first to third moisture meters are the same, record the water bucket mass and time; when the moisture contents measured by the first to fourth moisture meters are the same, record the water bucket mass, time and water depth in the thin-walled soil sampling pipe, and calculate the permeability coefficient; When the moisture contents measured by the first to fourth moisture meters are the same, it is considered that the soil swelling and deformation of the soil from the surface to the bottom of the thin-walled soil sampling pipe is stable, and the free swelling ratio is calculated; Step 6, test termination: after data collection and analysis are completed, stop the test and remove the device.

5. The method for testing the free swelling rate and permeability coefficient of expansive soil according to claim 4, characterized in that: In step 5, the formula for calculating the permeability coefficient is: ； where k is the soil permeability coefficient; Mass of the bucket recorded at the same moisture content measured by the first to third moisture meters; Mass of the bucket recorded at the same moisture content measured by the first to fourth moisture meters; Density of water; Time recorded at the same moisture content measured by the first to third moisture meters; Time recorded at the same moisture content measured by the first to fourth moisture meters; Depth from the bottom of the hole to the surface of the soil measured by the thin-walled soil auger; A is the area inside the core cutter; Depth of water above the soil surface; Depth of water in the thin-walled soil auger recorded at the same moisture content measured by the first to fourth moisture meters.

6. The method for testing free expansion ratio and permeability coefficient of expansive soil in-situ according to claim 4, characterized in that: In step 5, the formula for calculating the free swelling ratio is: ； wherein is the free expansion ratio, is displacement data recorded by the first Bluetooth digital dial gauge during the water injection process; is surface displacement data of the soil recorded by the second Bluetooth digital dial gauge.

Images