Test apparatus and test method for determining suction composition and deformation characteristics of compacted clay

Abstract

The present invention discloses a test device and a test method for measuring the suction composition and deformation characteristics of compacted clay, and relates to the fields of civil engineering (geotechnical) and geological engineering technology. The test device includes a one-dimensional confined deformation test unit, a vertical load control unit, a vertical deformation measurement unit, a suction control unit, and a suction measurement unit. The one-dimensional confined deformation test unit provides space for sample compression and sample deformation, the vertical load control unit controls the vertical load applied to the sample, the vertical deformation measurement unit automatically collects and stores the deformation data of the sample, the suction control unit applies target matrix suction or permeate suction to the sample, and the suction measurement unit simultaneously measures the matrix suction and total suction of the sample in equilibrium. The present invention can simultaneously measure the matrix suction and total suction of compacted clay under the action of load and chemical environment, providing a basis for establishing a chemical-hydraulic-mechanical coupling analysis model of compacted clay and ensuring the service safety of clay barriers.

Description

Technical Field

[0001] The invention relates to a test device and a test method for measuring the suction composition and deformation characteristics of compacted clay, and belongs to the technical fields of civil engineering (geotechnical) and geological engineering. Background Art

[0002] Clay barriers are widely used in the design of projects such as deep geological disposal of high-level radioactive waste, solid waste landfill, and contaminated site isolation to prevent pollutants from migrating to the biosphere. In such projects, clay barriers deform under the coupling of multiple fields (stress field, suction field, chemical field, and temperature field), which in turn affects their ability to block pollutants. Existing theories believe that the deformation behavior of saturated-unsaturated soils follows the effective stress principle, and the effective stress of clay soils needs to take into account the physical and chemical forces (manifested as adsorption suction s a ), capillary force (manifested as capillary suction s c ) and solute osmotic force (manifested as osmotic suction π). Therefore, it is necessary to determine the suction composition of compacted clay under chemical-hydraulic-mechanical coupling conditions and analyze the influence of suction composition on deformation characteristics.

[0003] Currently, there are relevant experimental studies on the deformation characteristics of compacted clay, but most studies only measure deformation characteristics in a single or simple coupled environment. Suction control and suction measurement technologies are relatively mature, and it is generally believed that matrix suction s m is the adsorption suction force s a and capillary suction s c The total suction is the sum of the three types of suction. Matrix suction can be measured using the contact filter paper method, and total suction using the separation filter paper method. However, these measurements are rarely performed simultaneously under load or chemical environment. Furthermore, load or chemical environment influences the suction composition (for example, unloading alters the specimen's suction state). Existing methods are unable to accurately determine the suction composition under coupled chemical, hydraulic, and mechanical conditions, nor can they determine the influence of suction composition on deformation characteristics.

[0004] Based on this, the present invention designs a test device and a test method for measuring the suction composition and deformation characteristics of compacted clay. Summary of the Invention

[0005] The present invention provides a test device and a test method for measuring the suction composition and deformation characteristics of compacted clay. The device and method are used to measure the suction composition and deformation characteristics of compacted clay under chemical-hydraulic-mechanical coupling conditions, providing a basis for establishing a chemical-hydraulic-mechanical coupling analysis model for compacted clay and ensuring the service safety of clay barriers.

[0006] To achieve the above object, the present invention adopts the following scheme:

[0007] The present invention provides a test device for measuring the suction composition and deformation characteristics of compacted clay, comprising a one-dimensional confined deformation test unit, a vertical load control unit, a vertical deformation measurement unit, a suction control unit, and a suction measurement unit; the one-dimensional confined deformation test unit provides space for sample compression and sample deformation, the vertical load control unit controls the vertical load applied to the sample through a single-lever weight loading method, the vertical deformation measurement unit automatically collects and stores the deformation data of the sample, the suction control unit applies target matrix suction or osmotic suction to the sample using a dialysis method or a salt solution saturation method, and the suction measurement unit uses a contact and separation filter paper method to simultaneously measure the matrix suction and total suction of the sample in a balanced state.

[0008] Preferably, the one-dimensional lateral confinement deformation test unit includes a base, a sample ring, an upper cover and bolts, and the base, the sample ring and the upper cover are connected by four bolts; a spiral water trough is provided inside the base, and a water inlet and joint, a water outlet and joint are provided on both sides of the base; a permeable stone, a porous pad and a loading cap are placed in the sample ring; the upper cover is provided with an axial hole and a shaft sleeve, and the loading shaft passes through the axial hole and the shaft sleeve and contacts the groove above the loading cap; the sample is located between the permeable stone and the porous pad; a base sealing ring is provided between the base and the sample ring, a top cover sealing ring is provided between the top cover and the sample ring, and a loading shaft sealing ring is provided between the axial hole and the shaft sleeve and the upper cover, so as to form a closed space inside the sample ring;

[0009] The vertical load control unit includes a loading platform, a pressure lever, and a weight. The one-dimensional lateral confinement test unit is placed on the loading platform. The force transmission point of the top crossbeam of the pressure lever is embedded in the groove at the top of the loading shaft. The vertical load applied to the sample is controlled by changing the mass of the weight.

[0010] The vertical deformation measurement unit includes a digital electronic dial indicator, a dial indicator bracket, a computer and data acquisition software. The digital electronic dial indicator displays the deformation of the sample in real time. The computer and data acquisition software collect and save the deformation data of the sample in real time and display the deformation-time relationship curve in real time.

[0011] The suction control unit includes a conical flask, a magnetic stirrer, a peristaltic pump, a suction control solution and a circulation pipeline. The suction control solution is pumped by the peristaltic pump through the circulation pipeline into and out of the spiral water tank of the base in the one-dimensional lateral confinement deformation test unit, and is combined with a semipermeable membrane or filter paper to control the suction state of the sample; the conical flask is placed on the magnetic stirrer to ensure that the concentration of the suction control solution is uniform; the suction control solution is distilled water, saline solution or polyethylene glycol solution; when it is necessary to control matrix suction, the suction control solution is polyethylene glycol, and the suction control unit further includes a semipermeable membrane, which is located between the sample and the permeable stone; when it is necessary to control osmotic suction, the suction control solution is distilled water or saline solution, and the suction control unit further includes filter paper, which is located between the sample and the permeable stone;

[0012] The suction measurement unit includes a contact measurement filter paper combination and a separation measurement filter paper combination. The contact measurement filter paper combination is located between the porous pad and the sample and is used to measure the matrix suction of the sample; the separation measurement filter paper combination is located between the loading cap and the porous pad and is used to measure the total suction of the sample; the contact measurement filter paper combination includes a contact protection filter paper and a contact measurement filter paper, one of the contact measurement filter papers is located between two of the contact protection filter papers, and the size of the contact measurement filter paper is smaller than the size of the contact protection filter papers; the separation measurement filter paper combination includes a separation protection filter paper and a separation measurement filter paper, one of the separation measurement filter papers is located between two of the separation protection filter papers, and the size of the separation measurement filter paper is smaller than the size of the separation protection filter papers; the matrix suction and total suction of the sample are calculated respectively according to the equilibrium moisture content of the contact measurement filter paper and the separation measurement filter paper.

[0013] The present invention also provides a test method for measuring the suction composition and deformation characteristics of compacted clay using the test device for measuring the suction composition and deformation characteristics of compacted clay, comprising the following steps:

[0014] Step 1: Press the sample: Take clay powder with the required moisture content and mass, use a pressure rod that matches the inner diameter of the sample ring, and use an electronic universal testing machine to press the sample in the sample ring;

[0015] Step 2: Assemble the one-dimensional lateral confined deformation test unit: Place the permeable stone in the base, place a semipermeable membrane of appropriate size on top of the permeable stone, and secure the semipermeable membrane to the base with the base sealing ring; place the sample ring with the sample on the base, and place the contact measurement filter paper assembly on top of the sample; place the porous pad, and place the separation measurement filter paper assembly on top of it; place the loading cap and cover it, push the loading shaft through the shaft hole and sleeve, and contact the loading cap; insert and tighten four bolts to connect and fix the base, sample ring, and cover;

[0016] Step 3: Connect the vertical load control unit and the vertical deformation measurement unit: Place the one-dimensional lateral confinement deformation test unit on the loading platform; adjust the position of the pressure lever so that the force transmission point of the top crossbeam of the pressure lever is embedded in the groove at the top of the loading shaft; fix the digital electronic dial indicator in the appropriate position of the dial indicator bracket so that the head of the indicator contacts the top crossbeam of the pressure lever; turn on the digital electronic dial indicator and connect it to the computer and data acquisition software;

[0017] Step 4. Connect the suction control unit: Use a circulation line to connect the peristaltic pump, the suction control solution in the conical flask, the water inlet and connectors on both sides of the base, and the water outlet and connectors;

[0018] Step 5: Vertical load control: Place weights of the required mass and apply the required vertical load to the specimen. This step can independently measure the deformation characteristics of the specimen under mechanical load.

[0019] Step 6: Osmotic Suction Control: After the deformation of the specimen under vertical load reaches stability, a salt solution of a specific concentration, or distilled water, is used as the suction control solution. The peristaltic pump is turned on to circulate the salt solution and osmotic suction control begins. The osmotic suction control process should last for no less than 15 days, and the vertical deformation of the specimen should reach stability. This step can obtain the deformation characteristics of the specimen under chemical-mechanical coupling or under one-dimensional free and pure water conditions. Afterwards, the test is terminated according to Step 8, and the suction composition of the specimen under chemical-mechanical coupling is determined according to Step 9. The matrix suction control in Step 7 can also be continued.

[0020] Step 7: Matrix suction control: After the deformation of the specimen under the vertical load and saline solution reaches stability, the suction control solution is replaced with a polyethylene glycol solution of a specific concentration. The peristaltic pump is turned on to circulate the polyethylene glycol solution, and matrix suction control begins. The matrix suction control process should last for no less than 15 days, and the vertical deformation of the specimen should reach stability. This step can be used to determine the deformation characteristics of the specimen under chemical-hydraulic-mechanical coupling. Matrix suction control can also be performed only after the deformation of the specimen under vertical load reaches stability, to measure the suction composition and deformation characteristics of the specimen under hydraulic-mechanical coupling.

[0021] Step 8. Stop the test: drain the suction control solution in the base and turn off the peristaltic pump; remove the suction control unit and the vertical deformation measurement unit, quickly remove the weights, and remove and disassemble the one-dimensional lateral confinement deformation test unit;

[0022] Step 9. Determine the matrix suction and total suction of the sample: Measure the moisture content of the contact and separation filter papers, and calculate the corresponding matrix suction and total suction. To avoid errors caused by changes in the moisture content of the filter papers, measure the mass of the contact and separation filter papers immediately after removing the sample.

[0023] Step 10: Determine the moisture content and dry density of the sample: Use an electronic universal testing machine to slowly push out the sample with a pressure rod, use the drying method to determine the moisture content, and the wax sealing method to determine the density, and calculate the dry density;

[0024] Step 11: Determine the suction composition of the sample under chemical-hydraulic-mechanical coupling conditions.

[0025] Preferably, the method of controlling osmotic suction comprises:

[0026] The osmotic suction is controlled by a salt solution. The maximum control value is determined by the solubility of the salt solution used. The salt solution concentration required for the target osmotic suction control is calculated according to the following formula:

[0027] π s =iCRT

[0028] Among them, π s is the osmotic suction of the salt solution, in Pa; i is the correlation coefficient; C is the concentration of the salt solution, in mol / L; R is the ideal gas constant, with a value of 8.314 Pa·m 3 ·K -1 ·mol -1 ; T is Kelvin temperature, unit is K.

[0029] Preferably, the method of matrix suction control comprises:

[0030] The matrix suction was controlled by dialysis within a range of 0–10 MPa. The concentration of the polyethylene glycol solution required to achieve the target matrix suction was calculated using the following formula:

[0031] s m =11c 2

[0032] Among them, s m is the matrix suction, unit is MPa; c is the mass concentration of polyethylene glycol solution.

[0033] Preferably, the method for determining stromal suction and total suction comprises:

[0034] Suction was measured using Whatman No. 42 filter paper as both a contact and a separation filter paper combination. The measurement range was the full range. Matrix suction s was calculated using the following formula: m and total suction s t :

[0035] logs m =2.909-0.0229ω f1 (ω f1 ≥47)

[0036] logs m=4.945-0.0673ω f1 (ω f1 <47)

[0037] Among them, s m is the matrix suction of the sample, in kPa, ω f1 It is the contact measurement of the equilibrium moisture content of the filter paper, in %;

[0038] logs t =8.778-0.222ω f2 (ω f2 ≥26)

[0039] logs t =5.31-0.0879ω f2 (ω f2 <26)

[0040] Among them, s t is the total suction of the sample, in kPa, ω f2 It is a separate measurement of the equilibrium moisture content of the filter paper in %.

[0041] Preferably, the method of determining the suction composition of a sample comprises:

[0042] The matrix suction and total suction of the distilled water saturated specimens under different vertical loads were measured, and the correlation function s between the saturated adsorption suction and the porosity ratio was determined. a,sat (e) Measure the matrix suction and total suction of samples saturated with salt solutions of different concentrations, and determine the correlation function π between saturated osmotic suction and salt solution concentration. sat (C); For any unsaturated sample under chemical-hydraulic-mechanical coupling conditions, the porosity ratio e and matrix suction s in equilibrium are measured. m and total suction s t Finally, the suction force composition is calculated according to the following formula:

[0043]

[0044] Among them, s a is the adsorption suction of the sample; s a,sat (e) is the correlation function between the adsorption suction and the porosity ratio of the sample under saturation; s c is the capillary suction of the sample; s m is the matrix suction of the sample; π is the osmotic suction of the sample; s t is the total suction force of the sample.

[0045] Compared with the prior art, the present invention has achieved the following technical effects:

[0046] The one-dimensional confined deformation test unit of the present invention provides space for sample compression and deformation. The vertical load control unit controls the vertical load applied to the sample via a pressure lever and weights. The vertical deformation measurement unit automatically collects and stores sample deformation data. The suction control unit applies target matrix suction or osmotic suction to the sample using dialysis or saline solution (containing pure water) saturation methods. The suction measurement unit simultaneously measures the matrix suction and total suction of the sample at equilibrium using contact and separation filter paper methods. This invention can simultaneously measure matrix suction and total suction under load or chemical environment. Through experimental research, it provides a basis for establishing a chemical-hydraulic-mechanical coupling analysis model for compacted clay soils and ensuring the service safety of clay barriers. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0048] Figure 1 Schematic diagram of a one-dimensional confined deformation test unit and a suction measurement unit of the present invention;

[0049] Figure 2 Schematic diagram of the vertical load control unit, vertical deformation measurement unit and suction control unit of the present invention;

[0050] Figure 3 Schematic diagram of a contact-type measurement filter paper assembly or a separate-type measurement filter paper assembly of a suction measurement unit of the present invention;

[0051] Among them, 1 is the base; 2 is the sample ring; 3 is the upper cover; 4 is the bolt; 5 is the water inlet and joint; 6 is the water outlet and joint; 7 is the spiral water trough; 8 is the permeable stone; 9 is the porous pad; 10 is the loading cap; 11 is the shaft hole and shaft sleeve; 12 is the loading shaft; 13 is the sample; 14 is the base sealing ring; 15 is the upper cover sealing ring; 16 is the loading shaft sealing ring; 17 is the loading platform; 18 is the pressure lever; 19 is the weight; 20 is the digital electronic hundred 21 is a dial indicator stand; 22 is a computer and data acquisition software; 23 is a conical flask; 24 is a magnetic stirrer; 25 is a peristaltic pump; 26 is a suction control solution; 27 is a circulation pipeline; 28 is a semipermeable membrane; 29 is a contact measurement filter paper combination, 29a is a contact measurement filter paper, and 29b is a contact protection filter paper; 30 is a separation measurement filter paper combination, 30a is a separation measurement filter paper, and 30b is a separation protection filter paper. DETAILED DESCRIPTION

[0052] To make the above-mentioned objects, features, and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. It is apparent that the embodiments described are only a portion of the embodiments of the present invention, not all of them. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0053] Example 1

[0054] As attached Figure 1 To the attached Figure 3 This embodiment provides a test apparatus for measuring the suction composition and deformation characteristics of compacted clay, comprising a one-dimensional confined deformation test unit, a vertical load control unit, a vertical deformation measurement unit, a suction control unit, and a suction measurement unit. The one-dimensional confined deformation test unit provides space for sample compression and deformation. The one-dimensional lateral confined deformation test unit mainly includes a base 1, a sample ring 2 and an upper cover 3. The sample 13 is located inside the sample ring 2, which provides space for sample compression and deformation of the sample 13. A spiral water trough 7 is set inside the base 1 for diversion. The water inlet and joint 5, and the water outlet and joint 6 are all located on the base 1. The spiral water trough 7 is connected to the water inlet and joint 5, and the water outlet and joint 6 on both sides. The vertical load control unit controls the vertical load applied to the sample 13 through a single-lever weight loading method, and the vertical deformation measurement unit automatically collects and stores the deformation data of the sample. The suction control unit is connected to the spiral water trough 7 inside the base 1 and is used to apply the target matrix suction or osmotic suction to the sample 13. The suction measurement unit is located inside the sample ring 2. The suction control unit uses the dialysis method or the salt solution saturation method to apply the target matrix suction or osmotic suction to the sample 13. The suction measurement unit uses the contact and separation filter paper methods to simultaneously measure the matrix suction and total suction of the sample 13 in the equilibrium state.

[0055] In this embodiment, the components of the one-dimensional lateral limit deformation test unit are made of stainless steel. The one-dimensional lateral limit deformation test unit also includes a loading shaft 12, an axis hole and a shaft sleeve 11, a loading cap 10, a porous pad 9 and a permeable stone 8; the loading cap 10, the porous pad 9, the sample 13 and the permeable stone 8 are placed from top to bottom inside the sample ring 2, the porous pad 9 is provided with a plurality of through holes, and the spiral water trough 7 is connected to the permeable stone 8; one end of the loading shaft 12 extends into the interior of the sample ring 2 and contacts the groove of the loading cap 10, and the other end is connected to the vertical load control unit.

[0056] In this embodiment, the upper cover 3, the sample ring 2 and the base 1 are arranged from top to bottom; the interior of the sample ring 2 is a closed space with an inner diameter of 61.8 mm and a wall thickness of 20 mm; the upper cover 3, the sample ring 2 and the base 1 are connected by four bolts 4; an upper cover sealing ring 15 is provided between the upper cover 3 and the sample ring 2, and a base sealing ring 14 is provided between the sample ring 2 and the base 1; the spiral water trough 7 is located inside the base 1 and has a width of 4 mm; the water inlet and joint 5 and the water outlet and joint 6 are located on both sides of the base and have a diameter of 5 mm; an axial hole and a shaft sleeve 11 are provided at the center of the upper cover 3, and a loading shaft sealing ring 16 is provided between the axial hole and the shaft sleeve 11 and the loading shaft 12, and the loading shaft 12 is located in the axial hole and the shaft sleeve 11.

[0057] In this embodiment, the vertical load control unit includes a loading platform 17, a pressure lever 18 and a weight 19, and the one-dimensional lateral limit deformation test unit is placed on the loading platform 17; the pressure lever 18 includes a first support rod and a second support rod, one end of the first support rod is hinged to the loading platform 17, and the weight 19 is located at the other end of the first support rod; one end of the second support rod is hinged to the middle of the first support rod, and the other end is connected to the groove at the top of the loading shaft 12; the vertical load applied to the sample is controlled by changing the mass of the weight 19, and the force transmission path is weight 19-pressure lever 18-loading shaft 12-loading cap 10-porous pad 9-sample 13.

[0058] In this embodiment, the vertical deformation measurement unit includes a digital electronic dial indicator 20, a dial indicator bracket 21 and a computer and data acquisition software 22; the dial indicator bracket 21 is set on the upper cover 3, and the digital electronic dial indicator 20 is set on the dial indicator bracket 21; the digital electronic dial indicator 20 is in contact with the top crossbeam of the second support rod of the pressure lever 18, and displays the deformation of the sample 13 in real time; the digital electronic dial indicator 20 is connected to the computer and data acquisition software 22, and transmits the measured data to the computer and data acquisition software 22; the computer and data acquisition software 22 collect and save the deformation data of the sample 13 in real time, and display the deformation-time relationship curve.

[0059] In this embodiment, the suction control unit includes a conical flask 23, a circulation pipeline 27 and a magnetic stirrer 24; the conical flask 23 is used to hold a suction control solution 26, which is distilled water, a saline solution or a polyethylene glycol solution; the conical flask 23 is located on the magnetic stirrer 24 to ensure a uniform concentration of the suction control solution 26; one end of the circulation pipeline 27 extends into the suction control solution 26 in the conical flask 23, and the other end is connected to the water inlet and the connector 5 of the spiral water trough 7; a peristaltic pump 25 is provided on the circulation pipeline 27, and the suction control solution 26 is transported by the peristaltic pump 25 through the circulation pipeline 27 into the spiral water trough 7 inside the base 1, and flows out from the water outlet and the connector 6 to the conical flask 23, thereby circulating and controlling the target suction of the sample 13.

[0060] In this embodiment, when it is necessary to control the matrix suction, the control solution is a polyethylene glycol solution, and the suction control unit also includes a semipermeable membrane 28; the semipermeable membrane 28 is a regenerated cellulose dialysis membrane, which is located between the sample 13 and the permeable stone 8; when it is necessary to control the osmotic suction, the control solution is distilled water or a salt solution, and the suction control unit also includes filter paper, which is located between the sample 13 and the permeable stone 8; the filter paper is used to separate the sample 13 and the permeable stone 8 to prevent soil particles from entering the circulation pipeline 27.

[0061] In this embodiment, the suction measurement unit includes a contact measurement filter paper assembly 29 and a separate measurement filter paper assembly 30; the contact measurement filter paper assembly 29 is located between the porous pad 9 and the sample 13, and is used to measure the matrix suction of the sample 13; the separate measurement filter paper assembly 30 is located between the loading cap 10 and the porous pad 9, and is used to measure the total suction of the sample 13.

[0062] In this embodiment, the contact measurement filter paper assembly 29 includes a contact protection filter paper 29a and a contact measurement filter paper 29b, one contact measurement filter paper 29b is located between the two contact protection filter papers 29a, and the size of the contact measurement filter paper 29b is smaller than the size of the contact protection filter paper 29a; the separation measurement filter paper assembly 30 includes a separation protection filter paper 30a and a separation measurement filter paper 30b, one separation measurement filter paper 30b is located between the two separation protection filter papers 30a, and the size of the separation measurement filter paper 30b is smaller than the size of the separation protection filter paper 30a; the matrix suction and total suction of the sample 13 are calculated respectively based on the equilibrium moisture content of the contact measurement filter paper 29b and the separation measurement filter paper 30b.

[0063] Example 2

[0064] This embodiment provides a test method for measuring the suction composition and deformation characteristics of compacted clay using the test device for measuring the suction composition and deformation characteristics of compacted clay described in Example 1, comprising the following steps:

[0065] Step 1: Pressing the sample 13: Place the sample ring 22 on an electronic universal testing machine, take clay powder with the required moisture content and mass, and pour it into the sample ring 22; use a pressing rod that matches the inner diameter of the sample ring 22, and press the sample 13 with a diameter of 61.8 mm and a height of 20 mm in the sample ring 22 at a rate of 0.5 mm / min using the electronic universal testing machine;

[0066] Step 2: Assemble the one-dimensional lateral confined deformation test unit: Place the permeable stone 8 in the base 1, place the semipermeable membrane 28 of appropriate size on top of the permeable stone 8, and secure the semipermeable membrane 28 to the base 1 with the base sealing ring 14; Place the sample ring 22 and sample 13 on the base 1, and place the contact measurement filter paper assembly 29 (Whatman No. 42 model), porous pad 9, separation measurement filter paper assembly 30 (Whatman No. 42 model), and loading cap 10 on top of the sample 13 from bottom to top; Cover the sample ring 22 with the upper cover 3, and push the loading shaft 12 through the shaft hole and sleeve 11 to contact the loading cap 10; Insert and tighten the four bolts 4 to connect and secure the base 1, sample ring 22, and upper cover 3;

[0067] Step 3: Connect the vertical load control unit and the vertical deformation measurement unit: Place the one-dimensional lateral limit deformation test unit on the loading platform 17; adjust the position of the pressure lever 18 so that the force transmission point of the top crossbeam of the pressure lever 18 is embedded in the groove at the top of the loading shaft 12; fix the digital electronic dial indicator 20 to the appropriate position of the dial indicator bracket 21, so that the head of the digital electronic dial indicator 20 contacts the top crossbeam of the pressure lever 18; turn on the digital electronic dial indicator 20, connect it to the computer and data acquisition software 22, and set the sampling interval to 10 seconds;

[0068] Step 4: Connect the suction control unit: Use the circulation line 27 to connect the peristaltic pump 25, the suction control solution 26 in the conical flask 23, and the water inlet and connector 5, and the water outlet and connector 6 on both sides of the spiral water tank 7. Do not start the suction control for now.

[0069] Step 5: Vertical load control: Place a 2.55 kg weight 19 and apply a 100 kPa vertical load to the sample 13. This step can be used to independently measure the deformation characteristics of the sample 13 under the mechanical load.

[0070] Step 6, osmotic suction control: After the deformation of sample 13 under a vertical load of 100 kPa reaches stability, a 0.1 mol / L NaCl solution is used as the suction control solution 26, corresponding to a target osmotic suction of 0.4 MPa; the peristaltic pump 25 is turned on to circulate the NaCl solution, and osmotic suction control begins; the osmotic suction control process should be no less than 15 days, and the vertical deformation of sample 13 should reach stability; this step can obtain the deformation characteristics of sample 13 under chemical-mechanical coupling (including one-dimensional free and pure water conditions); thereafter, the test can be terminated (i.e., step 8) and the suction composition of sample 13 under chemical-mechanical coupling can be measured (according to step 9), or the next step of matrix suction control can be continued;

[0071] In this step, the method for controlling the penetration suction is:

[0072] The osmotic suction is controlled by a salt solution. The maximum control value is determined by the solubility of the salt solution used. The salt solution concentration required for the target osmotic suction control is calculated according to the following formula:

[0073] π s =iCRT

[0074] Among them, π s is the osmotic suction of the salt solution, in Pa; i is the coefficient (2 for NaCl solution); C is the concentration of the salt solution, in mol / L; R is the ideal gas constant, with a value of 8.314 Pa·m 3 ·K -1 ·mol -1 ; T is Kelvin temperature, unit is K;

[0075] Step 7, matrix suction control: After the deformation of sample 13 stabilizes under a vertical load of 100 kPa and a 0.1 mol / L NaCl solution, the suction control solution 26 is replaced with a PEG20000 (polyethylene glycol with a molecular weight of 20,000) solution with a mass concentration of 0.302, corresponding to a target matrix suction of 1 MPa; the peristaltic pump 25 is turned on to circulate the PEG20000 solution, and matrix suction control begins; the matrix suction control process should be no less than 15 days, and the vertical deformation of sample 13 should be stable; this step can obtain the deformation characteristics of sample 13 under chemical-hydraulic-mechanical coupling; matrix suction control can also be performed only after the deformation of sample 13 under vertical load has stabilized, to measure the suction composition and deformation characteristics of sample 13 under hydraulic-mechanical coupling;

[0076] In this step, the method for controlling matrix suction is:

[0077] The matrix suction is controlled by dialysis, and the control range is generally 0-10 MPa. The concentration of PEG20000 solution required to control the target matrix suction is calculated according to the following formula:

[0078] s m =11c 2

[0079] Among them, s m is the target matrix suction, in MPa; c is the mass concentration of PEG20000 solution;

[0080] Step 8: Stop the test: After draining the suction control solution 26 inside the base 1, shut down the peristaltic pump 25; remove the suction control unit and the vertical deformation measurement unit, quickly remove the weight 19, and remove and disassemble the one-dimensional lateral confined deformation test unit;

[0081] Step 9: Determine the matrix suction and total suction of the sample 13: After removing the sample, immediately measure the moisture content of the contact-type measurement filter paper 29b and the separation-type measurement filter paper 30b, and calculate the matrix suction of the sample (s m ) and total suction (s t ):

[0082] logs m =2.909-0.0229ω f1 (ω f1 ≥47)

[0083] logs m =4.945-0.0673ω f1 (ω f1 <47)

[0084] Among them, ω f1 The equilibrium moisture content of the filter paper 29b is measured by contact method, in %; s m is the matrix suction of sample 13, in kPa;

[0085] logs t =8.778-0.222ω f2 (ω f2 ≥26)

[0086] logs t =5.31-0.0879ω f2 (ω f2 <26)

[0087] Among them, ω f2 Separate measurement of the equilibrium moisture content of the filter paper 30b, in %; s t is the total suction of sample 13, in kPa.

[0088] Step 10: Determine the moisture content and dry density of sample 13: Use an electronic universal testing machine to slowly push out sample 13 with a pressure rod at a speed of 1 mm / min. Determine the moisture content of sample 13 using a drying method and the density of sample 13 using a wax sealing method, and calculate the dry density of sample 13;

[0089]

[0090] Among them, ρ d is the dry density of sample 13, in g / cm 3 ; e is the porosity of sample 13; ρ is the density of sample 13, in g / cm 3 ;ω is the moisture content of sample 13, in %; Gs is the particle specific gravity; ρ w is the density of water in g / cm 3 ;

[0091] Step 11, determine the suction composition of sample 13 under chemical-hydraulic-mechanical coupling conditions:

[0092] Set the capillary suction force s of the distilled water saturated sample 13 c is zero, the osmotic suction π is the reference osmotic suction π0 caused by the adsorption of cations, and the adsorption suction s a is a function of the void ratio e a,sat (e), the matrix suction of the distilled water saturated sample 13 is s m,sat =s a,sat (e) The total suction force is s t,sat =π0+s a,sat (e); Referring to steps 1 to 10, the matrix suction and total suction of the distilled water saturated sample 13 under different vertical loads are measured to determine the reference penetration suction π0 and the saturated adsorption suction function s a,sat (e);

[0093] Set the capillary suction force s of the salt solution saturated sample 13 c is zero, and the osmotic suction π is a function of the salt solution concentration C sat (C), then the matrix suction of the salt solution saturated sample 13 is s m,sat =s a,sat (e) The total suction force is s t,sat =π sat (C)+s a,sat (e); Referring to steps 1 to 10, the matrix suction and total suction of the sample 13 saturated with salt solution of different concentrations were measured to determine the saturated osmotic suction function π sat (C);

[0094] For any unsaturated sample with a porosity of e under chemical-hydraulic-mechanical coupling conditions, assuming that the adsorption suction s a It is only related to the porosity ratio e, and the equilibrium matrix suction s is measured m and total suction s t Finally, the suction force composition is calculated according to the following formula:

[0095]

[0096] Among them, s a is the adsorption suction of the sample; s a,sat (e) is the saturated adsorption suction s a,sat Correlation function with porosity e; s c is the capillary suction of the sample; s m is the matrix suction of the sample; π is the osmotic suction of the sample; s t is the total suction force of the sample.

[0097] This embodiment integrates suction control and suction measurement technologies to achieve the determination of the suction composition of compacted clay under chemical-hydraulic-mechanical coupling conditions; this embodiment adopts an automatic deformation data acquisition system to achieve automated testing of the deformation characteristics of compacted clay under chemical-hydraulic-mechanical coupling conditions; the testing device of this embodiment is low-cost, the testing method is simple, and the test results are highly reliable.

[0098] This specification uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A test apparatus for determining the suction composition and deformation characteristics of compacted clay, characterized in that: The test system comprises a one-dimensional confined deformation test unit, a vertical load control unit, a vertical deformation measurement unit, a suction control unit, and a suction measurement unit. The one-dimensional confined deformation test unit provides space for sample compression and sample deformation. The vertical load control unit controls the vertical load applied to the sample through a single-lever weight loading method. The vertical deformation measurement unit automatically collects and stores sample deformation data. The suction control unit applies target matrix suction or osmotic suction to the sample using a dialysis method or a salt solution saturation method. The suction measurement unit uses a contact and separation filter paper method to simultaneously measure the matrix suction and total suction of the sample in a balanced state. The one-dimensional lateral limit deformation test unit includes a base, a sample ring, an upper cover and bolts, and the base, the sample ring and the upper cover are connected by four bolts; a spiral water trough is provided inside the base, and a water inlet and joint, a water outlet and joint are provided on both sides of the base; a permeable stone, a porous pad and a loading cap are placed in the sample ring; the upper cover is provided with an axial hole and a shaft sleeve, and the loading shaft passes through the axial hole and the shaft sleeve and contacts the groove above the loading cap; the sample is located between the permeable stone and the porous pad; a base sealing ring is provided between the base and the sample ring, a top cover sealing ring is provided between the top cover and the sample ring, and a loading shaft sealing ring is provided between the axial hole and the shaft sleeve and the upper cover, so as to form a closed space inside the sample ring; The vertical load control unit includes a loading platform, a pressure lever, and a weight. The one-dimensional lateral confinement test unit is placed on the loading platform. The force transmission point of the top crossbeam of the pressure lever is embedded in the groove at the top of the loading shaft. The vertical load applied to the sample is controlled by changing the mass of the weight. The suction control unit includes a conical flask, a magnetic stirrer, a peristaltic pump, a suction control solution and a circulation pipeline. The suction control solution is pumped into and out of the spiral water trough of the base in the one-dimensional lateral confinement deformation test unit by the peristaltic pump through the circulation pipeline, and is combined with a semipermeable membrane or filter paper to control the suction state of the sample; the conical flask is placed on the magnetic stirrer to ensure the uniform concentration of the suction control solution; the suction control solution is distilled water, saline solution or polyethylene glycol solution; when it is necessary to control matrix suction, the suction control solution is polyethylene glycol, and the suction control unit also includes a semipermeable membrane, which is located between the sample and the permeable stone; when it is necessary to control osmotic suction, the suction control solution is distilled water or saline solution, and the suction control unit also includes filter paper, which is located between the sample and the permeable stone.

2. The test device for measuring the suction composition and deformation characteristics of compacted clay according to claim 1, characterized in that: The vertical deformation measurement unit includes a digital electronic dial indicator, a dial indicator bracket, a computer and data acquisition software. The digital electronic dial indicator displays the deformation of the sample in real time. The computer and data acquisition software collect and save the deformation data of the sample in real time and display the deformation-time relationship curve in real time. The suction measurement unit includes a contact measurement filter paper combination and a separation measurement filter paper combination. The contact measurement filter paper combination is located between the porous pad and the sample and is used to measure the matrix suction of the sample; the separation measurement filter paper combination is located between the loading cap and the porous pad and is used to measure the total suction of the sample; the contact measurement filter paper combination includes a contact protection filter paper and a contact measurement filter paper, one of the contact measurement filter papers is located between two of the contact protection filter papers, and the size of the contact measurement filter paper is smaller than the size of the contact protection filter papers; the separation measurement filter paper combination includes a separation protection filter paper and a separation measurement filter paper, one of the separation measurement filter papers is located between two of the separation protection filter papers, and the size of the separation measurement filter paper is smaller than the size of the separation protection filter papers; the matrix suction and total suction of the sample are calculated respectively according to the equilibrium moisture content of the contact measurement filter paper and the separation measurement filter paper.

3. A test method for measuring the suction composition and deformation characteristics of compacted clay using the test device for measuring the suction composition and deformation characteristics of compacted clay according to claim 1, characterized in that: The following steps are involved: Step 1: Press the sample: Take clay powder with the required moisture content and mass, use a pressure rod that matches the inner diameter of the sample ring, and use an electronic universal testing machine to press the sample in the sample ring; Step 2: Assemble the one-dimensional lateral confined deformation test unit: Place the permeable stone in the base, place a semipermeable membrane of appropriate size on top of the permeable stone, and fix the semipermeable membrane to the base with a base sealing ring; Place the sample ring and sample on the base, and place the contact measurement filter paper assembly above the sample; place the porous pad, and place the separation measurement filter paper assembly on it; place the loading cap and cover it, push the loading shaft through the shaft hole and shaft sleeve, and contact the loading cap; insert and tighten four bolts to connect and fix the base, sample ring and cover; Step 3: Connect the vertical load control unit and the vertical deformation measurement unit: Place the one-dimensional lateral confinement deformation test unit on the loading platform; Adjust the position of the pressure lever so that the force transmission point of the top crossbeam of the pressure lever is embedded in the groove at the top of the loading shaft; fix the digital electronic dial indicator in the appropriate position of the dial indicator bracket so that the head of the indicator contacts the top crossbeam of the pressure lever; turn on the digital electronic dial indicator and connect it to the computer and data acquisition software; Step 4. Connect the suction control unit: Use a circulation line to connect the peristaltic pump, the suction control solution in the conical flask, the water inlet and connectors on both sides of the base, and the water outlet and connectors; Step 5: Vertical load control: Place weights of the required mass and apply the required vertical load to the specimen. This step can independently measure the deformation characteristics of the specimen under mechanical load. Step 6: Osmotic suction control: After the deformation of the specimen under vertical load reaches stability, a salt solution of a specific concentration or distilled water is used as the suction control solution. The peristaltic pump is turned on to circulate the salt solution and osmotic suction control begins. The osmotic suction control process should last no less than 15 days, and the vertical deformation of the specimen should reach stability. This step can obtain the deformation characteristics of the sample under chemical-mechanical coupling or under one-dimensional free and pure water conditions. Afterwards, the test is terminated according to step eight, and the suction composition of the sample under chemical-mechanical coupling is determined according to step nine. The matrix suction control in step seven can also be continued. Step 7: Matrix suction control: After the deformation of the specimen under the vertical load and saline solution reaches stability, the suction control solution is replaced with a polyethylene glycol solution of a specific concentration, and the peristaltic pump is turned on to circulate the polyethylene glycol solution, and matrix suction control is started; The matrix suction control process should be no less than 15 days, and the vertical deformation of the specimen should be stable; This step can obtain the deformation characteristics of the sample under the action of chemical-hydraulic-mechanical coupling. Matrix suction control can also be performed only after the deformation of the sample reaches stability under vertical load, to measure the suction composition and deformation characteristics of the sample under the action of hydraulic-mechanical coupling. Step 8. Stop the test: drain the suction control solution in the base and turn off the peristaltic pump; remove the suction control unit and the vertical deformation measurement unit, quickly remove the weights, and remove and disassemble the one-dimensional lateral confinement deformation test unit; Step 9. Determine the matrix suction and total suction of the sample: Measure the moisture content of the contact and separation filter papers, and calculate the corresponding matrix suction and total suction. To avoid errors caused by changes in the moisture content of the filter papers, measure the mass of the contact and separation filter papers immediately after removing the sample. Step 10: Determine the moisture content and dry density of the sample: Use an electronic universal testing machine to slowly push out the sample with a pressure rod, use the drying method to determine the moisture content, and the wax sealing method to determine the density, and calculate the dry density; Step 11: Determine the suction composition of the sample under chemical-hydraulic-mechanical coupling conditions.

4. The test method for determining the suction composition and deformation characteristics of compacted clay according to claim 3, characterized in that: Methods of penetrant suction control include: The osmotic suction is controlled by a salt solution. The maximum control value is determined by the solubility of the salt solution used. The salt solution concentration required for the target osmotic suction control is calculated according to the following formula: in, π s is the osmotic suction of the salt solution, in Pa; i is the correlation coefficient; C is the concentration of the salt solution, in mol / L; R is the ideal gas constant, with a value of 8.314 Pa·m 3 · K -1 ·mol -1 ; T is the temperature in Kelvin. K .

5. The test method for determining the suction composition and deformation characteristics of compacted clay according to claim 3, characterized in that: Methods of matrix suction control include: The matrix suction was controlled by dialysis within a range of 0–10 MPa. The concentration of the polyethylene glycol solution required to achieve the target matrix suction was calculated using the following formula: in, s m is the matrix suction, in MPa; c is the mass concentration of polyethylene glycol solution.

6. The test method for determining the suction composition and deformation characteristics of compacted clay according to claim 3, characterized in that: Methods for determining matrix suction and total suction include: Suction was measured using Whatman No. 42 filter paper as both a contact and a separation filter paper combination. The measurement range was the full range. Matrix suction was calculated using the following formula: s m and total suction s t : in, s m is the matrix suction of the sample, in kPa, ω f1 It is the equilibrium moisture content of the filter paper measured by contact method, and the unit is %; in, s t is the total suction of the sample, in kPa, ω f2 It is a separate measurement of the equilibrium moisture content of the filter paper in %.

7. The test method for determining the suction composition and deformation characteristics of compacted clay according to claim 3, characterized in that: Methods for determining the suction composition of a specimen include: The matrix suction and total suction of distilled water saturated samples under different vertical loads were measured to determine the correlation function between saturated adsorption suction and porosity ratio. s a,sat ( e ); measure the matrix suction and total suction of samples saturated with salt solutions of different concentrations, and determine the correlation function between saturated osmotic suction and salt solution concentration π sat ( C ); For any unsaturated sample under chemical-hydraulic-mechanical coupling conditions, the porosity ratio of the equilibrium state is measured e , matrix suction s m and total suction s t Finally, the suction force composition is calculated according to the following formula: in, s a is the adsorption suction of the sample; s a,sat ( e ) is the correlation function between the adsorption suction and the porosity ratio of the sample under saturated state; s c is the capillary suction of the sample; s m is the matrix suction of the sample; π is the penetration suction of the sample; s t is the total suction force of the sample.

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