CN113970493A - Testing device and testing method for shear stress-strain curve test sample under large-scale direct shearing of on-site coarse-grained soil - Google Patents
Testing device and testing method for shear stress-strain curve test sample under large-scale direct shearing of on-site coarse-grained soil Download PDFInfo
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Abstract
The invention provides a test device and a test method for shear stress-strain curve test samples under large-scale direct shearing of on-site coarse-grained soil, wherein a direct shearing test pit (1) is dug in a test site, an impermeable layer is paved at the bottom of the direct shearing test pit (1) and the coarse-grained soil is backfilled, a plurality of groups of coarse-grained soil samples (10) are arranged in the direct shearing test pit (1), a water injection area (5) and a non-water injection area (32) are arranged in the direct shearing test pit (1), a sample preparation area (33) is arranged in the non-water injection area (32), and a plurality of groups of coarse-grained soil samples (10) are arranged in the water injection area (5) and the non-water injection area (32). The invention can directly manufacture the sample in the field, and obtains the test analysis data of the influence of the dry-wet circulation effect on the field shear strength by simulating the actual conditions of rock and soil masses in different engineering fields.
Description
Technical Field
The invention relates to the technical field of soil mechanics tests, in particular to a test device and a test method for a shear stress-strain curve test sample under large-scale direct shearing of on-site coarse-grained soil.
Background
The coarse-grained soil is a soil-stone mixture with the grain size of 0.075-60 mm and the content (mass ratio) of grains larger than 50%. The cause of coarse-grained soil is generally complex, the coarse-grained soil has different grain sizes, complex material components, irregular structural distribution, large uneven coefficient and great difference of permeability coefficient. The mechanical properties of various components for composing coarse-grained soil under the action of external load are greatly different, and simultaneously, extremely complex interaction exists between the components, so that the components are extremely complex discontinuous medium materials. The characteristics of coarse-grained soil determine that the engineering properties of the coarse-grained soil are very complex, and a lot of difficulties are brought to the research of the coarse-grained soil. With the development of geotechnical engineering and the construction of large-scale rock mass engineering, especially the development of road and hydraulic and hydroelectric engineering construction, the soil-rock mixture is often used as a filler in engineering construction, and is increasingly paid more attention by scholars at home and abroad as a special geotechnical medium, and the mechanical characteristics of the geotechnical material have great relationship with the internal structure, size effect, particle shape and particle size composition. The change of water environment such as rain infiltration and evaporation, underground water level rising and falling and the like is a common natural phenomenon, and the repeated infiltration of water causes the original friction balance state among particles to be broken and the particle strength to be reduced, so that the particle edges and corners are broken and the particle positions are moved in a certain range, and the mechanical properties such as the strength, the stress-strain characteristic and the like of coarse-grained soil are changed. Therefore, the dry-wet cycle is not negligible as an important factor affecting the change of the long-term mechanical properties of coarse-grained soil, especially for high-fill projects of the falling zone.
However, the change of mechanical properties of coarse-grained soil under dry-wet cycle conditions is not paid enough attention at present, and the change is mainly shown in that many research objects in dry-wet cycle tests do not have coarse-grained soil at all or only adopt a simple dry-wet cycle method for research. In addition, many scholars have used laboratory tests to study the effect of the dry-wet cycling on the shear strength of coarse-grained soil. The coarse-grained soil sample for the indoor test is a remolded sample, the original cementing action is destroyed, the development of the crack generated by the dry-wet circulation action is limited by the size and the test conditions, and the influence of complete reaction on the shear strength is difficult. In practical engineering, limited by field conditions, researches on the influence of dry-wet cycling on field shear strength are not common.
At present, the dry-wet circulation of coarse-grained soil mainly adopts the methods of soaking and humidifying and naturally airing indoors. Wherein, the natural drying takes long time, the dehydration effect is poor, and the research on the problems is seriously limited.
Disclosure of Invention
In view of the defects in the prior art, the first object of the invention is to provide a device for testing a large-scale direct shear stress-strain curve sample of on-site coarse-grained soil. The invention can directly manufacture the sample in the field, and obtains the test analysis data of the influence of the dry-wet circulation effect on the field shear strength by simulating the actual conditions of rock and soil masses in different engineering fields.
In order to solve the technical problems, the invention is realized by the following technical scheme:
the test device for the shear stress-strain curve sample under the large-scale direct shearing of the on-site coarse-grained soil is characterized in that: dig at experimental place and establish the experimental trial pit of direct shear, the barrier layer is laid and coarse grained soil is backfilled to the bottom in the experimental trial pit of direct shear, sets up multiunit coarse grained soil sample in the experimental trial pit of direct shear, sets up water injection district and water injection district in the experimental trial pit of direct shear, is provided with sample preparation district in the water injection district, all be provided with multiunit coarse grained soil sample in water injection district and the water injection district not, coarse grained soil sample outside cover establishes the shearing box, sets up experimental frame system in the experimental trial pit of direct shear, sets up vertical pressure device and horizontal shearing device between experimental frame system and the coarse grained soil sample.
Further: the impermeable layer comprises a first layer of clay, a geomembrane and a second layer of clay which are sequentially paved at the bottom of the direct shear test pit; and a plurality of groups of coarse-grained soil samples in the water injection area and the sample preparation area are arranged according to the area.
Further: the testing frame system comprises a portal frame, first supports are correspondingly arranged on two sides of the bottom of the portal frame, an inclined support is arranged between the first supports and the portal frame for reinforcement, and balancing weights are placed on the inclined support; a plurality of test grooves are dug in the direct shear test pit after coarse-grained soil is backfilled, and a water injection area, a non-water injection area and a sample preparation area (33) are arranged along the length direction of the test grooves.
Further: coarse grain soil sample top in the water injection district is inserted and is equipped with heating rod and temperature sensor, and heating rod and temperature sensor all are connected with automatic tripping device, the position that the heating rod located on coarse grain soil sample can guarantee that coarse grain soil sample accomplishes dry wet cycle smoothly and handles.
Further: the vertical pressure device comprises a vertical force sensor, a vertical jack and a vertical displacement sensor, a slidable bearing plate is arranged on a cross beam at the top of the door-shaped frame and is connected with the vertical jack through the vertical force sensor, a cover plate is arranged below the vertical jack and is arranged above a coarse-grained soil sample, and the vertical displacement sensor is connected with the side wall of the shearing box.
Further: the horizontal shearing device comprises a horizontal jack, a horizontal displacement sensor and a horizontal force sensor, wherein the horizontal jack is fixedly arranged on a support rod on the side edge of the portal frame, the extending end of the horizontal jack is propped against the side wall of the shearing box through the horizontal force sensor, and the horizontal displacement sensor is connected with the horizontal jack.
A second object of the present invention is to: the test method of the test sample test device for the shear stress-strain curve test under the large direct shear of the on-site coarse-grained soil is provided, and comprises the following steps:
s1, digging a plurality of test grooves arranged side by side in a direct shear test pit, dividing a non-water injection region and a water injection region in the direct shear test pit, and dividing a sample preparation region in the water injection region;
s2, performing primary dry-wet cycle treatment in the sample preparation area by adopting an integral sample saturation method, and then drying in the air by adopting a natural drying method; the whole sample is naturally dried in the period, and the following steps are carried out:
s2-1, preparing a dry coarse-grained soil sample in a region without water injection, and performing a direct shear test;
s2-2, carrying out primary dry-wet cycle treatment on the area outside the sample preparation area in the water injection area by adopting a single sample saturation method, and then carrying out direct shear test;
s2-3, carrying out secondary dry-wet cycle treatment in the area outside the sample preparation area in the water injection area by adopting a single sample saturation method and a heating rod heating method, and then carrying out a direct shear test;
s3, after airing, dividing a first test area in the sample preparation area, performing secondary dry-wet circulation treatment on the area outside the first test area in the sample preparation area by adopting an integral sample saturation method, and airing by adopting a natural airing method;
s3-1, in the natural airing period, carrying out three times of dry-wet cycle treatment in a first test area by adopting a single sample saturation method and a heating rod heating method, and then carrying out a direct shear test;
s4, after airing, dividing a second test area in the sample preparation area, performing secondary dry-wet cycle treatment on the area outside the second test area by adopting an integral sample saturation method, and airing by adopting a natural airing method;
s4-1, in the natural airing period, performing dry-wet cycle treatment for four times in a second test area by adopting a single sample saturation method and a heating rod heating method, and then performing a direct shear test;
and S5, repeating the step S4 until all the direct shear tests are completed.
Further: the operation steps of the bulk sample saturation method are as follows: plugging two ends of a test groove in a sample preparation area, injecting water into the test groove, and permeating coarse-grained soil around the test groove by the water within 24 hours; the natural drying method comprises the following operation steps: the coarse-grained soil after infiltration is placed for one week.
Further: the single sample saturation method comprises the following operation steps:
t1: manually preparing a sample after determining the position of a coarse-grained soil sample point between two adjacent test tanks, taking the diameter of the cover plate as the taking diameter of the coarse-grained soil sample, shoveling out soil around the cover plate by using a small shovel to form a water injection pit, wherein the residual coarse-grained soil in the water injection pit is the coarse-grained soil sample used for the test, and the space between the coarse-grained soil sample and the pit wall of the water injection pit is a water injection space;
t2, sleeving a shearing box on the outer side of the coarse-grained soil sample, filling the gap between the shearing box and the coarse-grained soil sample with fine materials, and compacting;
t3, injecting water into the water injection space and the top of the coarse-grained soil sample, and maintaining a certain water surface height in the water injection space, so that the coarse-grained soil sample can be subjected to saturation treatment, and at the moment, the coarse-grained soil sample is subjected to one-time dry-wet cycle treatment;
the operation steps of the heating rod heating method are as follows:
a plurality of drill holes are evenly constructed on the top surface of the coarse-grained soil sample through the hand drill, the heating rod and the temperature sensor are placed in the drill holes, the heating rod and the temperature sensor are connected with the automatic tripping device, and the heating rod continuously heats until the periphery of the coarse-grained soil sample and the water injection at the top of the coarse-grained soil sample are evaporated.
Further: the direct shear test comprises the following operation steps:
r1, placing a test frame system at the periphery of a coarse-grained soil sample to be tested, respectively placing two first supports of the door-shaped frame in two adjacent different test grooves, simultaneously ensuring that the door-shaped frame can be placed horizontally, cleaning coarse-grained soil at the periphery of the coarse-grained soil sample, and ensuring that a horizontal jack can work normally;
r2, performing a direct shear test, and applying a corresponding vertical load to the coarse-grained soil sample to be tested through a vertical jack, wherein the vertical force sensor has a corresponding reading at the moment;
and after the R3 and the vertical load are applied to a specified numerical value, applying a horizontal load to the coarse-grained soil sample to be tested through a horizontal jack until the coarse-grained soil sample is sheared and damaged, recording the numerical value, and dismantling the test frame system.
Compared with the prior art, the invention has the following advantages and beneficial effects:
the test soil sample is undisturbed soil, has small disturbance, and can truly reflect the deterioration condition of the bonding strength of the sample generated by cementation under the action of dry-wet circulation; the invention can reflect the change of the mechanical property of the sample due to the penetration of water under the action of dry-wet circulation, and effectively simulate the environmental conditions of the rock in the hydro-fluctuation belt of the reservoir bank slope.
Drawings
FIG. 1 is a schematic diagram of a test pit of the present invention for a direct shear test of a test site;
FIG. 2 is a schematic structural view of the present invention;
FIG. 3 is a schematic structural view of a test frame system;
FIG. 4 is a schematic diagram of a heating rod for a dry-wet cycle treatment;
FIG. 5 is a schematic view of the structure of a horizontal pipe;
FIG. 6 is a schematic view of the counterweight structure;
FIG. 7 is a graph of shear stress versus horizontal displacement for a coarse soil sample after four dry and wet cycles;
FIG. 8 is a graph of shear stress versus normal stress for a coarse soil sample after four dry and wet cycles;
FIG. 9 is a graph of shear stress versus horizontal displacement for a coarse soil sample from five dry and wet cycles;
FIG. 10 is a graph of shear stress versus normal stress for a coarse soil sample over five dry and wet cycles;
FIG. 11 is a flow chart of the construction of the present invention.
Reference numerals: 1-testing test pits; 2-first layer clay; 3-geomembrane; 4-a second layer of clay; 5-water injection zone; 6-test tank; 7-clay block; 8-cover plate; 9-horizontal pipe; 10-coarse soil sample; 11-a cutting box; 12-a horizontal force sensor; 13-a heating rod; 14-a temperature sensor; 15-automatic tripping device; 16-a test frame system; 17-a counterweight block; 18-a diagonal brace; 19-a vertical force sensor; 20-a vertical displacement sensor; 22-a level bar; 23-a transparent tube; 24-a hose; 25-a vent hole; 26-a telescopic bracket; 27-a first bracket; 28-horizontal jack; 29-vertical jack; 30-a pressure bearing plate; 31-a horizontal displacement sensor; 32-non-water injection zone; 33-sample preparation area; 34-a first test zone; 35-a second test zone; 36-water injection pit.
Detailed Description
In order that those skilled in the art will better understand the technical solutions of the present invention, the following description of the preferred embodiments of the present invention is provided in conjunction with the specific examples, but it should be understood that the drawings are for illustrative purposes only and should not be construed as limiting the present invention; for the purpose of better illustrating the embodiments, certain features of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted. The positional relationships depicted in the drawings are for illustrative purposes only and are not to be construed as limiting the invention.
The invention is further illustrated by the following figures and examples, which are not to be construed as limiting the invention.
As shown in fig. 1 to 11, a direct shear test pit 1 is dug in a test site, an impermeable layer is laid at the bottom of the direct shear test pit 1, coarse soil is backfilled, a plurality of coarse soil samples 10 (in this embodiment, the coarse soil samples 10 have a height of 300mm and a diameter of 500mm) are arranged in the direct shear test pit 1, a water injection area 5 and a non-water injection area 32 are arranged in the direct shear test pit 1, a sample preparation area 33 is arranged in the non-water injection area 32, a plurality of coarse soil samples 10 are arranged in the water injection area 5 and the non-water injection area 32, a shear box 11 is sleeved outside the coarse soil samples 10, a test frame system 16 is arranged in the direct shear test pit 1, and a vertical pressure device and a horizontal shear device are arranged between the test frame system 16 and the coarse soil samples 10.
The impermeable layer comprises a first layer of clay 2, a geomembrane 3 and a second layer of clay 4 which are sequentially paved at the bottom of the direct shear test pit 1; the groups of coarse-grained soil samples 10 in the water injection zone 5 and the sample preparation zone 33 are arranged according to zones.
The test frame system 16 comprises a door-shaped frame, first supports 27 are correspondingly arranged on two sides of the bottom of the door-shaped frame, an inclined support 18 is arranged between the first supports 27 and the door-shaped frame for reinforcement, and a balancing weight 17 is placed on the inclined support 18; a plurality of test grooves 6 are dug in the direct shear test pit 1 after coarse-grained soil is backfilled, and a water injection area 5, a non-water injection area 32 and a sample preparation area 33 are arranged along the length direction of the test grooves 6; the balancing weight 17 is composed of a woven bag and coarse soil 5 inside, and in the embodiment, two balancing weights 17 are placed on each inclined bracket 18. The arrangement of the balancing weight 17 can ensure the stability of the portal frame and prevent the portal frame from being lifted off the ground when the vertical jack 29 works.
Coarse grained soil sample 10 top in the water injection district 5 is inserted and is equipped with heating rod 13 and temperature sensor 14, and heating rod 13 and temperature sensor 14 all are connected with automatic tripping device 15, the position that heating rod 13 located on coarse grained soil sample 10 can guarantee that coarse grained soil sample 10 accomplishes dry-wet cycle smoothly and handles, and automatic tripping device 15 sets for the temperature and is 50 ℃.
Preferably, three or four heating rods 13 are used and arranged in an equilateral triangle or parallelogram on the coarse soil sample 10, the heating rods 13 being arranged on the coarse soil sample 10 at a distance of 100mm from the edge of the shear box 11. The depth of insertion of the heating rod 13 on the coarse soil sample 10 is about 50mm and can be extended according to the height of the shear box 11, and the diameter of the heating rod 13 is 1/50 of the diameter of the coarse soil sample 10, and the heating rod is in the shape of a cylinder or a prism.
The vertical pressure device comprises a vertical force sensor 19, a vertical jack 29 and a vertical displacement sensor 20, a slidable bearing plate 30 is arranged on a cross beam at the top of the portal frame, the bearing plate 30 is connected with the vertical jack 29 through the vertical force sensor 19, a cover plate 8 is arranged below the vertical jack 29, the cover plate 8 is arranged above the coarse-grained soil sample 10, and the vertical displacement sensor 20 is connected with the side wall of the shearing box 11.
The horizontal shearing device comprises a horizontal jack 28, a horizontal displacement sensor 31 and a horizontal force sensor 12, wherein the horizontal jack 28 is fixedly arranged on a support rod on the side edge of the door-shaped frame, the extending end of the horizontal jack 28 is propped against the side wall of the shearing box 11 through the horizontal force sensor 12, and the horizontal displacement sensor 31 is connected with the horizontal jack 28. The vertical pressure device and the horizontal shearing device are connected with data acquisition equipment.
The invention also provides a test method of the test sample test device for the shear stress-strain curve test under the large-scale direct shear of the on-site coarse-grained soil, and the test method comprises the following steps:
s1, digging a plurality of test grooves 6 arranged in parallel in a direct shear test pit 1, dividing a non-water injection region 32 and a water injection region 5 in the direct shear test pit 1, and dividing a sample preparation region 33 in the water injection region 5;
s2, performing primary dry-wet cycle treatment in the sample preparation area 33 by adopting an integral sample saturation method, and then drying in the air by adopting a natural drying method; the whole sample is naturally dried in the period, and the following steps are carried out:
s2-1, preparing a dry coarse-grained soil sample in the non-water injection area 32, and performing a direct shear test;
s2-2, carrying out primary dry-wet cycle treatment on the area outside the sample preparation area 33 in the water injection area 5 by adopting a single sample saturation method, and then carrying out a direct shear test;
s2-3, carrying out secondary dry-wet cycle treatment in the area outside the sample preparation area 33 in the water injection area 5 by adopting a single sample saturation method and a heating rod heating method, and then carrying out a direct shear test;
s3, after airing, dividing the sample preparation area 33 into a first test area 34, performing secondary dry-wet circulation treatment on the area outside the first test area 34 in the sample preparation area 33 by adopting an integral sample saturation method, and airing by adopting a natural airing method;
s3-1, in the natural airing period, carrying out three times of dry-wet cycle treatment in the first test area 34 by adopting a single sample saturation method and a heating rod heating method, and then carrying out a direct shear test;
s4, after airing, dividing a second test area 35 in the sample preparation area 33, performing secondary dry-wet circulation treatment on the area outside the second test area 35 by adopting an integral sample saturation method, and airing by adopting a natural airing method;
s4-1, in the period of natural airing, performing dry-wet cycle treatment for four times in the second test area 35 by adopting a single sample saturation method and a heating rod heating method, and then performing a direct shear test;
and S5, repeating the step S4 until all the direct shear tests are completed.
The operation steps of the bulk sample saturation method are as follows: after the both ends of the test cell 6 in the sample preparation area 33 are plugged (in this example, plugging is performed by using the clay plug 7), water is injected into the test cell 6, and the water penetrates coarse-grained soil around the test cell 6 within 24 hours; the natural drying method comprises the following operation steps: the coarse-grained soil after infiltration is placed for one week.
The single sample saturation method comprises the following operation steps:
t1: manually preparing samples after determining the positions of coarse-grained soil sample points between two adjacent test tanks 6, shoveling out soil around a cover plate 8 by using a small shovel by taking the diameter of the cover plate 8 as the taking diameter of a coarse-grained soil sample 10 to form a water injection pit 36, wherein the residual coarse-grained soil in the water injection pit 36 is the coarse-grained soil sample 10 used for the test, and the space between the coarse-grained soil sample 10 and the pit wall of the water injection pit 36 is a water injection space;
t2, sleeving a shearing box 11 on the outer side of the coarse-grained soil sample 10, filling the gap between the shearing box 11 and the coarse-grained soil sample 10 with fine materials, and compacting;
t3, injecting water into the water injection space and the top of the coarse-grained soil sample 2, and maintaining a certain water surface height (in the embodiment, the water surface height is maintained at 10cm) in the water injection space, so that the coarse-grained soil sample 10 can be subjected to saturation treatment, and at this time, the coarse-grained soil sample 10 is subjected to one dry-wet cycle treatment;
the operation steps of the heating rod heating method are as follows:
a plurality of drill holes are uniformly constructed on the top surface of the coarse-grained soil sample 10 through a hand drill, a heating rod 13 and a temperature sensor 14 are placed in the drill holes, the heating rod 13 and the temperature sensor 14 are connected with an automatic tripping device 15, and the heating rod 13 is continuously heated (in the embodiment, the distance between the temperature sensor 14 and the heating rod 13 is about 50mm, and the heating rod 13 is continuously heated for 8 hours) until water injection around and at the top of the coarse-grained soil sample 10 is evaporated.
The direct shear test comprises the following operation steps:
r1, placing the test frame system 16 at the periphery of the coarse-grained soil sample 10 to be tested, respectively placing two first supports 27 of the door-shaped frame in two adjacent different test tanks 6, simultaneously ensuring that the door-shaped frame can be placed horizontally, cleaning coarse-grained soil at the periphery of the coarse-grained soil sample 10, and ensuring that the horizontal jack 28 can work normally;
r2, performing a direct shear test, and applying a corresponding vertical load to the coarse-grained soil sample 10 to be tested through the vertical jack 29, wherein the vertical force sensor 19 has a corresponding reading;
and R3, after the vertical load is applied to a specified value, applying a horizontal load to the coarse-grained soil sample 10 to be tested through the horizontal jack 28 until the coarse-grained soil sample 10 is sheared and damaged, recording the value, and dismantling the test frame system 16.
In step S1, a direct shear test pit 1 is excavated in a selected test site (in this embodiment, the length of the direct shear test pit 1 is 20m, the bottom width is 2m, the top width is 5m, and the depth is 1.2m), then a first layer of clay 2, a geomembrane 3, and a second layer of clay 4 (in this embodiment, the thickness of the second layer of clay 4 is 10cm) are sequentially laid at the bottom of the direct shear test pit 1, and then coarse-grained soil is backfilled and rolled on the second layer of clay 4 in layers according to the filling technical requirements of a field leveling area, wherein two layers are filled, i.e., a single layer is first virtually laid for 80cm, and is vibrated and rolled for 6 times, the thickness of the compacted coarse-grained soil is 50cm, and is then virtually laid for 80cm on the compacted coarse-grained soil, and is vibrated and rolled for 6 times, and the thickness of the compacted coarse-grained soil is 100cm altogether.
In this embodiment, a group of 4 coarse-grained soil samples are set for direct shear test in the dry coarse-grained soil sample test, the coarse-grained soil sample test processed in the primary dry-wet cycle, the coarse-grained soil sample test processed in the secondary dry-wet cycle, and the coarse-grained soil sample test processed in the multiple dry-wet cycles in the later period; that is, 4 coarse-grained soil samples were placed in each of two adjacent test cells 6, and the test was performed, as shown in fig. 11.
In the step R1, when two first supports 27 of the door-shaped frame need to be placed in two adjacent different test tanks 6, the depth of the two test tanks 6 is measured by using the horizontal tube 9, so as to ensure the depth of the two test tanks 6 to be consistent, and then the counterweight 17 is placed on the inclined support 18, so as to stabilize the door-shaped frame.
The invention adopts the combination of the integral sample saturation method and the single sample saturation method to manufacture the sample, thereby quickening the preparation time of the sample and improving the efficiency.
Level pipe 9 includes the scale, hyaline tube 23, hose 24 and telescopic bracket 26, the scale has two, all be provided with hyaline tube 23 on the scale, two hyaline tubes 23 link to each other through hose 24 in the bottom, have the measuring solution in hyaline tube 23, the top of hyaline tube 23 is reserved has air vent 25, open when using, guarantee that it links to each other with the atmosphere, and can inject the measuring solution into hyaline tube 23 through this air vent 25, the bottom surface of scale sets up a telescopic bracket 26, can promote the height of scale during the use.
Put two scales respectively in two different test tanks 6, two telescoping shores 26 highly keep unanimous, when the measuring fluid height in two hyaline tubes 23 was unanimous, place door style of calligraphy frame, numerical value on the scale is by supreme crescent down, if the measuring fluid height in two hyaline tubes 23 is inconsistent, dig through throwing to the test tank 6 that the scale numerical value is little for the measuring fluid height of two test tanks 6 reaches unanimity.
The test results in fig. 7 and 8 show that the internal friction angle phi of the coarse-grained soil sample 10 under four dry and wet cycles is 25.454 degrees, and the cohesive force c is 45 kpa; the test results in fig. 9 and 10 show that the coarse soil sample 10 has an internal friction angle phi of 24.986 degrees and a cohesive force c of 32kpa under five dry-wet cycles; in summary, the coarse-grained soil sample 10 has reduced internal friction angle and cohesive force after being subjected to dry-wet cycling, wherein the magnitude of the reduction of the cohesive force is larger than that of the internal friction angle, and the strength of the coarse-grained soil sample 10 is attenuated and deteriorated.
According to the description and the drawings of the invention, a person skilled in the art can easily manufacture or use the test device and the test method for the large-scale direct shear-shear stress-strain curve test sample of the field coarse-grained soil, and can produce the positive effects recorded in the invention.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and all simple modifications and equivalent variations of the above embodiments according to the technical spirit of the present invention are included in the scope of the present invention.
Claims (10)
1. The test device for the shear stress-strain curve sample under the large-scale direct shearing of the on-site coarse-grained soil is characterized in that: dig at the experimental place and establish direct shear test pit (1), the barrier layer is laid and the coarse grained soil is backfilled to the bottom of direct shear test pit (1), sets up multiunit coarse grained soil sample (10) in direct shear test pit (1), sets up water injection district (5) and non-water injection district (32) in direct shear test pit (1), is provided with sample preparation district (33) in non-water injection district (32), all be provided with multiunit coarse grained soil sample (10) in water injection district (5) and non-water injection district (32), coarse grained soil sample (10) outside cover is established and is sheared box (11), sets up test frame system (16) in direct shear test pit (1), sets up vertical pressure device and horizontal shearing device between test frame system (16) and coarse grained soil sample (10).
2. The on-site coarse-grained soil large-scale direct shear lower shear stress-strain curve test device according to claim 1, characterized in that: the impermeable layer comprises a first layer of clay (2), a geomembrane (3) and a second layer of clay (4) which are sequentially paved at the bottom of the direct shear test pit (1); the multiple groups of coarse-grained soil samples (10) in the water injection area (5) and the sample preparation area (33) are arranged according to areas.
3. The on-site coarse-grained soil large-scale direct shear lower shear stress-strain curve test device according to claim 1, characterized in that: the testing frame system (16) comprises a door-shaped frame, first supports (27) are correspondingly arranged on two sides of the bottom of the door-shaped frame, an inclined support (18) is arranged between the first supports (27) and the door-shaped frame for reinforcement, and a balancing weight (17) is placed on the inclined support (18); a plurality of test grooves (6) are dug in the direct shear test pit (1) after coarse-grained soil is backfilled, and a water injection area (5), a non-water injection area (32) and a sample preparation area (33) are arranged along the length direction of the test grooves (6).
4. The on-site coarse-grained soil large-scale direct shear lower shear stress-strain curve test device according to claim 1, characterized in that: coarse grained soil sample (10) top in water injection district (5) is inserted and is equipped with heating rod (13) and temperature sensor (14), and heating rod (13) and temperature sensor (14) all are connected with automatic tripping device (15), the position that heating rod (13) were located on coarse grained soil sample (10) can be guaranteed coarse grained soil sample (10) and accomplish dry wet cycle smoothly and handle.
5. The on-site coarse-grained soil large-scale direct shear lower shear stress-strain curve test device according to claim 3, characterized in that: the vertical pressure device comprises a vertical force sensor (19), a vertical jack (29) and a vertical displacement sensor (20), a slidable bearing plate (30) is arranged at the top of the door-shaped frame, the bearing plate (30) is connected with the vertical jack (29) through the vertical force sensor (19), a cover plate (8) is arranged below the vertical jack (29), the cover plate (8) is arranged above the coarse-grained soil sample (10), and the vertical displacement sensor (20) is connected with the side wall of the shearing box (11).
6. The on-site coarse-grained soil large-scale direct shear lower shear stress-strain curve test device according to claim 3, characterized in that: the horizontal shearing device comprises a horizontal jack (28), a horizontal displacement sensor (31) and a horizontal force sensor (12), wherein the horizontal jack (28) is fixedly arranged on a supporting rod on the side edge of the portal frame, the extending end of the horizontal jack (28) is propped against the side wall of the shearing box (11) through the horizontal force sensor (12), and the horizontal displacement sensor (31) is connected with the horizontal jack (28).
7. The test method of the test sample test device for the shear stress-strain curve test under the large-scale direct shear of the on-site coarse-grained soil is characterized by comprising the following steps of:
s1, digging a plurality of test grooves (6) arranged in parallel in a direct shear test pit (1), dividing a non-water injection area (32) and a water injection area (5) in the direct shear test pit (1), and dividing a sample preparation area (33) in the water injection area (5);
s2, performing one-time dry-wet cycle treatment in the sample preparation area (33) by adopting an integral sample saturation method, and then drying in the air by adopting a natural drying method; the whole sample is naturally dried in the period, and the following steps are carried out:
s2-1, preparing a dry coarse-grained soil sample in a non-water injection area (32), and performing a direct shear test;
s2-2, carrying out one-time dry-wet cycle treatment on the area outside the sample preparation area (33) in the water injection area (5) by adopting a single sample saturation method, and then carrying out a direct shear test;
s2-3, carrying out secondary dry-wet cycle treatment in the area outside the sample preparation area (33) in the water injection area (5) by adopting a single sample saturation method and a heating rod heating method, and then carrying out a direct shear test;
s3, after airing, dividing a first test area (34) in the sample preparation area (33), carrying out secondary dry-wet circulation treatment on the area outside the first test area (34) in the sample preparation area (33) by adopting an integral sample saturation method, and airing by adopting a natural airing method;
s3-1, in the natural airing period, carrying out three times of dry-wet cycle treatment in a first test area (34) by adopting a single sample saturation method and a heating rod heating method, and then carrying out a direct shear test;
s4, after airing, dividing a second test area (35) in the sample preparation area (33), carrying out three times of dry-wet cycle treatment on the area outside the second test area (35) by adopting an integral sample saturation method, and airing by adopting a natural airing method;
s4-1, in the natural airing period, performing dry-wet cycle treatment for four times in a second test area (35) by adopting a single sample saturation method and a heating rod heating method, and then performing a direct shear test;
and S5, repeating the step S4 until all the direct shear tests are completed.
8. The test method of the test sample test device for the large-scale direct shear lower shear stress-strain curve test of the on-site coarse-grained soil according to claim 7, which is characterized in that: the operation steps of the bulk sample saturation method are as follows: plugging two ends of a test groove (6) in a sample preparation area (33), injecting water into the test groove (6), and permeating coarse-grained soil around the test groove (6) by the water within 24 hours; the natural drying method comprises the following operation steps: the coarse-grained soil after infiltration is placed for one week.
9. The test method of the test sample test device for the large-scale direct shear lower shear stress-strain curve test of the on-site coarse-grained soil according to claim 7, which is characterized in that: the single sample saturation method comprises the following operation steps:
t1: manually preparing samples after determining the positions of coarse-grained soil sample points between two adjacent test tanks (6), shoveling out soil around a cover plate (8) by using a small shovel by taking the diameter of the cover plate (8) as the taking diameter of the coarse-grained soil sample (10) to form a water injection pit (36), wherein the residual coarse-grained soil in the water injection pit (36) is the coarse-grained soil sample (10) used for the test, and the space between the coarse-grained soil sample (10) and the pit wall of the water injection pit (36) is a water injection space;
t2, sleeving a shearing box (11) on the outer side of the coarse-grained soil sample (10), filling the gap between the shearing box (11) and the coarse-grained soil sample (10) with fine materials, and compacting;
t3, injecting water into the water injection space and the top of the coarse-grained soil sample (2), and maintaining a certain water surface height in the water injection space, so that the coarse-grained soil sample (10) can be subjected to saturation treatment, and at the moment, the coarse-grained soil sample (10) is subjected to one-time dry-wet cycle treatment;
the operation steps of the heating rod heating method are as follows:
a plurality of drill holes are uniformly constructed on the top surface of the coarse-grained soil sample (10) by adopting a hand drill, a heating rod (13) and a temperature sensor (14) are placed in the drill holes, the heating rod (13) and the temperature sensor (14) are connected with an automatic tripping device (15), and the heating rod (13) is continuously heated until water injection on the periphery and the top of the coarse-grained soil sample (10) is evaporated.
10. The test method of the test sample test device for the large-scale direct shear lower shear stress-strain curve test of the on-site coarse-grained soil according to claim 7, which is characterized in that: the direct shear test comprises the following operation steps:
r1, placing a test frame system (16) at the periphery of a coarse-grained soil sample (10) to be tested, respectively placing two first supports (27) of a door-shaped frame in two adjacent different test tanks (6), simultaneously ensuring that the door-shaped frame can be placed horizontally, cleaning coarse-grained soil at the periphery of the coarse-grained soil sample (10), and ensuring that a horizontal jack (28) can work normally;
r2, performing a direct shear test, and applying a corresponding vertical load to the coarse-grained soil sample (10) to be tested through a vertical jack (29), wherein the vertical force sensor (19) has a corresponding reading;
and R3, after a vertical load is applied to a specified value, applying a horizontal load to the coarse-grained soil sample (10) to be tested through a horizontal jack (28) until the coarse-grained soil sample (10) is sheared and damaged, recording the value, and dismantling the test frame system (16).
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