CN203869923U - Symmetrical layered sample pressing equipment for triaxial test sample preparation - Google Patents

Abstract

A symmetrical layered sample pressing device for the preparation of triaxial test samples. The main components of the device are: the outer walls of both ends of the soil sample cylinder are fitted with the grooves on the inner wall of the extension cylinder, and the diameter of the inner wall of the extension cylinder is not in the groove. The diameter of the inner wall of the soil sample cylinder is equal; the extension cylinder and the soil sample cylinder are covered with a pad set, and the pad set is composed of: the outer circumference of the back end of the outer pad protrudes outward to form a cover edge, and the front center of the outer pad is provided with a threaded There is a threaded hole in the center of the back of the middle pad, and a threaded protrusion in the center of the front, and there are two middle pads; there are threaded holes on the back of the inner pad, and the front is flat; the outer pad, the middle pad, the inner pad The pads are screwed to the corresponding threaded holes through protrusions; the height of the inner pad and the middle pad is 1/5 of the height of the soil sample cylinder; the sum of the heights of the inner pad and the outer pad minus the thickness of the cover is equal to the extension The height of the non-card slot part of the barrel. The uniformity of the sample prepared by the equipment can make the test result of the triaxial test more accurate and reliable.

Description

Symmetrical layered sample pressing equipment for triaxial test sample preparation

technical field

The utility model relates to a symmetrical layered sample pressing device and a sample preparation method for preparing triaxial test samples.

Background technique

The samples used in the triaxial test in geotechnical (civil engineering) tests are divided into two types: undisturbed soil samples and disturbed soil samples. The preparation of disturbed soil samples mainly includes the procedures of selecting soil samples, air-drying (or oven-drying), crushing, sieving, soil blending, and sample preparation. Among them, sample preparation is a very critical step. At this stage, there are mainly double-sided sample pressing method and layered compaction method.

Double-sided sample pressing method: pour all the soil samples required for sample preparation into the sample preparation cylinder, measure the height of the sample when the indenter contacts the soil sample, calculate the difference with the final required sample height, and control the drop of the indenter Speed, when the indenter drops to the design height, reverse the sample, control the loading time and load size, until the required sample height. In the sample preparation process of this method, because the sample is not layered, a large cumulative friction force is generated between the soil sample and the wall of the cylinder, so that the compactness in the middle of the sample is smaller than that at the two ends, resulting in uneven samples and large test errors. .

Layered compaction method: as described in Clause 18.3.3 of "Regulations for Geotechnical Tests for Railway Engineering" (TB10102-2004), use a hammer with a compaction plate to divide the soil samples required for sample preparation in the compaction cylinder. Layer compaction, the number of layers is 3 to 8 layers, the quality of each layer of soil samples should be equal, the contact surface of each layer should be planed, and after the last layer is compacted, the two ends of the sample in the compaction cylinder should be leveled. This method has the following disadvantages in the sample preparation process:

1. During the sample preparation process, the compactness of the sample is controlled by the volume. Since the diameter of the sample preparation cylinder is fixed, the compactness is controlled by the height; the quality of each layer of soil samples is equal, and the expected height of each layer after compaction is also the same. should be equal. However, after the first layer of soil sample is compacted at the bottom of the compaction cylinder and the surface is planed, the second layer of soil sample is directly compacted on the first layer of soil sample, and then the third layer is compacted sequentially from bottom to top. The last layer; therefore, the first layer of soil samples received the most compaction times, and the compaction work is the largest; after the sample preparation is completed, the height of the first layer of soil samples will be less than the expected height, on the contrary, the height of the last layer of soil samples will be higher than expected. As a result, the density of the sample gradually decreases from bottom to top, and the difference between the upper and lower ends is the largest, resulting in uneven density of the sample. Since the two ends of the sample are the direct force-bearing surfaces during the triaxial test, this unevenness Sexuality will seriously interfere with the stress state of the sample, resulting in a large deviation of the test data.

2. In the process of sample preparation, it is necessary to judge whether the compaction of each layer of soil samples has reached the required height by observing the scale of the ruler. The thickness of each layer of soil samples after compaction will be affected by large human factors and errors will also occur.

3. During the sample preparation process, the compaction of each layer of soil samples is manually operated, and it is difficult to ensure that the hammer guide rod remains vertical during the compaction process, which may easily cause the surface of each layer of soil samples to be uneven. At the same time, according to the requirements of the specification, when the surface of the last layer of soil sample (sample end face) is not level, the end face of the sample needs to be leveled, but the leveling process is difficult and time-consuming, which will greatly reduce the efficiency. Moreover, the leveling operation will also cause a large disturbance to the sample, reducing the uniformity of the end surface of the sample.

Utility model content

The purpose of this utility model is to provide a symmetrical layered sample pressing equipment for the preparation of triaxial test samples. Using this equipment for sample preparation can precisely control the compaction height and end surface level of each layer of soil samples, and the obtained test samples The uniformity of the sample is better, so that the test error of the triaxial test is small, and the test result is more accurate and reliable; and the operation is convenient, and the sample preparation efficiency is higher.

The technical scheme adopted by the utility model to realize the purpose of the invention is a symmetrical layered sample pressing device for triaxial test sample preparation, which is characterized in that:

The outer walls of both ends of the cylindrical soil sample tube fit into the slots on the inner wall of the extension tube, and the outer peripheral surface of the slot part of the extension tube protrudes outward to form a flange. The diameters of the inner walls of the cylinder are equal; the flanges of the extension cylinders at both ends of the soil sample cylinder are connected by screws;

Described extension tube and soil sample tube inner sleeve pad kit, the composition of pad kit is:

The outer peripheral surface of the back end of the outer spacer protrudes outward to form a cover edge, and the front center of the outer spacer is provided with a threaded protrusion; the back center of the middle spacer is provided with a threaded hole, and the front center is provided with a threaded protrusion. There are two intermediate spacers; the back of the inner spacer is provided with threaded holes, and the front is flat; the protrusion of the outer spacer is threaded with the threaded hole of the first middle spacer, and the protrusion of the first middle spacer is connected with the first middle spacer. The threaded holes of the two intermediate pads are threaded, and the protrusion of the second intermediate pad is threaded with the threaded hole of the inner pad; the specific method of the extension tube and the inner sleeve of the soil sample tube is: put the pad kit Insert the end of the inner cushion block into the inner cavity of the extension cylinder and the soil sample cylinder, and make the cover edge of the outer cushion block close to the mouth edge of the extension cylinder;

The heights of the inner pad and the middle pad are equal to 1/5 of the height of the soil sample cylinder; the sum of the heights of the inner pad and the outer pad minus the thickness of the cover edge is equal to the height of the non-grip part of the extension cylinder.

Furthermore, the outer walls of both ends of the soil sample cylinder of the present invention are conical in shape gradually narrowing toward the end surface of the soil sample cylinder; the slots on the inner wall of the extension cylinder are also conical in shape gradually narrowing toward the end surface of the soil sample cylinder.

Working principle and process of the present utility model are:

A. Take out the pad set inserted into the upper end of the extension tube and the inner cavity of the soil sample tube, and then fill the first layer of soil samples whose mass is 1/5 of the total mass of the sample into the soil sample tube and the extension tube; Insert the spacer set into the extension cylinder and the soil sample cylinder along the inner wall of the extension cylinder at the upper end until the cover edge touches the edge of the extension cylinder to compact the filled soil sample to the required compactness;

B. Turn the entire sample pressing equipment over 180° for the first time, take out the pad set located at the upper end of the extension cylinder and the inner cavity of the soil sample cylinder, plan the empty surface of the compacted soil sample, and calculate the mass as the total mass of the sample Fill 1/5 of the second layer of soil sample into the soil sample cylinder and the extension cylinder; remove the second intermediate cushion block from the taken out cushion block set, so that the protrusion of the outer cushion block is in line with the thread of the first intermediate cushion block Holes are threaded; then insert the spacer set into the extension tube and the soil sample tube along the inner wall of the extension tube at the upper end, until the edge of the cover touches the edge of the extension tube, and the filled second layer of soil sample is compacted to the desired level. the compactness;

C. Turn the entire sample pressing equipment over 180° for the second time, take out the extension cylinder and the pad set at the upper end of the inner cavity of the soil sample cylinder, plan the empty surface of the first layer of soil sample after compaction, and divide the mass into the sample Fill the third layer of soil samples with a total mass of 1/5 into the soil sample cylinder and the extension cylinder; remove the second intermediate cushion block from the taken out cushion block set, so that the protrusion of the outer cushion block is consistent with the first intermediate cushion block Threaded connection of the threaded hole; then insert the spacer set into the extension tube and the soil sample tube along the inner wall of the extension tube at the upper end, until the edge of the cover is pressed against the edge of the extension tube, and the filled third layer of soil sample is compacted to the required compactness;

D. Turn the entire sample pressing equipment over 180° for the third time, take out the block kit located at the upper end of the extension cylinder and the inner cavity of the soil sample cylinder, plan the empty surface of the second layer of soil sample after compaction, and then shave the surface of the soil sample with a mass of Fill the fourth layer of soil sample with 1/5 of the total mass of the sample into the soil sample cylinder and the extension cylinder; remove the first middle cushion block from the taken out cushion block set, so that the protrusion of the outer cushion block and the inner cushion block The threaded hole is threaded; then insert the spacer set into the extension tube and the soil sample tube along the inner wall of the extension tube at the upper end until the cover edge is pressed against the mouth edge of the extension tube, so that the extension tube and the soil sample can be pressed into the extension tube along the inner wall of the upper end until the edge of the cover touches the edge of the extension cylinder, and compact the filled fourth layer of soil samples to the required compactness;

E. Turn the entire sample pressing equipment over 180° for the fourth time, take out the pad set inserted into the extension cylinder and the upper end of the inner cavity of the soil sample cylinder, plan the empty surface of the third layer of soil sample after compaction, and then shave the surface of the soil sample with a mass of Fill the fifth layer of soil sample with 1/5 of the total mass of the sample into the soil sample cylinder and the extension cylinder; remove the first intermediate cushion block from the taken out cushion block set, so that the protrusion of the outer cushion block and the inner cushion block threaded connection through the threaded holes; then insert the spacer set into the extension tube and the soil sample tube along the inner wall of the extension tube at the upper end until the edge of the cover touches the edge of the extension tube, and compact the filled fifth layer of soil samples to the The required compactness is obtained, that is, the sample preparation is completed.

Compared with the prior art, the beneficial effects of the utility model are:

1. During the sample preparation process, the soil sample cylinder and the extension cylinders at both ends can be turned up and down by 180° as a whole, and the block kit can be assembled freely. The first layer of soil samples is pressed at a symmetrical position in the middle of the soil sample cylinder, and the next four layers of soil The samples are symmetrically distributed on both ends of the first layer of soil samples for pressing, so that the two ends of the whole sample after preparation are more uniform.

2. During the sample preparation process, the static pressure is used instead of the impact load. The soil samples after the first layer of compaction are less disturbed by the subsequent layers of soil samples than the layered compaction method. The first layer of soil samples prepared The difference in compactness from the subsequent layers of soil samples is small, and the uniformity of the overall sample composed of five layers of soil samples is better.

3. During the sample preparation process, the height of each middle pad is equal, and the height of each layer of soil samples is controlled by the edge of the cover against the edge of the extension cylinder, and the control standard automatically maintains the consistency of height. Therefore, the compactness of each layer of soil samples remains consistent after pressing, which realizes the equal mass and equal height layered pressing of the samples, and the sample preparation is more uniform and the sample preparation efficiency is higher.

4. During the sample preparation process, the level of the end surface of each layer of soil samples is controlled by the edge of the cover against the mouth of the extension cylinder, and the end surfaces of each pad are level with the mouth of the extension cylinder, so that each layer of soil samples The level of the end face avoids the leveling process of the end face of the sample and avoids the disturbance of the sample during leveling.

5. During the sample preparation process, due to the layered preparation and the constant change of the sample preparation direction, the interference of the friction force between the soil sample and the cylinder wall is reduced during the sample preparation process of the symmetrical layered compression method.

Below in conjunction with accompanying drawing and specific embodiment the utility model is described in further detail.

Description of drawings

Fig. 1 is a schematic cross-sectional structure diagram of a sample pressing device according to an embodiment of the present invention.

Fig. 2 is a schematic cross-sectional structural view of the sample pressing equipment according to the embodiment of the present invention after the upper and lower pad sets are removed.

Fig. 3a is a schematic diagram of the sample pressing equipment according to the embodiment of the present invention when the first layer of soil sample is pressed.

Fig. 3b is a schematic diagram of the sample pressing device according to the embodiment of the present invention when the second layer of pressing is completed.

Fig. 3c is a schematic diagram of the sample pressing equipment according to the embodiment of the present invention when the fifth layer of soil sample pressing (the whole sample has been made) is completed.

Fig. 4 is the stress-strain relationship graph obtained by unsaturated triaxial test of four samples (a total of eight samples) prepared by the method of the embodiment of the present invention and the layered compaction method respectively.

Detailed ways

Fig. 1, 2 show, the specific embodiment of the present utility model is, a kind of symmetrical layered sample pressing equipment of triaxial test sample preparation, wherein:

The outer walls of both ends of the cylindrical soil sample tube 1 fit into the slots on the inner wall of the extension tube 2, and the outer peripheral surface of the slot part of the extension tube 2 protrudes outward to form a flange 2a. The diameter of the inner wall is equal to the diameter of the inner wall of the soil sample cylinder; the flanges 2a of the extension cylinder 2 at both ends of the soil sample cylinder 1 are connected by a screw 3;

The extension tube 2 and the soil sample tube 1 are covered with a pad set, and the pad set is composed of:

The outer peripheral surface of the back end of the outer pad 4 protrudes outward to form a cover edge 4b, and the front center of the outer pad 4 is provided with a threaded protrusion 4a; the back center of the middle pad 5 is provided with a threaded hole, and the front center is provided with a threaded hole. There are two threaded protrusions 5a in the middle spacer 5; the back side of the inner spacer 6 is provided with a threaded hole, and the front is flat; the protrusion 4a of the outer spacer 4 is threadedly connected with the threaded hole of the first middle spacer 5, The protrusion 5a of the first intermediate pad 5 is threadedly connected with the threaded hole of the second intermediate pad 5, and the protrusion of the second intermediate pad 5 is screwed with the threaded hole of the inner pad 6; the extension tube 2 and The specific way of putting the cushion block kit inside the soil sample cylinder 1 is: insert the inner cushion block end of the cushion block kit into the inner cavity of the extension cylinder 2 and soil sample cylinder 1, and make the cover of the outer cushion block 4 press against the extension cylinder along 4b the edge of the mouth of 2;

The heights of the inner pad 6 and the middle pad 5 are equal to 1/5 of the height of the soil sample cylinder 1; the sum of the heights of the inner pad 6 and the outer pad 4 minus the thickness of the cover edge 4b is equal to the extension cylinder The height of the non-card slot part.

The outer walls of both ends of the soil sample cylinder 1 in this example are conical in shape gradually narrowing toward the end surface of the soil sample cylinder 1 , and the grooves on the inner wall of the extension cylinder 2 are also conical in shape gradually narrowing toward the end surface of the soil sample cylinder 1 .

Fig. 3a, Fig. 3b and Fig. 3c show, a kind of sample preparation method using the symmetrical layered sample pressing equipment prepared by the triaxial test sample of this example, described sample is prepared by 5 layers of layered compaction, its The specific operation steps are as follows:

A. Take out the pad set inserted into the upper end of the extension tube 2 and the inner cavity of the soil sample tube 1, and then fill the first layer of soil sample 7a whose mass is 1/5 of the total mass of the sample into the soil sample tube 1 and the extension tube 2 ;Then insert the taken-out spacer set into the extension tube 2 and the soil sample tube 1 along the inner wall of the extension tube 2 at the upper end, until the cover edge 4b presses against the mouth edge of the extension tube 2, and compact the filled soil sample 7a to the desired compactness;

B. Turn the entire sample pressing equipment over 180° for the first time, take out the pad set located at the upper end of the extension tube 2 and the inner cavity of the soil sample tube 1, plan the air surface of the compacted soil sample 7a, and divide the mass into the sample Fill the second layer of soil sample 7b with 1/5 of the total weight of the sample into the soil sample cylinder 1 and the extension cylinder 2; remove the second intermediate cushion block 5 from the cushion block set taken out, so that the protrusion 4a of the outer cushion block 4 Threaded connection with the threaded hole of the first intermediate pad 5; then insert the pad set into the extension tube 2 and the soil sample tube 1 along the inner wall of the extension tube 2 at the upper end until the cover edge 4b is against the mouth edge of the extension tube 2 , compact the filled second layer of soil sample 7b to the required compactness;

C. Turn the whole sample pressing equipment over 180° for the second time, take out the pad set at the upper end of the inner cavity of the extension tube 2 and the soil sample tube 1, plan the empty surface of the first layer of soil sample 7a after compaction, and remove the mass The third layer of soil sample 7c, which is 1/5 of the total mass of the sample, is filled in the soil sample cylinder 1 and the extension cylinder 2; the second intermediate cushion block 5 is removed from the taken out cushion block set, so that the protrusion of the outer cushion block 4 4a is threadedly connected to the threaded hole of the first intermediate pad 5; then insert the pad kit into the extension tube 2 and the soil sample tube 1 along the inner wall of the extension tube 2 at the upper end until the cover edge 4b is pressed against the extension tube 2 The edge of the mouth is used to compact the filled third layer of soil sample 7c to the required compactness;

D. Turn over the entire sample pressing device 180° for the third time, take out the pad set located at the upper end of the extension tube 2 and the inner cavity of the soil sample tube 1, plan the empty surface of the second layer of soil sample 7b after compaction, and then Fill the fourth layer of soil sample 7d whose mass is 1/5 of the total mass of the sample into the soil sample cylinder 1 and the extension cylinder 2; remove the first intermediate cushion block 5 from the taken out cushion block set, and make the outer cushion block 4 The protrusion of the inner pad 6 is threadedly connected with the threaded hole of the inner pad 6; then the pad set is inserted into the extension tube 2 and the soil sample tube 1 along the inner wall of the extension tube 2 at the upper end until the cover edge 4b is pressed against the mouth edge of the extension tube 2 , the inner wall of the extension cylinder 2 along the upper end is pressed into the extension cylinder 2 and the soil sample cylinder 1 until the cover edge 4b presses against the mouth edge of the extension cylinder 2, and the filled fourth layer of soil sample 7d is compacted to the desired the compactness;

E. Turn over the entire sample pressing device 180° for the fourth time, take out the pad set inserted into the upper end of the extension tube 2 and the inner cavity of the soil sample tube 1, plan the empty surface of the third layer of soil sample 7c after compaction, and then Fill the fifth layer of soil sample 7e with a mass of 1/5 of the total mass of the sample into the soil sample cylinder 1 and the extension cylinder 2; remove the first intermediate cushion block 5 from the taken out cushion block set, and make the outer cushion block 4 The protrusion of the inner pad 6 is threadedly connected with the threaded hole of the inner pad 6; then the pad set is inserted into the extension tube 2 and the soil sample tube 1 along the inner wall of the extension tube 2 at the upper end until the cover edge 4b is pressed against the mouth edge of the extension tube 2 , compact the filled fifth layer of soil sample 7e to the required compactness, that is, complete the sample preparation.

Test verification

A group of samples were respectively prepared by using the layered compaction method of silty clay and the sample pressing equipment and method of the utility model for unsaturated triaxial test, and the uniformity of the two sample preparation methods was compared.

1. Results and analysis of failure morphology of samples prepared by two methods after unsaturated triaxial test

Table 1 is a statistical table of the layered compaction method and the sample prepared by the utility model pressure sample equipment and its method after the unsaturated triaxial test.

Table 1 Statistics of damage patterns of each sample

Note: For sample preparation by layered compaction method, the normal loading of the sample means that the sample is loaded according to the lower end of the sample preparation and the upper end of the sample is upward, and the inverted sample means that the lower end of the sample preparation is upward and the upper end of the sample is loaded. Load the sample face down. When preparing samples by the symmetrical layered compression method, the end face where the last layer of soil samples is located is the upper end face. Upright loading of the sample means that the sample is loaded with the upper end of the sample preparation facing up and the lower end facing down, and the sample is loaded upside down when the sample is loaded with the lower end of the sample preparation facing up and the upper end of the sample is facing down. The purpose of the sample upright and upside-down mounting is to eliminate the impact on the test results caused by the inconsistent degrees of freedom between the loading top cap and the base of the test instrument.

It can be seen from Table 1 that for the four samples prepared by the layered compaction method, the damage position after the test always occurs at the upper end of the sample preparation, indicating that the upper end of the sample is looser than the lower end, which is consistent with the theoretical analysis and proves that The uniformity of sample preparation by layered compaction method is poor. Simultaneously table 1 also shows: each sample that makes with sample pressing equipment of the present utility model and method thereof, the damage position after the test randomly occurs in the upper, lower end and the middle of sample preparation, illustrates the upper, middle and lower parts of sample The compactness of each position is relatively uniform, which proves that the uniformity of the sample prepared by the sample pressing equipment and the method thereof of the utility model is better.

2. Stress-strain relationship and analysis of unsaturated triaxial test for samples prepared by two methods

Fig. 4 shows the stress-strain relationship curves of all the samples prepared by the layered compaction method and the method of the utility model for the unsaturated triaxial shear test. Table 2 is a summary of the dry density, peak deviatoric stress and peak deviatoric stress corresponding strain of each sample.

Table 2 Summary of dry density, peak deviatoric stress and peak deviatoric stress corresponding strain of each sample

Since the bearing capacity and deformation of the sample are determined by the part with a small density, when the average density of different samples is the same, the bearing capacity of the sample in the uniform state is higher than that in the uneven state, and the deformation is also smaller. big. As can be seen from Fig. 4 and table 2, under the same confining pressure condition, the peak deviatoric stress and the strain of the sample prepared by the utility model method are all obviously higher than the sample prepared by the layered compaction method, therefore, the utility model method The uniformity of the prepared sample is better than that prepared by the layered compaction method.

Claims (2)

1. the symmetrical layering pressure-like equipment that prepared by triaxial test sample, is characterized in that:

The outer wall of the two ends of columniform soil sample tube (1) all with the draw-in groove fit of exntension tubs (2) inwall, the outer peripheral face outwardly convex at exntension tubs (2) draw-in groove position forms flange (2a), and the inner diameter at the non-draw-in groove of exntension tubs (2) position equates with the inner diameter of soil sample tube; Between the flange (2a) of the exntension tubs (2) of soil sample tube (1) two ends, by screw rod (3), connect;

Described exntension tubs (2) and soil sample tube (1) inner sleeve cushion block external member, the composition of cushion block external member is:

The outer peripheral face outwardly convex of the back end of outer cushion block (4) forms cover rim (4b), and the front center of outer cushion block (4) is provided with threaded projection (4a); The center, the back side of middle cushion block (5) is provided with threaded hole, and front center is provided with threaded projection (5a), and middle cushion block (5) has two; The back side of interior cushion block (6) is provided with threaded hole, positive smooth; The projection (4a) of outer cushion block (4) is threaded with the threaded hole of cushion block (5) in the middle of first, in the middle of first, the projection (5a) of cushion block (5) is threaded with the threaded hole of cushion block (5) in the middle of second, and the projection of second middle cushion block (5) is threaded with the threaded hole of interior cushion block (6); The concrete mode of exntension tubs (2) and soil sample tube (1) inner sleeve cushion block external member is: the interior cushion block end of cushion block external member is inserted to the inner chamber of exntension tubs (2) and soil sample tube (1), and make the cover rim (4b) of outer cushion block (4) push against the opening's edge of exntension tubs (2);

Described interior cushion block (6) and the height of middle cushion block (5) are equal to 1/5 of soil sample tube (1) height; The thickness that the height sum of interior cushion block (6) and outer cushion block (4) deducts cover rim (4b) equals the height at the non-draw-in groove of exntension tubs (2) position.

2. the symmetrical layering pressure-like equipment that prepared by triaxial test sample according to claim 1, it is characterized in that: the outer wall of the two ends of described soil sample tube (1) is to the diminishing taper shape of soil sample tube (1) end face, and the draw-in groove of exntension tubs (2) inwall is also to the diminishing taper shape of soil sample tube (1) end face.