CN114166601B - Bidirectional press-in type triaxial sample preparation device and method based on soil stress history - Google Patents
Bidirectional press-in type triaxial sample preparation device and method based on soil stress history Download PDFInfo
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Abstract
本发明公开了基于土体应力历史的双向压入式三轴试样制备装置及方法。反力顶板位于底座正上方，反力顶板通过若干固定杆和底座固定连接，通过若干固定杆与反力顶板连接，底座和反力顶板均安装有相配适的垫板，底座顶面中心设有下垫板，下垫板顶面与下部升降头底面进行刚性连接，反力顶板底面中心设有上垫板，上垫板下表面与上部升降头进行刚性连接，下垫板和上垫板之间安装为液压系统和制样模具。本发明保证了土样的均匀性和上下表面的平整性，控制了土样的密实度，模拟了土样在地基中所受的竖向应力和应力历史，解决了三轴土样脱模易于失败的难题，装置结构简单，操作便捷，准确性和成功率高。
The invention discloses a bidirectional press-in type triaxial sample preparation device and method based on soil stress history. The reaction force top plate is located directly above the base. The reaction force top plate is fixedly connected to the base through a number of fixing rods, and is connected to the reaction force top plate through a number of fixing rods. The base and the reaction force top plate are both installed with matching pads, and the center of the top surface of the base is provided with Bottom plate, the top surface of the bottom plate is rigidly connected with the bottom surface of the lower lifting head, the center of the bottom surface of the reaction top plate is provided with an upper plate, the lower surface of the upper plate is rigidly connected with the upper lifting head, and the bottom plate and the upper plate are connected rigidly. In-room installation for hydraulic system and sample making mold. The invention ensures the uniformity of the soil sample and the flatness of the upper and lower surfaces, controls the compactness of the soil sample, simulates the vertical stress and stress history of the soil sample in the foundation, and solves the problem that the triaxial soil sample is easy to demould. The problem of failure is that the device has simple structure, convenient operation, high accuracy and success rate.
Description
Technical Field
The invention belongs to a soil sample preparation device and method in the technical field of civil engineering tests, and particularly relates to a bidirectional press-in type triaxial soil sample preparation device and method based on soil stress history.
Background
The conventional triaxial test is used as an important test means in the field of geotechnical engineering, and can effectively determine the mechanical property of soil. For triaxial test of disturbed soil, the preparation quality of the soil sample plays a decisive role in the test precision and the reliability of data. The soil sample of the triaxial compression test needs to be made into a cylindrical standard soil sample with the diameter of 3.91cm and the height of 8.0cm, and the soil samples obtained by different preparation methods have different problems. According to the sample preparation requirements of test procedures on disturbed soil, the method mainly comprises a sample impacting method and a sample pressing method, wherein the sample impacting method and the sample pressing method respectively control compaction density through impacting and static pressing. Although the traditional method has simple equipment and convenient use, the sample preparation has a plurality of problems: 1) The density of the soil sample is difficult to accurately control, the uniformity is not high, and the phenomenon of 'top compact and bottom loose' occurs; 2) The repeated impact load effect of the sample hitting method influences the structural property of the soil sample, and the hitting hammer is difficult to ensure absolute verticality, so that an artificially manufactured inclined layering surface is generated, and the diaphragm can generate relative dislocation; 3) The back pressure and the confining pressure on the upper end and the lower end of the soil sample during sample preparation cannot be controlled, so that the real stress path on the soil sample is difficult to simulate; 4) For non-cohesive soil such as sandy soil, silt and the like, a soil sample is easy to fall off after preparation or is easy to scatter after forming; 5) Due to the fact that unsaturated cohesive soil has matrix suction and cohesive force, particularly after soil sample improvement materials such as tung oil and glutinous rice paste are added, the water content, the pore ratio and the like of remolded soil are changed, and soil sample demoulding failure is easily caused after steel pairs are separated to form a film or a three-flap film; considering the method of direct extrusion, a large stress difference is caused at two ends to destroy the uniformity of the soil sample, and the friction force formed by the side wall can drag and damage the side face of the sample. Due to the problems of the traditional triaxial soil sample preparation method, the sample preparation success rate is low, the smooth proceeding of a triaxial test is seriously influenced, and the research on the mechanical properties of remolded soil is not facilitated. Therefore, there is a need to develop a triaxial soil sample preparation apparatus and method suitable for soil tests, and apply the apparatus and method to the related field.
Disclosure of Invention
Aiming at the defects in the existing soil sample preparation technology, the invention aims to provide a bidirectional press-in type triaxial test soil sample preparation device and method. The device can accurate control soil sample density, has guaranteed the homogeneity of soil sample and the level and smooth of upper and lower surface, has simulated the vertical stress and the stress history that soil sample received in the ground when system appearance to overcome the problem that the drawing of patterns easily fails under the above-mentioned condition, had better engineering application and popularization nature.
In order to realize the purpose, the technical scheme adopted by the invention is as follows:
1. a bidirectional press-in type triaxial sample preparation device based on soil stress history comprises:
the device includes the base, the counter-force roof, hydraulic system and system appearance mould, the counter-force roof is located directly over the base, the counter-force roof is through a plurality of dead levers and base fixed connection, be connected with the counter-force roof through a plurality of dead levers, the backing plate that matches suitable is all installed to base and counter-force roof, base top surface center is equipped with the lower bolster, the lower bolster top surface carries out rigid connection with lower part lift head bottom surface, counter-force roof bottom surface center is equipped with the upper padding plate, the upper padding plate lower surface carries out rigid connection with upper portion lift head, the installation is hydraulic system and system appearance mould between lower bolster and the upper padding plate.
The hydraulic system comprises a lifting platform, a lower dowel bar, a lower pressing disc, an upper dowel bar and a hydraulic loading head, wherein the lifting platform is fixedly arranged at the movable end at the upper end of the lower lifting head, the lower end of the lower dowel bar is fixed on the lifting platform, and the upper end of the lower dowel bar is fixedly connected with the lower pressing disc; the hydraulic loading head is fixedly arranged at the movable end of the lower end of the upper lifting head, the upper end of the upper dowel bar is fixed on the hydraulic loading head, and the lower end of the upper dowel bar is fixedly connected with the upper pressure applying disc; and a soil sample is arranged between the lower pressing disc and the upper pressing disc.
The sample preparation mould comprises three valves, a lantern ring, intramembrane filter paper, lower filter paper and upper filter paper, wherein the annular three valves are arranged around the soil sample, the lantern ring is sleeved outside the three valves, and the lantern ring is positioned and installed on the fixing rod through a positioning buckle; the filter paper in the membrane is arranged between the middle part of the inner peripheral surface of the three-valve membrane and the soil sample, and the lower filter paper and the upper filter paper are respectively arranged on the top surface of the lower pressing disc and the bottom surface of the upper pressing disc.
The fixing rods comprise thin upper sections and thick lower sections, each fixing rod is provided with a positioning buckle, the positioning buckles are sleeved on the thin upper sections of the fixing rods and clamped at the step between the thin upper sections and the thick lower sections, the outer side faces of the three-valve membranes are provided with positioning protrusions, the positioning protrusions of the three-valve membranes are arranged in the positioning buckles, and the lantern rings are positioned and installed on the steps formed on the top faces of the positioning buckles.
The inner diameters of the three valves are consistent with the diameters of the lower pressing disk and the upper pressing disk, so that the lower pressing disk and the upper pressing disk can vertically reciprocate in the three valves.
The size of the filter paper in the membrane is consistent with the inner diameter of the tri-valve, after the filter paper is wetted, the horizontal circumference is attached to the inner wall of the tri-valve, the sizes of the upper filter paper and the lower filter paper are consistent with the sizes of the surfaces of the pressing disks of the upper pressing disk and the lower pressing disk which respectively correspond to the upper filter paper and the lower filter paper, and the wetted filter paper is respectively attached to the upper surface of the lower pressing disk and the lower surface of the upper pressing disk.
The lower dowel bar is divided into three parts by two scale marks along the vertical axial direction of the lower dowel bar, and the two scale marks are respectively a first scale mark and a second scale mark from top to bottom; and the height difference between the lower edge of the intramembrane filter paper and the lower edge of the tri-valve membrane is the sum of the axial length of the lower dowel bar and the thickness of the lower pressing disc;
the upper dowel bar is divided into three equal parts by making two scale marks along the vertical axial direction of the upper dowel bar, and the two scale marks are a first scale mark and a second scale mark from bottom to top respectively; and the height difference between the upper edge of the filter paper in the membrane and the upper edge of the three-flap membrane is the axial length of the upper force transmission rod plus the thickness of the upper pressure disk.
2. A sample preparation method of a bidirectional press-in type triaxial sample preparation device based on soil stress history comprises the following steps:
the method comprises the following steps: the lower lifting head drives the lifting platform to descend, the lower filter paper is pasted on the upper surface of the lower pressing disc after being wetted, the upper lifting head drives the hydraulic loading head to ascend, and the upper filter paper is pasted on the lower surface of the upper pressing disc after being wetted;
step two: combining the three-valve membranes and attaching the in-membrane filter paper to the inner wall, so that the height difference between the lower edge of the in-membrane filter paper and the lower edge of the three-valve membrane is the sum of the axial length of the lower dowel bar and the thickness of the lower pressing disc, and the height difference between the upper edge of the in-membrane filter paper and the upper edge of the three-valve membrane is the sum of the axial length of the upper dowel bar and the thickness of the upper pressing disc; using a lantern ring to clamp the outer side of the tri-valve, placing the tri-valve on a lower pressure applying disc, and enabling the lower pressure applying disc to enter the interior of the tri-valve;
step three: according to the history of the stress of the soil sample in the foundation, calculating the consolidation pressure in the early stage of the soil body and the time required by compaction, according to the density and the size of the prepared soil sample, calculating the mass of the required soil sample, weighing the soil sample and pouring the soil sample into the three-valve structure at one time;
step four: lifting the three valves and fixing the three valves on the positioning buckles, so that the upper pressure application disc enters the three valves, and meanwhile, the descending height of the lifting table is adjusted through the lower lifting head and the ascending height of the hydraulic loading head is adjusted through the upper lifting head, so that the lower edge of the three valves is flush with the first scale mark of the lower dowel bar, and the upper edge of the three valves is flush with the first scale mark of the upper dowel bar;
step five: upper portion lift head cooperation hydraulic pressure loading head loops through upper portion dowel steel and upper portion and exerts pressure the disc and evenly apply in soil sample upper surface with axial pressure, lower portion lift head cooperation elevating platform loops through lower portion dowel steel and lower portion and exerts pressure the disc and evenly apply in soil sample lower surface with axial pressure, during the loading simultaneously through lower portion lift head adjustment elevating platform descending height and through the overhead ascending height of upper portion lift head adjustment hydraulic pressure loading, when exerting pressure on upper portion disc and soil sample upper surface contact, obtain this moment axial force through hydraulic pressure loading head, consolidation pressure and the size of axial force in earlier stage of the contrast:
if the early consolidation pressure is larger than the axial force at the moment, increasing the axial force applied by the hydraulic loading head to enable the early consolidation pressure to be equal to the axial force at the moment, and performing simultaneous working and bidirectional pressing on the soil sample by the lower lifting head and the upper lifting head according to the set time required by compaction, wherein the axial force is kept unchanged in the pressing process;
if the early consolidation pressure is equal to the axial force at the moment, keeping the axial force at the moment unchanged, simultaneously working and bidirectionally pressing the soil sample into the soil sample through the lower lifting head and the upper lifting head according to the set time required by compaction, and keeping the axial force unchanged in the pressing process;
if the early consolidation pressure is smaller than the axial force at the moment, reducing the axial force applied by the hydraulic loading head to enable the early consolidation pressure to be equal to the axial force at the moment, performing simultaneous working and bidirectional pressing on the soil sample by the lower lifting head and the upper lifting head after the set time required by compaction, and keeping the axial force unchanged in the pressing process;
step six: when the lower edges and the upper edges of the three valves are flush with second scale marks of the lower force transmission rod and the upper force transmission rod respectively, the compaction of the soil sample is finished, so that the lower pressure applying disc reaches the lower edge position of the filter paper in the membrane at the moment, the upper pressure applying disc reaches the upper edge position of the filter paper in the membrane, and the preparation of the soil sample is finished;
step seven: the upper lifting head drives the hydraulic loading head to rise to enable the upper pressing disc to be separated from the prepared soil sample, the three valves are taken down from the positioning buckle, the three valves are removed, the whole soil sample inside the three valves is taken out from the lower pressing disc, and the completely prepared triaxial soil sample is obtained after the filter paper in the membrane is peeled.
Compared with the prior art, the invention has the following beneficial technical effects:
according to the invention, the uniformity and the flatness of the upper and lower surfaces of the soil sample are ensured by compacting the soil sample in two directions, the compactness of the soil sample is controlled, the vertical stress and the stress history of the soil sample in a foundation are simulated during sample preparation, and the problem that the triaxial soil sample is easy to lose mould due to the arrangement of the filter paper on the inner wall of the three-petal membrane is solved. In conclusion, the device meets the preparation requirement of geotechnical test specifications on the soil sample, has the advantages of simple structure, convenience in operation and high accuracy and success rate, and can better meet the requirements of scientific research and engineering on the triaxial soil sample.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic view of the construction of an apparatus for preparing triaxial soil samples according to the present invention;
FIG. 2 is a sectional view of a structure 1/4 of an apparatus for preparing triaxial soil samples according to the present invention;
FIG. 3 is a schematic view of the three valves and their adjacent structure in the triaxial soil sample preparation device of the present invention;
FIG. 4 is a top view of a tri-valve and its internal structure in a tri-axial soil sample preparation device of the present invention;
FIG. 5 is a schematic diagram of a filter paper in a tri-valve and pressing disk of the tri-axial soil sample preparation device according to the present invention;
FIG. 6 is a schematic view of the compaction process in the triaxial soil sample preparation method of the present invention.
Description of reference numerals: 1. a base; 2. a lower base plate; 3. a lower lifting head; 4. a lifting platform; 5. a lower dowel bar; 6. a lower pressing disk; 7. lower filter paper; 8. three valves; 9. a collar; 10. positioning a buckle; 11. filtering paper in the membrane; 12. soil sampling; 13. upper filter paper; 14. an upper pressing disk; 15. an upper dowel bar; 16. a hydraulic loading head; 17. an upper lifting head; 18. an upper base plate; 19. a counter-force top plate; 20. a lower gasket; 21. a fixing rod; 22. an upper gasket; 23. a nut; 24. a first scale mark; 25. a second tick mark.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings, and it is to be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1-2, the manufacturing apparatus of this embodiment includes a base 1, a reaction top plate 19, a hydraulic system and a sample preparation mold, the reaction top plate 19 is located directly above the base 1, the reaction top plate 19 is fixedly connected to the base 1 through a plurality of fixing rods 21, the plurality of fixing rods 21 are uniformly distributed at intervals along a circumference, lower gaskets 20 are respectively installed at the lower ends of the fixing rods 21 and the joint of the base 1, upper gaskets 22 are respectively installed at the upper ends of the fixing rods 21 and the joint of the reaction top plate 19, the reaction top plate 19 is connected to the plurality of fixing rods 21, appropriate base plates are respectively installed on the base 1 and the reaction top plate 19, a lower base plate 2 is arranged at the center of the top surface of the base 1, the top surface of the lower base plate 2 is rigidly connected to the bottom surface of the lower lifting head 3, an upper base plate 18 is arranged at the center of the bottom surface of the reaction top plate 19, the lower surface of the upper base plate 18 is rigidly connected to the upper lifting head 17, and the hydraulic system and the sample preparation mold are installed between the lower base plate 2 and the upper base plate 18.
As shown in fig. 1, the base 1 is a disk shape, the reaction top plate 19 has a plurality of through holes, the fixing rods 21 are thin and thick, the lower ends of the fixing rods are perpendicular to the base 1 and are fixed in the slots of the base 1 in parallel, the upper ends of the fixing rods penetrate through the through holes of the reaction top plate 19 and are fixed on the upper and lower bottom surfaces of the reaction top plate 19 respectively through nuts 23, the nuts 23 are fixed on the upper and lower surfaces of the reaction top plate 19, and an upper gasket 22 is installed between the nuts 23 and the surface of the reaction top plate 19.
The lower lifting head 3 and the upper lifting head 17 have lifting motion functions, and can be implemented by a pressurizing structure or other mechanical structures.
The hydraulic system comprises a lifting platform 4, a lower dowel bar 5, a lower pressing disc 6, an upper pressing disc 14, an upper dowel bar 15 and a hydraulic loading head 16, wherein the lifting platform 4 is fixedly arranged at the movable end of the upper end of the lower lifting head 3, the lower dowel bar 5 is vertically arranged up and down along the direction parallel to the fixed rod 21, the lower end of the lower dowel bar 5 is fixed on the lifting platform 4, and the upper end of the lower dowel bar 5 is fixedly connected with the lower pressing disc 6; the hydraulic loading head 16 is fixedly arranged at the movable end of the lower end of the upper lifting head 17, the upper dowel bar 15 is vertically arranged up and down along the direction parallel to the fixed rod 21, the upper end of the upper dowel bar 15 is fixed on the hydraulic loading head 16, and the lower end of the upper dowel bar 15 is fixedly connected with the upper pressure applying disc 14; a soil sample 12 is arranged between the lower pressing disc 6 and the upper pressing disc 14; the lifting head can move up and down in the direction vertical to the base plate, the hydraulic loading head 16 controls the axial force, the axial force is applied to the dowel bar, and the dowel bar transmits the axial force to the pressure applying disc to compact the surface of the soil sample 12.
As shown in fig. 3, the sample preparation mold comprises a three-valve 8, a lantern ring 9, intra-membrane filter paper 11, lower filter paper 7 and upper filter paper 13, wherein an annular three-valve 8 is arranged around a soil sample 12, the lantern ring 9 is sleeved outside the three-valve 8, the three-valve 8 is clamped and fixed through the lantern ring 9, and the lantern ring 9 is positioned and installed on a fixing rod 21 through a positioning buckle 10; an intramembrane filter paper 11 is arranged between the middle part of the inner peripheral surface of the three-valve 8 and a soil sample 12, and a lower filter paper 7 and an upper filter paper 13 are respectively arranged on the top surface of the lower pressing disc 6 and the bottom surface of the upper pressing disc 14, so that the filter papers are attached to the inner wall of the three-valve and the surface of the pressing disc.
As shown in fig. 4, the fixing rod 21 includes a thin upper section and a thick lower section, each fixing rod 21 is provided with a positioning buckle 10, as shown in fig. 1, the positioning buckle 10 is sleeved on the thin upper section of the fixing rod 21 and clamped at a step between the thin upper section and the thick lower section, the outer side surface of the tri-valve 8 is provided with a positioning protrusion, after the tri-valve 8 is combined, the positioning protrusion of the tri-valve 8 is placed in the positioning buckle 10, so that the positioning buckle 10 is horizontally connected with the fixing rod 21, the tri-valve 8 is kept at a fixed height position, and the lantern ring 9 is positioned on the step formed on the top surface of the positioning buckle 10.
As shown in fig. 2 and 4, the inner diameter of the tri-valve 8 is consistent with the diameters of the lower pressing disk 6 and the upper pressing disk 14, so that the lower pressing disk 6 and the upper pressing disk 14 can vertically reciprocate in the tri-valve 8 in a penetrating manner.
As shown in fig. 4 and 5, the size of the intramembrane filter paper 11 is consistent with the inner diameter of the tri-valve 8, after wetting the filter paper, the filter paper is wound in a circle and then horizontally and circumferentially attached to the inner wall of the tri-valve 8, the size of the upper filter paper 13 and the size of the lower filter paper 7 are consistent with the size of the surface of the upper pressing disc 14 and the surface of the lower pressing disc 6 which respectively correspond to the filter paper, and after wetting, the filter paper is respectively attached to the upper surface of the lower pressing disc 6 and the lower surface of the upper pressing disc 14.
As shown in fig. 5, the in-membrane filter paper 11, the upper filter paper 13 and the lower filter paper 7 are respectively disposed on the circumferential surface, the top surface and the bottom surface of the soil sample 12 to form a cylinder shape, so that the soil sample is completely wrapped.
The lower dowel bar 5 is divided into three parts by two scale marks along the upper and lower axial directions of the lower dowel bar, and the two scale marks are a first scale mark 24 and a second scale mark 25 from top to bottom respectively; and the height difference between the lower edge of the intramembrane filter paper 11 and the lower edge of the three-flap membrane 8 is 2/3 of the axial length of the lower dowel bar 5 plus the thickness of the lower pressure-applying disc 6; the upper dowel bar 15 is divided into three equal parts by two scale marks along the upper and lower axial directions of the upper dowel bar, and the two scale marks are a first scale mark 24 and a second scale mark 25 from bottom to top respectively; and the height difference between the upper edge of the inner membrane filter paper 11 and the upper edge of the tri-lobe membrane 8 is 2/3 of the axial length of the upper force transmission rod 15 plus the thickness of the upper pressure application disc 14.
The hydraulic loading head 16 provides vertical axial force, the upper lifting head 17 is rigidly connected with the hydraulic loading head 16, the lower lifting head 3 is rigidly connected with the lifting platform 4, the lower lifting head 3 and the upper lifting head 17 move simultaneously during sample preparation, and the displacement directions are all the geometric centers of the vertical pressing disc pointing to the soil sample 12.
The invention brings the effects of synchronous control and equal displacement in the triaxial sample preparation process through the displacement control of the reaction top plate 19 and the upper and lower lifting heads, and realizes the vertical uniformity and surface smoothness of the prepared soil sample.
The invention controls the axial force in the soil sample preparation process through the hydraulic loading head 16, brings the effect of freely controlling the axial force and the pressurizing and pressure-releasing time on sample preparation, realizes the simulation of the real vertical stress on the soil body in the foundation, and solves the problem that the step-by-step pressurizing preparation is considered in the soil sample preparation due to different stress histories on the soil body.
According to the invention, the soil sample 12 is wrapped by the filter paper after being prepared, the filter paper is loose and has strong air permeability, the vacuum negative pressure and the matrix suction force generated by the direct contact between the three valves 8, the lower pressing disc 6 and the upper pressing disc 14 and the soil sample 12 are eliminated, the soil sample 12 is smoothly demoulded, and the innovative situation is that: filter paper has previously been used to separate solutions from solids and has not been used in soil sample preparation to eliminate negative pressure.
The embodiment also provides a using method of the device, which comprises the following steps:
the method comprises the following steps: the lower lifting head 3 drives the lifting platform 4 to descend, the lower filter paper 7 is pasted on the upper surface of the lower pressing disc 6 after being wetted, the upper lifting head 17 drives the hydraulic loading head to ascend, the upper filter paper 13 is pasted on the lower surface of the upper pressing disc 14 after being wetted, and the lower pressing disc 6 is ensured to be low enough to be sleeved with the three valves 8;
step two: combining the three valves 8 and attaching the in-membrane filter paper 11 on the inner wall, so that the height difference between the lower edge of the in-membrane filter paper 11 and the lower edge of the three valves 8 is 2/3 of the axial length of the lower dowel bar 5 plus the thickness of the lower pressure disk 6, and the height difference between the upper edge of the in-membrane filter paper 11 and the upper edge of the three valves 8 is 2/3 of the axial length of the upper dowel bar 15 plus the thickness of the upper pressure disk 14; using the collar 9 to tighten outside the tri-valve 8, the tri-valve 8 is placed on the lower pressure disc 6, so that the lower pressure disc 6 enters inside the tri-valve 8; the tri-valve 8 is not sleeved outside the upper pressure applying disc 14.
Step three: according to the history of the stress of the soil sample 12 in the foundation, calculating the consolidation pressure of the soil body in the early stage and the time required by compaction, according to the density and the size of the prepared soil sample 12, calculating the mass of the required soil sample 12, weighing the soil sample, and pouring the soil sample into the three-valve 8 at one time;
step four: lifting the three-valve 8 and fixing the three-valve 8 on the positioning buckle 10, so that the upper pressure applying disc 14 enters the three-valve 8, and simultaneously, the descending height of the lifting platform 4 is adjusted through the lower lifting head 3 and the ascending height of the hydraulic loading head is adjusted through the upper lifting head 17, so that the lower edge of the three-valve 8 is flush with the first scale line 24 of the lower dowel bar 5, and the upper edge of the three-valve 8 is flush with the first scale line 24 of the upper dowel bar 15; as shown in fig. 6 (a), the distance between the lower pressure-applying disk 6 and the lower edge of the filter paper 11 in the membrane is ensured to be consistent with the distance between the upper pressure-applying disk 14 and the upper edge of the filter paper 11 in the membrane, and the distance is 1/3 of the axial length of the dowel bar;
step five: the upper lifting head 17 is matched with the hydraulic loading head 16 to apply axial pressure to the upper surface of the soil sample 12 through the upper dowel steel 15 and the upper pressing disc 14 in sequence, the lower lifting head 3 is matched with the lifting platform 4 to apply the axial pressure to the lower surface of the soil sample 12 through the lower dowel steel 5 and the lower pressing disc 6 in sequence and uniformly and symmetrically, the descending height of the lifting platform 4 is adjusted through the lower lifting head 3 and the ascending height of the hydraulic loading head is adjusted through the upper lifting head 17 during loading, when the upper pressing disc 6 is contacted with the upper surface of the soil sample 12, the axial force at the moment is obtained through the hydraulic loading head 16, and the consolidation pressure and the axial force at the early stage are compared:
if the early consolidation pressure is larger than the axial force at the moment, increasing the axial force applied by the hydraulic loading head 16 to enable the early consolidation pressure to be equal to the axial force at the moment, and slowly and bidirectionally pressing the soil sample 12 through the lower lifting head 3 and the upper lifting head 17 after the set time required by compaction, wherein the axial force is kept unchanged in the pressing process;
if the early consolidation pressure is equal to the axial force at the moment, keeping the axial force at the moment unchanged, slowly and bidirectionally pressing the soil sample 12 through the lower lifting head 3 and the upper lifting head 17 after the set time required by compaction, and keeping the axial force unchanged in the pressing process;
if the early consolidation pressure is smaller than the axial force at the moment, reducing the axial force applied by the hydraulic loading head 16 to ensure that the early consolidation pressure is equal to the axial force at the moment, slowly and bidirectionally pressing the soil sample 12 by simultaneously working the lower lifting head 3 and the upper lifting head 17 after the set time required by compaction, and keeping the axial force unchanged in the pressing process;
therefore, when the upper surface and the lower surface of the soil body are in contact with the pressing disc and the hydraulic loading head can independently control the application of the axial force, earlier consolidation pressure and the contact of the soil body and the pressing disc are compared, and the simulation of real vertical stress and stress history is realized.
Step six: when the lower edge and the upper edge of the three valves 8 are flush with the second scale marks 25 of the lower dowel bar 5 and the upper dowel bar 15 respectively, the compaction of the soil sample 12 is finished, see fig. 6 (b), so that the lower pressure applying disc 6 reaches the position of the lower edge of the intramembrane filter paper 11, the upper pressure applying disc 14 reaches the position of the upper edge of the intramembrane filter paper 11, and the preparation of the soil sample 12 is finished;
step seven: the hydraulic loading head is driven to ascend through the upper lifting head 17, so that the upper pressing disc 14 is separated from the prepared soil sample 12 firstly, the three-valve 8 is taken down from the positioning buckle 10, the three-valve 8 is taken off, the whole soil sample 12 inside the three-valve 8 is taken out from the lower pressing disc 6, the completely prepared triaxial soil sample is obtained after the filter paper 11 in the membrane is peeled off, and finally the lifting table 4 can be driven to descend through the lower lifting head 3 to prepare next time.
According to the invention, the real vertical stress and stress history borne by the prepared soil sample 12 in the foundation can be simulated through the setting of the early consolidation pressure, and the prepared soil sample 12 can be used for obtaining soil body parameters which are closer to the original foundation soil.
The principle and the implementation mode of the present invention are explained by applying specific examples in the present specification, and the above descriptions of the examples are only used to help understanding the method and the core idea of the present invention; meanwhile, for a person skilled in the art, the specific embodiments and the application range can be changed according to the idea of the present invention. In view of the above, the present disclosure should not be construed as limiting the invention.
Claims (6)
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