CN107607374A - A kind of hollow cylinder pilot system suitable for unsaturated soil - Google Patents

Abstract

The invention discloses a kind of hollow cylinder pilot system suitable for unsaturated soil, it is related to earthwork test Instrument.The pilot system can be achieved to be controlled the hollow torsion shear test of unsaturated soil of suction by axially forming with torsion drive device, balancing gate pit, inside and outside confined pressure, air pressure and backpressure controllers, data acquisition unit and computer.Axially and torsion drive device can provide axial stress and moment of torsion；Pressure chamber base studs with high air-entry value pottery clay plates, and pottery clay plates are connected with hollow cylinder sample bottom；Inside and outside confined pressure, air pressure and backpressure controllers input interface and pore water are arranged at balancing gate pit bottom（Gas）Pressure sensor measures interface；Local displacement sensor, the inside and outside wall radial displacement of test test specimen and axial displacement can be set in balancing gate pit；Contacted at the top of sample by permeable stone with sample cap；Sample cap is provided with hole air pressure inlet and outlet, application and measurement for hole air pressure；Sample cap top is axle power/torque sensor, can determine the axial stress and shear stress of unsaturation sample, realizes the measure of unsaturated soils theory parameter under the conditions of principal stress axis rotation.

Description

A Hollow Cylindrical Test System Applicable to Unsaturated Soil

technical field

The invention belongs to the technical field of geotechnical engineering test equipment, in particular to a hollow cylinder test system suitable for unsaturated soil.

Background technique

Problems encountered in engineering practice such as uneven settlement and wetting deformation of roadbeds and dams, uneven settlement of extremely thick fill formed by Pingshan reclamation, collapsibility of large-thickness loess, swelling and shrinking of expansive soil, deep The instability of foundation pits and high slopes, the overburden design of urban waste landfills, and the long-term performance of buffer materials for deep geological repositories of high-level radioactive waste under coupled thermal-hydraulic-mechanical-chemical conditions all involve unsaturated soil Mechanics problem. In most engineering practices involved in the field of geotechnical engineering, such as roadbed filling, foundation pit excavation, slope slippage and even coal mine roadway excavation, the angle between the direction of the large principal stress and the vertical direction on the soil will occur. Changes, especially for high-speed railways and highway foundations, high-speed traffic cyclic loads will cause the angle α between the large principal stress σ ₁ of the foundation soil and the vertical direction to change momentarily, resulting in the continuity of the principal stress axis of the foundation soil unit. The cycle will cause the accumulation of pore pressure in the soil, aggravate the accumulated plastic strain of the soil, and cause the change of the secondary anisotropy and strength of the soil. In actual engineering, if this change is ignored, the deformation of unsaturated soil will be underestimated and the engineering design will be unsafe.

At present, the main instruments for testing the mechanical properties of unsaturated soil include: unsaturated soil consolidation instrument, direct shear instrument, air permeability instrument, standard triaxial instrument, temperature control triaxial instrument, multi-functional triaxial instrument and geotechnical CT-triaxial instrument etc., through experimental research, revealed the water-air movement law of unsaturated soil and special soil, and many important mechanical characteristics laws such as deformation, strength, yield, water volume change, collapsibility, swelling, mesostructure evolution, and temperature effect; The axiomatic theoretical system of rock and soil mechanics and the stress state variables of unsaturated soil in various combinations; the theoretical formula of the effective stress of anisotropic porous media and the theoretical formula of the effective stress of unsaturated soil; the establishment of the unsaturated soil Constitutive model pedigree of collapsible loess and expansive soil and generalized soil-water characteristic curve model pedigree considering density, net mean stress and deviatoric stress respectively; established three-dimensional consolidation theory of unsaturated soil and its consolidation model pedigree ; Independently developed a series of software for analyzing consolidation problems, and obtained analytical solutions for one-dimensional consolidation problems and numerical solutions for two-dimensional consolidation problems, forming a complete theoretical system. However, most of the unsaturated soil problems encountered in engineering practice rotate in the direction of the principal stress axis. The existing research results show that the mechanical properties of the soil will change significantly under the condition of the principal stress axis rotation, while the current unsaturated soil directly The experimental equipment such as shear instrument, consolidation instrument and triaxial instrument cannot yet consider the influence of the rotation of the principal stress axis, and the research on the strength and deformation characteristics of unsaturated soil caused by the rotation of the principal stress axis cannot be carried out.

In order to solve the defects of the prior art, the present invention proposes a hollow cylinder test system suitable for unsaturated soil, which can meet the mechanical characteristics of unsaturated soil under the principal stress axis directional shear and cyclic rotation stress path of the control and measurement suction conditions The requirements of the test provide test data and scientific basis for the study of the strength characteristics, deformation characteristics, anisotropy and non-coaxial characteristics of unsaturated soil under the condition of principal stress axis deflection, and can promote the development of experimental unsaturated soil mechanics.

Contents of the invention

The technical problem to be solved by the present invention is to provide a hollow cylinder test system suitable for unsaturated soil, which can carry out the hollow torsional shear test of unsaturated soil under the condition of principal stress axis rotation.

In order to solve the above technical problems, the technical solution adopted in the present invention is: a hollow cylinder test system suitable for unsaturated soil, including: axial and torsional driving device, hollow cylinder pressure chamber, internal and external confining pressure, air pressure and reaction pressure controller; data acquisition system and computer control system.

The axial and torsional driving device is composed of an axial (torsion) motor and a driver, including two brushless DC servo motors that drive the ball screw and the spline shaft through a toothed transmission belt.

The base of the hollow cylindrical pressure chamber is fixed on the top of the driving device, and the base of the hollow cylindrical pressure chamber includes inner and outer pressure, air pressure and back pressure connecting pipelines and is connected with inner and outer pressure, air pressure and back pressure sensors. The top seat of the hollow cylindrical pressure chamber is equipped with an interchangeable load torque sensor, and the top cover of the pressure chamber is lifted and lowered by a lifting frame connected to an electric motor, so that the sample is in a suitable position.

The internal and external pressure, air pressure and back pressure controllers are controlled by servo stepping motors, and the control of internal and external pressure, air pressure and back pressure is realized by changing the volume of the controller. The air pressure controller is suitable for air with extremely low stiffness, and the specification parameters are 2MPa/1000cc air pressure/volume controller; the inner peripheral pressure controller (2), peripheral pressure controller (1) and reverse The pressure controller (3) is suitable for liquid controllers, and the specifications are 2MPa/200cc water pressure/volume controllers. The controller is filled with degassed water, which is used to control the pore water pressure (back pressure) and measure the pore water volume change △ V . Adding the changes in the volumes of air and water in the pores gives an estimate of the change in the total volume of the sample.

The base of the hollow cylindrical pressure chamber is inlaid with an annular high air intake value pottery clay plate (HAEPD) (11), so that the water in the hollow cylindrical soil sample can pass through but the applied gas cannot pass through. In order to achieve the purpose of both controlling the suction of the matrix and allowing drainage, the ventilation pressure of the annular high air intake value clay plate is 5 Bar.

The base of the hollow cylindrical pressure chamber includes internal and external pressure, air pressure and back pressure intake (water) pipelines, which can pass through the internal pressure controller (2), peripheral pressure controller (1), air pressure controller (4) Apply internal and external pressure, air pressure and back pressure with the back pressure controller (3); the base of the pressure chamber is connected with the air pressure sensor (31) and the pore pressure sensor (29), which can test the pore air pressure and pore water pressure of the sample; The specifications of the internal and external pressure and back pressure controllers are 2MPa/200cc water pressure/volume controllers; the specifications of the air pressure controllers are 2MPa/1000cc air pressure/volume controllers (4).

A local outer wall displacement sensor (13) and an LVDT displacement sensor are installed at the lower 1/4 position of the hollow cylindrical pressure chamber, which can test the radial displacement and axial displacement of the outer wall of the specimen; the inner wall of the specimen is equipped with a Hall effect sensor And LVDT displacement sensor, can test the radial displacement and axial displacement changes of the inner wall of the sample; according to the radial displacement and axial displacement changes of the inner and outer walls of the test, the test force state analysis can be carried out.

The bottom of the hollow cylindrical sample is connected with the annular clay plate (11), so that the water exerted by the back pressure can pass through but the gas cannot pass through; the top of the sample is connected with the permeable stone (20), and the upper part of the permeable stone (20) is connected with the sample cap (34 ), the pore air pressure is connected through the reserved hole on the sample cap (34), so that the air applied by the air pressure controller is connected with the pore gas in the sample, so as to measure and control the pore air pressure in the soil sample and the whole test sample. The volume of air in the sample system changes, thereby controlling the matrix suction of the sample.

The signal conditioning means includes analog signal conditioning and digital signal conditioning. Analog signal conditioning includes an 8-channel PC board that provides excitation voltages, zeroing and setting gain values for each sensor. The computer board is installed in a separate unit (DIT). Digital signal conditioning is built into the DIT, including an 8-channel computer board for connecting digital signals from HSDAC cards to motor controllers and other devices.

The digital control system is based on the GDSDCS high-speed digital control system, which has displacement and load closed-loop feedback. GDSDCS is equipped with 16bit data acquisition (A/D) and 16bit control output (D/A) devices, which operate at a control frequency of 10Hz per channel, and each cycle can have 1000 data control and collection points; each cycle at 1Hz There can be 10 000 data control and collection points.

The hollow cylinder test system of unsaturated soil can control the proportional gain K _p , integral gain K _I and differential gain K _D through its own PID controller to realize the principal stress axis rotation test and directional shear of samples with different stress paths test.

Compared with the existing technology, the beneficial effect of the present invention is that by adding clay plates, air pressure/volume controllers, pore air pressure sensors, inner/outer wall displacement sensors, etc. on the basis of the existing hollow cylinder test system, the Test the radial, axial and circumferential displacements and stresses of the inner/outer walls of unsaturated soil samples during principal stress axis-oriented shear and rotation tests. The device structure of the invention is reasonable, easy to use, meets the requirements of unsaturated soil mechanical properties test under the condition of principal stress axis directional shear and cyclic rotation for controlling and measuring suction, and is useful for studying unsaturated soil under the condition of principal stress axis deflection. Strength characteristics, deformation characteristics, anisotropy and non-coaxial characteristics provide experimental data and scientific basis, which can promote the development of experimental unsaturated soil mechanics.

Description of drawings

The present invention will be further described below in conjunction with drawings and embodiments.

Figure 1 is the overall structure of the GDS unsaturated soil hollow cylinder test system

Figure 2 is a structural diagram of the pressure chamber

Figure 3 is the connection pipeline diagram of the pressure chamber system

Figure 4 is the layout of the pore pressure exhaust valve and the pressure sensor

Figure 5 is the layout of pore water pressure exhaust valve and water pressure sensor

Among them: 1. Peripheral pressure control system; 2. Internal pressure control system; 3. Back pressure control system; 4. Air pressure control system; 5. Data control/acquisition system; 6. Computer control system; 7. Axial force (axis 8. Torque (torsion shear angle) control system; 9. Pore water pressure control valve; 10. Pore air pressure control valve; 11. High air intake value clay plate; 12. External pressure chamber; 13. Partial Outer wall displacement sensor; 14. Axial force/torque coupling sensor; 15. Peripheral pressure control valve; 16. Internal pressure control valve; 17. Back pressure control valve; 18. Air pressure control valve; 19. Sensor connection cable; 20. Permeable stone; 21. Internal pressure chamber; 22. Peripheral pressure inlet; 23. Air pressure inlet; 24. Back pressure inlet; 25. Internal pressure inlet; 26. Pore water outlet; 27. Pore gas outlet; 28. Three-way valve ;29, pore water pressure sensor; 30, drainage valve; 31, pore air pressure sensor; 32, exhaust valve; 33, axial force, torque loading base; 34, sample cap; 35, axial displacement sensor; 36, Instrument frame; 37. Instrument base.

specific embodiment

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

A hollow cylinder test system suitable for unsaturated soil, including: axial and torsional driving device, hollow cylinder pressure chamber, internal and external confining pressure, air pressure and back pressure controller; signal adjustment device, digital control system and computer control system .

The axial and torsional driving device is composed of an axial (torsion) motor and a driver, including two brushless DC servo motors that drive the ball screw and the spline shaft through a toothed transmission belt.

The base of the hollow cylindrical pressure chamber is fixed on the top of the driving device. The base of the hollow cylindrical pressure chamber includes internal and external pressure, air pressure and back pressure connecting pipelines and is connected with internal and external pressure, air pressure and pore water pressure sensors. The top seat of the hollow cylindrical pressure chamber is equipped with an interchangeable load torque sensor, and the top cover of the pressure chamber is lifted and lowered by a lifting frame connected to an electric motor, so that the sample is in a suitable position.

The internal and external pressure, air pressure and back pressure controllers are controlled by servo stepping motors, and the control of internal and external pressure, air pressure and back pressure is realized by changing the volume of the controller. The air pressure controller is suitable for extremely low stiffness air controllers, and the specifications are 2MPa/1000cc air pressure/volume controllers; the internal and external pressure and back pressure controllers are suitable for liquid controllers, and the specifications are 2MPa/200cc water pressure/volume controller. The controller is filled with degassed water, which is used to control the pore water pressure (back pressure) and measure the pore water volume change. Adding the changes in the volumes of air and water in the pores gives an estimate of the change in the total volume of the sample.

The base of the hollow cylindrical pressure chamber is inlaid with an annular high air intake value pottery clay plate (HAEPD) (11), so that the water in the hollow cylindrical soil sample can pass through but the applied gas cannot pass through. In order to achieve the purpose of both controlling the suction of the matrix and allowing drainage, the ventilation pressure of the annular high air intake value clay plate is 5 Bar.

The base of the hollow cylindrical pressure chamber includes internal and external pressure, air pressure and back pressure intake (water) pipelines, which can pass through the internal pressure controller (2), peripheral pressure controller (1), air pressure controller (4) Apply internal and external pressure, air pressure and back pressure with the back pressure controller (3); the base of the pressure chamber is connected with the air pressure sensor (31) and the pore pressure sensor (29), which can test the pore air pressure and pore water pressure of the sample; The specifications of the internal and external pressure and back pressure controllers are 2MPa/200cc water pressure/volume controllers; the specifications of the air pressure controllers are 2MPa/1000cc air pressure/volume controllers (4).

A local outer wall displacement sensor (13) and an LVDT displacement sensor are installed at the lower 1/4 position of the hollow cylindrical pressure chamber, which can test the radial displacement and axial displacement of the outer wall of the specimen; the inner wall of the specimen is equipped with a Hall effect sensor And LVDT displacement sensor, can test the radial displacement and axial displacement changes of the inner wall of the sample; according to the radial displacement and axial displacement changes of the inner and outer walls of the test, the test force state analysis can be carried out.

The bottom of the hollow cylindrical sample is connected with the annular clay plate (11), so that the water exerted by the back pressure can pass through but the gas cannot pass through; the top of the sample is connected with the permeable stone (20), and the upper part of the permeable stone (20) is connected with the sample cap (34 ), the pore air pressure is connected through the reserved hole on the sample cap (34), so that the air applied by the air pressure controller is connected with the pore gas in the sample, so as to measure and control the pore air pressure in the soil sample and the whole test sample. The volume of air in the sample system changes, thereby controlling the matrix suction of the sample.

The signal conditioning means includes analog signal conditioning and digital signal conditioning. Analog signal conditioning includes an 8-channel PC board that provides excitation voltages, zeroing and setting gain values for each sensor. The computer board is installed in a separate unit (DIT). Digital signal conditioning is built into the DIT, including an 8-channel computer board for connecting digital signals from HSDAC cards to motor controllers and other devices.

The digital control system is based on the GDSDCS high-speed digital control system, which has displacement and load closed-loop feedback. GDSDCS is equipped with 16bit data acquisition (A/D) and 16bit control output (D/A) devices, which operate at a control frequency of 10Hz per channel, and each cycle can have 1000 data control and collection points; each cycle at 1Hz There can be 10 000 data control and collection points.

The hollow cylinder test system of unsaturated soil can control the proportional gain K _p , integral gain K _I and differential gain K _D through its own PID controller to realize the principal stress axis rotation test and directional shear of samples with different stress paths test.

The test steps are as follows:

(1) Prepare a hollow cylindrical sample. The preparation method of the undisturbed sample is as follows: use a soil cutter to cut the soil sample into a cylindrical sample with a diameter of Φ = 100 mm and h = 200 mm. Then the cylindrical sample is put into the casing, and the inner core is cut on the inner diameter soil cutter; the preparation method of the remodeling sample is to prepare a cylindrical sample with the same dry density and the same size as the original sample in the cylindrical casing, and then in the cylindrical casing Cut the inner core on the inner diameter soil cutter to prepare a hollow cylindrical sample.

(2) Saturated clay panels

①Close the valves of the pressure chamber without installing the sample, and fill the pressure chamber with anaerobic water (such as distilled water).

②Open the drain valve and confining pressure valve of the pressure chamber, and apply a confining pressure of 300 kPa to 400 kPa until more water is discharged from the drain valve.

③ Flush the air bubbles accumulated under the clay plate, open the water filling valve, let airless water flow through the spiral groove under the clay plate, rinse for 30 seconds, and close the water filling valve.

④Repeat step ③ until there is continuous water discharge from the drain valve, then remove the pressure.

(3) Install the sample

① Fix the prepared hollow cylindrical sample in the sample loader, and install the inner membrane and outer mold. The sample loader consists of a base, an intimal spacer, a top cover, a cap and a stand. Sample loading is mainly divided into five steps: installation of the bottom of the inner membrane, installation of the outer mold, installation of the top cover, installation of the top of the inner membrane and installation of the cap. When it is necessary to test the local radial strain of the hollow cylindrical sample, a tin foil sheet should be attached to the lower 1/4 position of the outer wall of the sample before loading the sample, as the sensing surface of the local strain sensor. The tin foil should be as small as possible to meet the deformation range of the sample, so as to reduce the influence on the stress of the sample.

②Remove the upper cover of the pressure chamber, and wipe off the remaining water on the top surface of the clay plate with a wet towel.

③Translate the sample into the pressure chamber, and fix the sample base on the turntable of the pressure chamber with screws.

④After positioning the sample, install the local outer wall displacement sensor (13) and LVDT displacement sensor.

(4) Connecting pipelines

Connect the internal and external pressure, air pressure and back pressure controller pipelines with the corresponding communication holes on the pressure chamber base and the pressure chamber cap, so that the internal and peripheral pressure, air pressure and back pressure pipelines are connected.

① Connect the internal pressure pipeline

First, exhaust the internal pressure access pipeline, and connect it to the internal pressure communication hole of the top cover after there is no air in the pipeline; then control the drainage of the internal pressure controller to make the residual air in the internal pressure chamber of the sample Discharge from the internal pressure communication hole; after the exhaust is completed, connect the internal pressure exhaust pipe to the internal pressure communication hole; finally open the exhaust valve, and then perform drainage control on the internal pressure controller. After the air exhaust is completed, close the exhaust valve.

② Connect the back pressure pipeline

Connect the inlet pipe of the back pressure controller to the water inlet pipe of the clay plate, and connect the outlet pipe to the pore water pressure valve. After exhausting the pipeline, close the pore water pressure valve.

③Connect the pneumatic pipeline

Connect the access tube of the air pressure controller to the inlet of the sample cap (34) and communicate with the sample. The pore air pressure is applied to the air pressure controller, so that the pore air pressure is connected with the air pressure outlet of the sample cap (34) and connected to the pore air pressure sensor to measure or apply the pore air pressure.

④ Connect the external pressure pipeline

After the internal pressure, back pressure and air pressure pipelines are connected, lower the pressure outer cover and tighten it with screws to ensure that the pressure chamber is sealed. Open the water inlet valve of the pressure chamber, and use a self-priming water pump to fill the chamber of the pressure chamber with water until the water outlet valve on the top of the pressure chamber continues to discharge water, close the water outlet valve and the water inlet valve of the pressure chamber, and prepare to start the test.

(4) Measurement of initial matrix suction

After the pipeline is connected, adjust the position of the axial displacement sensor so that the sample is fully in contact with the clay plate at the base of the pressure chamber. After the sample is installed, fill the pressure chamber with anaerobic water, apply the same value of internal and external pressure and simultaneously apply pore air pressure, keep the internal and external pressure 5~10 kPa higher than the air pressure, and prevent the rubber membrane from being swollen and cracked. Keep this state for about 12 to 18 hours until the pore water pressure is stable, and the initial matrix suction of the sample is obtained, ready to enter the next test.

(5) Start the computer control system and start the experiment

Start the unsaturated soil test control module in the GDSLAB software, and realize the control of the internal pore water pressure and pore air pressure of the sample through the back pressure controller and air pressure controller, so that the water pressure and air pressure in the sample are evenly distributed, that is, the suction balance is achieved state. The internal and external pressures of the same value are applied through the internal and external pressure controller (1), and the axial pressure is applied through the axial pressure controller to make the axial stress equal to the radial stress and hoop stress of the sample, and carry out isotropic pressure Consolidation. After the drainage of the sample is stable, the principal stress axis directional shear test and the cyclic rotation test of the controlled suction can be carried out on the sample according to the test objectives.

Claims (7)

1. a kind of hollow cylinder pilot system suitable for unsaturated soil, including：Axial direction and torsion drive device, hollow cylinder pressure Power room, inside and outside confined pressure, air pressure and backpressure controllers；Data collecting system and computer control system；Described axial direction, reverse Drive device is by axial direction（Reverse）Motor and driver composition, including ball-screw and splined shaft are driven by flat-toothed belt Two brushless type direct current servo motors；The hollow cylinder pressure chamber base is fixed on the top of drive device, hollow cylinder pressure Power room base includes inside and outside confined pressure, air pressure and back-pressure connecting line and is connected with inside and outside confined pressure, air pressure and back-pressure sensor；It is empty Heart cylindrical pressure ceiling seat is equipped with interchangeable load torque sensor, and balancing gate pit's top cover is connected on an electric motor by one Crane realize descending operation, sample is in suitable position；Inside and outside confined pressure, air pressure and the backpressure controllers are by watching Stepper motor control is taken, the control of inside and outside confined pressure, air pressure and back-pressure is realized by changing controller volume；The air pressure Controller is applied to the controller of the air of extremely low rigidity, and specifications parameter is 2MPa/1000cc air pressures/fixing fabric structure device； The inside and outside confined pressure and backpressure controllers are applied to the controller of liquid, and specifications parameter is 2MPa/200cc hydraulic pressure/fixing fabric structure Device, what is be full of in controller is degassed water, for controlling pore water pressure (back-pressure) and the water volume change of measurement hole, by hole Air is added the change that can be evaluated whether sample cumulative volume with the change of the volume of water in gap.

A kind of 2. hollow cylinder pilot system suitable for unsaturated soil according to claim 1, it is characterised in that：It is described Hollow cylinder pressure chamber base is inlaid with the high air-entry value pottery clay plates of annular（HAEPD）, so that the water in hollow cylinder soil sample can be with By can not be by and the gas that applies, so as to reach both can control matric suction and can draining purpose, the annular is high Air-entry value pottery clay plates venting pressure value 5Bar.

A kind of 3. hollow cylinder pilot system suitable for unsaturated soil according to claim 1, it is characterised in that：It is described Hollow cylinder pressure chamber base includes inside and outside confined pressure, air pressure and back-pressure air inlet（Water）Pipeline, interior confined pressure controller can be passed through（2）、 Peripheral pressure controller（1）, gas pressure regulator（4）And backpressure controllers（3）Apply inside and outside confined pressure, air pressure and back-pressure；Balancing gate pit bottom Seat is connected with baroceptor and sensor for pore water pressure, can be with the hole air pressure and pore water pressure of test sample；The inside and outside confined pressure It is 2MPa/200cc hydraulic pressure/fixing fabric structure device with backpressure controllers specifications parameter；The gas pressure regulator specifications parameter is 2MPa/ 1000cc air pressures/fixing fabric structure device.

A kind of 4. hollow cylinder pilot system suitable for unsaturated soil according to claim 1, it is characterised in that：It is described Downward 1/4 position sets local outer wall displacement transducer in the middle part of hollow cylinder balancing gate pit inner chamber（13）With LVDT displacement transducers, The radial displacement of test specimen outer wall and axial displacement change can be tested；Sample inwall passes equipped with hall effect sensor and LVDT displacements Sensor, can test sample inwall radial displacement △r _iAnd axial displacement △zChange；According to experiment inside and outside wall radial displacement and axle It can carry out testing stress analysis to change in displacement.

A kind of 5. hollow cylinder pilot system suitable for unsaturated soil according to claim 1, it is characterised in that：It is hollow Cylinder sample bottom and annular pottery clay plates（11）It is connected, so that the water that back-pressure applies can be by that can not pass through and gas；Sample Top and permeable stone（20）It is connected, permeable stone（20）Top and sample cap（34）It is connected, hole air pressure passes through sample cap（34）On Reserving hole channel is connected, and the porous gases in the air and sample that make to apply by gas pressure regulator connect, to measure, control soil sample In pore air pressure and whole sample system hollow gas product change, so as to Control Assay matric suction.

6. according to a kind of hollow cylinder pilot system suitable for unsaturated soil described in claim 1, it is characterised in that:It is described Pressure chamber base upper surface be provided with annular pottery clay plates（11）, sample cap（34）Lower surface is provided with permeable stone（20）Plate, examination Sample and annular pottery clay plates（11）And permeable stone（20）Plate is bottom-up to be enclosed with one layer of rubber membrane, rubber membrane and pressure chamber base and Sample cap（34）Groove between be provided with annular seal washer.

A kind of 7. hollow cylinder pilot system suitable for unsaturated soil according to claim 1, it is characterised in that：It is non-full Proportional gain can be controlled by the PID controller of its own with the hollow cylinder pilot system of soilK _p, storage gainK _IAnd differential GainK _DCome come realize the sample of different stress paths orientation shearing test and principal stress axis rotation experiment.