CN111229478A - Centrifuge system for unsaturated frozen soil and matric potential testing method - Google Patents
Centrifuge system for unsaturated frozen soil and matric potential testing method Download PDFInfo
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Abstract
The invention discloses a centrifuge system of unsaturated frozen soil and a matric potential testing method, wherein four soil samples are centrifugally drained through revolution, multiple groups of data points can be obtained at one time, the volume of the soil samples is maintained through rotation without large deformation caused by compaction, and the matric potential calculation result is more accurate; the centrifugal water collecting devices are positioned at two ends of the centrifugal tube, can collect water discharged by centrifugation in real time, can be taken down from the centrifugal tube for weighing after centrifugation is finished at a certain rotation speed, does not need to disassemble the centrifugal tube each time, and can pour out drained water, thereby realizing continuous measurement; the temperature control device controls the centrifugal temperature of the soil sample by introducing circulating liquid around the centrifugal tube, and positive and negative temperature control can be realized by adjusting the temperature of the circulating liquid in the liquid storage tank. According to the method, the relation curve among the matrix potential, the temperature and the unfrozen water content of the unsaturated frozen soil is calculated and drawn according to the rotating speed, the water discharge and the centrifugal temperature of the centrifugal machine, and the soil-water characteristics and the freezing characteristics of the unsaturated frozen soil are visually represented.
Description
Technical Field
The invention belongs to the technical field of geotechnical engineering, and particularly relates to a centrifuge system for unsaturated frozen soil and a matric potential testing method.
Background
The permafrost and the seasonal permafrost are widely distributed on land, and are easy to frost heaving or thaw sinking under the action of temperature change, thereby causing great harm to high-speed railways and expressways in cold regions. The existing research shows that temperature change and water migration in soil are important factors for inducing freeze thawing, and matrix potential in soil is a key factor for controlling water migration.
In unsaturated soils, the relationship between matric potential and water content can be expressed in the Soil Water Characteristic Curve (SWCC). Research shows that the water holding capacity of the soil body is improved in the process of freezing the soil body, if the soil particles and the ice crystals are regarded as a mixed matrix, the phenomenon that the suction force of the mixed matrix is increased in the process of freezing is shown, and researchers start from measuring the content of unfrozen water in the frozen soil and establish corresponding models for researching the specific mechanism of the potential change of the mixed matrix. In the field of frozen soil, the freezing characteristic curve (SFCC) is regarded as an important medium capable of describing basic properties of soil body like SWCC, and reflects the relation between the content of unfrozen water in the frozen soil and the temperature. Therefore, how to combine the two matters together to comprehensively study the relationship among the matric potential, the unfrozen water content and the temperature of unsaturated frozen soil becomes a subject of general attention of scholars in the field of frozen soil at present. However, in the existing research, most of the data are needed by measuring SWCC and SFCC of unsaturated frozen soil respectively, so that two curves are obtained, and the method has a long measurement period and is difficult to reflect the property of the same soil sample at the same time; another scholars measure one curve through experiments, and predict the other curve based on the similarity of SWCC and SFCC, but the accuracy of the curve needs to be verified.
The principle of the centrifugal method is that a centrifugal field is used for simulating a gravity field, different centrifugal forces are obtained by adjusting the rotating speed, corresponding water content is recorded, and then the relation between the soil sample matrix potential and the water content is obtained. However, the current centrifuge method has the following disadvantages: (1) only the SWCC of the soil sample at the positive temperature can be measured, and the SFCC at the negative temperature needs to be measured by other methods; (2) the accuracy of the soil-water potential calculation result is influenced by the height change of the soil sample in the centrifugation process; (3) after the centrifugation is finished at a certain rotation speed, the centrifugal tube containing the soil sample needs to be taken out for weighing, the centrifuged water is poured out, and the water is put back after balance distribution, so that the process is more complicated, and the continuous measurement aspect needs to be improved.
Disclosure of Invention
In view of the defects of the prior art, the invention aims to provide a centrifuge system for unsaturated frozen soil and a matric potential testing method, by which the relation among the matric potential, temperature change and water migration of unsaturated frozen soil can be rapidly obtained.
The invention provides a centrifugal machine system for unsaturated frozen soil, which comprises a centrifugal device, a centrifugal water collecting device, a temperature control device and an intelligent control device, wherein the centrifugal device is connected with the centrifugal water collecting device;
the centrifugal device is used for separating unfrozen water in unsaturated frozen soil and comprises a rotating device, a fastening part and a centrifugal tube, wherein the rotating device comprises a revolution device and a low-speed rotation device, and the low-speed rotation device is arranged below the centrifugal tube; the revolution device comprises a central rotating shaft and a rotating arm, the tail end of the rotating arm is provided with a free rotor, and the lower end of the free rotor is provided with a rotating shaft connected with the free rotor; the low-speed rotation device comprises a rotation rotating shaft and a rotation turntable arranged on the rotation rotating shaft; the fastening part is arranged between the rotating shaft and the rotation rotating shaft and comprises an upper lantern ring, a lower lantern ring and a fastening bolt, the upper lantern ring is fixed at the tail end of the rotating shaft, the lower lantern ring is fixed at the tail end of the rotation rotating shaft, the fastening part is used for fixing a centrifugal tube, and the centrifugal tube revolves and rotates at a low speed under the action of the revolution device and the low-speed rotation device; the centrifugal tube comprises a tube body and a built-in spiral tube, wherein the tube body is of a cylindrical structure with raised threads at two ends, the tube body comprises an outer wall of the tube body and an inner wall of the tube body, a hollow cavity is formed between the outer wall of the tube body and the inner wall of the tube body, the built-in spiral tube is arranged in the hollow cavity, and an inlet end and an outlet end of the built-in spiral tube are positioned on the same side of the centrifugal tube;
the centrifugal water collecting devices are arranged at two ends of the centrifugal tube and comprise water collecting barrels and water permeable parts, the water collecting barrels are screwed in and fixed at two ends of the centrifugal tube through threads to be connected into a whole, and the centrifugal water collecting devices can be detached through screwing out;
the temperature control device comprises a liquid storage tank and a guide pipe, the liquid storage tank is fixedly arranged on the rotation turntable, the guide pipe extends upwards along the rotation rotating shaft and is connected with the inlet end and the outlet end of the built-in spiral pipe through metal sleeves, and circulating liquid is filled in the liquid storage tank;
the intelligent control device is used for controlling the rotating speed of the revolution device and the low-speed rotation device, controlling the temperature of the centrifugal tube and collecting and recording data.
In a specific embodiment, the water collecting cylinder comprises a cylinder body and a waterproof partition plate arranged in the cylinder body, the waterproof partition plate and the bottom of the cylinder body are combined to form a closed cavity, the waterproof partition plate is provided with a waterproof vent valve and a check valve, the waterproof partition plate is provided with an upper threaded hole and a lower threaded hole, the waterproof vent valve is arranged on the upper threaded hole, the check valve is arranged on the lower threaded hole, and the water outlet end of the check valve is arranged in the closed cavity; the side of barrel is equipped with the air vent, and the barrel opening part is equipped with the sunken screw thread identical with the protruding screw thread in centrifuging tube both ends, and the inboard of sunken screw thread is equipped with the annular position circle of taking the buckle.
In a specific embodiment, the permeable component is circular and comprises a permeable stone and filter paper, the permeable stone is fixed on the annular positioning ring of the cylinder body through a buckle, and the filter paper is arranged between the permeable stone and the soil sample to filter unfrozen water.
In a specific embodiment, the circulating liquid is a substance with low freezing temperature and no toxicity, and is preferably alcohol.
In one specific embodiment, the intelligent control device is controlled by a computer and is used for displaying the rotating speed and the temperature.
The invention also provides a method for measuring the relationship among the matric potential, the temperature change and the water holding rate of unsaturated frozen soil by using the centrifuge system, which comprises the following steps:
(1) preparing a soil sample: taking soil samples of the same soil to be measured by a cutting ring, wherein every four soil samples form a group, and the soil particle mass of each group of soil samples is MSSoaking the glass fiber in water, and exhausting air to saturate;
(2) weighing: weighing mass m of centrifugal water collecting device in full-empty statej0；
(3) Sample loading: putting the cutting ring and the soil sample into four centrifuge tubes, installing a water collecting cylinder, permeable stones and filter paper, respectively weighing the whole mass and fixing the whole mass by using a fastening part;
(4) setting parameters: setting the revolution speed n of the centrifugeg1And the rotation speeds n of the four rotation turntablesz1Respectively setting the temperature T of the circulating liquid in the four liquid storage tanks1、T2、T3、T4(wherein T is1Positive temperature and negative temperature in the rest), setting the measuring time;
(5) after the centrifugation at the first-stage rotating speed is finished, the mass M of the four soil sample drainage water at different temperatures is measuredj1,T1、Mj1,T2、Mj1,T3、Mj1,T4；
(6) The centrifugal water collecting device is arranged back to the two sides of the corresponding centrifugal tube, and the revolution speed n of the next-stage centrifugal machine is setgmAnd the rotation speeds n of the four rotation turntableszmRepeating the steps (4) to (5) at each level of rotation speed, and measuring the drainage M of each soil sample at the corresponding rotation speed and temperaturejm,T1、Mjm,T2、Mjm,T3、Mjm,T4；
(7) Setting the revolution speed n of the last stage centrifugeguAnd the rotation speeds n of the four rotation turntableszuTo obtain the corresponding water discharge Mju,T1、Mju,T2、Mju,T3、Mju,T4Calculating the rotational speed ng(u-1)Corresponding water holding capacity theta ofj(u-1),Tn＝(Mju,Tn-Mj(u-1),Tn)/MSSequentially calculating to obtain the rotating speed ng(u-2)Corresponding water holding capacity theta ofj(u-2),TnTo thetaj1,Tn；
(8) Adjusting the temperature: set the next set of temperatures T1′、T2′、T3′、T4', repeating steps (3) to (7);
(9) calculating the matrix potential psi of the frozen soil;
(10) and obtaining a relation curve among the matrix potential psi, the temperature T and the water holding capacity theta of the unsaturated frozen soil.
In a specific embodiment, in step (9), the matric potential ψ of frozen soil is obtained by:
because the soil sample rotates while revolving, the volume change of the soil sample is approximately 0 in the mode, and therefore, the height of the soil sample does not need to be corrected:
in formula (1):
n is revolution speed (unit: revolution/minute);
r1the distance (unit: centimeter) from the central rotating shaft to the outermost side of the centrifugal tube during centrifugation;
h is the distance (unit: cm) from the center of the soil sample to the outermost side of the centrifugal tube during centrifugation.
Compared with the prior art, the invention has the following advantages:
1) the invention adopts the temperature control device, can be used for measuring the SWCC of the soil sample like a traditional centrifuge when the centrifugal test is carried out at the positive temperature, and can measure the relation among the matrix potential, the temperature change and the water holding rate of the unsaturated frozen soil when the centrifugal test is carried out at the negative temperature.
2) The low-speed rotation device is added in the centrifuge, so that the volume change of the soil sample under the compaction action in the centrifugation process can be effectively prevented, and the matric potential value in the test is influenced.
3) The invention adopts the detachable water collecting device to collect the centrifugal water, obtains the water discharge amount at each rotating speed by weighing, ensures the measurement continuity, does not need to pour out and measure the discharged water every time, and shortens the test period.
4) The fastening part for the centrifugal cylinder is fixed between the low-speed rotation device and the revolution device, so that the centrifugal cylinder can be effectively prevented from displacing in the centrifugal process, and the centrifugal deviation caused by mass change in the soil sample freezing process can be balanced due to the rigidity of the rotation rotating shaft, and a balance tube device of the traditional centrifugal device is omitted.
Drawings
FIG. 1 is a schematic view of a centrifuge testing system of the present invention.
FIG. 2 is a cross-sectional view of a centrifuge tube and a centrifugal water collection device in accordance with one embodiment of the present invention in an attached configuration.
Fig. 3 is a top view of fig. 1.
FIG. 4 is a graph showing the relationship among matric potential ψ, temperature T and water holding capacity θ of unsaturated frozen earth.
Wherein, the sequence numbers in the figure:
1-a centrifugal device;
11-centrifuging the tube; 110-a tube body; 111-built-in spiral tube; 112-raised threads; 113-the outer wall of the tube body; 114-inner wall of tube body; 115-an inlet end; 116-an outlet end;
12-a central rotating shaft; 13-a rotating arm; 14-a free rotor; 15-a rotating shaft; 16-a rotation shaft; 17-a rotation turntable; 181-an upper collar; 182-a lower collar; 183-fastening bolts;
2-a centrifugal water collecting device; 21-a water collecting cylinder; 22-a barrel body; 23-a waterproof partition; 24-a closed cavity; 25-waterproof vent valve; 26-a check valve; 27-a vent hole; 28-recessed threads; 291-ring-shaped positioning ring; 292-porous stone; 293-filter paper;
3-a temperature control device; 31-a liquid storage tank; 32-a catheter; 33-a metal sleeve;
4-an intelligent control device;
5-soil sample;
6-cutting ring.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
As shown in fig. 1 to fig. 3, the centrifugal system for unsaturated frozen soil disclosed in this embodiment includes a centrifugal device 1, a centrifugal water collecting device 2, a temperature control device 3, and an intelligent control device 4;
the centrifugal device 1 is used for separating unfrozen water in unsaturated frozen soil and comprises a rotating device, a fastening part and centrifugal tubes 11, wherein the rotating device comprises a revolution device and a low-speed rotation device, and the low-speed rotation device is arranged below the four centrifugal tubes 11; the revolution device comprises a central rotating shaft 12 and a rotating arm 13, wherein the tail end of the rotating arm 13 is provided with a free rotor 14, and the lower end of the free rotor 14 is provided with a rotating shaft 15 connected with the free rotor; the low-speed rotation device comprises a rotation rotating shaft 16 and a rotation turntable 17 arranged on the rotation rotating shaft 16; the fastening part is arranged between the rotating shaft 15 and the rotating shaft 16 and comprises an upper lantern ring 181, a lower lantern ring 182 and a fastening bolt 183, the upper lantern ring 181 is fixed at the tail end of the rotating shaft 15, the lower lantern ring 182 is fixed at the tail end of the rotating shaft 16, the fastening part is used for fixing the centrifugal tube 11, and the centrifugal tube revolves and rotates at a low speed under the action of the revolution device and the low-speed rotation device; the centrifugal tube 11 comprises a tube body 110 and a built-in spiral tube 111, wherein the tube body 110 is of a cylindrical structure with raised threads 112 at two ends, the tube body 110 comprises a tube body outer wall 113 and a tube body inner wall 114, a hollow cavity is formed between the tube body outer wall 113 and the tube body inner wall 114, the built-in spiral tube 111 is arranged in the hollow cavity, and an inlet end 115 and an outlet end 116 of the built-in spiral tube 111 are positioned on the same side of the centrifugal tube;
the centrifugal water collecting devices 2 are arranged at two ends of the centrifugal tube 11 and comprise water collecting barrels 21 and water permeable components, the water collecting barrels 21 are screwed in and fixed at two ends of the centrifugal tube 11 through threads to be connected into a whole, and the centrifugal water collecting devices can be detached through screwing out; the water collecting cylinder 21 comprises a cylinder body 22 and a waterproof partition plate 23 arranged in the cylinder body, the waterproof partition plate 23 and the bottom of the cylinder body are combined to form a closed cavity 24, the waterproof partition plate 23 is provided with a waterproof vent valve 25 and a check valve 26, the waterproof partition plate 23 is provided with an upper threaded hole and a lower threaded hole, the waterproof vent valve 25 is installed on the upper threaded hole, the check valve 26 is installed on the lower threaded hole, and the water outlet end of the check valve 26 is arranged in the closed cavity 24; the side surface of the barrel body 22 is provided with a vent hole 27, the opening of the barrel body 22 is provided with a recessed thread 28 matched with the raised threads 112 at the two ends of the centrifugal tube, and the inner side of the recessed thread 28 is provided with an annular positioning ring 291 with a buckle; the water permeable component is circular and comprises a water permeable stone 292 and filter paper 293, the water permeable stone 292 is fixed on the annular positioning ring 291 of the cylinder body 22 through a buckle, and the filter paper 293 is arranged between the water permeable stone 292 and the soil sample 5 to realize the filtration of unfrozen water;
the temperature control device 3 comprises a liquid storage tank 31 and a guide pipe 32, the liquid storage tank 31 is fixedly arranged on the rotation turntable 17, the guide pipe 32 extends upwards along the rotation rotating shaft 16 and is connected with an inlet end 115 and an outlet end 116 of a built-in spiral pipe through a metal sleeve 33, and circulating liquid is filled in the liquid storage tank 31; the circulating liquid is a nontoxic substance with low freezing temperature, and preferably alcohol;
the intelligent control device 4 is used for controlling the rotating speed of the revolution device and the low-speed rotation device, controlling the temperature of the centrifugal tube and collecting and recording data; the intelligent control device is controlled by a computer and is used for displaying the rotating speed and the temperature.
The embodiment of the invention relates to a method for measuring the relation among the matric potential, the temperature change and the water holdup of unsaturated frozen soil by using a centrifuge system, which comprises the following steps:
(1) preparing a soil sample: taking soil samples of the same soil to be measured by using a cutting ring 6, wherein every four soil samples form a group, and the soil particles of each group of soil samples have the mass of MSSoaking the glass fiber in water, and exhausting air to saturate;
(2) weighing: weighing the mass m of the centrifugal water collecting device 2 in the full empty statej0；
(3) Sample loading: putting the cutting rings 6 and the soil sample 5 into four centrifuge tubes 11, installing a water collecting cylinder 21, a permeable stone 292 and filter paper 293, respectively weighing the whole mass and fixing the whole mass by using a fastening part;
(4) setting parameters: setting the revolution speed n of the centrifugeg1And the rotation speeds n of the four rotation turntablesz1Respectively setting the temperature T of the circulating liquid in the four liquid storage tanks1、T2、T3、T4(wherein T is1Positive temperature and negative temperature in the rest), setting the measuring time;
(5) after the centrifugation is finished at the first-stage rotating speed, taking down the centrifugal water collecting device 2 from two sides of a centrifugal tube, and weighing the mass m of the centrifugal water collecting device 2 at the momentj1Determining the mass M of the discharged waterj1,T1＝mj1-mj0Similarly, the mass M of the discharged water of the remaining three soil samples at different temperatures was measuredj1,T2、Mj1,T3、Mj1,T4；
(6) The centrifugal water collecting device is arranged back to the two sides of the corresponding centrifugal tube, and the revolution speed n of the next-stage centrifugal machine is setgmAnd the rotation speeds n of the four rotation turntableszmRepeating the steps (4) to (5) at each level of rotation speed, and measuring the drainage M of each soil sample at the corresponding rotation speed and temperaturejm,T1、Mjm,T2、Mjm,T3、Mjm,T4；
(7) Setting the revolution speed n of the last stage centrifugeguAnd the rotation speeds n of the four rotation turntableszuTo obtain the corresponding water discharge Mju,T1、Mju,T2、Mju,T3、Mju,T4Calculating the rotational speed ng(u-1)Corresponding water holding capacity theta ofj(u-1),Tn＝(Mju,Tn-Mj(u-1),Tn)/MSSequentially calculating to obtain the rotating speed ng(u-2)Corresponding water holding capacity theta ofj(u-2),TnTo thetaj1,Tn；
(8) Adjusting the temperature: set the next set of temperatures T1′、T2′、T3′、T4', repeating steps (3) to (7);
(9) calculating the matrix potential psi of the frozen soil;
because the soil sample rotates while revolving, the volume change of the soil sample is approximately 0 in the mode, and therefore, the height of the soil sample does not need to be corrected:
in the formula:
n is revolution speed (unit: revolution/minute);
r1the distance (unit: centimeter) from the central rotating shaft to the outermost side of the centrifugal tube during centrifugation;
h is the distance (unit: cm) from the center of the soil sample to the outermost side of the centrifugal tube during centrifugation;
(10) and obtaining a relation curve among the matrix potential psi, the temperature T and the water holding capacity theta of the unsaturated frozen soil.
Based on the existing research, in the freezing process, the improvement of the matrix potential of unsaturated frozen soil is influenced by the icing effect of the soil, and the liquid water pressure in the phase change is influenced by the pressure P of an adsorption water filmdAnd the ice phase point capillary force PSTwo parts are formed. Capillary force P during centrifugationSAnd (3) overcoming the defect that capillary water is discharged, wherein the water remained in the soil sample is adsorption water, and the measured water retention rate theta is the content of the adsorption water in the unsaturated frozen soil.
According to the invention, four soil samples are subjected to centrifugal drainage through revolution, multiple groups of data points can be obtained at one time, and the volume of the soil samples is maintained through rotation without large deformation caused by compaction, so that the matric potential calculation result is more accurate; the centrifugal water collecting devices are positioned at two ends of the centrifugal tube, can collect water discharged by centrifugation in real time, can be taken down from the centrifugal tube for weighing after centrifugation is finished at a certain rotation speed, does not need to disassemble the centrifugal tube each time, and can pour out drained water, thereby realizing continuous measurement; the temperature control device controls the centrifugal temperature of the soil sample by introducing circulating liquid around the centrifugal tube, and positive and negative temperature control can be realized by adjusting the temperature of the circulating liquid in the liquid storage tank. According to the method, the relation curve among the matrix potential, the temperature and the unfrozen water content of the unsaturated frozen soil is calculated and drawn according to the rotating speed, the water discharge and the centrifugal temperature of the centrifugal machine, and the soil-water characteristics and the freezing characteristics of the unsaturated frozen soil are visually represented.
Claims (7)
1. A centrifugal machine system for unsaturated frozen soil is characterized by comprising a centrifugal device, a centrifugal water collecting device, a temperature control device and an intelligent control device;
the centrifugal device is used for separating unfrozen water in unsaturated frozen soil and comprises a rotating device, a fastening part and a centrifugal tube, wherein the rotating device comprises a revolution device and a low-speed rotation device, and the low-speed rotation device is arranged below the centrifugal tube; the revolution device comprises a central rotating shaft and a rotating arm, the tail end of the rotating arm is provided with a free rotor, and the lower end of the free rotor is provided with a rotating shaft connected with the free rotor; the low-speed rotation device comprises a rotation rotating shaft and a rotation turntable arranged on the rotation rotating shaft; the fastening part is arranged between the rotating shaft and the rotation rotating shaft and comprises an upper lantern ring, a lower lantern ring and a fastening bolt, the upper lantern ring is fixed at the tail end of the rotating shaft, the lower lantern ring is fixed at the tail end of the rotation rotating shaft, the fastening part is used for fixing a centrifugal tube, and the centrifugal tube revolves and rotates at a low speed under the action of the revolution device and the low-speed rotation device; the centrifugal tube comprises a tube body and a built-in spiral tube, wherein the tube body is of a cylindrical structure with raised threads at two ends, the tube body comprises an outer wall of the tube body and an inner wall of the tube body, a hollow cavity is formed between the outer wall of the tube body and the inner wall of the tube body, the built-in spiral tube is arranged in the hollow cavity, and an inlet end and an outlet end of the built-in spiral tube are positioned on the same side of the centrifugal tube;
the centrifugal water collecting devices are arranged at two ends of the centrifugal tube and comprise water collecting barrels and water permeable parts, the water collecting barrels are screwed in and fixed at two ends of the centrifugal tube through threads to be connected into a whole, and the centrifugal water collecting devices can be detached through screwing out;
the temperature control device comprises a liquid storage tank and a guide pipe, the liquid storage tank is fixedly arranged on the rotation turntable, the guide pipe extends upwards along the rotation rotating shaft and is connected with the inlet end and the outlet end of the built-in spiral pipe through metal sleeves, and circulating liquid is filled in the liquid storage tank;
the intelligent control device is used for controlling the rotating speed of the revolution device and the low-speed rotation device, controlling the temperature of the centrifugal tube and collecting and recording data.
2. The centrifuge system for unsaturated frozen soil according to claim 1, wherein the water collecting barrel comprises a barrel body and a waterproof partition plate arranged in the barrel body, the waterproof partition plate and the bottom of the barrel body are combined to form a closed cavity, the waterproof partition plate is provided with a waterproof vent valve and a check valve, the waterproof partition plate is provided with an upper threaded hole and a lower threaded hole, the waterproof vent valve is arranged on the upper threaded hole, the check valve is arranged on the lower threaded hole, and the water outlet end of the check valve is arranged in the closed cavity; the side of barrel is equipped with the air vent, and the barrel opening part is equipped with the sunken screw thread identical with the protruding screw thread in centrifuging tube both ends, and the inboard of sunken screw thread is equipped with the annular position circle of taking the buckle.
3. The centrifuge system for unsaturated frozen soil according to claim 2, wherein the water permeable member is circular and comprises a water permeable stone and a filter paper, the water permeable stone is fixed on the annular positioning ring of the barrel body by a buckle, and the filter paper is arranged between the water permeable stone and the soil sample to filter the unfrozen water.
4. The centrifuge system for unsaturated frozen soils according to claim 1 wherein the circulating fluid is a relatively low freezing temperature, non-toxic substance, preferably alcohol.
5. The centrifuge system for non-saturated frozen earth of claim 1, wherein said intelligent control means is computer controlled for display of rotation speed and temperature.
6. The centrifuge system according to any one of claims 1 to 5, wherein the centrifuge system measures a relationship between matric potential, temperature change and water holding capacity of unsaturated frozen soil, and comprises the steps of:
(1) preparing a soil sample: taking soil samples of the same soil to be measured by a cutting ring, wherein every four soil samples form a group, and the soil particle mass of each group of soil samples is MSSoaking the glass fiber in water, and exhausting air to saturate;
(2) weighing: weighing mass m of centrifugal water collecting device in full-empty statej0；
(3) Sample loading: putting the cutting ring and the soil sample into four centrifuge tubes, installing a water collecting cylinder, permeable stones and filter paper, respectively weighing the whole mass and fixing the whole mass by using a fastening part;
(4) setting parameters: setting the revolution speed n of the centrifugeg1And the rotation speeds n of the four rotation turntablesz1Respectively setting the temperature T of the circulating liquid in the four liquid storage tanks1、T2、T3、T4(wherein T is1Positive temperature and negative temperature in the rest), setting the measuring time;
(5) after the centrifugation at the first-stage rotating speed is finished, the mass M of the four soil sample drainage water at different temperatures is measuredj1,T1、Mj1,T2、Mj1,T3、Mj1,T4；
(6) The centrifugal water collecting device is arranged back to the two sides of the corresponding centrifugal tube, and the revolution speed n of the next-stage centrifugal machine is setgmAnd the rotation speeds n of the four rotation turntableszmRepeating the steps (4) to (5) at each level of rotation speed, and measuring the drainage M of each soil sample at the corresponding rotation speed and temperaturejm,T1、Mjm,T2、Mjm,T3、Mjm,T4；
(7) Setting the revolution speed n of the last stage centrifugeguAnd the rotation speeds n of the four rotation turntableszuTo obtain the corresponding water discharge Mju,T1、Mju,T2、Mju,T3、Mju,T4Calculating the rotational speed ng(u-1)Corresponding water holding capacity theta ofj(u-1),Tn＝(Mju,Tn-Mj(u-1),Tn)/MSSequentially calculating to obtain the rotating speed ng(u-2)Corresponding water holding capacity theta ofj(u-2),TnTo thetaj1,Tn；
(8) Adjusting the temperature: set the next set of temperatures T1′、T2′、T3′、T4', repeating steps (3) to (7);
(9) calculating the matrix potential psi of the frozen soil;
(10) and obtaining a relation curve among the matrix potential psi, the temperature T and the water holding capacity theta of the unsaturated frozen soil.
7. The centrifuge system according to claim 6, wherein the relation among matric potential, temperature change and water holding capacity of the unsaturated frozen soil is obtained by the following method in step (9):
because the soil sample rotates while revolving, the volume change of the soil sample is approximately 0 in the mode, and therefore, the height of the soil sample does not need to be corrected:
in formula (1):
n is revolution speed (unit: revolution/minute);
r1the distance (unit: centimeter) from the central rotating shaft to the outermost side of the centrifugal tube during centrifugation;
h is the distance (unit: cm) from the center of the soil sample to the outermost side of the centrifugal tube during centrifugation.
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