CN109765259B - Method and device for determining upper limit change rule of frozen soil based on soil water and salt change - Google Patents
Method and device for determining upper limit change rule of frozen soil based on soil water and salt change Download PDFInfo
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- CN109765259B CN109765259B CN201910046499.2A CN201910046499A CN109765259B CN 109765259 B CN109765259 B CN 109765259B CN 201910046499 A CN201910046499 A CN 201910046499A CN 109765259 B CN109765259 B CN 109765259B
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Abstract
The invention discloses a method and a device for determining an upper limit change rule of frozen soil based on soil water salt change, and the method and the device comprise an outer box body, an inner box body, a data acquisition module and a system control and data acquisition computer, wherein the inner box body is positioned in the outer box body, the upper ends of the outer box body and the inner box body are respectively provided with an outer box cover and an inner box cover, and a heating module and a refrigerating module are arranged between the outer wall of the left side of the inner box body and the inner wall of the outer box body. The monitoring sensor buried in the soil sample can monitor the conditions of water migration and salt accumulation of the soil sample during freezing and thawing of the frozen soil in seasons, the initial conditions and the boundary conditions of differential equations of water conduction and salt conduction of the soil can be determined according to the measurement of the sensor, an analytic solution is solved according to a separation variable method, finally, an upper limit position change rule is obtained by substituting the analytic solution formula in combination with a water and salt judgment standard, and the monitoring of a test process and test data is more accurately controlled by a computer system.
Description
Technical Field
The invention relates to the technical field of geotechnical test and measurement, in particular to a method and a device for determining an upper limit change rule of frozen soil based on soil water salt change.
Background
According to statistics, frozen soil exists in 70% of the global land area, wherein 14% of the frozen soil is permafrost soil, and 56% of the frozen soil is seasonal frozen soil; china is the third frozen soil big country in the world, wherein the distribution area of the frozen soil for many years is 2.068 multiplied by 106km2The soil occupies 21.5 percent of the national soil area of China, and the distribution area of the seasonal frozen soil is wide and is 5.137 multiplied by 106km2The frozen soil occupies 53.5 percent of the national soil area in China, the total area of the frozen soil and the soil occupies about 3/4 percent of the total area of the country, the upper limit change of a frozen soil roadbed is mainly caused by repeated freezing and thawing of the soil due to temperature change, and the freezing and thawing of the soil is a very complex process accompanied with physical, chemical and mechanical phenomena and sub-processes, and mainly comprises upper limit position change, water migration, salt accumulation and the like.
Therefore, it can be understood that the main part affecting the road stability in the permafrost region is the seasonal melting layer near the upper limit and above the upper limit. The seasonal thawing layer is active, the thawing change along with the change of climate and geological conditions directly endangers the stability of the roadbed and the safety of the road building, and the position and the change of the upper limit are comprehensively acted by various natural conditions and directly reflect the characteristics of the seasonal thawing layer, so that the determination of the position and the change of the upper limit of the permafrost soil is an important content of engineering investigation of frozen soil areas.
Disclosure of Invention
Technical problem to be solved
Aiming at the defects of the prior art, the invention provides a method and a device for determining the upper limit change rule of frozen soil based on the change of soil water and salt, and solves the problem that the determination of the position of the upper limit of permafrost and the change rule thereof are difficult to survey engineering in frozen soil regions.
(II) technical scheme
In order to achieve the purpose, the invention is realized by the following technical scheme: a method for determining the upper limit change rule of frozen soil based on the change of water and salt in soil includes such steps as sampling frozen soil, freeze thawing in test box, determining the upper boundary condition by the functions of the water content in soil and salt in the inserted sensor fixing ring on the top surface of frozen soil sample, averaging the data, calculating the lower boundary condition by the functions of the water content in soil and salt in soil, and determining the initial condition by the functions of the water content in soil and salt in frozen soil sample, the water content in soil and salt in soil Determining a function obtained by data of the water content theta of the soil and the salt content w of the soil measured by the sensor;
after determining the initial condition and boundary condition of the formula, solving and resolving an analytic solution according to a separation variable method to obtain a formula II, and finally, calculating and judging the upper limit change process of the frozen soil according to the formula II by combining soil moisture and salinity judgment indexes as follows:
(1) water transfer equation by soil freezing and thawing
In the formula: theta is the volume water content (cm) of the soil3·cm-3) D is the diffusion coefficient (cm) of water in soil3·s-1) T is time(s), z is the dimension component (cm) of the soil body in the z-axis direction, l is the seasonal frozen soil sample height (cm), l1The permafrost sample height (cm);
when the initial condition is that t is equal to 0, θ (z,0) is equal to θ1(z)；
When the boundary condition is that z is equal to 0, θ (0, t) is equal to θ2(t)；
z＝l+l1When, theta (l + l)1,t)＝θ3(t)；
The analytical solution obtained by the separation variable method is:
wherein
t0To test the end time of the experiment, n＝1,2,3···；θiDetermining a moisture content function for the test data of the inserted soil moisture and salinity sensors;
according to a formula II, the water content theta of any depth z at any time t can be obtained, the difference value of the upper water content and the lower water content of the interface of the permafrost and the seasonal frozen soil is taken as a judgment basis, the time t and the time t can be regulated according to the specification of a specific test requirement by a computer, the time t and the time t are substituted into the formula II to carry out assignment trial calculation until the water content difference value delta theta of two adjacent z parts is suddenly changed and the delta theta is obviously and rapidly increased, namely the water content theta is determined to be the upper limit position z of the1，z1Averaging two similar z values, if more than one z occurs1Taking the maximum value as a standard;
the continuous adjustment time t can be set at the test time t1Simulating to obtain the on-site time t1' inner permafrost upper limit position change rule;
(2) conduction equation of freeze-thaw salt from soil
In the formula: w is the salt content (g cm) of the soil-3) Dsh is the hydrodynamic dispersion coefficient (cm) of the salt under the concentration gradient2·s-1)；
When the initial condition is that t is 0, w (z,0) is w1(z)；
When the boundary condition is that z is equal to 0, w (0, t) is equal to w2(t)；
z＝l+l1When, w (l + l)1,t)＝w3(t)；
The analytical solution obtained by the separation variable method is:
wherein
t0To test the end of the experiment, n ═ 1,2,3 ·; w is aiDetermining a salinity function for the test data of the inserted soil moisture and salinity sensor;
according to a formula, the salt content w of any depth z at any time t can be obtained, the time t is substituted into the formula by a computer to carry out assignment trial calculation by taking the larger difference between the salt content of the permafrost and the salt content of the seasonal frozen soil at the upper part and the lower part of the interface as a judgment basis until the salt content difference delta w of two adjacent Z parts is mutated and the delta w is obviously increased, namely the salt content w is determined as the upper limit position z of the permafrost2，z2Averaging two similar z values, if a plurality of z occur2Taking the maximum value as a standard;
the continuous adjustment time t can be simulated at the test time t1 to obtain the on-site time t1' inner permafrost upper limit position change rule;
(3) in summary, the annual frozen soil upper limit position obtained by different formula analysis solutions is
According to a similar theory, the ratio of the freeze-thaw variation of the sample model observed in the test to the freeze-thaw variation of the upper limit of the on-site prototype frozen soil is also 1: a, so that the upper limit of the on-site prototype frozen soil is az, and the change rule of the upper limit position of the on-site frozen soil can be obtained according to the formula.
A device for determining the upper limit change rule of frozen soil based on the change of soil water and salt comprises an outer box body, an inner box body, a data acquisition module and a system control and data acquisition computer, wherein the inner box body is positioned in the outer box body, the upper ends of the outer box body and the inner box body are respectively provided with an outer box cover and an inner box cover, a heating module and a refrigerating module are arranged between the left outer wall of the inner box body and the inner wall of the outer box body and are respectively communicated with the inner box body, a water replenishing device is arranged between the right outer wall of the inner box body and the inner wall of the outer box body, a sunlight simulation lamp is arranged above the left inner wall of the inner box body, the bottom of the inner wall of the inner box body is fixedly connected with a metal sample table base, a rotating motor is arranged in the metal sample table base, a metal rotating shaft is arranged on an output shaft of the rotating motor, the device comprises a cylindrical magnet rotating platform, a plurality of sample grooves are arranged at the top of the cylindrical magnet rotating platform, an infrared distance measuring sensor is installed at the top end of each sample groove, a compaction device is installed below an inner box cover, each sample groove comprises a sample groove outer wall, a sample groove inner wall and a sample groove base, a lifting cylinder is installed at the bottom of the sample groove base, a lifting cylinder air guide pipe hole and a lifting cylinder switch are arranged on the outer side of the lifting cylinder, a movable sliding plate is fixedly connected to the top of the lifting cylinder, a heat preservation layer is fixedly connected to the inner wall of the sample groove, two sides of the movable sliding plate are in contact with the inner wall of the heat preservation layer of the sample groove, a permafrost sample is placed on the movable sliding plate, semiconductor refrigeration sheets are placed at the bottom and the peripheral positions of the permafrost sample, the permafrost sample is with the inside solid fixed ring of bayonet sensor that is provided with of frozen soil sample in season, the solid fixed ring of bayonet sensor is provided with a plurality ofly, and by lower supreme even setting, the solid fixed ring of bayonet sensor is including solid fixed ring inner wall and solid fixed ring outer wall, solid fixed ring inner wall surface is provided with sensor fixed slot, sensor fixed slot evenly sets up, sensor fixed slot internally mounted has bayonet soil moisture and salinity sensor, bayonet soil moisture and salinity sensor inboard are provided with soil moisture and salinity sensor response probe, soil moisture and salinity sensor response probe are located the solid fixed ring inboard of bayonet sensor, and soil moisture and salinity sensor response probe set up to different length.
Preferably, the t can be regulated according to the specification of specific test requirements, and the t1Much less than t1'。
Preferably, the compaction device is including driving actuating cylinder, it passes through pressure device fixing bolt and interior case lid fixed connection to drive actuating cylinder top, drive actuating cylinder's telescopic link bottom and install the support frame, the support frame middle part is connected with the telescopic link bottom through support frame connecting bolt, support frame bottom fixedly connected with pressure head, the quantity and the position of pressure head all with the quantity and the position one-to-one in sample groove.
Preferably, the inner box cover of the outer box cover is respectively provided with a pull ring, the outer box body, the inner box body, the outer box cover and the inner box cover are all made of heat-insulating metal materials, the inner wall of the outer box body is coated with a heat-insulating material layer, the control end of the daylight analog lamp is connected with a system control and data acquisition computer, and a heat-insulating layer is arranged between the inner wall of the sample groove and the heat-insulating layer.
Preferably, bayonet soil moisture all is connected with data acquisition module through experimental data transmission wire with salinity sensor and infrared distance measuring sensor, data acquisition module output is connected with system control and data acquisition computer input, heating module and refrigeration module all are connected with system control and data acquisition computer through experimental data transmission wire.
Preferably, the moisturizing device includes mah-jong bottle, distilled water transmission pipe, moisturizing device shower nozzle, distilled water transmission pipe connects, can dismantle distilled water transmission pipe and tube-shape revolving stage ponding and retrieve the bottle, mah-jong bottle is located the position between the inner wall of the right side outer wall of box and outer box in the box, mah-jong bottle passes through distilled water transmission pipe, distilled water transmission pipe and connects and can dismantle distilled water transmission pipe and be connected with moisturizing device shower nozzle, the top of the inside tube-shape magnet revolving stage of box in the moisturizing device shower nozzle is located, the control end and the electric connection of system control and data acquisition computer of moisturizing device shower nozzle.
(III) advantageous effects
The invention provides a method and a device for determining an upper limit change rule of frozen soil based on soil water and salt change. The method has the following beneficial effects:
(1) during test simulation, the method can monitor the water change and salt migration change conditions of the frozen soil in the season in the freeze thawing process, can determine the initial conditions and boundary conditions of soil water conduction and salt conduction differential equations according to the measurement of the sensors, solves the analytic solutions according to the separation variable method, calculates the upper limit change rule of the frozen soil according to the judgment standard taking the soil water content and the soil salt content as indexes, and is controlled by a computer system in the test process and test data monitoring, so that the test result is more accurate.
(2) According to the method and the device for determining the upper limit change rule of the frozen soil based on the water and salt change of the soil, on-site sampling is not only suitable for undisturbed soil, but also can be used for automatically preparing a sample indoors according to the soil quality type to be researched in order to research the influence of multiple factors on the upper limit of the frozen soil.
(3) According to the method and the device for determining the upper limit change rule of the frozen soil based on the soil water salt change, the test box can accurately simulate the actual temperature, precipitation and illumination change conditions of the frozen soil field, the change process is controlled by a computer system, and the change of the natural environment can be simulated to the maximum extent. The cylindrical magnet rotating platform drives the sample groove to rotate, so that the simulated environmental changes such as temperature, rainfall, sunshine and the like are more uniform.
(4) According to the method and the device for determining the upper limit change rule of the frozen soil based on the soil water salt change, the sample tank can reach the height required by the test by adjusting the height of the bottom plate, so that the phenomenon that the distance between a soil body sample and the upper surface of the sample tank is too large due to too high sample tank, the soil body temperature and precipitation illumination simulation error occurs, and the phenomenon that a plurality of sample tanks with different specifications need to be prepared due to the sample size requirement can be avoided.
(5) According to the method for testing the upper limit change rule of the frozen soil, the large frozen soil test prototype is modeled and simplified by using the similarity criterion, and the model test result can be used for a reverse-thrust prototype. According to the established proportional relation, the size of the model and the test time are adjusted, the test process is greatly accelerated, the long-time environmental change of a field can be simulated in a short time, and the monitoring time is greatly shortened.
Drawings
FIG. 1 is a schematic structural view of the present invention as a whole;
FIG. 2 is a schematic view of the structure of a sample cell according to the present invention;
FIG. 3 is a schematic view of a plug-in sensor retainer ring of the present invention;
FIG. 4 is a schematic view of the arrangement of the cylindrical magnet turntable and the sample tank according to the present invention;
FIG. 5 is a schematic view of a detachable pressurizing device according to the present invention;
FIG. 6 is a schematic view showing the structure of the size of a sample cell according to the present invention.
In the figure: 1 outer box body, 2 inner box body, 3 outer box cover, 4 inner box cover, 5 metal sample table base, 6 metal rotating shaft, 7 cylindrical magnet rotating table, 8 sample groove outer wall, 9 sample groove inner wall, 10 sample groove base, 11 heat preservation layer, 12 heat insulation layer, 13 lifting cylinder, 14 lifting cylinder air guide pipe hole, 15 lifting cylinder switch, 16 movable sliding plate, 17 years frozen soil sample, 18 seasons frozen soil sample, 19 semiconductor refrigeration sheet, 20 insertion type soil moisture and salinity sensor, 21 insertion type sensor fixing ring, 22 fixing ring inner wall, 23 sensor fixing clamping groove, 24 soil moisture and salinity sensor induction probe, 25 infrared distance measurement sensor, 26 refrigeration module, 27 heating module, 28 water replenishing device nozzle, 29 distilled water transmission conduit, 30 mahalanobis bottle, 31 simulation daylight lamp, 32 test data transmission wire, 33 data acquisition module, 34 system control and data acquisition computer, 35 a fixing bolt of a pressurizing device, 36 a driving cylinder, 37 an expansion rod, 38 a support frame connecting bolt, 39 a support frame, 40 a pressure head, 41 a distilled water transmission conduit joint, 42 a detachable distilled water transmission conduit and 43 a cylindrical rotating table accumulated water recovery bottle.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious 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.
Referring to fig. 1-6, the present invention provides a technical solution: a device for determining the upper limit change rule of frozen soil based on the change of soil water and salt comprises an outer box body 1, an inner box body 2, a data acquisition module 33 and a system control and data acquisition computer 34, wherein the inner box body 2 is positioned inside the outer box body 1, the upper ends of the outer box body 1 and the inner box body 2 are respectively provided with an outer box cover 3 and an inner box cover 4, a heating module 27 and a refrigerating module 26 are arranged between the left outer wall of the inner box body 2 and the inner wall of the outer box body 1, the heating module 27 and the refrigerating module 26 are respectively communicated with the inner box body 2, a water replenishing device is arranged between the right outer wall of the inner box body 2 and the inner wall of the outer box body 1, a sunlight simulation lamp 31 is arranged above the left inner wall of the inner box body 2, the bottom of the inner wall of the inner box body 2 is fixedly connected with a metal sample table base 5, a rotating, the top of the metal rotating shaft 6 is fixedly connected with a cylindrical magnet rotating platform 7, the top of the cylindrical magnet rotating platform 7 is provided with a sample groove, the top end of the sample groove is provided with an infrared distance measuring sensor 25, a compacting device is arranged below the inner box cover 4, the sample groove is provided with a plurality of sample grooves, each sample groove comprises a sample groove outer wall 8, a sample groove inner wall 9 and a sample groove base 10, the bottom of the sample groove base 10 is provided with a lifting cylinder 13, the outer side of the lifting cylinder 13 is provided with a lifting cylinder air guide pipe hole 14 and a lifting cylinder switch 15, the top of the lifting cylinder 13 is fixedly connected with a movable sliding plate 16, the sample groove inner wall 9 is fixedly connected with a heat preservation layer 11, two sides of the movable sliding plate 16 are in contact with the inner wall of the heat preservation layer 11 of the sample groove, the movable sliding plate 16 is provided with a permafrost sample 17, semiconductor, permafrost sample 17 is provided with the solid fixed ring 21 of bayonet sensor with the inside solid fixed ring 21 of frozen soil sample 18 in season, the solid fixed ring 21 of bayonet sensor is provided with a plurality ofly, and by lower supreme even setting, the solid fixed ring 21 of bayonet sensor is including solid fixed ring inner wall 22 and solid fixed ring outer wall, solid fixed ring inner wall 22 surface is provided with sensor fixed slot 23, sensor fixed slot 23 evenly sets up, 23 internally mounted of sensor fixed slot has bayonet soil moisture and salinity sensor 20, bayonet soil moisture is provided with soil moisture and salinity sensor inductive probe 24 with salinity sensor 20 inboard, soil moisture and salinity sensor inductive probe 24 are located the solid fixed ring 21 inboards of bayonet sensor, and soil moisture and salinity sensor inductive probe 24 set up to different length.
The compaction device comprises a driving cylinder 36, the top of the driving cylinder 36 is fixedly connected with an inner box cover 4 through a pressurizing device fixing bolt 35, a supporting frame 39 is installed at the bottom of a telescopic rod 37 of the driving cylinder 36, the middle of the supporting frame 39 is connected with the bottom of the telescopic rod 37 through a supporting frame connecting bolt 38, a pressure head 40 is fixedly connected to the bottom of the supporting frame 39, and the number and the position of the pressure head 40 correspond to the number and the position of the sample groove one to one.
The inner box cover 4 of the outer box cover 3 is respectively provided with a pull ring, the outer box body 1, the inner box body 2, the outer box cover 3 and the inner box cover 4 are all made of heat insulation metal materials, the inner walls of the outer box body, the inner box body, the outer box cover 3 and the inner box cover 4 are all coated with heat insulation material layers, the control end of the daylight analog lamp 31 is connected with a system control and data acquisition computer 34, and a heat insulation layer 12 is arranged between the inner wall 9 of the sample groove and.
Plug-in soil moisture and salinity sensor 20 and infrared distance measuring sensor 25 all are connected with data acquisition module 33 through experimental data transmission wire 32, and data acquisition module 33 output is connected with system control and data acquisition computer 34 input, and heating module 27 and refrigeration module 26 all are connected with system control and data acquisition computer 34 through experimental data transmission wire 32.
The water supplementing device comprises a mahalanobis bottle 30, a distilled water transmission conduit 29, a water supplementing device spray head 28, a distilled water transmission conduit joint 41, a detachable distilled water transmission conduit 42 and a cylindrical rotating table accumulated water recovery bottle 43, the mahalanobis bottle 30 is positioned between the outer wall of the right side of the inner box body 2 and the inner wall of the outer box body 1, the mahalanobis bottle 30 is connected with the water supplementing device spray head 28 through the distilled water transmission conduit 29, the distilled water transmission conduit joint 41 and the detachable distilled water transmission conduit 42, the water supplementing device spray head 28 is positioned at the top of the cylindrical magnet rotating table 7 in the inner box body 2, and the control end of the water supplementing device spray head 28 is electrically connected with the system control and data acquisition computer 34.
When the portable permafrost testing device is used, a permafrost sample 17 is placed above the movable sliding plate 16, a seasonal frozen soil sample 18 is placed above the permafrost sample 17, semiconductor refrigerating sheets 19 are placed at the bottom and around the inside of the permafrost sample 17 and used for preparing the permafrost sample and maintaining the low-temperature condition of the soil sample, a plurality of plug-in type sensor fixing rings 21 are arranged in the permafrost sample 18 and the permafrost sample 17 from bottom to top, each plug-in type sensor fixing ring 21 is provided with a plurality of sensor fixing clamping grooves 23, the plug-in type soil moisture and salinity sensors 20 are fixed in the sensor fixing clamping grooves 23, signals measured by the soil moisture and salinity sensor induction probes 24 are transmitted to an external data acquisition module 33 and a system control and data acquisition computer 34 through a test data transmission lead 32, the heating and cooling rates of the refrigeration module 26 and the heating module 27 are controlled by computer PID control software, the PID temperature control software is installed in the system control and data acquisition computer 34, can synchronously display the current temperature and automatically draw a temperature curve, can automatically set temperature changes such as sine, cosine, linearity and the like, is suitable for a temperature control system ranging from-40 ℃ to +80 ℃, digitally displays the set temperature and the actual temperature, and mainly controls the refrigeration module 26 and the heating module 27 to work;
a humidity control system is arranged in a system control and data acquisition computer 34, a distilled water spraying mode is adopted by a water supplementing device, the water supplementing device can be installed and disassembled according to test requirements, a Ma bottle 30 for storing distilled water and a water supplementing device spray head 28 are connected through a distilled water transmission conduit 29, a distilled water transmission conduit joint 41 and a detachable distilled water transmission conduit 42, the distilled water spraying rate and time are controlled by computer control software, the water supplementing device has the function that a soil sample and the distilled water in the Ma bottle 30 are in hydraulic connection in a test environment so as to simulate the environment water supplementing condition of a soil body in a freezing and thawing process, a sunlight simulation lamp 31 arranged in the inner box body 2 mainly simulates the sun illumination condition of the soil body in the freezing and thawing process, the test environment is enabled to be closer to the natural environment, and the illumination intensity and time are controlled by the computer control software;
the plug-in soil moisture and salt sensors 20 are fixed in the sensor fixing clamping grooves 23 to form a measuring network buried in a soil sample, the plug-in sensor fixing rings 21 are uniformly distributed in the seasonal frozen soil sample 18 and the perennial frozen soil sample 17 from bottom to top, the plug-in soil moisture and salt sensors 20 can measure and determine initial conditions of a moisture conduction equation and a salt conduction equation, the plug-in soil moisture and salt sensors 20 on the uppermost surface of the seasonal frozen soil can measure and determine upper boundary conditions of the moisture conduction equation and the salt conduction equation, and the plug-in soil moisture and salt sensors 20 on the lowermost surface of the perennial frozen soil can measure and determine lower boundary conditions of the moisture conduction equation and the salt conduction equation;
the pressurizing device can be arranged on the inner box cover 4 through a pressurizing device fixing bolt 35 and can be arranged and disassembled along with the opening of the inner box cover 4, and the sample is disassembled after being manufactured; the pressure head 40 can be vertically pressed into the sample groove, the compaction speed and the process of the pressure head 40 can be controlled by a control system arranged in the system control and data acquisition computer 34, the system control and data acquisition computer 34 can control the experiment process, and the system control and data acquisition computer 34 comprises a test control interface, a soil moisture data acquisition interface and a soil salinity data acquisition interface;
the simulation structure and method need to be adopted in the test, and the following theory is needed for the acceleration of the simulation test time:
because the on-site frozen soil test consumes longer time, the method provided by the invention aims to reduce time cost and achieve the effect of simulating long-time environmental change in a shorter time, and based on a similarity principle, a proportional relation between the size of a frozen soil model and the test time is established to achieve the purpose of accelerating the test time. The method relies on a three-dimensional water transmission differential equation and a salt transmission differential equation to carry out a frozen soil model test similarity criterion derivation process as follows:
(1) differential control equation for moisture transport:
0≤x≤d，0≤y≤d，0≤z≤l+l1，t≥0
in the formula: theta is the volume water content (cm) of the soil3·cm-3) (ii) a D is the diffusion coefficient (cm) of water in soil3·s-1) (ii) a t is time(s); x, y and z are respectively the size component (cm) of the soil body in the x-axis y-axis z-axis direction, l is the seasonal frozen soil sample height (cm), l1The height (cm) of the permafrost sample and the d of the inner diameter (cm) of the sample groove.
When the initial condition is that t is equal to 0, θ (x, y, z,0) is equal to θ4(x,y,z)；
When the boundary condition is that z is equal to 0, θ (x, y,0, t) is equal to θ5(x,y,t)；z＝l+l1When, θ (x, y, l + l)1,t)＝θ6(x,y,t)
x＝0，θ(0,y,z,t)＝θ7(y,z,t)；x＝d，θ(d,y,z,t)＝θ8(y,z,t)；
y＝0，θ(x,0,z,t)＝θ9(x,z,t)；y＝d，θ(x,d,z,t)＝θ10(x,z,t)；
According to a similar theory, the method can be simplified as follows:
in the formula CD、Ct、ClRespectively are diffusion coefficient, time and geometric similar constant of water in soil of the soil body; thetaiA moisture content function determined for the test data of the plug-in soil moisture and salinity sensor 20.
(2) Salt transport differential control equation:
0≤x≤d，0≤y≤d，0≤z≤l+l1，t≥0
in the formula: w is the salt content (g cm) of the soil-3) (ii) a Dsh is the hydrodynamic dispersion coefficient (cm) of salt under concentration gradient2·s-1)。
When the initial condition is that t is 0, w (x, y, z,0) is w4(x,y,z)；
When the boundary condition is that z is equal to 0, w (x, y,0, t) is equal to w5(x,y,t)，z＝l+l1When, w (x, y, l + l)1,t)＝w6(x,y,t)；
x＝0，w(0,y,z,t)＝w7(y,z,t)；x＝d，w(d,y,z,t)＝w8(y,z,t)；
y＝0，w(x,0,z,t)＝w9(x,z,t)；y＝d，w(x,d,z,t)＝w10(x,z,t)；
According to a similar theory, the method can be simplified as follows:
in the formula CDsh、Cθ、Ct、ClRespectively are similar constants of hydrodynamic dispersion coefficient, volume water content, time and geometry of salt under the concentration gradient of the soil body; w is aiA salinity function determined for the inserted soil moisture and salinity sensor 20 test data.
The initial condition and boundary condition of the formula ninthly are obtained by solving functions after the data are measured by the plug-in soil moisture and salinity sensors 20 arranged on the upper surface, the lower surface and the whole height of the sample.
In summary, when undisturbed soil is used for making the model, the following results are obtained:
CD＝CDsh＝1
order: cθ＝Cw1 (namely, the test humidity and the salinity adopt the same values as the natural conditions, and the similarity constants are 1)
When undisturbed soil is used as a sample model material, the similar proportion of test moisture and salt to the site prototype is Cθ＝CwWhen 1, CD＝CDshThe available time scaling factor is the square of the model geometric dimension scaling factor, so the geometric ratio of the test model to the field prototype is assumed to be ClWhen a is 1 (a is a constant), the ratio of the test time to the field is Ct＝1:a2And the ratio of the freeze-thaw variation of the sample model observed in the test to the upper limit freeze-thaw variation of the frozen soil of the on-site prototype is also 1: a.
A method for determining the upper limit change rule of frozen soil based on the change of soil water and salt comprises the following steps:
(1) preparing a sample by testing: sample size calculation was performed according to the above-described similarity theory: determining the test time t from the specific test requirements1And the site time t to be simulated1'(t1Much less than t1') obtaining a model time ratio of Ct＝t1:t1'＝1:a2(a is a constant); so that the geometric proportion of the obtained model is Cl1: a, and thenAccording to the seasonal frozen soil height L and the perennial frozen soil height L to be simulated on site1The model is obtained by calculating the height of the seasonal frozen soil sample
The permafrost sample has the height of
The test sample preparation can be divided into two cases: preparing a first undisturbed soil sample, namely cutting seasonal frozen soil and permafrost soil taken from a simulation site according to a test calculation size to prepare a sample; the permafrost sample is taken from an undisturbed permafrost layer, and the soil taking depth is in the range of-5 to-10 m; taking a seasonal frozen soil sample from an undisturbed frozen soil seasonal freeze-thaw cycle layer, wherein the soil taking depth is in the range of-1 to-5 m;
secondly, preparing a soil sample indoors, and preparing the sample indoors in order to research the influence of multiple factors on the upper limit of the frozen soil; and drying and washing salt of the soil sample taken from the site, and then preparing the sample again indoors according to the simulated soil water content and salt content data. When preparing the frozen soil, firstly, the height l of a permafrost sample 17 is calculated1And selecting a corresponding mould according to the height l of the seasonal frozen soil sample 18, and adjusting the sample groove lifting cylinder 13 to change the height of the sample groove, wherein the height adjustment of the sample groove is determined by the measurement of an infrared distance measuring sensor 25. According to the calculated heights l of the permafrost and the seasonal frozen soil samples1L, the inner diameter d of the sample groove and the dry density rho of the soil sample are calculated to obtain the required 18 dry mass m of the seasonally frozen soil sample after drying and salt washing for multiple times1＝ρπ(d/2)2l and permafrost sample 17 dry mass m2＝ρπ(d/2)2l1. Then according to the volume water content theta and the salt content w of the frozen soil with known data, preparing deionized water, NaCl and Na with corresponding mass2SO4、NaHCO3Mixing NaCl and Na2SO4、NaHCO3Uniformly mixing according to a certain proportion, dissolving in deionized water with corresponding mass, adding saline solution into dry soil after salt is completely dissolved in the solution, adding the solution while stirring to uniformly mix the saline solution and the soil, and sealing until the mixture is moldedThe material is kept in the charging basket for 12 hours, so as to ensure that the moisture and the salt in the soil body are uniformly distributed. Coating a layer of anti-freezing silicone oil on the side wall of the model box to reduce the friction force of the side wall; the method comprises the steps of firstly, filling permafrost layer by layer, embedding the permafrost layer into a plug-in type sensor fixing ring 21 when filling, placing semiconductor refrigerating sheets 19 at the bottom and the periphery of a soil sample, compacting each layer of the filled soil by using a compacting device until the required height is reached, adjusting the semiconductor refrigerating sheets 19 to the lowest temperature for refrigerating for 12 hours, scraping the upper layer, filling seasonal frozen soil layer by layer after the permafrost sample 17 is manufactured, embedding the permafrost layer into the plug-in type sensor fixing ring 21 layer by layer when filling, and compacting each layer of the filled soil by using the compacting device until the required height is reached. The compacting device is disassembled after use.
(2) Controlling the test process: the temperature, humidity and illumination conditions of the test are consistent with those of field undisturbed soil, the sample tank is placed on the cylindrical magnet rotating table 7 of the box body 2 in the test after sampling or sample preparation is finished, and the metal rotating shaft 6 and the cylindrical magnet rotating table 7 are driven to rotate by the restarting motor, so that the sample tank is driven to rotate uniformly in the box body.
According to the test time t1And the site time t to be simulated1'(t1Much less than t1') frozen ground site t1The time temperature, precipitation and illumination field data are input into the system control and data acquisition computer 34 according to the temperature change data of t1' time, the computer system controls the refrigeration module 26 and the heating module 27 to regulate and control the temperature, and the data are processed at t1Reappeared to the test chamber over time. Inputting the data into computer, and controlling the spray rate of water replenishing device spray head 28 by computer software to make t on site1Precipitation at time t1The time is uniformly reduced to the cylindrical magnet rotating platform 7. The irradiation frequency and time of the daylight simulation lamp 31 are adjusted in the same way, so that the site t is enabled1The amount of illumination radiation at time t1The test box is irradiated uniformly in time.
(3) Test results measurement: the soil moisture and salinity monitoring system is a plug-in soil moisture and salinity sensor 20The sensor 20 is arranged in a plug-in sensor fixing ring 21 and is embedded in a soil sample, and the height l + l from the upper surface of the seasonal frozen soil sample 18 of the sample tank to the contact surface of the perennial frozen soil sample 17 and the movable sliding plate 161A plurality of plug-in sensor fixing rings 21 are uniformly distributed in the middle, and data measured by the sensors can be collected by a data acquisition module and input into a computer system for storage and output.
The upper limit of the frozen soil is calculated as follows:
after frozen soil sample preparation and sampling and freeze-thaw test in a test box, the upper boundary condition of the formula (i) can be determined by functions obtained by data of soil moisture content theta and soil salinity w measured by the plug-in type sensor fixing rings 21 on the uppermost surface of the seasonally frozen soil sample 18 and the soil salt content w, the lengths of the sensor probes are different, the functions are calculated after averaging, the lower boundary condition of the formula (i) can be determined by functions obtained by data of soil moisture content theta and soil salinity w measured by the salt sensors 20 and the plug-in type sensor fixing rings 21 on the lowermost surface of the permafrost sample 17, namely the contact surface of the sample cell movable sliding plate 16 and the permafrost sample 17, and the initial condition of the formula (i) is determined by functions obtained by data of soil moisture content theta and soil salinity w measured by the plug-in type sensor fixing rings 21 from the top to the bottom in the seasonally frozen soil sample 18 and the permafrost sample 17 Determining a function obtained by theta and the data of the salt content w of the soil;
after determining the initial condition and boundary condition of the formula, solving and resolving an analytic solution according to a separation variable method to obtain a formula II, and finally, calculating and judging the upper limit change process of the frozen soil according to the formula II by combining soil moisture and salinity judgment indexes as follows:
(1) water transfer equation by soil freezing and thawing
In the formula: theta is the volume water content (cm) of the soil3·cm-3) D is the diffusion coefficient (cm) of water in soil3·s-1) T is time(s), z is the dimension component (cm) of the soil body in the z-axis direction, l is the seasonal frozen soil sample height (cm),l1the permafrost sample height (cm);
when the initial condition is that t is equal to 0, θ (z,0) is equal to θ1(z)；
When the boundary condition is that z is equal to 0, θ (0, t) is equal to θ2(t)；
z＝l+l1When, theta (l + l)1,t)＝θ3(t)；
The analytical solution obtained by the separation variable method is:
wherein
t0To test the end of the experiment, n ═ 1,2,3 ·; thetaiA moisture content function determined for the test data of the plug-in soil moisture and salinity sensor 20;
according to the formula II, the water content theta of any depth z at any time t can be obtained, because the water content of the permafrost and the seasonal frozen soil has a certain difference value, the water of the permafrost is in a frozen state, the liquid water content of the seasonal frozen soil is far higher than that of the permafrost, the difference value of the upper water content and the lower water content of the interface of the permafrost and the seasonal frozen soil is taken as a judgment basis, the time t and the time t can be regulated according to the specification of specific test requirements by a computer, the time t is substituted into the formula II for assignment trial calculation until the water content difference value delta theta at the position close to the z is suddenly changed and the delta theta is obviously increased, namely the upper limit position z of the1，z1Averaging two similar z values, if more than one z occurs1Taking the maximum value as a standard;
the continuous adjustment time t can be set at the test time t1Simulating to obtain the on-site time t1' inner permafrost upper limit position change rule;
(2) is prepared from soil jellyConduction equation of fused salt
In the formula: w is the salt content (g cm) of the soil-3) Dsh is the hydrodynamic dispersion coefficient (cm) of the salt under the concentration gradient2·s-1)；
When the initial condition is that t is 0, w (z,0) is w1(z)；
When the boundary condition is that z is equal to 0, w (0, t) is equal to w2(t)；
z＝l+l1When, w (l + l)1,t)＝w3(t)；
The analytical solution obtained by the separation variable method is:
wherein
t0To test the end of the experiment, n ═ 1,2,3 ·; w is aiA salt content function determined for the test data of the insertion type soil moisture and salt content sensor 20;
according to a formula, salt content w of any depth z at any time t can be obtained, salt content of permafrost and seasonal frozen soil has a certain difference, soil salt exists in liquid water in an ionic form, water of the permafrost is in a frozen state, liquid water content of the seasonal frozen soil is far higher than that of the permafrost, salt content of the seasonal frozen soil is also higher than that of the permafrost, and therefore the difference between salt content of the permafrost and salt content of the seasonal frozen soil is larger than that of the permafrost, so that the difference between salt content of the permafrost and salt content of the seasonal frozen soil at any depth z is used as a judgment basis, the time t is substituted into the formula by a computer for assignment trial calculation until salt content difference delta w between salt content of two adjacent z is changed, and delta w is obviously increased rapidly, namely the salt content w is determinedLimit position z2，z2Averaging two similar z values, if a plurality of z occur2Taking the maximum value as a standard;
the continuous adjustment time t can be set at the test time t1Simulating to obtain the on-site time t1' inner permafrost upper limit position change rule;
(3) in summary, the annual frozen soil upper limit position obtained by different formula analysis solutions is
According to a similar theory, the ratio of the freeze-thaw variation of the sample model observed in the test to the freeze-thaw variation of the upper limit of the on-site prototype frozen soil is also 1: a, so that the upper limit of the on-site prototype frozen soil is az, the variation rule of the upper limit position of the on-site frozen soil can be obtained according to the formula, and the time t can be continuously adjusted during the test time t1Simulating to obtain the on-site time t1' inner permafrost upper limit position change condition.
t can be regulated according to specific test requirements1Much less than t1'。
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation. The use of the phrase "comprising one of the elements does not exclude the presence of other like elements in the process, method, article, or apparatus that comprises the element.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (6)
1. A method for determining an upper limit change rule of frozen soil based on soil water salt change comprises an outer box body (1), an inner box body (2), a data acquisition module (33) and a system control and data acquisition computer (34), wherein the inner box body (2) is positioned inside the outer box body (1), the upper ends of the outer box body (1) and the inner box body (2) are respectively provided with an outer box cover (3) and an inner box cover (4), a heating module (27) and a refrigerating module (26) are installed between the outer wall of the left side of the inner box body (2) and the inner wall of the outer box body (1), the heating module (27) and the refrigerating module (26) are respectively communicated with the inner box body (2), and a water replenishing device is arranged between the outer wall of the right side of the inner box body (2) and the inner wall of the outer box body (1), the solar simulation lamp (31) is installed above the inner wall of the left side of the inner box body (2), the bottom of the inner wall of the inner box body (2) is fixedly connected with a metal sample table base (5), a rotating motor is installed inside the metal sample table base (5), a metal rotating shaft (6) is installed on an output shaft of the rotating motor, a cylindrical magnet rotating table (7) is fixedly connected to the top of the metal rotating shaft (6), a sample groove is arranged at the top of the cylindrical magnet rotating table (7), an infrared distance measuring sensor (25) is installed at the top end of the sample groove, a compacting device is installed below the inner box cover (4), the sample groove is provided with a plurality of sample grooves, each sample groove comprises a sample groove outer wall (8), a sample groove inner wall (9) and a sample groove base (10), a lifting cylinder (13) is installed at the bottom of the sample groove base (10), and a lifting cylinder air guide hole (14) and a, the portable slide board (16) of lift cylinder (13) top fixedly connected with, sample inslot wall (9) fixedly connected with heat preservation (11), portable slide board (16) both sides contact with heat preservation (11) inner wall of sample groove, perennial frozen soil sample (17) have been placed on portable slide board (16), semiconductor refrigeration piece (19) have all been placed to the bottom of perennial frozen soil sample (17) and position all around, seasonal frozen soil sample (18) have been placed at perennial frozen soil sample (17) top, be provided with bayonet sensor solid fixed ring (21) inside perennial frozen soil sample (17) and seasonal frozen soil sample (18), bayonet sensor solid fixed ring (21) are provided with a plurality ofly, and by supreme setting down, bayonet sensor solid fixed ring (21) includes solid fixed ring inner wall (22) and solid fixed ring outer wall, the surface of the inner wall (22) of the fixing ring is provided with a sensor fixing clamping groove (23), the sensor fixing clamping groove (23) is uniformly arranged, an insertion type soil moisture and salinity sensor (20) is arranged inside the sensor fixing clamping groove (23), a soil moisture and salinity sensor induction probe (24) is arranged on the inner side of the insertion type soil moisture and salinity sensor (20), the soil moisture and salinity sensor induction probe (24) is located on the inner side of the insertion type sensor fixing ring (21), and the soil moisture and salinity sensor induction probes (24) are arranged to be different in length;
after frozen soil sample preparation and sampling and freeze-thaw test in the device, the upper boundary condition of the formula (I) can be determined by a function obtained by data of the water content theta of the inserted soil in the sensor fixing ring (21) on the uppermost surface of the seasonal frozen soil sample (18) and the water content theta and the salt content w of the soil measured by the salt sensor (20), the lengths of the sensor probes are different, the functions are calculated after averaging the data, the lower boundary condition of the formula (I) can be determined by a function obtained by data of the water content theta of the soil and the salt content w of the soil measured by the salt sensor (20) and the inserted soil in the sensor fixing ring (21) on the contact surface of the movable sliding plate (16) and the perennial frozen soil sample (17), and the initial condition of the formula (I) is determined by the functions obtained by data of the water content theta of the soil and the salt content w of the soil measured by the seasonal frozen soil sample (18) and the inserted sensor fixing ring (21) on the uppermost surface of the perennial frozen soil sample (17) Determining a function obtained by data of the water content theta of the soil and the salt content w of the soil measured by the plug-in soil water content and salt content sensor (20);
after determining the initial condition and boundary condition of the formula, solving and resolving an analytic solution according to a separation variable method to obtain a formula II, and finally, calculating and judging the upper limit change process of the frozen soil according to the formula II by combining soil moisture and salinity judgment indexes as follows:
(1) soil freezing and thawing water transfer equation
In the formula: theta is the volume water content of soil and the unit is cm3·cm-3D is the diffusion coefficient of water in soil, and the unit is cm2·s-1T is time and is expressed in units of s, z is the dimension component of the soil body in the z-axis direction and is expressed in units of cm, l is the height of the seasonal frozen soil sample and is expressed in units of cm and l1The height of the permafrost sample is cm;
when the initial condition is that t is equal to 0, θ (z,0) is equal to θ1(z)；
When the boundary condition is that z is equal to 0, θ (0, t) is equal to θ2(t)；
z＝l+l1When, theta (l + l)1,t)＝θ3(t)；
The analytical solution obtained by the separation variable method is:
wherein
t0To test the end of the trial, n is 1,2,3 …; thetaiA moisture content function determined for the test data of the plug-in soil moisture and salinity sensor (20);
according to the formula II, the water content theta at any depth z and at any time t can be obtained, the difference value of the upper water content and the lower water content of the interface of the permafrost and the seasonal frozen soil is taken as a judgment basis, the time t and the time t can be regulated according to the specification of a specific test by a computer, the time t and the time t are substituted into the formula II to carry out assignment trial calculation until the water content of two positions close to z is obtainedThe difference delta theta is mutated and obviously and rapidly increased, namely the difference delta theta is determined as the upper limit position z of the permafrost1，z1Is the average of two similar z values, if more than one z occurs1Taking the maximum value as a standard;
the continuous adjustment time t can be set at the test time t1Simulating to obtain the on-site time t1' inner permafrost upper limit position change rule;
(2) soil freezing and thawing salinity conduction equation
In the formula: w is the salt content of the soil and the unit is g cm-3Dsh is the hydrodynamic dispersion coefficient of salt under concentration gradient, and the unit is cm2·s-1；
When the initial condition is that t is 0, w (z,0) is w1 (z);
when the boundary condition is that z is equal to 0, w (0, t) is equal to w2 (t);
z＝l+l1when, w (l + l)1,t)＝w3(t)；
The analytical solution obtained by the separation variable method is:
wherein
t0To test the end of the trial, n is 1,2,3 …; w is aiA salinity function determined for the test data of the inserted soil moisture and salinity sensor (20);
according to a formula, the salt content w of any depth z at any time t can be obtained, and the difference of the salt content of the permafrost and the salt content of the seasonally frozen soil on the upper and lower surfaces of the interface is largeFor the judgment basis, substituting the time t into a formula (sixth) by a computer to carry out assignment trial calculation until the salt content difference delta w of two adjacent Z parts is mutated and the delta w is obviously increased, namely the time t is determined as the upper limit position z of the permafrost2，z2Is the average of two similar z values, if a plurality of z values appear by trial calculation2Taking the maximum value as a standard;
the continuous adjustment time t can be set at the test time t1Simulating to obtain the on-site time t1' inner permafrost upper limit position change rule;
(3) in summary, the annual frozen soil upper limit position obtained by different formula analysis solutions is
According to a similar theory, the ratio of the freeze-thaw variation of the sample model observed in the test to the freeze-thaw variation of the upper limit of the on-site prototype frozen soil is also 1: a, so that the upper limit of the on-site prototype frozen soil is az, and the change rule of the upper limit position of the on-site frozen soil can be obtained according to the formula.
2. The method for determining the upper limit change law of the frozen soil based on the change of the water and the salt of the soil according to claim 1, wherein the method comprises the following steps: the t can be regulated according to the specific test requirements, and the t1Much less than t1'。
3. The method for determining the upper limit change law of the frozen soil based on the change of the water and the salt of the soil according to claim 1, wherein the method comprises the following steps: the compaction device is including driving actuating cylinder (36), drive actuating cylinder (36) top and pass through pressure device fixing bolt (35) and interior case lid (4) fixed connection, drive telescopic link (37) bottom installation of actuating cylinder (36) and support frame (39), support frame (39) middle part is passed through support frame connecting bolt (38) and is connected bottom telescopic link (37), support frame (39) bottom fixedly connected with pressure head (40), the quantity and the position of pressure head (40) all with the quantity and the position one-to-one in sample groove.
4. The method for determining the upper limit change law of the frozen soil based on the change of the water and the salt of the soil according to claim 1, wherein the method comprises the following steps: the utility model discloses a solar simulation lamp, including outer case lid (3), interior case lid (4), outer box (1), interior box (2), outer case lid (3) and interior case lid (4) are equipped with the pull ring respectively, all use thermal-insulated metal material to make outer box (1), interior box (2), outer case lid (3) and interior case lid (4), and the insulating material layer is all smeared to the inner wall, daylight simulation lamp (31) control end is connected with system control and data acquisition computer (34), the position between sample inslot wall (9) and insulating layer (11) is provided with insulating layer (12).
5. The method for determining the upper limit change law of the frozen soil based on the change of the water and the salt of the soil according to claim 1, wherein the method comprises the following steps: plug-in soil moisture all is connected with data acquisition module (33) through test data transmission wire (32) with salinity sensor (20) and infrared distance measuring sensor (25), data acquisition module (33) output is connected with system control and data acquisition computer (34) input, heating module (27) and refrigeration module (26) are all connected with system control and data acquisition computer (34) through test data transmission wire (32).
6. The method for determining the upper limit change law of the frozen soil based on the change of the water and the salt of the soil according to claim 1, wherein the method comprises the following steps: the moisturizing device includes mah-jongg bottle (30), distilled water transmission pipe (29), moisturizing device shower nozzle (28), distilled water transmission pipe joint (41), can dismantle distilled water transmission pipe (42) and tube-shape revolving stage ponding and retrieve bottle (43), mah-jongg bottle (30) are located the position between the right side outer wall of inner box (2) and the inner wall of outer box (1), mah-jongg bottle (30) are connected with moisturizing device shower nozzle (28) through distilled water transmission pipe (29), distilled water transmission pipe joint (41) and can dismantle distilled water transmission pipe (42), moisturizing device shower nozzle (28) are located the top of inner box (2) inside tube-shape magnet revolving stage (7), the control end and the system control and data acquisition computer (34) electric connection of moisturizing device shower nozzle (28).
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