CN116087054A - CPTU-based freeze-thawing soft clay permeability coefficient distribution measurement method - Google Patents
CPTU-based freeze-thawing soft clay permeability coefficient distribution measurement method Download PDFInfo
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- 230000035699 permeability Effects 0.000 title claims abstract description 44
- 239000004927 clay Substances 0.000 title claims abstract description 28
- 238000010257 thawing Methods 0.000 title claims abstract description 22
- 238000000691 measurement method Methods 0.000 title claims abstract description 11
- 230000008014 freezing Effects 0.000 claims abstract description 80
- 238000007710 freezing Methods 0.000 claims abstract description 80
- 238000012360 testing method Methods 0.000 claims abstract description 57
- 239000002689 soil Substances 0.000 claims abstract description 51
- 239000013307 optical fiber Substances 0.000 claims abstract description 46
- 238000000034 method Methods 0.000 claims abstract description 44
- 230000035515 penetration Effects 0.000 claims abstract description 33
- 230000003068 static effect Effects 0.000 claims abstract description 19
- 230000008569 process Effects 0.000 claims abstract description 17
- 238000009529 body temperature measurement Methods 0.000 claims abstract description 11
- 239000012774 insulation material Substances 0.000 claims abstract description 7
- 239000011248 coating agent Substances 0.000 claims abstract description 6
- 238000000576 coating method Methods 0.000 claims abstract description 6
- 239000000523 sample Substances 0.000 claims description 73
- 230000007246 mechanism Effects 0.000 claims description 31
- 230000000149 penetrating effect Effects 0.000 claims description 17
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 16
- 238000005259 measurement Methods 0.000 claims description 11
- 239000011148 porous material Substances 0.000 claims description 11
- 230000003204 osmotic effect Effects 0.000 claims 2
- 230000008859 change Effects 0.000 abstract description 11
- 238000010276 construction Methods 0.000 abstract description 7
- 238000012544 monitoring process Methods 0.000 abstract description 4
- 238000005070 sampling Methods 0.000 abstract description 4
- 230000036760 body temperature Effects 0.000 abstract description 2
- 230000009974 thixotropic effect Effects 0.000 abstract description 2
- 239000007788 liquid Substances 0.000 description 5
- 238000010586 diagram Methods 0.000 description 3
- 238000002474 experimental method Methods 0.000 description 3
- 239000000835 fiber Substances 0.000 description 3
- 238000006073 displacement reaction Methods 0.000 description 2
- 230000002829 reductive effect Effects 0.000 description 2
- 238000004062 sedimentation Methods 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 238000012937 correction Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000011065 in-situ storage Methods 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 230000000670 limiting effect Effects 0.000 description 1
- 230000013011 mating Effects 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000036961 partial effect Effects 0.000 description 1
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- 239000003507 refrigerant Substances 0.000 description 1
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- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
- G01N15/082—Investigating permeability by forcing a fluid through a sample
- G01N15/0826—Investigating permeability by forcing a fluid through a sample and measuring fluid flow rate, i.e. permeation rate or pressure change
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- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
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- G01N15/0806—Details, e.g. sample holders, mounting samples for testing
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Abstract
The invention relates to a CPTU-based freeze-thawing soft clay permeability coefficient distribution measurement method, which comprises the steps of exploring permeability coefficient changes of different positions of a soft clay stratum before and after freezing, constructing a test box, and coating a thermal insulation material on the test box; designing a model soil body system and a freezing system according to engineering cases; designing a test soil body temperature monitoring system based on an optical fiber temperature measurement principle; designing a device for collecting point location permeability coefficients of different areas of a test soil body based on a micro pore-pressure static Cone Penetration Test (CPTU) method; and dividing and designing relevant data acquisition areas and acquisition points according to engineering requirements and actual test temperature fields. Compared with the prior art, the method can more accurately obtain the permeability change distribution of the thixotropic soft clay in different areas before and after freezing and thawing, reduces the influence caused by manual sampling disturbance in the original related permeability coefficient acquisition process, provides a reference for the permeability coefficient change value of the area after the actual freezing method construction, and provides a judgment basis for the area where leakage easily occurs.
Description
Technical Field
The invention relates to the field of geotechnical engineering, in particular to a method for measuring the permeability coefficient distribution of freeze thawing soft clay for micro pore-pressure static sounding (CPTU).
Background
With the construction of urban underground facilities, an artificial stratum freezing method is widely applied to the construction of underground projects such as subway side channels, river-crossing tunnels and the like in areas with soft clay weak stratum such as Shanghai as a green construction method. However, with the increase of engineering cases, the problems of leakage in partial areas after the construction of the artificial stratum freezing method, uneven settlement after the complete melting of the stratum, and the like are caused.
The soil permeability coefficient is a parameter directly reflecting the soil permeability, and has important significance for researching the problem of stratum settlement and leakage by a freezing method. Therefore, the accurate acquisition of the soil permeability coefficient of the research area becomes a key for solving the post-construction problem of the freezing method.
In China, the most main method for measuring the permeability coefficient of the soil body is to take a ring cutter soil sample for indoor permeability test after the test. However, for soft clay which is easy to be disturbed, the soft clay is in a fragile soft soil structure after freeze thawing, disturbance is inevitably caused in the sampling process by adopting the method, the field actual condition cannot be accurately simulated, the time consumption is long, and the cost is high.
Therefore, it is necessary to provide a soil permeability coefficient distribution measurement scheme for freeze-thawing soft clay.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a CPTU-based freeze-thawing soft clay permeability coefficient distribution measurement method.
The aim of the invention can be achieved by the following technical scheme:
a CPTU-based freeze-thawing soft clay permeability coefficient distribution measurement method comprises the following steps:
building a test box, and coating a thermal insulation material on the test box;
presetting the position of a frozen curtain boundary in a test box;
setting a freezing pipe in a test box, wherein the freezing pipe is arranged in the center of the test box in a plane form parallel to the side wall of the test box, putting a soil sample in the test box, using the soil sample at the first side of the freezing pipe for temperature measurement, using the soil sample at the second side of the freezing pipe for sounding, burying a transverse temperature measuring optical fiber group I in the soil sample at the first side of the freezing pipe according to a preset freezing curtain boundary, selecting a plurality of planes at the first side of the freezing pipe along the advancing direction of a freezing front, and respectively setting a longitudinal temperature measuring optical fiber group II;
the freezing operation is started by connecting a circulating pump with a freezing pipe, whether the frozen curtain boundary of the soil body frozen is up to a preset frozen curtain boundary is detected by utilizing a transverse temperature measuring optical fiber group I, if so, the freezing operation is stopped, otherwise, the step is repeated;
obtaining the temperature area division of the soil body according to the measurement data of the longitudinal temperature measuring optical fiber groups II in a plurality of planes, and determining each touch point;
after the soil body is restored to room temperature, the probes of the micro pore-pressure static cone penetration system are distributed and extended to each penetration point to obtain pore water pressure, probe penetration speed and cone head resistance;
and calculating the permeability coefficient of each penetration point based on the pore water pressure, the probe penetration speed and the cone head resistance. Further, the formula for calculating the permeability coefficient is:
πa 2 U＝S'·K·i
wherein a is the radius of the probe, U is the penetrating speed of the probe, S' is the water flow surface area of the probe, K is the permeability coefficient of soil, an external sphere wrapping the probe is formed in the probing process, and i is the hydraulic gradient at the surface of the sphere.
Further, the probe water flow surface area is:
where α represents the probe cone angle.
Further, the micro-pore-pressure static cone penetration system comprises a first movable frame, a first driving mechanism, a second movable seat, a second driving mechanism, a penetration mechanism, a probe rod and a probe;
the two ends of the first movable frame are connected with two parallel side walls of the test box, and the first driving mechanism is connected with the first movable frame and used for driving the first movable frame to slide along the two parallel side walls of the test box;
the second movable seat is arranged on the first movable frame, the second driving mechanism is connected with the second movable seat and is used for driving the second movable seat to slide on the first movable frame, and the first movable frame is perpendicular to the running track of the second movable seat;
the penetrating mechanism is arranged on the second movable seat, one end of the probe rod is connected with the penetrating mechanism, and the other end of the probe rod is connected with the probe.
Further, a rack structure is arranged on the surface of the probe rod.
Further, the micro-pore-pressure static cone penetration system also comprises a controller, wherein the controller is connected with the first driving mechanism, the second driving mechanism, the penetration mechanism and the sensor on the probe.
Further, the transverse temperature measuring optical fiber group I is arranged on a preset frozen curtain boundary plane and comprises three temperature measuring optical fibers with different depths.
Further, three groups of longitudinal temperature measuring optical fiber groups II are arranged in each plane, each group of longitudinal temperature measuring optical fiber groups II comprises three temperature measuring optical fibers with the same depth as the depth of the transverse temperature measuring optical fiber groups I, and the three groups of longitudinal temperature measuring optical fiber groups II are sequentially arranged at different positions of the plane.
Further, the temperature measuring optical fiber is connected with a temperature measuring instrument.
Further, the system also comprises a total control terminal, wherein the total control terminal is connected with the thermometer, the circulating pump and the micro pore-pressure static cone penetration system.
Compared with the prior art, the invention has the following beneficial effects:
(1) The permeability coefficient of soft clay after freeze thawing is measured by micro pore-pressure static sounding (CPTU), so that the large disturbance of sampling to the fragile soft soil structure after freeze thawing can be avoided, the disturbance to the original soil body is small, the obtained permeability coefficient has high precision, the measurement of in-situ permeability coefficient distribution is realized, and a reference basis is provided for accurate positioning grouting after a freezing method is used.
(2) Compared with the traditional method, the CPTU method for measuring the soil permeability coefficient has the advantages of short time, short test period and low cost.
(3) The temperature fields in the soil body are symmetrically distributed, the temperature measuring areas and the sounding areas are symmetrically distributed, the influence of temperature monitoring on the sounding areas is avoided, disturbance is further reduced, and measurement accuracy is improved.
Drawings
FIG. 1 is a schematic diagram of the connection of a test chamber and associated equipment;
FIG. 2 is a schematic diagram of the temperature zone division of the test chamber;
FIG. 3 is a schematic illustration of a touch point location;
reference numerals: 1. the device comprises a penetrating mechanism, a second movable seat, a first movable frame, a probe, a freezing pipe, a circulating pump, a test box, a box base, a transverse temperature measuring optical fiber set I (frozen curtain boundary), a longitudinal temperature measuring optical fiber set II (frozen area monitoring), a thermometer and a general control terminal.
Detailed Description
The invention will now be described in detail with reference to the drawings and specific examples. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, and obviously, the described embodiment is only a part of the embodiment of the present invention, but not all the embodiments, and the protection scope of the present invention is not limited to the following embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.
In the drawings, like structural elements are referred to by like reference numerals and components having similar structure or function are referred to by like reference numerals. The dimensions and thickness of each component shown in the drawings are arbitrarily shown, and the present invention is not limited to the dimensions and thickness of each component. For clarity of illustration, the mating relationships between the various components are shown with some places in the drawings appropriately scaled and the distances between the components increased or decreased.
Reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic may be included in at least one implementation of the invention. In the description of the present invention, it should be understood that the terms "first," "second," and "third," etc. in the description and claims of the invention and in the above figures are used for distinguishing between different objects and not for describing a particular sequential order. Furthermore, the terms "comprise" and "have," as well as any variations thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, system, article, or apparatus that comprises a list of steps or elements is not limited to only those listed steps or elements but may include other steps or elements not listed or inherent to such process, method, article, or apparatus.
In the description of the embodiments of the present invention, it should be understood that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," "outer," and the like indicate orientations or positional relationships based on those shown in the drawings, or those conventionally put in place when the product of the application is used, or those conventionally understood by those skilled in the art, merely for convenience of description and simplicity of description, and do not indicate or imply that the device or element to be referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the application.
In the description of the embodiments of the present invention, it should also be noted that, unless explicitly specified and limited otherwise, the terms "disposed," "mounted," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the terms in this application will be understood by those of ordinary skill in the art in a specific context.
Example 1:
a freeze thawing soft clay permeability coefficient distribution measuring method based on micro-pore-pressure static sounding (CPTU) comprises the following steps:
(1) The method comprises the steps of building a test box 7, coating a heat insulation material on the test box 7, sealing the lower part of the test box 7, and arranging a box base 8, wherein the box base 8 is filled with the heat insulation material, and coating the heat insulation material outside the side wall of the test box 7, so as to isolate the influence of external temperature on soil in the test box 7;
(2) Determining a model proportion according to an actual engineering case and the size of the test box 7, and determining the position of a frozen curtain boundary in the test box 7, wherein the frozen curtain boundary is a preset rough position and is not a real frozen curtain boundary in a subsequent experiment;
the frozen curtain boundary is the boundary between the frozen region near the freezing pipe 5 and the phase change region far from the freezing pipe 5. According to engineering specifications, the temperature of the freezing region is lower than-10 ℃, and the temperature of the phase change region is between-10 ℃ and 0 ℃.
(3) As shown in fig. 1, a freezing pipe 5 is arranged in a test box 7, the freezing pipe 5 is arranged in the center of the test box 7 in a plane form parallel to the side wall of the test box 7, a soil sample is put into the test box 7, the soil sample at the first side of the freezing pipe 5 is used for measuring temperature, the soil sample at the second side of the freezing pipe 5 is used for sounding, a transverse temperature measuring optical fiber group I9 is buried in the soil sample at the first side of the freezing pipe 5 according to a preset freezing curtain boundary, a plurality of planes are selected at the first side of the freezing pipe 5 along the advancing direction of a freezing front, and longitudinal temperature measuring optical fiber groups II 10 are respectively arranged;
according to actual engineering cases, the (4) th layer of muddy clay in Shanghai city is adopted, a mud method is adopted to remodel the sample to be saturated, the sample is filled into the test box 7 in a layered mode, temperature measuring fibers are arranged in a layered mode, the temperature measuring instrument 11 is connected with the temperature measuring fibers and the master control terminal 12, measurement data of the temperature measuring fibers are obtained and sent to the master control terminal 12, and the initial temperature of the core is obtained. After filling, prepressing the soil sample by adopting a prepressing preloading method, and after prepressing to stabilize sedimentation, carrying out the next step after the sedimentation amount of the soil body meets the requirement;
the loop-removing freezing pipe 5 is positioned at the center of the bottom of the test box 7, and is welded and penetrated in the test box 7, so that the temperature fields inside the test box 7 are symmetrically distributed along the freezing pipe 5 in the freezing process, and the freezing pipe 5 can be used as a plane-shaped freezing source, the temperature fields at the two sides of the freezing pipe are uniformly distributed, and ideally, the same depth temperature is the same, and the temperature at the same horizontal distance from the freezing pipe 5 is the same.
The test process can be divided into three main areas, namely a frozen area, a phase change area and an unfrozen area according to the temperature distribution (shown in figure 2). In order to be close to the freezing condition of the actual engineering case as much as possible, a preset freezing curtain boundary is determined according to the actual engineering case, the transverse temperature measuring optical fiber group I9 is arranged on a preset freezing curtain boundary plane and comprises three temperature measuring optical fibers with different depths, and the transverse temperature measuring optical fiber group I is mainly used for judging whether the actual freezing curtain boundary reaches the preset freezing curtain boundary in the freezing process, so that the transverse temperature measuring optical fiber group I is only required to be provided with the temperature measuring optical fibers with different depths on the preset freezing curtain boundary plane.
In order to determine the temperature distribution in the test process, three groups of longitudinal temperature measuring optical fiber groups II 10 are arranged in each plane along the advancing direction of the freezing front, each group of longitudinal temperature measuring optical fiber groups II 10 comprises three temperature measuring optical fibers with the same depth as the depth of the transverse temperature measuring optical fiber groups I9, and the three groups of longitudinal temperature measuring optical fiber groups II 10 are sequentially arranged at different positions of the plane, so that the temperature distribution of a soil body can be fully measured by the groups of longitudinal temperature measuring optical fiber groups II 10 which are arranged at multiple points, and the condition of a temperature field inside the soil body can be obtained. Ideally, the boundary lines among the freezing region, the phase change region and the unfrozen region are straight lines, however, in practical experiments, the side wall of the test box 7 cannot achieve absolute heat preservation and insulation, so that the external environment temperature can influence the boundary lines among the freezing region, the phase change region and the unfrozen region, and radians exist on the boundary lines, so that each group of transverse temperature measuring optical fiber groups I9 can be finely adjusted, and three groups of longitudinal temperature measuring optical fiber groups II 10 on the same plane can be located in the same arc surface. Similarly, when the second side of the freezing pipe 5 is selected for the probe point, the arc may be slightly set as shown in fig. 3.
And assembling the miniature pore-pressure static cone penetration system. The upper parts of the two parallel side walls of the test box 7 are provided with guide rails, two ends of the first movable frame 3 are respectively connected to the guide rails at the upper parts of the two side walls, and the first movable frame 3 is driven by a first driving mechanism to move along the guide rails; the second movable seat 2 is arranged on the first movable frame 3, the second movable seat 2 is driven by the second driving mechanism to slide on the first movable frame 3, and the first movable frame 3 is perpendicular to the running track of the second movable seat 2; the penetrating mechanism 1 is arranged on the second movable seat 2, the first movable frame 3 and the second movable seat 2 can realize transverse and longitudinal movement of the penetrating mechanism 1, one end of the probe rod is connected with the penetrating mechanism 1, the other end of the probe rod is connected with the probe 4, the penetrating mechanism 1 can drive the probe rod and the probe 4 on the probe rod to extend into different depths of soil bodies at different speeds, and the probe 4 extends to each penetration point of the soil sample at the second side of the freezing pipe 5 for measurement. The surface of the probe rod is provided with a rack structure, the probe 4 is a conical probe 4, and a sensor for measuring parameters such as cone head resistance, pore water pressure after the cone head and the like is arranged in the probe 4. The controller is connected with the first driving mechanism, the second driving mechanism and the penetrating mechanism 1, the general control terminal 12 further realizes the transverse displacement, the longitudinal displacement and the penetrating depth of the probe 4 through the controller, and the controller is connected with the sensor in the probe 4, acquires the measurement data of the sensor and sends the measurement data to the general control terminal 12.
And (3) correcting the initial positions of the first movable frame 3, the second movable seat 2 and the penetrating mechanism 1 of the micro pore-pressure static sounding system, installing a sounding rod and a sounding probe 4 after finishing correction, checking whether the sounding process is normal, and checking the sounding rate and the sounding position control condition.
The main control terminal 12 is connected with the thermometer 11, the circulating pump 6 and the micro pore-pressure static cone penetration system; the change of the test temperature field can be fed back in real time through the thermometer 11, and the penetration position and the penetration process can be automatically operated through the controller.
(4) The circulating pump 6 is connected with the freezing pipe 5 to start freezing operation, a transverse temperature measuring optical fiber set I9 is used for detecting whether the frozen curtain boundary of soil body freezing reaches a preset frozen curtain boundary, if so, the freezing operation is stopped, otherwise, the step is repeated;
the freezing pipes 5 are connected with the circulating pump 6, so that the circulation condition of the freezing liquid is checked, whether the problems of night leakage, unsmooth circulation of the freezing liquid and the like exist or not is checked, and each freezing pipe 5 can keep the circulation flow of the freezing liquid. The constant temperature circulating pump 6 is connected with the freezing pipe 5 to provide refrigeration for the freezing process and ensure the temperature difference requirement of the refrigerant loop.
The circulation pump 6 is started, the temperature of the frozen liquid is reduced, and then the frozen liquid is circulated. And in the test process, temperature data are collected, a temperature field distribution diagram is drawn, the circulating pump 6 is stopped after the transverse temperature measuring optical fiber set I9 (frozen curtain boundary) reaches the preset temperature, and the actual freezing condition of the soil body is considered to be consistent with the freezing condition of the actual engineering case at the moment, so that the soil body freezing condition simulation of the actual engineering case is completed.
(5) Obtaining the temperature area division of the soil body according to the measurement data of the longitudinal temperature measuring optical fiber groups II 10 in a plurality of planes, and determining each touch point; the experimenter can determine the final point location of the piezocone penetration from the obtained temperature field distribution, as shown in fig. 3.
(6) After the soil body is restored to room temperature, the probes 4 of the micro pore pressure cone penetration system are distributed and extended to each penetration point, pore water pressure change is measured when the probes 4 penetrate into the designated position, the process of dissipating excess pore water pressure is monitored after the probes 4 penetrate into the designated depth, and finally the obtained data are summarized and recorded to obtain and record the data such as pore water pressure, penetrating speed of the probes 4, cone head resistance and the like;
(7) And calculating the permeability coefficient of each penetration point based on the pore water pressure, the penetration speed of the probe 4 and the cone head resistance.
According to the principle of pore-pressure static cone penetration, the cone head forms an external sphere which just can wrap the cone head, the surface area S 'of water flow at the cone head is a part of the surface area S of the external sphere, and the surface area S' of the sphere is related to the diameter a of the cone head and the angle alpha of the cone head. The volume permeation speed is equal to the spherical radial flow speed, and the volume permeation speed is obtained by:
πa 2 U＝S'·K·i
wherein a is the radius of the pore-pressure static cone penetration probe 4, alpha is the cone angle of the probe 4, U is the penetration speed of the probe 4, S' is the cone head water flow surface area, K is the soil permeability coefficient, i is the hydraulic gradient at the surface of the sphere, and the pore water pressure ratio and cone tip resistance obtained by combining CPTU data can be determined together.
The invention provides a CPTU-based freeze-thawing soft clay permeability coefficient distribution measurement method, which comprises the steps of exploring permeability coefficient changes of different positions of a soft clay stratum before and after freezing, constructing a test box, and coating a thermal insulation material on the test box; designing a model soil body system and a freezing system according to engineering cases; designing a test soil body temperature monitoring system based on an optical fiber temperature measurement principle; designing a device for collecting point location permeability coefficients of different areas of a test soil body based on a micro pore-pressure static Cone Penetration Test (CPTU) method; dividing and designing relevant data acquisition areas and acquisition points according to engineering requirements and actual test temperature fields; and calculating to obtain the soil permeability coefficient by using the measurement data of the micro pore-pressure static cone penetration system. Compared with the prior art, the method can more accurately obtain the permeability change distribution of the thixotropic soft clay in different areas before and after freezing and thawing, reduces the influence caused by manual sampling disturbance in the original related permeability coefficient acquisition process, provides a reference for the permeability coefficient change value of the area after the actual freezing method construction, and provides a judgment basis for the area where leakage easily occurs.
The foregoing describes in detail preferred embodiments of the present invention. It should be understood that numerous modifications and variations can be made in accordance with the concepts of the invention by one of ordinary skill in the art without undue burden. Therefore, all technical solutions which can be obtained by logic analysis, reasoning or limited experiments based on the prior art by the person skilled in the art according to the inventive concept shall be within the scope of protection defined by the claims.
Claims (10)
1. The CPTU-based freeze-thawing soft clay permeability coefficient distribution measurement method is characterized by comprising the following steps of:
building a test box, and coating a thermal insulation material on the test box;
presetting the position of a frozen curtain boundary in a test box;
setting a freezing pipe in a test box, wherein the freezing pipe is arranged in the center of the test box in a plane form parallel to the side wall of the test box, putting a soil sample in the test box, using the soil sample at the first side of the freezing pipe for temperature measurement, using the soil sample at the second side of the freezing pipe for sounding, burying a transverse temperature measuring optical fiber group I in the soil sample at the first side of the freezing pipe according to a preset freezing curtain boundary, selecting a plurality of planes at the first side of the freezing pipe along the advancing direction of a freezing front, and respectively setting a longitudinal temperature measuring optical fiber group II;
the freezing operation is started by connecting a circulating pump with a freezing pipe, whether the frozen curtain boundary of the soil body frozen is up to a preset frozen curtain boundary is detected by utilizing a transverse temperature measuring optical fiber group I, if so, the freezing operation is stopped, otherwise, the step is repeated;
obtaining the temperature area division of the soil body according to the measurement data of the longitudinal temperature measuring optical fiber groups II in a plurality of planes, and determining each touch point;
after the soil body is restored to room temperature, the probes of the micro pore-pressure static cone penetration system are distributed and extended to each penetration point to obtain pore water pressure, probe penetration speed and cone head resistance;
and calculating the permeability coefficient of each penetration point based on the pore water pressure, the probe penetration speed and the cone head resistance.
2. The method for measuring the osmotic coefficient distribution of freeze-thawing soft clay based on CPTU according to claim 1, wherein the osmotic coefficient is calculated according to the formula:
πa 2 U＝S'·K·i
wherein a is the radius of the probe, U is the penetrating speed of the probe, S' is the water flow surface area of the probe, K is the permeability coefficient of soil, an external sphere wrapping the probe is formed in the probing process, and i is the hydraulic gradient at the surface of the sphere.
3. The method for measuring the permeability coefficient distribution of freeze-thawing soft clay based on CPTU according to claim 1, wherein the probe water flow surface area is as follows:
where α represents the probe cone angle.
4. The CPTU-based freeze-thaw soft clay penetration coefficient distribution measurement method according to claim 1, wherein the micro-pore-pressure static sounding system comprises a first movable frame, a first driving mechanism, a second movable seat, a second driving mechanism, a penetrating mechanism, a probe rod and a probe;
the two ends of the first movable frame are connected with two parallel side walls of the test box, and the first driving mechanism is connected with the first movable frame and used for driving the first movable frame to slide along the two parallel side walls of the test box;
the second movable seat is arranged on the first movable frame, the second driving mechanism is connected with the second movable seat and is used for driving the second movable seat to slide on the first movable frame, and the first movable frame is perpendicular to the running track of the second movable seat;
the penetrating mechanism is arranged on the second movable seat, one end of the probe rod is connected with the penetrating mechanism, and the other end of the probe rod is connected with the probe.
5. The CPTU-based freeze-thaw soft clay permeability coefficient distribution measurement method according to claim 4, wherein a rack structure is arranged on the surface of the probe rod.
6. The method for measuring the permeability coefficient distribution of freeze-thawing soft clay based on CPTU according to claim 4, wherein the micro-pore-pressure static sounding system further comprises a controller, and the controller is connected with the first driving mechanism, the second driving mechanism, the penetrating mechanism and the sensor on the probe.
7. The CPTU-based freeze-thawing soft clay permeability coefficient distribution measurement method according to claim 1, wherein the transverse temperature measurement optical fiber group I is arranged on a preset frozen curtain boundary plane and comprises three temperature measurement optical fibers with different depths.
8. The CPTU-based freeze-thawing soft clay permeability coefficient distribution measurement method according to claim 1, wherein three longitudinal temperature measurement optical fiber groups II are arranged in each plane, each longitudinal temperature measurement optical fiber group II comprises three temperature measurement optical fibers with the same depth as the transverse temperature measurement optical fiber group I, and the three longitudinal temperature measurement optical fiber groups II are sequentially arranged at different positions of the plane.
9. The method for measuring the permeability coefficient distribution of freeze-thawing soft clay based on CPTU according to claim 7 or 8, wherein the temperature measuring optical fiber is connected with a temperature measuring instrument.
10. The method for measuring the permeability coefficient distribution of freeze-thawing soft clay based on CPTU according to claim 9, further comprising a master control terminal, wherein the master control terminal is connected with a thermometer, a circulating pump and a micro pore-pressure static cone penetration system.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116657671A (en) * | 2023-08-01 | 2023-08-29 | 同济大学 | Test method for horizontal force load test of offshore wind power pile |
| CN117054315A (en) * | 2023-10-13 | 2023-11-14 | 东北林业大学 | Frozen soil permeability coefficient measurement system |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116657671A (en) * | 2023-08-01 | 2023-08-29 | 同济大学 | Test method for horizontal force load test of offshore wind power pile |
| CN116657671B (en) * | 2023-08-01 | 2023-10-13 | 同济大学 | Test method for horizontal force load test of offshore wind power pile |
| CN117054315A (en) * | 2023-10-13 | 2023-11-14 | 东北林业大学 | Frozen soil permeability coefficient measurement system |
| CN117054315B (en) * | 2023-10-13 | 2024-01-09 | 东北林业大学 | Frozen soil permeability coefficient measurement system |
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