CN113295563B - Method for treating cold region expansive soil channel based on phase change material temperature control composite - Google Patents
Method for treating cold region expansive soil channel based on phase change material temperature control composite Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/60—Investigating resistance of materials, e.g. refractory materials, to rapid heat changes
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D3/00—Improving or preserving soil or rock, e.g. preserving permafrost soil
- E02D3/005—Soil-conditioning by mixing with fibrous materials, filaments, open mesh or the like
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D3/00—Improving or preserving soil or rock, e.g. preserving permafrost soil
- E02D3/02—Improving by compacting
- E02D3/10—Improving by compacting by watering, draining, de-aerating or blasting, e.g. by installing sand or wick drains
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D3/00—Improving or preserving soil or rock, e.g. preserving permafrost soil
- E02D3/12—Consolidating by placing solidifying or pore-filling substances in the soil
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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
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
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- 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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- G—PHYSICS
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- 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
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
- G01N15/088—Investigating volume, surface area, size or distribution of pores; Porosimetry
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- G—PHYSICS
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- G01N17/00—Investigating resistance of materials to the weather, to corrosion, or to light
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/02—Details
- G01N3/06—Special adaptations of indicating or recording means
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
- G01N3/18—Performing tests at high or low temperatures
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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
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
- G01N2015/0846—Investigating permeability, pore-volume, or surface area of porous materials by use of radiation, e.g. transmitted or reflected light
Abstract
The invention discloses a method for compositely treating an expansive soil channel in a cold region based on temperature control of a phase-change material, which comprises the following steps of: selecting a phase-change material, and testing the phase-change material to obtain the optimal doping amount of the phase-change material; selecting a fiber material, and testing the fiber material to obtain the optimal doping amount of the fiber material; performing a phase change temperature control composite fiber reinforced channel model test according to the optimal doping amount of the phase change material and the optimal doping amount of the fiber material to obtain the optimal doping depth of the phase change material and the optimal doping depth and evolution law of the fiber material; based on the optimal doping depth of the phase-change material and the optimal doping depth and evolution law of the fiber material, and according to the actual situation on site, the longitudinal and transverse drainage bodies of the channel are constructed, and the water leakage of the channel is drained in an accelerated manner. The method for treating the expansive soil in the cold region integrates active treatment and passive treatment, and is a composite treatment technology for the expansive soil channel in the cold region with unified control, prevention, discharge and seepage phases, and the method has wide engineering application prospect.
Description
Technical Field
The invention relates to the technical field of composite treatment of expansive soil channels in cold regions, in particular to a method for composite treatment of expansive soil channels in cold regions based on temperature control of phase-change materials.
Background
At present, the main hydraulic buildings in long-distance water transfer engineering in China are channels, and safe operation of water supply channels has great significance for relieving water consumption contradiction and reasonably allocating water resources. The safe operation of the channel is linked with the water loss in the water supply process, and according to statistics, nearly 450 km of various water delivery channels are owned by China at present, but the utilization rate of channel water only accounts for 53 percent of the total water delivery amount. The main cause of channel leakage is the failure of the impermeable layer caused by the structural damage of the channel. Therefore, the good structure of the channel in the process of controlling the water supply is the key for ensuring the water supply capacity of the channel.
The water supply channel is a linear project and inevitably passes through the expansive soil area. Research by numerous scholars shows that the expansive soil has the characteristics of fracture property, expansion and contraction property, strength attenuation property, hypercoagulability and the like, and is difficult to improve due to poor properties, so that the expansive soil is called cancer in the engineering field. In the process of channel operation, because the initial construction level of construction is not enough, an anti-seepage drainage system is not considered to be laid, and in addition, in the construction process, an anti-seepage film and a concrete lining plate are damaged, so that channel water infiltrates and is directly contacted with channel foundation expansive soil, and the stability of a channel slope is reduced; the channel forms obvious dry-wet alternation and freeze-thaw cycling action on the canal base expansive soil together with the characteristics of water supply and water cut-off of the channel and the climate along the channel such as high temperature in summer and severe cold in winter. Under the action of the environment, the expansive soil is obviously cracked, so that the engineering property of the expansive soil is degraded, thereby inducing the catastrophe of the side slope of the expansive soil channel and seriously influencing the water supply of a heavy economic area and a residential area.
The problem of treating the canal base expansive soil is mostly researched from the aspect of improving the stability of the canal base soil, and technologies such as modification, fiber addition, optimization grading, cement pile reinforcement and the like are successively provided to passively cope with some specific engineering technical problems of the expansive soil channel in the operation process.
Most of the prior methods for treating the canal-based expansive soil are traditional passive treatments such as soil body modification and seepage prevention improvement, but still have the defects of insufficient applicability in cold regions, complex treatment operation steps, higher cost, easy secondary pollution to the environment and the like; from the actual treatment effect, the phenomena of uneven settlement and liquid water enrichment of the soil body still exist, and the overall stability of the expansive soil channel is adversely affected.
Disclosure of Invention
The invention aims to provide a method for compositely treating an expansive soil channel in a cold region based on temperature control of a phase-change material, which aims to solve the problems in the prior art, and the temperature control material is applied to the expansive soil channel so as to actively regulate and control the internal temperature field of the expansive soil channel and further improve the overall stability of the channel; then taking the expansive soil channel phase-change temperature control processing technology as an entry point, and reinforcing the composite fibers to reduce the cracks of the channel expansive soil; and the bottom of the channel is provided with an efficient longitudinal and transverse drainage system to accelerate the drainage of the water leakage of the channel, and the method is a composite treatment technology for the expansive soil channel in the cold region, which integrates active treatment and passive treatment and has unified control, prevention, drainage and seepage phases, and has wide engineering application prospect.
In order to achieve the purpose, the invention provides the following scheme: the invention provides a method for compositely treating an expansive soil channel in a cold region based on temperature control of a phase-change material, which comprises the following steps of:
selecting a phase-change material, and testing the phase-change material to obtain the optimal doping amount of the phase-change material;
selecting a fiber material, and testing the fiber material to obtain the optimal doping amount of the fiber material;
performing a phase change temperature control composite fiber reinforced channel model test according to the optimal doping amount of the phase change material and the optimal doping amount of the fiber material to obtain the optimal doping depth of the phase change material and the optimal doping depth and an evolution rule of the fiber material;
constructing a channel longitudinal and transverse drainage system according to the actual situation on site, wherein the channel longitudinal and transverse drainage system is used for accelerating the drainage of water leakage in a channel;
and performing treatment on the expansive soil channel in the cold region based on the optimal doping depth of the phase-change material, the optimal doping depth and evolution law of the fiber material and the channel longitudinal and transverse drainage system.
Preferably, the phase change material test comprises a freeze-thaw cycle test and a thermal stability analysis test.
Preferably, the freeze-thaw cycle test comprises the steps of:
preparing a sample added with the phase-change material;
carrying out freeze-thaw cycling on the sample, and respectively carrying out volume deformation measurement, unconfined compressive strength test and microscopic test to obtain the volume deformation result, soil body mechanical index and surface porosity of the sample;
and obtaining the optimal doping amount of the phase-change material according to the volume deformation result, the soil body mechanical index and the surface porosity.
Preferably, the sample preparation comprises the steps of:
collecting engineering site soil, tedding the soil, rolling and sieving the tedded soil to obtain primary treated soil;
doping a phase change material with a certain proportion into the primary processing soil material and uniformly mixing to obtain sample soil, wherein the phase change material comprises mPCM and pPCM;
adding distilled water into the sample soil according to the preset water content of the sample, uniformly stirring, filling into a sealing bag, sealing for 24 hours, preparing the sample, and wrapping the sample for sealing.
Preferably, the volumetric deformation measurement comprises the steps of:
grouping the samples, each group comprising a plurality of the samples;
sequentially measuring the diameter and the height of three different positions of each sample in each group in the freezing and thawing process, and calculating the average diameter and the average height of each sample;
calculating the volume of each of said samples based on the average diameter and average height of each of said samples, and calculating the average volume of each of said samples based on each of said sample volumes.
Preferably, the unconfined compression strength test adopts an unconfined compression tester.
Preferably, the microscopic test comprises the following steps:
sampling the samples subjected to different freezing and thawing cycle times to obtain sample samples;
converting liquid water in pores of the sample into amorphous ice by adopting a liquid nitrogen vacuum cooling drying method;
sublimating the amorphous ice to obtain original gaps and structures of the sample, and carrying out image analysis on the original gaps and structures to obtain the surface porosity of the sample after different freezing and thawing times.
Preferably, the fiber material is tested through an unconfined compressive strength test and an electron microscope scanning test, so that the strength response rule of the same fiber material after different doping amounts and multiple dry-wet circulation actions is obtained, and the influence of different doping amounts of the fiber material on the compressive strength and the crack inhibition effect of the channel is proved.
Preferably, the changes of the temperature, the water content, the displacement and the pore water pressure of the channel are measured, the average values of the width, the length and the depth of the crack of the channel in different stages of wetting, drying, freezing and melting are collected, and the optimal doping depth of the phase-change material and the optimal doping depth of the fiber material are determined.
Preferably, the drainage system is moved about freely and quickly to the channel includes a plurality of header tanks, support campshed, drainage pipe way, the header tank set up respectively in the bottom and the bank slope of channel, the header tank passes through drainage pipe connects, support the campshed edge the side slope setting of channel.
The invention discloses the following technical effects:
the invention applies the phase-change temperature control material to the expansive soil channel to actively regulate and control the internal temperature field of the expansive soil channel, thereby improving the overall stability of the channel; taking an expansive soil channel phase-change temperature control treatment technology as an entry point, and adopting composite fibers for reinforcement to reduce cracks of the channel expansive soil; and the bottom of the channel is provided with an efficient longitudinal and transverse drainage system to accelerate the drainage of the water leakage of the channel, and the method is a composite treatment technology for the expansive soil channel in the cold region, which integrates active treatment and passive treatment and has unified control, prevention, drainage and seepage phases, and has wide engineering application prospect.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is a flow chart of a method for treating a cold region expansive soil channel based on phase change material temperature control compounding according to the invention;
FIG. 2 is a surface temperature distribution curve along a line from 11 months in 2013 to 11 months in 2014 in the example of the invention;
FIG. 3 is a schematic diagram of a method for measuring the height and diameter of a sample according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a phase change material resisting external temperature variation according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of a wet-dry freeze-thaw cycle model apparatus according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of a phase-change temperature-control composite fiber reinforced channel model according to an embodiment of the present invention;
FIG. 7 is a front view of a drainage system in an embodiment of the present invention;
FIG. 8 is a schematic view of comprehensive treatment of expansive soil channels in cold regions according to an embodiment of the present invention.
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.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
The invention provides a method for compositely treating an expansive soil channel in a cold region based on temperature control of a phase-change material, which takes northern Xinjiang water delivery channel engineering as an example and refers to a figure 1, and comprises the following steps of:
s1, selecting a phase-change material, and testing the phase-change material to obtain the optimal doping amount of the phase-change material.
Phase Change Materials (PCM) are used as a novel temperature control material, a large amount of latent heat can be generated through conversion between a solid Phase and a liquid Phase, the internal temperature field of a soil body can be regulated and controlled, the expansion and contraction characteristics of the soil body are reduced, and the stability of the soil body is further improved. The application adopts a Paraffin-based phase change material, which comprises two different forms of Microcapsule phase change materials (mPCM for short) and Paraffin-based liquid phase change materials (Paraffin-based liquid phase change materials for short). The pPCM is liquid at room temperature, and the enthalpy value is 258J/g; the mPCM is composed of two parts, namely a core material and a shell material, wherein the core material is pPCM, the shell material is melamine resin, the mass ratio of the core to the wall is about 9:1, the enthalpy value is 198.1J/g, the physical appearance of the mPCM is white to slightly white powder, and the particle size is 8-12 mm. The mPCM is very stable at high temperature, when the mPCM is heated to 200 ℃, the leakage rate is less than 1 percent, the expansion and contraction in the phase change process can be ignored, and the performance is stable at extremely high and low temperature.
In the embodiment, volume deformation test, unconfined compressive strength test, differential scanning calorimetry thermal cycle and electron microscope scanning test are carried out on the three types of expansive soil improved by pPCM and mPCM with different doping amounts, so that the change rule of the volume, mechanical property and thermal stability of the improved expansive soil under the action of freeze-thaw cycle is determined, the influence of different doping amounts of the phase-change material on the soil body strength and volume deformation of the expansive soil is proved, the optimal doping amount of the phase-change material is obtained, and the doping amount with the best effect on the soil body strength and volume deformation of the expansive soil is the optimal doping amount. The incorporation amounts in this example were 5%, 8% and 10%, respectively.
First, the sample used was prepared.
The sample is prepared by adopting a static pressure method, and certain improvement is made on the condition that an interlayer weak zone is easy to exist in the conventional layered compaction sample preparation method. The method comprises the following specific steps:
(1) and (3) tedding, naturally airing and rolling the soil material transported back from the engineering site, and screening the soil material by using a 2mm sieve to obtain the primarily treated soil material, wherein the initial water content of the primarily treated soil material is measured to be 3.71%.
(2) 5% of mPCM, 5% of pPCM, 8% of mPCM, 8% of pPCM, 10% of mPCM and 10% of pPCM were added to the primary treated soil according to the incorporation ratios (5%, 8% and 10% by weight of dry soil) of the test targets, and the incorporated soil was uniformly mixed to obtain 6 kinds of sample soils, respectively.
(3) And uniformly spraying the required distilled water into all the obtained sample soil by using a sprayer according to the preset water content of the sample, uniformly stirring, filling into a sealing bag, and sealing for 24 hours to uniformly distribute the water in the sample soil.
(4) And (5) preparing a sample by using an automatic sampling machine. Firstly, the weighed mixed soil material is carefully placed into a mould by using a paper cup and is uniformly stirred by using an iron rod, and then the equipment is started. The descending speed is controlled to be fast at the beginning, when the descending distance is close to 80mm, the speed is gradually slowed down, when the speed reaches 80mm, the speed stays for 30 seconds, the rebound of the sample is avoided, and the load is controlled to slowly rise. The above operation was repeated with the mould inverted, except that the drop depth was slightly greater than 80mm, since there was still a small amount of springback in the soil. And after the preparation of the sample is finished, taking out the sample by using an automatic stripper, wherein the whole process only needs to put the mould at a proper position, then start a switch, and take out the sample completely. In the preparation of the test specimens, the degree of compaction of all the obtained test specimens was controlled to 95%, the water contents of the test specimens for the volume deformation test were 10% and 20%, respectively, and the water contents of the remaining test specimens for the volume deformation test were 18.4%, the height of the test specimens was 80mm, and the diameter was 39.1 mm.
(5) And wrapping the prepared sample with a preservative film, grouping and numbering, and putting the sample into a sealing bag slightly larger than the sample for later use, so as to ensure that the sample is not contacted with the outside and avoid moisture loss.
And secondly, performing a freeze-thaw cycle test on the sample, measuring the volume deformation, unconfined compressive strength test and micro test of the sample in the freeze-thaw cycle process, and obtaining the volume deformation result, soil body mechanical index and surface porosity of the sample.
This embodiment uses a programmable high/low temperature tester to perform an indoor simulation test. Taking the surface temperature distribution of 2013-2014 observed in a certain meteorological station along the main canal section of the channel in northern Xinjiang as an example, the freezing and thawing process of the expansive soil channel in the cold region can be simplified into the trapezoidal temperature distribution, as shown in fig. 2, the environment temperature simplification control process shown in table 1 in the indoor simulation site environment temperature control process is finally determined according to the channel temperature change, and the freezing and thawing cycle times of the sample are designed to be 7.
TABLE 1
Measuring the volume deformation of the sample in the freeze-thaw cycle process to obtain the volume deformation result of the sample:
as the volume deformation of the samples in the process of freeze-thaw cycles has unevenness and minuteness, 5 parallel samples are arranged in each freeze-thaw cycle, as shown in FIG. 3, 3 diameter measurements are respectively carried out along the height 1/3 of each sample, 3 height measurements are respectively carried out along the vertical direction of the upper end surface and the lower end surface of each sample, and the average value of the diameter and the height of the samples is calculated by the following calculation method:
wherein the content of the first and second substances,
is the average diameter, D1、D2、D3Each of the diameters of 3 measurements were taken,
is the average height, H1、H2、H3Height of 3 measurements each.
Using the average of the diameter and height of each pattern according to the volume formula:
wherein V represents a volume. The volume of each sample was calculated, the volumes of 5 samples were calculated in sequence, and finally the average of the 5 sample volumes was taken as the test value. After the measurement of the size of the sample is finished every time, the sample is weighed by an electronic balance, the moisture change condition of the sample in the freezing-thawing cycle process is analyzed, and the loss of moisture and the test error caused by external supply are avoided.
Carrying out unconfined compressive strength test on the sample in the freeze-thaw cycle process to obtain the soil body mechanical index of the sample:
and performing an unconfined compressive strength test by using an unconfined compressive tester so as to obtain mechanical indexes of the expansive soil samples subjected to multiple freeze-thaw cycles under different mixing amounts, wherein the mechanical indexes include but are not limited to unconfined compressive strength, failure strain and mechanical attenuation coefficient. The unconfined compressive strength tests are respectively carried out on the samples (each group is provided with 3 parallel samples) subjected to the freeze-thaw cycle effects of 0 (initial state), 1, 3 and 7 times, the shear test is stopped when the axial strain reaches 20%, and the shear rate is 1 mm/min.
Carrying out a microscopic test on the sample in the freeze-thaw cycle process to obtain the surface porosity of the sample:
the microscopic test employs a galvano-mirror scanner. Cutting a soil sample with the volume of 8mm multiplied by 10mm from samples subjected to different freezing and thawing cycle times, adopting a liquid nitrogen vacuum cooling drying method to convert liquid water in soil pores into amorphous ice in a liquid nitrogen environment at the temperature of about 200 ℃ to keep the soil sample in an original state without expansion, putting the sample frozen by liquid nitrogen into a vacuum drier to sublimate the amorphous ice into vapor to be discharged, ensuring the original pores and structure of a soil body to the maximum extent, spraying a metal coating film on the sample, putting the metal coating film and a base into a sample area of a scanning electron microscope, adjusting the position of the sample, focusing the metal coating film near an observation area, and selecting a representative point to take a picture. Respectively carrying out electron microscope scanning on the modified soil with the PCM mixing amount of 0%, 5%, 8% and 10% after different freezing and thawing times, wherein the scanning times are set as 100, 1000 and 5000.
Quantitative analysis is carried out on the Image scanned by the electron microscope through Image processing software Image-Pro Plus (IPP), and relevant parameters of soil body pores, such as particle morphology, pore size, area and the like, can be extracted. And (3) selecting a proper threshold value to carry out binarization processing on the image under 100 times, and denoising and dividing the pores to obtain the surface porosity of the sample after different freezing and thawing times, namely the proportion of the pores on a certain plane of the soil body.
Carrying out a thermal stability analysis test on the sample to obtain the phase change temperature and latent heat of the sample with different doping amounts of the phase change material:
in the embodiment, Differential Scanning Calorimetry (DSC) is adopted to test the phase change temperature and latent heat of the improved soil of different phase change materials, a QL-2000 differential scanning calorimeter is adopted as a test instrument, the test temperature range is-160-700 ℃, a pneumatic diaphragm pump is configured, nitrogen is adopted for refrigeration, the flow of purge gas is kept between 8-12 mL/min, and the cooling and heating rates are set to be 5 ℃/min. The weight of the sample is 10 +/-2 mg, and the precision is 10-4g, weighing the sample by using a high-precision balance. At the start of the test, the temperature was lowered from room temperature to-23 ℃ for 2 minutes, raised to 22 ℃ and the sample was held at 22 ℃ for 2 minutes and then cooled to-23 ℃ to maintain the temperature range consistent with that of the freeze-thaw cycle samples.
Experiments show that in the whole freezing and thawing cycle test process, the pPCM does not show a good improvement effect due to leakage, so that the freezing and thawing performance of a soil body can be difficult to improve by directly doping the pPCM, and a doping method with lower pPCM leakage needs to be searched.
As can be analyzed, 5% of the mPCM content can reduce the volume change by about 9%, 8% of the mPCM content can reduce the volume change by about 34%, and the volume change reduction degree is increased to about 39% as the content is increased to 10%. The mPCM is a paraffin phase-change material which is stable in performance and wrapped by a high polymer material, can store or release heat in a latent heat mode in the process of freeze-thaw cycle to resist damage of external temperature change to a soil body, and the mPCM with lower content can inhibit attenuation of the freeze-thaw cycle to the strength of the soil body; meanwhile, the mPCM shell is made of a high polymer material and has certain brittleness, so that the effect of high doping amount is not good. 8% of the heat released by the MPCM phase change is "stored" between the soil particles, so that the latent heat of phase change of the expansive soil is reduced by about 10.93% respectively. Meanwhile, the widths of phase change peaks are slightly increased, and supercooling is slowed down to different degrees, which shows that in a test temperature interval, the formation of the ice lens is delayed by the doping and mechanical blending action of mPCM, and the ice lens is beneficial to improving the internal temperature field of the trench soil and improving the thermal stability of the soil body. The crack is slightly increased compared with the plain soil sample in the initial state by doping the mPCM, the increase of the pore after 7 times of freezing and thawing is obviously reduced compared with the plain soil, and the macroscopic expression is that the mechanical strength of the soil body is firstly reduced and then gradually increased along with the increase of the number of freezing and thawing cycles to be larger than that of the plain expansive soil.
Therefore, the 8% of the doping amount of the mPCM is selected to improve the freeze-thaw performance of the expansive soil, namely the 8% of the doping amount of the mPCM is determined to be the optimal doping amount through the test process.
As shown in fig. 4, the heat released and stored by PCM phase change resists the external temperature change, delays the formation of the ice lens, reduces the migration and freezing of free water among the soil particles, and weakens the frost heaving force of solid water, so that the clay mineral in the soil particles loses water, the soil particle shrinkage is reduced, and the pores among the soil particles become smaller; when the soil body melts, the clay minerals in the soil grains absorb water less because the frozen soil grains lose less water, the expansion rate of the soil grains is correspondingly reduced, and the change of the pores among the soil grains is further weakened. Therefore, the PCM stores or releases heat in a latent heat mode along with positive and negative fluctuation of the environmental temperature, can regulate and control the internal temperature field of the expansive soil sample, reduces expansion and shrinkage of soil particles and repeated freezing and thawing of pore water, and greatly slows down fatigue damage (pore coarsening, structure loosening and the like) of a soil microstructure.
S2, selecting a fiber material, and testing the fiber material to obtain the optimal doping amount of the fiber material.
By means of unconfined compressive strength test and electron microscope scanning test, the strength response rule after different fiber material mixing amount and multiple dry-wet circulation action is obtained, and the influence of different fiber material mixing amount on the compressive strength and the crack inhibiting effect is proved.
The basalt fiber used in this example was a strand-like fiber obtained by pressing a fiber filament having a diameter of 13 μm and a length of 6 mm. Before the fiber is mixed with soil, the strip fiber is torn off and then is uniformly mixed into the expansive soil body by a small mixer, so that the distribution form of the fiber in the expansive soil is random.
Setting a dry-wet circulation environment:
the wet process adopts an air pumping saturation method commonly used in soil mechanics experiments to pump the sample for 6 hours and soak the sample for 24 hours so as to ensure the saturation of the sample.
In the drying process, a natural air drying method is adopted to place the sample in a shade place, an electronic balance is adopted to monitor the mass, and when the mass is 0.7 times of the saturation value, the test is finished.
The results show that: the incorporation of basalt fibers converts soil from brittle failure to plastic failure. The basalt fiber mainly plays a role in lapping a three-dimensional grid structure or a bridge in the improved soil sample, and reduces the influence of dry-wet circulation on the pore damage of a soil body, so that the strength of the soil body is enhanced, and the development of channel cracks is reduced.
Through comprehensive analysis, basalt fibers with the doping amount of 0.75 percent are selected to inhibit the development of expansive soil cracks.
S3, performing a phase change temperature control composite fiber reinforced channel model test according to the optimal doping amount of the phase change material and the optimal doping amount of the fiber material, and obtaining the optimal doping depth of the phase change material and the optimal doping depth and evolution law of the fiber material.
First, preparing a test device:
the test equipment is a wet-dry freeze-thaw cycle model device, and mainly comprises a main model box, a water replenishing device, a temperature sensor, a refrigeration system and a heat source (bath heater) as shown in fig. 5.
The length, width and height of the model box are 120cm, 80cm and 80cm, in order to meet the strength of the model box and the observation requirements in the test, a steel plate with the thickness of 1cm is adopted as the framework of the model box, and 1cm of toughened glass is used as a baffle plate around the model box. Meanwhile, the periphery of the model box is wrapped by a sponge heat-insulating material with the thickness of 5cm, so that the channel model is ensured to be frozen in a one-way manner from top to bottom.
The drying system adopts an Opu bath heater and can generate mixed radiation similar to natural sunlight. It is often used for indoor test sunlight and sun simulation.
The refrigerating system is similar to a household refrigerator for refrigeration, a refrigerant is sucked by a compressor in a gaseous state, vapor compressed into high temperature and high pressure enters a condenser through an exhaust pipe, the refrigerant dissipates heat into outside air, is condensed into high pressure liquid, enters a capillary tube through a filter, is intercepted and depressurized, and enters an evaporator for vaporization.
Second, calculating the channel size of the model
The section of a reference northern Jiang expansive soil channel side slope is trapezoidal, the channel height is about 5m, the channel water depth is about 4m, and the slope ratio of the two side channels is 1: 2. And performing a small-scale slope model test on the phase change material and the basalt fiber improved soil with the determined optimal doping amount, wherein the proportion is 1: 10, and the doping depths are 5cm, 10cm and 15cm respectively.
Thirdly, manufacturing a channel model and embedding a sensor
In order to reduce the friction between the soil and the model box, a certain amount of vaseline is uniformly coated on the inner wall of the model box before the model is manufactured. And then determining the mass of the wet soil of each layer according to the compaction degree (95%) and the optimal water content of the plain soil. Adopting a hammering method to hammer expansive soil into a model box in 6 layers, wherein in order to avoid weak surfaces between layers, the previous layer needs to be roughened when the next layer is tamped, and in the tamping process, different types of sensors are embedded according to preset positions. In the phase-change temperature-control composite fiber reinforcement model test, a pore water pressure sensor, a water content sensor, a displacement sensor and a continuous temperature sensor need to be arranged for monitoring the saturation state, channel deformation and temperature in the model in real time and researching the stability evolution law of the phase-change material temperature-control basalt fiber reinforcement channel. Referring to fig. 6 for typical sensor arrangement, after a model test is finished, a soil sample is dried to test the moisture content, and a miniature cross plate shearing instrument is used for a strength test.
Step four, calculating the time required by the processes of wetting, drying, freezing and melting
Dividing the expansive soil channel in the cold region into a wet period and a dry period by taking the water supply and water cut-off time of the expansive soil channel in the cold region as a node; and dividing the expansive soil channel in the cold region into a melting period and a freezing period by taking the surface temperature positive temperature time and the surface temperature negative temperature time as nodes. In a complete wet-dry freeze-thaw cycle period from 2013 to 2014, "wet" is 139 days, "dry" is 57 days, "freeze" is 132 days, and "thaw" is 36 days. According to a similar theory, the duration of the corresponding time period is T — real/365 × 168. For example, in the wet-dry freeze-thaw cycle, the duration of each phase within 7 days is as follows: the wet time is 63.98h, the dry time is 26.24h, the frozen time is 60.76h, and the thawing time is 16.57h, wherein h is hour.
Fifth step, simulating the processes of ' wet ', ' dry ', ' freeze ' and ' melt
The channel model is first placed in a wet-dry freeze-thaw cycle model apparatus along with a model box. (1) And (5) opening the water replenishing device, and conveying water into the channel model according to the preset water level depth for 63.98 h. (2) And (3) closing the water replenishing device, opening a drain hole valve at the bottom of the model box to completely drain water in the channel, and then starting a drying system (bath heater) to control the temperature to be 40 ℃ and keep the temperature for 26.24 hours. (3) Then, the drying system is closed, the temperature control system is started, the temperature of the frozen state is controlled to be-22 ℃, and the duration time is 60.76 h; the temperature of the "melt" state was controlled at 22 ℃ for 16.57h, and then shut down. At this point, a complete cycle of wet-dry freeze-thaw cycles is completed, and 3 cycles are completed in sequence.
Sixth step, determining method of optimal doping depth of phase change material and basalt fiber
The temperature sensor, the water content sensor, the displacement sensor and the pore water pressure sensor read data every 3h in a longer period of a 'wet' stage and a 'freeze' stage, and read data every 1h in a shorter period of a 'dry' stage and a 'melt' stage. And respectively selecting 3cm multiplied by 3cm areas near the displacement sensor, opening the bath heater, observing the change of the crack by using a camera, selecting 4 cracks in the selected areas, measuring the width, the length and the depth of the crack every 3 hours, and taking the average value of the widths, the lengths and the depths. By analyzing the changes of the readings of the temperature sensor, the water content sensor, the displacement sensor and the pore water pressure sensor and the condition of crack development, the optimal doping depth and the evolution rule of the phase-change material and the basalt fiber can be determined.
S4, constructing a longitudinal and transverse drainage system of the channel, and arranging the efficient longitudinal and transverse drainage system at the bottom of the channel to accelerate the drainage of the water leakage of the channel according to the actual situation of the engineering site.
The long-distance water delivery channel bed is in a high water level soaking state for a long time, hidden dangers can be caused to engineering operation safety operation, and a three-dimensional seepage prevention and drainage system of the channel under different seepage conditions of the channel is further provided according to the aging and damage conditions of the seepage prevention film of the channel, as shown in figures 7-8.
In the embodiment, a water collecting well technology is adopted, and the main structure of the water collecting well consists of a water collecting tank, supporting row piles and a drainage pipeline. Two water collecting tanks are arranged at the bottom of the channel, 1 water collecting tank is arranged on the bank slope, and the water collecting tanks are used for temporarily storing accumulated water. And arranging a water collecting tank every 1km, and hoisting the tank wall by using a prefabricated large-caliber concrete pipe. Because the volume of the water collecting tank is limited, the water collecting tank at the bottom of the canal needs to be conveyed to the top of the canal through a drainage pipeline periodically, and then the water in the upper water collecting tank is discharged through a water pump.
Before the foundation of the water collection tank is excavated, the supporting row piles are required to support and protect the canal dikes on two sides, so that the canal dikes are prevented from collapsing during construction. When the excavation section is enough for two water collecting tank positions, the water collecting tank is required to be installed and the channel section is required to be recovered in time. After the construction is finished, the number of the water collecting tanks is required, and a joint with the longitudinal drainage body is reserved. And then the next water collecting well is constructed.
Wherein the size and the arrangement depth of the water collecting tank, the size of the longitudinal slope at the bottom of the canal and the like are specifically planned according to the actual situation of the canal engineering, and the water collecting tank can be generally set as the longitudinal slope 1/500 with the volume of 1-4 m3。
The invention aims to provide an active processing method, which aims to protect the normal operation of a channel on the basis of the channel field environment. The temperature control material (phase change material) is applied to the expansive soil channel to actively regulate and control the internal temperature field of the expansive soil channel, so that the overall stability of the channel is improved; then taking the expansive soil channel phase-change temperature control processing technology as an entry point, and reinforcing the composite fibers to reduce the cracks of the channel expansive soil; and the bottom of the channel is provided with an efficient longitudinal and transverse drainage system to accelerate the drainage of the water leakage of the channel, and the method is a composite treatment technology for the expansive soil channel in the cold region, which integrates active treatment and passive treatment and has unified control, prevention, drainage and seepage phases, and has wide engineering application prospect.
1. Temperature control of the phase-change material:
when the soil body is frozen, the heat released and stored by PCM phase change is resisted with the external temperature change, the formation of an ice lens is delayed, the migration and freezing of free water among soil particles are reduced, and the frost heaving force of solid water is weakened, so that the water loss of clay minerals in the soil particles is reduced, the shrinkage of the soil particles is reduced, and the pores among the soil particles are reduced; when the soil body melts, the clay minerals in the soil grains absorb water less because the frozen soil grains lose less water, the expansion rate of the soil grains is correspondingly reduced, and the change of the pores among the soil grains is further weakened. Therefore, the PCM stores or releases heat in a latent heat mode along with positive and negative fluctuation of the environmental temperature, can regulate and control the internal temperature field of the expansive soil sample, reduces expansion and shrinkage of soil particles and repeated freezing and thawing of pore water, and greatly slows down fatigue damage (pore coarsening, structure loosening and the like) of a soil microstructure.
2. Fiber reinforcement reduces the crack:
in the basalt fiber reinforced expansive soil, basalt fibers and soil particles are mutually wound and connected, and the generated friction action can improve the tensile strength of a soil body and reduce the shrinkage deformation of the soil body, so that the development of cracks of the soil body under the action of dry-wet circulation is inhibited.
3. Channel longitudinal and transverse drainage system:
the method has the advantages that a complete drainage system is established, a construction method is innovated, the anti-seepage capability of the structural joint is enhanced, the water delivery safety of the engineering under the complex geological condition is guaranteed, the water delivery capability is improved, the labor intensity is reduced, and the construction cost is saved.
In the description of the present invention, it is to be understood that the terms "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on those shown in the drawings, are merely for convenience of description of the present invention, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention.
The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solutions of the present invention can be made by those skilled in the art without departing from the spirit of the present invention, and the technical solutions of the present invention are within the scope of the present invention defined by the claims.
Claims (9)
1. A method for treating a cold region expansive soil channel based on phase change material temperature control compounding is characterized by comprising the following steps: the method comprises the following steps:
selecting a phase-change material, and testing the phase-change material to obtain the optimal doping amount of the phase-change material, wherein the phase-change material adopts a paraffin-based phase-change material and comprises a microcapsule phase-change material mPCM and a paraffin-based liquid phase-change material pPCM;
selecting a fiber material, and testing the fiber material to obtain the optimal doping amount of the fiber material;
performing a phase change temperature control composite fiber reinforced channel model test according to the optimal doping amount of the phase change material and the optimal doping amount of the fiber material to obtain the optimal doping depth of the phase change material and the optimal doping depth and an evolution rule of the fiber material;
constructing a channel longitudinal and transverse drainage system according to actual field conditions, wherein the channel longitudinal and transverse drainage system is used for accelerating drainage of leakage water in a channel, and comprises a plurality of water collection tanks, drainage pipes and supporting row piles, the water collection tanks are respectively arranged at the bottom of the channel and on a bank slope, the water collection tanks are connected through the drainage pipes, and the supporting row piles are arranged along the side slope of the channel;
and performing treatment on the expansive soil channel in the cold region based on the optimal doping depth of the phase-change material, the optimal doping depth and evolution law of the fiber material and the channel longitudinal and transverse drainage system.
2. The method for treating the expansive soil channel in the cold region based on the phase-change material temperature control compounding of claim 1, wherein the method comprises the following steps: the phase change material test comprises a freeze-thaw cycle test and a thermal stability analysis test.
3. The method for treating the expansive soil channel in the cold region based on the phase-change material temperature control compounding of claim 2, wherein the method comprises the following steps: the freeze-thaw cycle test comprises the following steps:
preparing a sample added with the phase-change material;
carrying out freeze-thaw cycling on the sample, and respectively carrying out volume deformation measurement, unconfined compressive strength test and microscopic test to obtain the volume deformation result, soil body mechanical index and surface porosity of the sample;
and obtaining the optimal doping amount of the phase-change material according to the volume deformation result, the soil body mechanical index and the surface porosity.
4. The method for treating the expansive soil channel in the cold region based on the phase-change material temperature control compounding of claim 3, wherein the method comprises the following steps: the sample preparation comprises the following steps:
collecting engineering site soil, tedding the soil, rolling and sieving the tedded soil to obtain primary treated soil;
doping a phase change material with a certain proportion into the primary processing soil material and uniformly mixing to obtain sample soil, wherein the phase change material comprises mPCM and pPCM;
adding distilled water into the sample soil according to the preset water content of the sample, uniformly stirring, filling into a sealing bag, sealing for 24 hours, preparing the sample, and wrapping the sample for sealing.
5. The method for treating the expansive soil channel in the cold region based on the phase-change material temperature control compounding of claim 4, wherein the method comprises the following steps: the volumetric deformation measurement comprises the following steps:
grouping the samples, each group comprising a plurality of the samples;
sequentially measuring the diameter and the height of three different positions of each sample in each group in the freezing and thawing process, and calculating the average diameter and the average height of each sample;
calculating the volume of each of said samples based on the average diameter and average height of each of said samples, and calculating the average volume of each of said samples based on each of said sample volumes.
6. The method for treating the expansive soil channel in the cold region based on the phase-change material temperature control compounding of claim 4, wherein the method comprises the following steps: the unconfined compression resistance test adopts an unconfined compression resistance instrument.
7. The method for treating the expansive soil channel in the cold region based on the phase-change material temperature control compounding of claim 4, wherein the method comprises the following steps: the microscopic test comprises the following steps:
sampling the samples subjected to different freezing and thawing cycle times to obtain sample samples;
converting liquid water in pores of the sample into amorphous ice by adopting a liquid nitrogen vacuum cooling drying method;
sublimating the amorphous ice to obtain original pores and structures of the sample, and carrying out image analysis on the original pores and structures to obtain the surface porosity of the sample after different freezing and thawing times.
8. The method for treating the expansive soil channel in the cold region based on the phase-change material temperature control compounding of claim 1, wherein the method comprises the following steps: the fiber material is tested through an unconfined compressive strength test and an electron microscope scanning test, the strength response rule of the fiber material after different doping amounts and multiple dry-wet circulation actions is obtained, and the influence of different doping amounts on the compressive strength and the crack inhibition effect of the channel is proved.
9. The method for treating the expansive soil channel in the cold region based on the phase-change material temperature control compounding of claim 1, wherein the method comprises the following steps: and measuring the changes of the temperature, the water content, the displacement and the pore water pressure of the channel, acquiring the average values of the width, the length and the depth of the crack of the channel in different stages of wetting, drying, freezing and melting, and determining the optimal doping depth of the phase-change material and the optimal doping depth of the fiber material.
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