Water pumping drainage type pressure steam pre-melting method and system for frozen soil region

Abstract

The invention discloses a water pumping drainage type pressure steam pre-melting method and system for a frozen soil region, and the method comprises the steps: investigating the fluctuating deformation condition of a road surface, selecting a road section with serious frost heaving, thaw collapse and differential settlement diseases, and determining the depth and range of a soil-containing ice layer; steam injection holes are formed above the soil-containing ice layer treatment layers on the two sides of the roadbed slope, and water pumping drainage holes are formed in the center of the roadbed; the steam generator is used for heating, steam is injected into the soil-containing ice layer, water pumping and drainage are conducted at the same time, and steam targeted ice melting is achieved; and during steam heating and water pumping, a geophysical prospecting method is adopted to monitor the pre-melting progress and effect. High-temperature steam is conveyed into the soil body through the steam pipe, when the high-temperature steam makes contact with the low-temperature soil body, heat conduction can occur, solid ice in frozen soil is melted, and after frozen soil and soil-containing ice layers within the climate warming and humidifying influence range are completely melted, the melting range is accurately controlled in a water pumping and drainage mode, and the frozen soil in the frozen soil and the soil-containing ice layers are fully melted. The foundation bearing capacity is improved, and the possibility of frozen soil melting settlement deformation is reduced.

Description

Technical Field

[0001] The invention relates to a water pumping and drainage type pressure steam pre-thawing method and system in a frozen soil area, belonging to the field of foundation treatment. Background Art

[0002] my country is the third largest country with frozen soil in the world. The permafrost area accounts for about 10% of the world's permafrost area and 22.3% of my country's total land area. The permafrost and seasonally frozen soil areas account for more than 70% of my country's total land area, mainly distributed in the northeast and western regions of my country. Frozen soil can be divided into seasonal frozen soil and permafrost according to the length of time the soil remains frozen. Seasonal frozen soil is affected by seasonality, freezing in winter and melting in summer in a cyclical freeze-thaw cycle; permafrost refers to a frozen state that lasts for two years or more, with a large freezing depth. The upper part of the permafrost is called the active layer, which is frozen in winter and melted in summer. According to the latest statistics, the areas of permafrost, seasonal frozen soil and unfrozen soil on the Qinghai-Tibet Plateau are 1.06×10^6 square kilometers (40%), 1.46×10^6 square kilometers (56%), and 0.03×10^6 square kilometers (1%) respectively. Affected by global warming and rising summer temperatures, the melting of the permafrost active layer interacts with the climate, and the Qinghai-Tibet Plateau has a clear warming trend. The warming rate in the past 40 years is about 2 times higher than the global warming rate in the same period. Existing research results show that the active layer in the hinterland of the Qinghai-Tibet Plateau has increased significantly, and the increase rate of the active layer in the Yellow River Basin and the Yangtze River Basin can reach 0.5~1.0cm / year, and the degradation of permafrost is showing an accelerating trend.

[0003] Frozen soil is an unstable soil that is extremely sensitive to temperature changes. Under the influence of climate change and human factors, it is extremely susceptible to thermal disturbances that cause the redistribution of the temperature field. In recent years, due to the influence of global warming, the Qinghai-Tibet Plateau has shown a significant trend of warming and wetting. The upper limit of frozen soil in high-temperature and high-ice-content frozen soil areas has gradually moved downward, and the accumulation of water on the surface and active layer has intensified. Linear projects such as railways and highways built on permafrost will inevitably change the surface conditions, resulting in changes in the surface radiation energy structure and the surface heat balance, which will in turn cause the thickness of the permafrost active layer at the bottom of the roadbed and near the foot of the slope to increase, the temperature of the frozen soil to rise, and even the melting of the permafrost, which will eventually lead to a decrease in the stability of engineering structures, roadbed settlement, road slurrying, longitudinal cracks in the road surface, uneven deformation waves in the road surface and other diseases. In order to prevent and control road diseases, new roadbed and pavement structures are generally adopted to ensure the stability of the roadbed in frozen areas. The roadbed structures adopted mainly include block stone roadbed, thermal rod roadbed, crushed stone slope roadbed and other engineering measures. However, from the perspective of long-term operation, these new roadbed structures still have serious frozen soil roadbed diseases. Therefore, it is urgent to develop a repair and control technology for roadbed diseases in frozen soil areas. Summary of the invention

[0004] The present invention provides a method and system for pre-thawing frozen soil by pumping and drainage pressure steam, which solves the problems disclosed in the background technology. The present invention is used for pre-thawing frozen soil in the roadbed area to be built, so as to avoid the occurrence of diseases caused by changes in the frozen soil during the service of the roadbed; it can also be used for repairing and treating diseases of roadbeds in service. For example, when the roadbed in service cracks, the method of the present invention is used to melt the expanded frozen soil layer and level the roadbed.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: A method for pre-thawing frozen soil by pumping and drainage pressure steam: Conduct geological surveys in the construction area to obtain the geological structure of the area; According to the geological structure of the region, calculate the changes in the active layer of the region; Determine the depth H and range of the treatment layer containing soil ice layer in the active layer of the roadbed area to be built according to the results of the active layer change; Laying steam pipes and water pumping pipes within the range of the soil-containing ice layer; The steam pipe is provided with a plurality of steam injection holes, one end of the steam pipe is connected to the steam generator, and the other end extends to the depth H of the treatment layer and is sealed; One end of the water pumping pipeline is connected to a water pump, and the other end extends to the depth H of the treatment layer; The steam generator injects steam into the soil-containing ice layer and frozen soil layer through the steam injection hole of the steam pipeline for pre-melting. The water generated during the pre-melting process is discharged through the water pump using the pumping pipeline; The pre-melting process of the soil-containing ice layer is monitored in real time until the soil-containing ice layer is pre-melted to the treatment layer depth H.

[0006] Furthermore, the method for calculating the change of the active layer in the area is as follows: the thickness of the active layer affected during the service life of the highway is calculated.

[0007] In order to survey the thickness of the soil-containing ice layer, is the growth rate of the active layer, and T is the service life of the highway.

[0008] Furthermore, a method for real-time monitoring of the pre-melting process of the soil-containing ice layer is to use a high-density electrical method to evaluate the pre-melting effect and range in real time.

[0009] Furthermore, the methods for real-time evaluation of the pre-ablation effect and range using high-density electrical method include: Laying a high-density electrical method test line above the soil-containing ice layer treatment layer; Invert formation information based on high-density electrical test results to determine the scope and direction of steam melt water; At preset intervals, the thickness reduction of the soil-containing ice layer before and after treatment is compared; After a period of steam pre-melting, the residual thickness of the ice layer containing soil is calculated; When the lower limit of the thickness range of the soil-containing ice layer after pre-melting treatment reaches the treatment layer depth H, the pre-melting treatment is completed.

[0010] The present invention also provides a frozen soil area pumping and drainage type pressure steam pre-thawing system, comprising: The geological exploration module is used to conduct geological exploration of the construction area and obtain the geological structure of the area; The active layer calculation module is used to calculate the changes of the active layer in the region according to the geological structure of the region; The processing layer depth module is used to determine the depth H and range of the processing layer containing the soil ice layer in the active layer of the roadbed area to be built according to the active layer change results; The steam pre-melting module is provided with a steam pipe and a steam generator; a plurality of steam injection holes are arranged on the steam pipe, one end of the steam pipe is connected to the steam generator, and the other end extends to the depth H of the treatment layer and is sealed; the steam generator injects steam into the soil-containing ice layer and the frozen soil layer through the steam injection holes of the steam pipe for pre-melting; The pumping module is provided with a water pump and a pumping pipe; one end of the pumping pipe is connected to the water pump, and the other end extends to the depth H of the treatment layer; the water generated during the pre-melting process is discharged through the water pump using the pumping pipe; The monitoring module is used to monitor the pre-melting process of the soil-containing ice layer in real time until the soil-containing ice layer is pre-melted to the processing layer depth H.

[0011] Furthermore, the steam pipe is provided with steam injection holes every 30 to 50 cm.

[0012] Furthermore, the construction area includes a roadbed to be built, and the steam pipelines are distributed on both sides of the slope of the roadbed to be built.

[0013] Furthermore, the water pumping pipeline is located in the center of the roadbed to be built.

[0014] The beneficial effects achieved by the present invention are: The present invention transports high-temperature steam into the soil through a steam pipe. When the high-temperature steam contacts the low-temperature soil, heat conduction occurs, causing the solid ice inside the frozen soil to melt. After all the ice-rich frozen soil and soil-containing ice layers within the range affected by climate warming and humidification are melted, the melting range is accurately controlled by pumping water, thereby improving the bearing capacity of the foundation and reducing the possibility of melting, settlement and deformation of frozen soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the process of the water pumping and drainage type pressure steam pre-thawing method in frozen soil areas of the present invention; Figure 2 This is a schematic diagram of the structure of the water pumping and drainage type pressure steam pre-thawing system in frozen soil areas of the present invention; Figure 3 It is a schematic diagram of the positions of the steam injection hole and the water pumping hole in the present invention; Figure 4 This is a comparison diagram of the strata before (left) and after (right) pre-melting inversion using the high-density electrical method of the present invention. DETAILED DESCRIPTION

[0016] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention. Example

[0017] like Figure 1 As shown, this embodiment provides a water pumping and drainage pressure steam pre-thawing method in a frozen soil area, comprising the following steps: Conduct geological surveys in the construction area to obtain the depth and thickness of the soil-containing ice layer and ice-rich frozen soil, the upper limit of the frozen soil, and determine the repair location; Geophysical exploration uses high-density electrical methods to obtain formation resistivity distribution maps through formation inversion information; Compare the geological survey drilling data to determine the depth and range of the active layer and permafrost layer; Combined with regional meteorological data, determine the growth rate of the active layer in the permafrost area and calculate its range of change; The thickness of active layer affected during the service life of the highway ; In the formula, In order to obtain the thickness of the active layer, is the growth rate of the active layer, which is taken as 0.5~1.0cm / year with reference to the growth rate in the Yellow River Basin, and T is the service life of the highway, which is taken as 15 years; Based on the comprehensive survey results and the predicted changes in the active layer depth, the depth H of the soil-containing ice layer treatment layer is determined; the depth H of the soil-containing ice layer treatment layer is the lower limit of the soil-containing ice layer; Steam pipes are laid on both sides of the slope of the roadbed to be built; The steam pipeline is buried to the soil-ice layer treatment layer H, and the bottom is sealed; Steam injection holes are drilled every 30-50 cm on the steam pipe as steam target outlets; Lay out water pumps and water pumping pipes in the center of the roadbed to be built; The buried depth of the pumping pipeline is to the depth H of the soil-ice treatment layer; The steam pipeline is connected to the steam generator, the steam generator is turned on, water is added and heated to generate steam; Steam is injected into the ice-containing soil layer and the frozen soil layer through the steam pipeline, and the injection pressure is about 600kPa; When steam is injected, the water pump is turned on to pump out water; While injecting steam and pumping water, high-density electrical method is used to evaluate the pre-melting effect and scope in real time; Lay a high-density electrical test line above the roadbed soil-containing ice layer treatment layer for testing; Invert formation information based on high-density electrical test results to determine the scope and direction of steam melt water; Every 1 hour, the thickness reduction of the soil-containing ice layer before and after treatment was compared; After 10 h of steam pre-melting, calculate the residual thickness of the ice layer containing soil; According to the inversion stratigraphic information from geophysical exploration, the thickness reduction of the frozen soil active layer can be determined; When the lower limit of the soil-containing ice layer after pre-melting treatment reaches the preset treatment layer depth H, the pre-melting treatment is considered to be completed; Stop injecting steam and continue pumping water for 2 hours until all the melt water is pumped out.

[0018] In order to verify the reliability of this method, the drop curve and flow rate formed by the melt water flow are calculated and compared with those before melting. The calculation process is as follows: Record the steam injection volume and water pumping volume, calculate the ice melting efficiency, and calculate the melt water and water pumping volume according to the following formula; According to Darcy's law, V=KJ, where v is the seepage velocity; K is the permeability coefficient; J is the hydraulic gradient; According to the Dupuit hypothesis, the hydraulic head does not change with depth, and the hydraulic gradient and infiltration rate at each point on the same vertical profile are The penetration rate can be expressed as: ; Where x is the horizontal distance from the steam injection hole; is the hydraulic head function; In the time ∆t, the difference in water volume between the water flow from the frozen ground melting on one side and the water flow pumped out on the other side is: ; Where q is the single-width flow rate of meltwater flow; is the horizontal distance between the calculation section and the steam injection hole; h is the thickness of the submerged flow in the calculation section; In the time ∆t, the vertical recharge is W∆x∆t, where W is the infiltration recharge per unit area. According to the continuity principle, the total change in the amount of water in the soil during the time ∆t is equal to the increment of the water volume in the soil caused by the change in the water surface, that is: ; In the formula, is the water supply degree or dynamic viscosity coefficient; Substituting the above equation, we get the basic equation for the unsteady movement of groundwater in a phreatic aquifer: the Boussinesq equation: ; Take a unit width of a section along the water flow direction and establish a mathematical model: ; Where h1 and h2 are the thickness of the phreatic current at the meltwater and pumping locations, respectively; By integrating and solving the above equation, we can obtain the equation of the fall curve of the frozen soil melting water flow: ; Where, L is the distance between the meltwater starting point and the pumping point; Finally, the cross-sectional water flow rate is obtained according to Darcy's law : ; . Example

[0019] like Figure 2 As shown, this embodiment provides a frozen soil area pumping and drainage type pressure steam pre-thawing system, comprising: The geological exploration module is used to conduct geological exploration of the construction area and obtain the geological structure of the area; The active layer calculation module is used to calculate the changes of the active layer in the region according to the geological structure of the region; The processing layer depth module is used to determine the depth H and range of the processing layer containing the soil ice layer in the active layer of the roadbed area to be built according to the active layer change results; The steam pre-melting module is provided with a steam pipe and a steam generator; a plurality of steam injection holes are arranged on the steam pipe, one end of the steam pipe is connected to the steam generator, and the other end extends to the depth H of the treatment layer and is sealed; the steam generator injects steam into the soil-containing ice layer and the frozen soil layer through the steam injection holes of the steam pipe for pre-melting; The pumping module is provided with a water pump and a pumping pipe; one end of the pumping pipe is connected to the water pump, and the other end extends to the depth H of the treatment layer; the water generated during the pre-melting process is discharged through the water pump using the pumping pipe; The monitoring module is used to monitor the pre-melting process of the soil-containing ice layer in real time until the soil-containing ice layer is pre-melted to the processing layer depth H.

[0020] The steam pipe is provided with steam injection holes every 30 to 50 cm.

[0021] The construction area includes a roadbed to be built, and the steam pipelines are distributed on both sides of the slope of the roadbed to be built.

[0022] The pumping pipeline is located in the center of the roadbed to be built. A filter screen can be arranged at the water inlet of the pumping pipeline.

[0023] In addition, temporary steel sheet piles can be set at the edge of the pre-melting area for water stopping according to actual needs.

[0024] like Figure 3 As shown, the steam injection hole is centrally diffused, and the water extraction holes are distributed around the steam injection hole. This distribution method can improve the efficiency of pre-melting and water extraction.

[0025] like Figure 4 As shown, the monitoring module uses high-density electrical method to evaluate the progress of steam pre-thawing and the efficiency of frozen soil thawing in real time. According to the geophysical inversion results, if there is no obvious frozen soil distribution within the preset processing range, it is considered that the pre-thawing is completed.

[0026] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

[0027] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the scope of the claims of the present invention to be approved.

Claims

1. A water pumping and drainage pressure steam pre-thawing method in frozen soil areas, characterized in that: Conduct geological surveys in the construction area to obtain the geological structure of the area; According to the geological structure of the region, calculate the changes in the active layer of the region; Determine the depth H and range of the treatment layer containing soil ice layer in the active layer of the roadbed area to be built according to the results of the active layer change; Laying steam pipes and water pumping pipes within the range of the soil-containing ice layer; The steam pipe is provided with a plurality of steam injection holes, one end of the steam pipe is connected to the steam generator, and the other end extends to the depth H of the treatment layer and is sealed; One end of the water pumping pipeline is connected to a water pump, and the other end extends to the depth H of the treatment layer; The steam generator injects steam into the soil-containing ice layer and frozen soil layer through the steam injection hole of the steam pipeline for pre-melting. The water generated during the pre-melting process is discharged through the water pump using the pumping pipeline; The pre-melting process of the soil-containing ice layer is monitored in real time until the soil-containing ice layer is pre-melted to the treatment layer depth H.

2. The method for pre-thawing frozen soil areas by pumping and drainage type pressure steam according to claim 1, characterized in that: The method for calculating the change of the active layer in this area is to calculate the thickness of the active layer affected during the service life of the highway. ; In order to survey the thickness of the soil-containing ice layer, is the growth rate of the active layer, and T is the service life of the highway.

3. The method for pre-thawing frozen soil areas by pumping and drainage type pressure steam according to claim 1, characterized in that: The method for real-time monitoring of the pre-melting process of the soil-containing ice layer is to use high-density electrical method to evaluate the pre-melting effect and scope in real time.

4. The method for pre-thawing frozen soil areas by pumping and drainage type pressure steam according to claim 3, characterized in that: Methods for real-time evaluation of pre-ablation effect and range using high-density electrical methods include: Laying a high-density electrical method test line above the soil-containing ice layer treatment layer; Invert formation information based on high-density electrical test results to determine the scope and direction of steam melt water; At preset intervals, the thickness reduction of the soil-containing ice layer before and after treatment is compared; After a period of steam pre-melting, the residual thickness of the ice layer containing soil is calculated; When the lower limit of the thickness range of the soil-containing ice layer after pre-melting treatment reaches the treatment layer depth H, the pre-melting treatment is completed.

5. A water-pumping and drainage pressure steam pre-thawing system for frozen soil areas, characterized in that: include: The geological exploration module is used to conduct geological exploration of the construction area and obtain the geological structure of the area; The active layer calculation module is used to calculate the changes of the active layer in the region according to the geological structure of the region; The processing layer depth module is used to determine the depth H and range of the processing layer containing the soil ice layer in the active layer of the roadbed area to be built according to the active layer change results; The steam pre-melting module is provided with a steam pipe and a steam generator; a plurality of steam injection holes are arranged on the steam pipe, one end of the steam pipe is connected to the steam generator, and the other end extends to the depth H of the treatment layer and is sealed; the steam generator injects steam into the soil-containing ice layer and the frozen soil layer through the steam injection holes of the steam pipe for pre-melting; The pumping module is provided with a water pump and a pumping pipe; one end of the pumping pipe is connected to the water pump, and the other end extends to the depth H of the treatment layer; the water generated during the pre-melting process is discharged through the water pump using the pumping pipe; The monitoring module is used to monitor the pre-melting process of the soil-containing ice layer in real time until the soil-containing ice layer is pre-melted to the processing layer depth H.

6. The frozen soil area pumping and drainage pressure steam pre-thawing system according to claim 5 is characterized by: The steam pipe is provided with steam injection holes every 30 to 50 cm.

7. The frozen soil area pumping and drainage type pressure steam pre-thawing system according to claim 5 is characterized by: The construction area includes a roadbed to be built, and the steam pipelines are distributed on both sides of the slope of the roadbed to be built.

8. The frozen soil area pumping and drainage pressure steam pre-thawing system according to claim 6 is characterized by: The water pumping pipeline is located in the center of the roadbed to be built.

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