A method and system for pressure steam pre-melting by pumping and draining in permafrost regions

Abstract

The application discloses a kind of frozen soil area pumping drainage type pressure steam pre-melting method and system, comprising: surveying the deformation of surface, selecting frost heaving and uneven settlement disease serious road section, determining the depth and range of soil ice layer;Steam injection hole is arranged above the soil ice layer treatment layer on the side of roadbed slope, pumping drainage hole is arranged in the center of roadbed;Steam generator is heated and injected into soil ice layer, while pumping drainage, steam target melting ice is realized;While steam heating and pumping, monitoring pre-melting progress and effect are carried out using geophysical prospecting method.The high-temperature steam is transported to the interior of soil body by steam pipe, when high-temperature steam contacts with low-temperature soil body, heat conduction occurs, solid ice in the interior of frozen soil melts, after all the ice-rich frozen soil and soil ice layer in the climate warm and humid influence range are melted, the melting range is accurately controlled by pumping drainage, the bearing capacity of foundation is improved, and the possible deformation of frozen soil melting settlement is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to a frozen soil area pumping drainage type pressure steam pre-melting method and system, belonging to the field of foundation treatment. BACKGROUND

[0002] China is the third largest frozen soil country in the world, with permafrost area accounting for about 10% of the world's permafrost area, 22.3% of China's total land area, and more than 70% of China's total land area in permafrost and seasonal frozen soil area, mainly distributed in the northeast and west of China. 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 seasons, freezing in winter and thawing in summer, and is in a periodic freezing and thawing cycle. Permafrost refers to the frozen state lasting for two years or more, with a large frozen depth. The upper part of permafrost is called active layer, which is in a state of freezing in winter and thawing 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. Influenced by global warming and rising summer temperatures, the active layer of permafrost on the Qinghai-Tibet Plateau is melting and interacting with the climate, and the warming trend is obvious, with a rate 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 active layer in the Yellow River and Yangtze River basins has increased at a rate of 0.5~1.0 cm / year, and the degradation of permafrost is accelerating.

[0003] Frozen soil is a kind of unstable soil body that is extremely sensitive to temperature changes. Under the influence of climate change and human factors, it is extremely susceptible to thermal disturbance, which causes redistribution of temperature field. In recent years, influenced by global warming, the Qinghai-Tibet Plateau has shown a significant warming and humidification trend, the upper limit of frozen soil in high-temperature and high-ice-content frozen soil areas has gradually moved down, and the surface and active layer water has intensified. Linear engineering such as railway and highway built on permafrost will inevitably change the surface conditions, leading to changes in surface radiation energy structure and surface heat budget, and further causing the active layer thickness of permafrost under the roadbed and near the slope toe to increase, the frozen soil temperature to rise, and even the permafrost to melt, ultimately leading to a decrease in the stability of engineering structures, roadbed subsidence, road slurry, road surface longitudinal cracks, and uneven deformation waves. In order to prevent and control road diseases, new roadbed and pavement structures are generally adopted to ensure the stability of frozen soil areas. The roadbed structures mainly include block stone roadbed, thermal rod roadbed, and gravel slope roadbed engineering measures. However, from the long-term operation effect, these new roadbed structures still have serious frozen soil roadbed diseases. Therefore, it is urgent to develop a repair and treatment technology for frozen soil area in-service highway roadbed diseases. SUMMARY

[0004] The application provides a frozen soil area water pumping and drainage type pressure steam pre-melting method and system, which solves the problems disclosed in the background art. The application is used for pre-melting the frozen soil layer in the area where the roadbed is to be built, so as to avoid diseases caused by the change of the frozen soil layer during the service of the roadbed. The application can also be used for repairing and treating the diseases of the in-service roadbed, for example, when the in-service roadbed expands and cracks, the application is used to melt the expanded frozen soil layer and level the roadbed.

[0005] In order to solve the above technical problems, the technical scheme adopted by the application is:

[0006] A frozen soil area water pumping and drainage type pressure steam pre-melting method comprises the following steps:

[0007] Geological exploration is performed on the construction area to obtain the geological structure of the area;

[0008] According to the geological structure of the area, the change of the active layer in the area is calculated;

[0009] According to the change result of the active layer, the treatment layer depth H and the range of the soil ice layer in the active layer of the area where the roadbed is to be built are determined;

[0010] Steam pipes and water pumping pipes are arranged in the range of the soil ice layer;

[0011] A plurality of steam injection holes are arranged on the steam pipes, one end of the steam pipes is connected to a steam generator, and the other end of the steam pipes extends to the treatment layer depth H and is subjected to hole sealing treatment;

[0012] One end of the water pumping pipes is connected to a water pump, and the other end of the water pumping pipes extends to the treatment layer depth H;

[0013] The steam generator injects steam into the soil ice layer and the frozen soil layer through the steam injection holes of the steam pipes for pre-melting, and the water generated in the pre-melting process is discharged through the water pumping pipes by the water pump;

[0014] The pre-melting process of the soil ice layer is monitored in real time until the soil ice layer is pre-melted to the treatment layer depth H.

[0015] Further, 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 period of the road is calculated

[0016] The thickness of the soil ice layer is obtained through surveying, The growth rate of the active layer is T, and T is the service period of the road.

[0017] Further, the method for monitoring the pre-melting process of the soil ice layer in real time is as follows: high-density electrical method is used to evaluate the pre-melting effect and range in real time.

[0018] Further, the method for evaluating the pre-melting effect and range in real time by using the high-density electrical method comprises:

[0019] laying a high-density electrical testing line above the soil ice layer treatment layer;

[0020] inversion of stratum information according to the high-density electrical testing result, judgment of the steam melting water range and trend;

[0021] every preset time, comparing the thickness reduction amount before and after the soil ice layer treatment;

[0022] after a period of steam pre-melting, calculating the residual thickness of the soil ice layer;

[0023] when the lower limit of the soil ice layer thickness range after the pre-melting treatment reaches the treatment layer depth H, the pre-melting treatment is completed.

[0024] The application also provides a frozen soil area water pumping drainage type pressure steam pre-melting system, comprising:

[0025] a geological exploration module for geological exploration of a construction area to obtain the geological structure of the area;

[0026] a active layer calculation module for calculating the active layer change of the area according to the geological structure of the area;

[0027] a treatment layer depth module for determining the treatment layer depth H and range of the soil ice layer in the active layer of the area to be built roadbed according to the active layer change result;

[0028] a steam pre-melting module provided with a steam pipeline and a steam generator; a plurality of steam injection holes are arranged on the steam pipeline, one end of the steam pipeline is connected with the steam generator, the other end of the steam pipeline extends to the treatment layer depth H and is subjected to hole sealing treatment; the steam generator injects steam into the soil ice layer and the frozen soil layer through the steam injection holes of the steam pipeline for pre-melting;

[0029] a water pumping module provided with a water pump and a water pumping pipeline; one end of the water pumping pipeline is connected with the water pump, and the other end of the water pumping pipeline extends to the treatment layer depth H; the water generated in the pre-melting process is discharged through the water pump and the water pumping pipeline;

[0030] a monitoring module for real-time monitoring of the pre-melting process of the soil ice layer until the soil ice layer is pre-melted to the treatment layer depth H.

[0031] Further, the steam injection holes are arranged on the steam pipeline every 30-50 cm.

[0032] Further, the construction area includes the to-be-built roadbed, and the steam pipeline is distributed on both sides of the to-be-built roadbed slope.

[0033] Further, the water pumping pipeline is located in the center of the to-be-built roadbed.

[0034] The application has the following beneficial effects:

[0035] The present application transports high-temperature steam into the soil body through a steam pipe, and when the high-temperature steam contacts the low-temperature soil body, heat conduction occurs, causing the solid ice inside the frozen soil to melt, and after the ice-rich frozen soil and the soil ice layer within the climate warming and humidification influence range are completely melted, the melting range is precisely controlled through water pumping and drainage, the bearing capacity of the foundation is improved, and the possibility of frozen soil melting and settlement deformation is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 Fig. 1 is a flowchart of the frozen soil area water pumping and drainage type pressure steam pre-melting method of the present application;

[0037] Figure 2 Fig. 2 is a structural diagram of the frozen soil area water pumping and drainage type pressure steam pre-melting system of the present application;

[0038] Figure 3 Fig. 3 is a diagram showing the positions of the steam injection hole and the water pumping hole in the present application;

[0039] Figure 4 Fig. 4 is a comparison chart of the stratum before pre-melting (left) and after pre-melting (right) by high-density electrical method inversion in the present application. DETAILED DESCRIPTION

[0040] The present application will be further described below in conjunction with the drawings. The following examples are only used to more clearly illustrate the technical solutions of the present application, and cannot be used to limit the protection scope of the present application. EMBODIMENT

[0041] As shown in Fig. 1, the present embodiment provides a frozen soil area water pumping and drainage type pressure steam pre-melting method, which comprises the following steps: Figure 1

[0042] Geological exploration is carried out in the construction area to obtain the depth and thickness of the soil ice layer and the ice-rich frozen soil, the upper limit position of the frozen soil, and to determine the repair position;

[0043] Geophysical exploration adopts high-density electrical method to obtain the stratum resistivity distribution map through stratum inversion information;

[0044] The active layer and the permanent frozen soil layer depth and range are determined by comparing the geological exploration drilling data;

[0045] The active layer growth rate in the frozen soil area is determined in combination with the regional meteorological data, and the change range is calculated;

[0046] The active layer thickness affected during the service period of the highway ;

[0047] In the formula, is the active layer thickness obtained by surveying, ​For the growth rate of active layer, reference is made to the growth rate of the Yellow River Basin, and 0.5-1.0 cm / year is taken; T is the service period of the highway, and 15 years is taken;

[0048] Based on the comprehensive survey results and the predicted depth change of the active layer, the depth H of the soil ice layer treatment layer is determined; the depth H of the soil ice layer treatment layer is the lower limit of the soil ice layer;

[0049] Steam pipes are arranged on both sides of the to-be-built roadbed slope;

[0050] The steam pipes are buried to the depth H of the soil ice layer treatment layer, and the bottom is subjected to hole sealing treatment;

[0051] Steam injection holes are punched every 30-50 cm of the steam pipes, serving as steam targeting outlets;

[0052] A water pump and a water pumping pipe are arranged in the center of the to-be-built roadbed;

[0053] The water pumping pipe is buried to the depth H of the soil ice layer treatment layer;

[0054] The steam pipes are connected to a steam generator, the steam generator is opened, water is added and heated to generate steam;

[0055] The ice-containing soil layer and the frozen soil layer are injected with steam through the steam pipes, and the injection pressure is about 600 kPa;

[0056] The steam injection is simultaneously performed with the opening of the water pumping pump for water pumping and drainage;

[0057] While the steam injection and water pumping are performed, high-density electrical method is used to evaluate the pre-melting effect and range in real time;

[0058] A high-density electrical method test line is laid on the soil ice layer treatment layer of the roadbed, and testing is performed;

[0059] Based on the high-density electrical method test results, stratum information is inversed, and the steam melting water range and trend are determined;

[0060] Every 1 h, the thickness reduction amount of the soil ice layer before and after the treatment is compared;

[0061] After 10 h of steam pre-melting, the residual thickness of the soil ice layer is calculated;

[0062] Based on the geophysical inversion stratum information, the reduction thickness of the active layer of frozen soil is determined;

[0063] When the lower limit of the soil ice layer after the pre-melting treatment reaches the preset treatment layer depth H, it is considered that the pre-melting treatment is completed;

[0064] The steam injection is stopped, and the water pumping is continuously maintained for 2 h until all the melting water is pumped out.

[0065] To verify the reliability of the method, the drawdown curve and flow rate of the thawing water flow are calculated and compared with those before thawing, and the calculation process is as follows:

[0066] The steam injection amount and pumping amount are recorded, the ice melting efficiency is calculated, and the thawing water and pumping water amount are calculated according to the following formula:

[0067] According to Darcy's law V=KJ, wherein v is the seepage velocity; K is the permeability coefficient; and J is the hydraulic gradient;

[0068] According to the Dupuit assumption, the water head does not change with the depth, the hydraulic gradient and the seepage velocity of each point on the same vertical section are equal, and the seepage velocity can be represented as:

[0069] wherein x is the horizontal distance from the steam injection hole;

[0070] ;

[0071] wherein x is the horizontal distance from the steam injection hole; is the water head function;

[0072] The water amount difference between the thawing water flow from one side of the frozen soil and the water flow pumped out from the other side in At time is:

[0073] ;

[0074] wherein q is the unit width flow rate of the thawing water flow; is the horizontal distance of the calculation section from the steam injection hole; h is the phreatic flow thickness of the calculation section;

[0075] The vertical direction recharge amount in At time is WΔxΔt, W is the unit area recharge amount, and according to the continuity principle, the total change of the water amount in the soil body in At time is equal to the increment of the water volume in the soil body caused by the water surface change, that is:

[0076] ;

[0077] wherein is the specific yield or dynamic viscosity coefficient;

[0078] Substituting the above formula, the basic equation of the unsteady motion of the groundwater in the phreatic aquifer is obtained: Boussinesq equation:

[0079] ;

[0080] A mathematical model is established along the unit width of a section in the water flow direction:

[0081] ;

[0082] wherein h1 and h2 are the phreatic flow thicknesses of the thawing water and the pumping water, respectively;

[0083] Integrating the above equation, the falling curve equation of the water flow in the thawing soil is obtained:

[0084] ;

[0085] In the formula, L is the distance between the water starting point and the pumping point.

[0086] Finally, the water flow of the section is obtained according to the Darcy law :

[0087] ;

[0088] . Embodiment

[0089] As Figure 2 shown, the embodiment provides a thawing soil area pumping drainage type pressure steam pre-thawing system, comprising:

[0090] A geological exploration module is configured to perform geological exploration on a construction area to obtain a geological structure of the area.

[0091] An active layer calculation module is configured to calculate active layer changes in the area according to the geological structure of the area.

[0092] A treatment layer depth module is configured to determine a treatment layer depth H and a range of soil ice layers in the active layer of a to-be-built roadbed area according to the active layer change result.

[0093] A steam pre-thawing module is provided with a steam pipeline and a steam generator. A plurality of steam injection holes are arranged on the steam pipeline. One end of the steam pipeline is connected to the steam generator, and the other end of the steam pipeline extends to the treatment layer depth H and is subjected to hole sealing treatment. The steam generator injects steam into the soil ice layers and the frozen soil layers through the steam injection holes of the steam pipeline for pre-thawing.

[0094] A water pumping module is provided with a water pump and a water pumping pipeline. One end of the water pumping pipeline is connected to the water pump, and the other end of the water pumping pipeline extends to the treatment layer depth H. The water generated during the pre-thawing process is discharged through the water pumping pipeline by the water pump.

[0095] A monitoring module is configured to monitor the pre-thawing process of the soil ice layers in real time until the soil ice layers are pre-thawed to the treatment layer depth H.

[0096] The steam injection holes of the steam pipeline are arranged every 30-50 cm.

[0097] The construction area includes a to-be-built roadbed, and the steam pipeline is distributed on both sides of the to-be-built roadbed slope.

[0098] The water pumping pipeline is located in the center of the to-be-built roadbed. A filter screen can be arranged at the water inlet of the water pumping pipeline.

[0099] In addition, temporary steel sheet piles can be arranged at the edge of the pre-fusion area to prevent water leakage according to actual needs.

[0100] As shown in Figure 3 The steam injection holes are centrally dispersed, and the water pumping holes are distributed around the steam injection holes, which can improve the efficiency of pre-fusion and water pumping.

[0101] As shown in Figure 4 The monitoring module uses high-density electrical method to evaluate the progress of steam pre-fusion and the efficiency of frozen soil melting in real time. According to the geophysical inversion result, it is considered that the pre-fusion is completed if there is no obvious frozen soil distribution in the preset treatment range.

[0102] The above only describes the preferred embodiments of the present application. It should be noted that, for those skilled in the art, without departing from the technical principles of the present application, a number of improvements and modifications can be made, and these improvements and modifications should be considered as the protection scope of the present application.

[0103] The above only describes the embodiments of the present application and is not used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the scope of the claims of the present application.

Claims

1. A method for thawing soil area by pumping water and draining steam, characterized in that: geological exploration is conducted in the construction area to obtain the geological structure of the area; the active layer change of the area is calculated according to the geological structure of the area; the treatment layer depth H and the range of the soil ice layer in the active layer of the area to be built are determined according to the active layer change result; a steam pipe and a water pumping pipe are arranged in the range of the soil ice layer; a plurality of steam injection holes are arranged on the steam pipe, one end of the steam pipe is connected to a steam generator, the other end of the steam pipe extends to the treatment layer depth H and is subjected to hole sealing treatment; one end of the water pumping pipe is connected to a water pump, the other end of the water pumping pipe extends to the treatment layer depth H; the steam generator injects steam into the soil ice layer and the frozen soil layer through the steam injection holes of the steam pipe for pre-melting, and the water generated during the pre-melting process is discharged by the water pump through the water pumping pipe; the pre-melting process of the soil ice layer is monitored in real time until the soil ice layer is pre-melted to the treatment layer depth H; the method for monitoring the pre-melting process of the soil ice layer in real time is to evaluate the pre-melting effect and range in real time by using high-density electrical method; the method for evaluating the pre-melting effect and range in real time by using high-density electrical method comprises: laying a high-density electrical method test line above the soil ice layer treatment layer; inverting stratum information according to the high-density electrical method test result to determine the steam melting water range and trend; comparing the thickness reduction amount of the soil ice layer before and after treatment every preset time; calculating the residual thickness of the soil ice layer after a period of steam pre-melting; when the lower limit of the thickness range of the soil ice layer after pre-melting treatment reaches the treatment layer depth H, the pre-melting treatment is completed; the construction area includes a to-be-built roadbed, and the steam pipe is distributed on both sides of the to-be-built roadbed slope; the water pumping pipe is located in the center of the to-be-built roadbed. ​ ​ ​ ​ ​ ​ ​ ​ The method for calculating the change of the active layer in the area is to calculate the thickness of the active layer affected during the service period of the highway ; To survey the thickness of the soil ice layer, is the active layer growth rate, T is the service life of the road; ​ ​ ​ ​ ​ ​ ​ ​ ​

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