In the high-cold frozen soil area of ​​Qingxie Railway, the size and distribution of water content in the subgrade soil layer and the seasonal change of external temperature are the main factors affecting the stability of the roadbed. For groundwater subgrade in the permafrost region, if it is immersed in groundwater for a long time, the water will destroy the stability of the subgrade project in different ways and to varying degrees. On the one hand, the erosion and infiltration of groundwater will soften the foundation rock, which will reduce the strength of the foundation and increase the compressibility. Under the external load, the subgrade engineering will be greatly deformed. On the other hand, the subgrade project is above the frozen line and the soil is rich. Containing groundwater, when freezing, not only does the water in the soil become an increase in ice volume, but the water tends to migrate and redistribute due to the effect of freezing due to the effect of freezing, forming an ice interlayer or ice pile to cause the foundation to heave. When frost heaving, the roadbed is unevenly lifted, and it is unevenly submerged when it is melted. The roadbed project is deformed year after year, and cracks appear in the light, and the heavy ones endanger the use. Therefore, the reliable drainage and water interception measures for the groundwater subgrade in the permafrost region are an important link to ensure the stability of the groundwater subgrade in the permafrost regions. 2 Project Overview + 150 sections, located in the hilly area south of Tanggula Mountain, with a total length of 337km along the topography, the gullies and beams are horizontal, the mountain is round and the slope is gentle, the mountain is narrow and the valley is wide, and it belongs to the deep seasonal frozen soil area. The maximum freezing depth is There is no large surface water system in the 350cm line. There are only wetland marshes and small streams in the valley. The surface water system is mainly supplied by glacial meltwater and atmospheric precipitation. The water temperature is low, the flow varies greatly with the season, and the groundwater type is Quaternary. Pore ​​diving, bedrock fissure water, abundant water. The geology along the line is complicated, and unfavorable geological phenomena such as groundwater roads and foundation springs appear in phases, with a total of more than 10 places, which brings disadvantages to the roadbed construction in the cold area. In order to ensure the stability of the subgrade of the groundwater section in the permafrost region during construction, we boldly adopted the technology of thermal insulation seepage and ditch to successfully solve the engineering geological problems such as frost heaving, melting and sinking of the groundwater subgrade in the permafrost region. 3 Insulation seepage water Drainage structure of the first ditch The water infiltration ditch is set in the groundwater layer, with good water permeability, filtration, water collection and frost resistance, can reduce, cut off or drain the groundwater, and drain the nearby soil. An underground drainage facility that improves the bearing capacity and stability of the foundation. When dealing with groundwater subgrade engineering, the appropriate type of seepage should be selected according to the type of groundwater, the depth of aquifer burial, the permeability coefficient of the stratum, etc., and then trenches should be excavated on one or both sides of the subgrade as needed to set up trenching. The groundwater is collected or intercepted into the seepage by utilizing the water permeability and water collection of the seepage. In the Fushui deep road section, after the road excavation, the washed gravel can be replaced at the bottom of the crucible as a seepage layer, and the groundwater is introduced into the longitudinal ditches on both sides of the subgrade through the seepage layer. When longitudinal ditches are provided on both sides of the subgrade, lateral ditches may be provided between the longitudinal ditches, and the water is concentrated to one side through the lateral ditches, and then the water is discharged from the subgrade through the drainage concealed pipes connected to the ditches, thereby achieving the drainage of the subgrade. The soil within the range enhances the strength and stability of the foundation. 1Drainage structure of the deep road seepage ditch is used to treat the deep ground water in the deep ditch. The vertical drainage seepage ditch is provided under the side ditch on one side or both sides of the road. The seepage width is 1. 5m, and the washed gravel is filled inside. 450gm2 non-woven permeable geotextile, geotextile peripheral 01m thick medium coarse sand cushion. The drainage pipe in the seepage trench is made of 200mm double-wall corrugated pipe with a wall thickness of 50mm. The pipe wall is provided with 70X3mm2 holes in the range of 240, the longitudinal spacing is 150mm, and a layer of 450gm2 non-woven permeable geotextile is wrapped, and the overlap length between the cloths is not less than 20am. Filling the gravel soil within 35m of the slope (the content of powder clay is less than 15%), the step of excavating 20m wide between the slope and the replacement soil, and the one-way warp-knitted high-strength polyester geogrid from the side ditch and the above slope. And back up the 2 5m road surface under the 0 930m range to fill the gravel soil (powder content less than 15%) within 3035m, replace the washed gravel and set 4% drainage slope to the seepage. 450gm2 non-woven geotextile filter layer is laid between the gravel soil and the washed gravel. The bed is filled with twenty-eight ash soil, and an XPS (thickness 008m) insulation board is laid between the two-eight ash soil and the gravel soil, as shown. 32 Drainage structure of shallow road seepage ditch When the shallow water is used to treat the shallow groundwater, the vertical drainage seepage is provided next to the side ditch on one side or both sides of the road. The structure of the seepage ditch is the same as that of the deep road. When the foundation pit is backfilled, the viscous soil is filled on both sides of the seepage to the elevation of the top surface of the seepage ditch, and the gravel is backfilled to the top of the seepage. The cohesive soil layer not less than 05m is not less than 50m above the top surface of the seepage trench as the insulation layer and the protective layer, and the height of the top surface of the drainage pipe from the top surface of the cohesive soil layer is not less than the insulation depth specified by the design. And should set 2% 4% drainage cross slope on the top surface of the protective layer. In addition to the seepage, you can choose whether to set the gutter according to the drainage needs, as shown. When the drainage structure of the seepage ditch of the embankment is treated by the seepage ditches to treat the groundwater of the embankment foundation, longitudinal drainage seepage is provided outside the slope of one side or both sides of the embankment foundation. The structure of the seepage trench is the same as that of the deep road seepage. When the foundation pit is backfilled, the cohesive soil is filled on both sides of the seepage to the elevation of the top surface of the seepage ditch. The shallow road seepage and drainage drainage structure (unit: m) is backfilled with coarse-grained soil on the inflow side of the seepage, and is used on the embankment side. Backfilling of the original soil. The cohesive soil is filled between the upper part of the seepage and the embankment slope. The thickness of the fill should ensure that the height of the top surface of the drain pipe from the top surface of the cohesive soil layer is not less than the insulation depth specified in the design, and should be on the top surface of the protective layer. Set a drainage cross slope of no less than 4%. Outside the slope of the protective layer, you can choose whether to set the drain according to the drainage needs, as shown. 4 Insulation seepage water ditch construction insulation water seepage ditch treatment deep road å ‘ groundwater construction process flow insulation seepage water ditch treatment shallow road å ‘ groundwater construction process heat preservation seepage water ditch treatment embankment foundation groundwater construction process flow 5 construction precautions narrow and deep trenches, pay attention to safety during construction; At the same time, attention should be paid to strengthening on-site command and control to protect various underground pipelines. Try to avoid the rainy season construction, and make drainage facilities such as permanent drainage ditch and gutter before construction. During the construction, the water in the foundation pit shall not be discharged into the seepage to prevent contamination of the gravel and block the drain pipe. Avoid large-scale blasting methods when excavating roads. During the construction of the seepage trench, the slope is carried out from the downhill to the upper slope. The excavation shall be completed as soon as possible, and then the next section of construction shall be carried out. All engineering materials entering the construction site must be sampled and retested in strict accordance with the requirements of relevant technical standards, and materials that do not meet the design and specification requirements shall not be used. The materials after admission should be strengthened to prevent contamination, aging and failure of materials. Before the excavation of the road and the ditches, the domes or drains should be made to prevent rainwater from flowing into the roads or seepage. Road excavation should correctly mark the side pile connecting line, often check the slope excavation slope, correct the deviation in time, and prevent over-under-excavation. For the slope to be protected, when the protection cannot be followed by the excavation construction, the protective layer of a certain thickness should be temporarily reserved, and the slope should be dug after the slope protection. Drainage channels should be connected to bridges and culverts, lines and external drainage systems. Drainage of ditch water shall not cause damage to roadbeds, farmland, pastures and other buildings. Ensure that the water flowing out of the outlet is drained downstream, and there must be no accumulated soil or pits on the ground. Carefully do the anti-freeze measures for seepage, drainage, and water outlets to ensure that the depth of the burial and insulation measures meet the design and specification requirements. The foundation of the seepage and inspection wells must be placed on a stable formation. Corresponding engineering measures should be taken to stabilize the unstable formation to ensure the stability of the foundation. For deep-watered pits or foundation pits that are unstable, if the slope excavation cannot keep the slope stable, temporary support should be used to strengthen the pit wall. Do a good job of connecting the pipes to ensure that the pipe joints and the transition joints are firmly connected, the pipes are not blocked, the drainage slope is smooth, and the water flow is smooth. 6 Construction effect During the construction of the 22-section of the Golmud-Lhasa section of the Qinghai-Tibet Railway, we used the above construction techniques and construction techniques to deal with various types of subgrade groundwater projects such as deep roads, shallow roads and embankment foundations, all of which achieved good waterproofing. The effect of precipitation, the bearing capacity of the foundation is obviously improved, the stability of the subgrade is obviously enhanced, and the effect is remarkable. +300 sections, with a total length of 175m, pass through the road to the alpine hilly area where the terrain is undulating. The maximum depth of the road is more than 9m, which is a deep road. We replaced the cutting slope and basement according to the treatment method of deep road and groundwater, and set up the basement seepage. The slope after treatment is stable, and the bearing capacity and stability of the dry roadbed of the bed fill meet the design and specification requirements. Silty clay and Jurassic shale sandwich sandstone. The maximum freezing depth is 281on. After the roadbed excavation, there are many groundwaters exposed. The stable water level is basically the same as the shoulder. The water seepage is 0.5m3h. After the design is changed, the vertical drainage channel in the right side of the line intercepts the groundwater and cuts the groundwater. At the end point, the diversion pipe is used to discharge the groundwater out of the subgrade, and the subsoil layer is not replaced. After about one month of seepage construction, the bearing capacity of the basement increased significantly, the upper layer of soil was basically consolidated, and the strength of the basement met the strength requirements of the bed. +460 segments, the full length of 160m is the seepage treatment project at the bottom of the embankment. Since the construction of the embankment is in the dry season, there is no groundwater in the basement. After the construction, the groundwater in the rainy season is exposed. The basic body of the large amount of groundwater infiltration causes the filling of the basement of the large area to be wet, and the foot of the subgrade is formed in some sections. The use of thermal water seepage and ditch to treat groundwater in subgrade works in alpine regions can not only improve the bearing capacity and stability of the foundation, but also avoid the frost heaving, melting and sinking damage of the groundwater, and reduce the filling height of the line engineering embankment, saving a lot of engineering investment. At the same time, it can also avoid the interference of groundwater on the line design, reduce the difficulty of line selection and avoid the increase of excessive cost of the bridge due to the influence of groundwater. The technology of thermal water seepage and ditch is not only applicable to the groundwater treatment project of groundwater with shallow or no fixed aquifer in highways and railways in the permafrost region, and groundwater treatment engineering of similar structures, and under the same conditions in non-cold frozen soil areas. Groundwater treatment projects are also applicable, and only need to adjust the insulation measures according to local weather conditions. (Finish) Ac Heat Exchanger,Tube Heat Exchanger,Finned Pipe Heat Exchanger,Aluminium Heat Exchanger Suzhou Green New Material Technology Co., Ltd. , https://www.szgreenvip.com
Treatment of subgrade groundwater in permafrost regions by thermal infiltration and gully