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Metro deep excavation and environmental effects caused by control measures


Abstract: Subway construction of deep foundation pit a great impact on the surrounding environment, the need to take reasonable measures to protect them. Nanjing Metro on the excavation of deep excavation in spatial and temporal effects of precipitation on the ground outside the pit subsidence, construction and other construction information to discuss issues arising from the environment, and proposed environmental protection measures.
Keywords: excavation; environmental protection; space-time effect; precipitation; uplift; land subsidence; information; monitoring 1 Overview subway construction in recent years as China's development, more and more cities to build subways. The subway excavation of deep excavation with a difficult, long duration, high cost and impact on the surrounding environment and other issues, it has become an urgent need to overcome urban construction problems, environmental protection has become one of the foundation pit in many problems a top priority. Therefore, Metro foundation construction will directly affect the cost of excavation and security, while protecting adjacent buildings (or pipe) and to ensure the safety of its normal use has a major economic and social benefits. This paper by the Chinese Alliance WWW.LWLM.COM collected. 2 environmental effects caused by excavation subway deep excavation project has the following characteristics: (1) deep excavation construction environmental conditions are relatively poor. As the high-level, high-rise buildings are concentrated in urban centers and along main streets, building density, population density, traffic jams, small construction site, construction of the hands and feet shackled. (2) excavation deeper and deeper. Owners to conserve land, full use of underground space of the original base area and set the stations, civil defense, engine room and fire facilities, so the subway structure corresponding increase in the depth and layers. (3) must set a viable and reliable technology support structure to ensure safety, but taking into account the surrounding underground gas, Sheung Shui, water, telecommunications, cable and other lines of influence, to minimize this series of buildings and facilities damage effects. (4) As competition increases, the owners of the cost, progress, project quality requirements are increasing,christian louboutin france, a corresponding increase in the difficulty of construction. 2.1 reduce environmental effects caused by groundwater lower the groundwater levels caused by environmental effects were as follows: (1) lower the groundwater levels caused by land subsidence; (2) groundwater infiltration and sabotage caused by the collapse pit; (3) pit cause inrush base soil cracking. In the excavation process, commonly used dewatering to achieve lower water level, consolidation of soil, slope stability and ease of excavation purposes. Meanwhile, the foundation pit, the ground water level caused by land subsidence, and the corresponding water level to form a funnel-centric land subsidence deformation zone, resulting in sub-range of buildings, roads, pipelines and other facilities due to uneven settlement of the fracture, tilt, affect their normal use and safety. Lower the groundwater levels caused by climate change mechanisms: (1) reduce the water level in the groundwater to reduce the soil building uplift of the ground by the compression and soft soil settlement; (2 ) so that the soil pore water from the discharge. Deformation of soil consolidation, compressing the process of settlement itself, the precipitation process, often taking the water away with some fine soil particles in the soil, causing the surrounding land subsidence. Land subsidence and water table is the corresponding landing, the landing surface distribution of the water table would inevitably lead to differential settlement of adjacent buildings. Local surface subsidence reaches a certain level, the building will be cracking, tilting or even collapse phenomenon; (3) excavation, the pit, head around the water table there is a certain difference in the hydrodynamic pressure, pit soil flow occurs (soil) losses, potential corrosion, resulting in loose soil structure and damage caused by the collapse pit. (4) When the pit, outside the relatively large gap between the water level, water pressure or the lower part of the pit there, so that the original excavation of earth pressure reduced to a certain extent, the pressure of water head pressure is greater than the pit bottom soil floating gravity the formation of piping, side Chung phenomenon, resulting in cracking of the base soil. 2.2 supporting structure deformation and displacement caused by environmental effects supporting structure deformation and displacement caused by environmental effects were as follows: (1) destruction of the supporting structure itself which led to slope instability; (2) supporting structure uplift the overall damage caused by excavation; (3) The supporting structure of the deformation and displacement caused by damage to adjacent buildings and facilities. Supporting structure deformation and displacement caused by the environmental effects of the mechanism are: (1) unloading pit to change the Bottom of the original foundation soil stress state in the excavation, pressure decreases in weight of soil, soil-elastic effect to the pit bottom have some springback deformation (uplift), the performance of elastic uplift Bottom, Bottom of the central uplift characterized by the highest flexibility in the excavation uplift stopped soon after the stop, basically does not cause the soil to the pit outside the pit move; with the excavation depth increases, the height difference inside and outside the pit formed by a variety of loading and overloading of the role of the ground around the outside wall move soil to the pit, up to the Bottom of the plastic deformation produced, characterized by the middle of a small bulge on both sides of a large state; (2) have a greater plasticity around the pit area, and cause land subsidence; (3) pit bottom exposed for too long, so that pit water, on the one hand, making the clay rheology, will increase pressure on the wall passive zone of soil displacement and soil to the pit wall displacement, thereby increasing the surface subsidence. (4) supports the destruction or anti-pull bolt system is strong enough, or the rod and the rod itself breaks the connection is not strong anchor seat supporting structure caused by the loss of carrying capacity of the system support structure embedded deep enough uplift caused by excavation, and to reduction or loss of foundation strength. 3 excavation pit in the Environmental Protection for the protection of the environment, the protection of people accumulated a lot of experience, such as the stiffness of the envelope used to carry out excavation outside the foundation reinforcement to improve the soil's resistance to deformation of the pit nearby buildings and structures to reinforce the foundation or foundation treatment, building the foundation and set the partition between the partition wall and the grouting of pile or protected by a small amount of grouting effect deformation of transmission and other measures; despite protection methods vary widely, but its role in the mechanism of nothing more than to reduce the impact of excavation, retaining the environment to improve resistance to deformation, three kinds of ways to cut off the influence. 3.1 excavation in the spatial and temporal effects of environmental protection law is to address the overall stability of the deep pit and pit-week strata displacement control, the reference NATM tunnel construction theory of space-time effects and a lot of soft soil foundation made a practice of calculation and control of structural deformation and the formation around the pit displacement method. Through a large number of soft soil foundation practice, people have realized: in the pit during the construction, excavation for each excavation step geometry of space, no enclosure wall exposed area and time to support the construction of pit deformation parameters have significant correlation. Consider the effects of time and space The main features of the construction steps are: According to pit size, geometry, retaining walls and support structure system layout, excavation and foundation reinforcement construction conditions,ralph lauren pas cher, in accordance with limit Time effect method emphasizes design and construction of close cooperation have changed the design conditions and construction conditions inconsistent with the status quo, proven, scientifically developed to consider effects of excavation and support space construction design, reliable, rational use of soil body itself in the excavation process to control the displacement of the potential to control the displacement and the pit-week formation of environmental protection purposes. To change the current excavation pit for the week of ground displacement and control unreasonably costly foundation reinforcement approach. Starting from the engineering practicality and reliability in the foundation pit structure (retaining wall, retaining wall to support and reinforce the passive zone of soil) the internal force and deformation, using flexible calculation method used is relatively simple mechanical model and design parameters of the project, but the overall effect of which reflect the pit deformation parameters --- the most important integrated passive zone of the pit retaining wall level resistance coefficient,ed hardy paris, according to a certain geological and construction conditions, to make an empirical correction. This parameter is the integrated indicator of soil mechanics, and every step of the excavation pit size and the space function of exposure time, its value is based on certain construction conditions, the excavation pit in the measured deformation data, the anti- analysis and design control standards derived from outside the Netherlands and other based on the same time, a reasonable selection of construction process and construction parameters to improve the design basis and to provide assurance to implement the design in order to effectively solve the rheology of strata in the deep pit deformation control design does not meet the actual problem. Selected according to the design of excavation the main construction parameters, according to the pit size, geometry, support forms, the depth of excavation and foundation reinforcement conditions, to submit a detailed operational open digging and support the construction process and construction parameters. Excavation and support of the construction process is based on the basic Each excavation depth and excavation retaining wall passive zone of soil formation in the middle part of the pit before excavation works to retain the embankment into a support wall, the earth embankment section size against the retaining wall according to the requirements of set, are also major design parameters; in strict accordance with the selected construction parameters of the construction process and construction, the construction on the complex factors that become more clear and regular construction factors, their effects can be caused by better spatial and temporal meet the design requirements expected. In a rectangular pit, the excavation and support of the technical points of construction is, according to a certain length of sub-excavation and pouring of the structure, in subdivided each excavation layer. Short sections on each floor excavation and support, with the digging with support, prestressed, small pieces of excavation and support of each of the construction time limit within certain limits. Irregular pit in the construction, a stratified basin excavation method, in the middle part of each layer of the excavation and pouring the range of installation or support, and will support both ends of the supporting wall of the root of the embankment, sub- step, symmetric and real-time to install or remove the cast during the retaining wall to withstand some support. Each step of the excavation and support construction time, according to the methods support the specific circumstances of a given explicit control values. Excavation in the use of space-time effect in the law, the pit structure parameters, the foundation soil (including reinforced soil) parameters and process parameters are interdependent construction and jointly play a role in controlling the deformation of the basic elements, which are based on the design of control excavation deformation, deformation control design elements. 3.2 foundation pit in order to reduce dewatering of the surrounding building (structure) and the impact of hazards, usually take the following measures: (1) the use of closed form retaining wall or other sealing measures, such as diaphragm walls, locking steel sheet pile, piles, jet grouting piles, soil-cement mixing pile, will be well-point set in the pit, the depth of the well pipe does not exceed the depth of the retaining wall , only the pit water level reduced, and the water level outside the pit will remain at the original level; (2) According to project the actual situation, make appropriate adjustments well point pipe buried depth; general,ralph lauren pas cher, well point pipe burial depth should make precipitation within the pit under the surface in the Bottom of 0.5 ~ 1.0m; such as seal-shaped retaining wall in the absence of the case, not only the foundation pit pit water level, water level also fell outside the pit. If the rain-affected zone within the range of building (structures), and pipelines need to be protected, it can ensure the pit does not occur in the sand and the groundwater does not flow into the condition from the Pit to appropriately increase well point tube design elevation; ( 3) dewatering zone with precipitation time, outward, downward expansion, if the points in which two rows of wells, pit quickly formed a precipitation surface, pit slow expansion outside surface precipitation. Therefore, when the point set deep wells, with the precipitation time, you can properly control the pumping and vacuum pumping equipment. When the water level observation wells to meet the design water level control value, adjust the equipment so that pumping and suction vacuum is low and to control the pit outside the purpose of surface precipitation; (4) dewatering and recharge using a combination of technology, well point of precipitation with the need to protect the building tube-wells, pipelines between the set point of recharge wells, recharge wells, or recharge sand sand ditch, continuing with the clean water rinse, (to avoid clogging of soil pores occurs, reduce the permeability of the land affected by back filling effect) recharge, to form a water curtain to reduce the settlement; (5) well points should be run continuously to avoid gaps and repeatedly pumping, because each will have a settlement of precipitation, increasing the number of times repeated pumping, bringing the total settlement amount accumulated to a considerable extent. (6) to reduce the pit dewatering, reduced precipitation surface outward expansion, to prevent the foundation soil under the building foundation near the water level dropped due to soil erosion resulting from the settlement, before the dewatering, the need to control the settlement of the building foundation periphery, arranged grouting holes, grouting pressure control.
     
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