| As the city land resources are dwindling, the development of underground sPace has become an important way for the sustainable development of cities, and the foundation pit engineering is one of the most important projects. The in-depth study of foundation pit engineering has become one of the important contents of national urbanization development.In the process of foundation pit excavation, soil pressure, ground overloading, geotechnical property, rainstorm and other accidental factors are the main reasons for the foundation pit accidents. Foundation pit engineering of Beijing Yao-scientist detection lab suffered a once-in-a-century heavy rain disaster twice in the process of construction, causing serious disasters such as foundation pit slope movement and rupture. According to the soil foundation pit stability problem under the effect of heavy rain, foundation pit being built in foundation pit engineering of Yao-scientist detection lab is systematically analyzed through the combinative method of on-site measurement, theoretical analysis and numerical simulation in this Paper, which is based on foundation pit engineering of Yao-scientist detection lab. Under this special condition, the relevant rules of foundation pit deformation in the process of foundation pit excavation are found. The characteristics of soil foundation pit deformation evolution are studied. The stability of soil foundation pit under the effect of heavy rain is systematically understood. The control measures to the stability of deep foundation pit are carried out under this special condition and the proper reinforcement means are determined. The following main conclusions can be obtained:(1) Considering the shearing action caused by the friction of the remaining wall and the soil as well as lateral earth pressure of the soil nailing wall with cut slope angle. In view of row piles and diaphragm, circular and catenary, the two shapes of minor principle stress arch, are theoretically analyzed, considering the effect of the angle of internal friction on the inclination of sliding plane of soil behind remaining wall. According to two shapes of soil arch, the average vertical earth pressure was computed. Then, the coefficient of earth pressure versus the angle of internal friction and the angle of wall friction was obtained. Using the coefficient on the method of horizontal differential element to compute active earth pressure on remaining structure. The theoretical formulate for active earth pressure, the resultant force and its acting point was obtained.(2) Describe the present situation of field engineering and hydrogeologic conditions in detail, basic retaining and protection of foundation pits project is designed according to the situations in the field. Soil-nailing wall is used on the east side of foundation pit, anchored-piles in row is used on the other sides. Specific design Parameters of anchored-piles in row profile and foundation pit dewatering scheme are given out. A new type underground diverting wall technology which is used jet grouting and stirring is analyzed, and the reinforcement mechanism of cement-soil, supporting structure of the cement-soil mixing pile wall, the piling method of cement-soil pile made by jet grouting and stirring and the basic technical Parameters of the forming method of row piles underground diverting wall are analyzed in detail.(3) This Paper analyzed the stability of foundation pit under strong rainfall conditions with FLAC3 D numerical simulation. Firstly, the basic principle of Mohr-Coulomb Model is introduced; secondly, the evolution rules of stress and displacement of foundation pit slope under different support system, including support and non-support, different reinforced support system and further reinforced support system are simulated through modeling, the main conclusions are as follows:①By analyzing evolution rules of stress and displacement of foundation pit slope respectively adding bolt in the foundation-3m,-5.8m,-11 m under the supporting condition. On the displacement side, observing the lateral amount of foundation pit at the depth of-9m, it is confirmed that the lateral deformation of each side of the foundation pit is the smallest adding the bolt in-5.8m in the foundation pit. In this state, lateral deformation of each side of the foundation pit is respectively reduced to 44.8%, 40.55%, 38.74%, and 40.55% under design supporting condition. In the 0 m depth of the foundation pit, namely, The edge of the foundation pit, when adding the bolt in-5.8m in the foundation pit lateral deformation of each side of the foundation pit is reduced to respectively 45.68%, 32.46%, 34.47%, and 35.97% under designed the supporting condition, which can also satisfy the stability requirements. On the stress side, stress of each side of the foundation pit slope reduce a certain extent, and slope stress reduce biggest at the depth of-5.8m.②In order to seek the best way to reinforce the foundation pit, using the numerical simulation to com Pare the evolution rules of stress and displacement of foundation pit slope respectively adding bolt in different position of the foundation including-5.8m only,-3 m and-5.8 m,-3m and-11 m,-5.8m and-11 m,-3 m,-5.8 m and-11 m, foundation pit slope displacement are close to each other. Considering the factors of cost and difficulty of construction, we can confirm reinforcement support by adding bolt in-5.8m is more economic and reasonable.(4)Using field measurement method to obtain related data, namely, according to monitoring the prestressed of anchor, reinforcement stress of pile, horizontal displacement of foundation pit slope and the settlement changing rule with time of buildings surrounding foundation pit. the following conclusions can be obtained① The locked actual prestress of the bolt can not reach the design value after the anchor tensioned, indicating that during tensioning and locking, the bolt prestress loses severely. Tensioning and locking construction processes need to improved to reduce locked prestress loss.②Seeing from the steel stress meter data, the slope pile can be regarded as a continuous beam on many supports rather than cantilever beam to study. Reinforcement stress is rising due to foundation pit’s keep digging, however, the stress condition of pile is changed because of applying anchor, which can not be shown as cantilever pile. The stress state of reinforcement is also changed.③when observe the horizontal displacement and settlement of foundation pit, we can see that horizontal displacement of the observation points are all increasing with time, and the changing curve of all the horizontal displacement are similar. The Settlement and elevation curves of points which are settling smaller performed oscillation characteristics. The four edges of foundation pit are settling biggest, and the places far away from the foundation pit edge are settling small. Horizontal displacement and settlement on the north slope are greater than that on the south slope at the corresponding points. This may be because that the north slope is closer to buildings than the south slope, causing this phenomenon.(5) According to the twice rainstorm disasters during the construction of foundation pit, the moving process of north and south slope is introduced. The Paper also analyzes the process of Rainfall and infiltration of foundation pit, the influence factor of Rainfall and infiltration on foundation pit deformation is confirmed base on the headwaters expedition. The emergency disposal scheme is drawn up according to the foundation pit deformation due to the rainfall. Using the scheme of anchor reinforcement to deal with the foundation pit deformation, which guarantee the stability and normal use of the foundation pit effectively. |
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