| With the rapid development of global economy and urbanization, there is a growing pressure on urban ground transportation and human living space. High-rise and underground buildings are built in growing vigorously, consequently, the number, depth and scale of the deep foundation pit are increasing. Dewatering is essential to ensure the dried and safe excavation environment of the deep foundation pit. Dewatering and subsequent excavation can cause an uneven settlement of the surrounding soil and the changing of environment and even serious engineering accident, which brings great hazards and risks to the property and safety of people, so it is particularly important to accurately predict the deformation caused by the dewatering and excavation. The comprehensive theoretical analysis, formula derivation, numerical simulation study and field monitoring are carried out for the deformation of surrounding soil, building and supporting structure caused by dewatering and excavation of foundation pit. The main work and conclusions achieved are listed as follows:1、The ground settlement caused by dewatering of foundation pit involves many factors, including the multi-well effect, and it is very difficult to get the accurate solution of the theoretical calculation. The single well pumping and completed dewatering test is carried out in the West Railway Station deep excavation project, and a series of site monitoring work is completed. It is concluded that the change law of underground water level and surface settlement of the various distance of wel1 is obtained with the different deep of dewatering. The results of comparison show that the effect of multi-well is more significantly on the groundwater level only in the region of near well. Based on the Dupuit assumption and the layer-wise summation method, ignoring the impact of multi-well effect, a simplified calculation method is proposed to calculate the ground settlement caused by dewatering of foundation pit, the calculation results of method is consistent with the field monitoring data.2、There is a difference between the norm algorithm and actual situation of the settlement caused by dewatering. Analysis of the settlement mechanism and based on the effective stress principle of unsaturated soil, the improved algorithm of the settlement of surrounding soils caused by dewatering is deduced in the drainage soil layer. The improved algorithm and normulization algorithm is appled to an engineering case which is monitored dynamically. Comparing shows the result of improved algorithm is closer to the actual monitoring value and slightly less than norm algorithm.3 、 The deformation of the soil layer after dewatering includes horizontal displacement and vertical settlement. It is concluded that the basic reason of soil deformation is the seepage force through analyzing the mechanism of deformation and transformation mechanism of seepage force. The direction of seepage force is given by groundwater seepage mechanics. Based on a series of hypothetical assumptions, the simplified mechanical model of soil micro unit is established and the improved algorithm considering the seepage force of soil settlement caused by dewatering is derived, which is appled to an engineering case and the result of algorithm is closer to the actual monitoring value.4、Dewatering induces uneven settlement and inclined of building. Taking pile foundation as the research object, and analyzing the settlement mechanism of the pile after dewatering, taking pile side negative friction resistance and the neutral position as the starting point, the improved equivalent calculation model of single pile settlement is established. Based on norm algorithm, empirical formula and considering unsaturated soil affect the effective stress increments in drainage soil layer, the calculation method of uneven settlement after dewatering of single pile and pile group is given respectively, which has high practical value and is testified by the deep foundation pit dewatering engineering case of Tumendun.5、The whole process simulation is carried out for the deformation of ground and buildings near the deep foundation pit of West Railway Station and Tumendun after dewatering by the large finite difference software FLAC3 D and fluid-solid coupling algorithm. Compare the numerical simulation with the aforementioned theoretical algorithm, it is concluded that the result of simulation is slightly less than theoretical algorithm, which is regarded as basic coincidence. Therefore, the theoretical algorithm is verified.6、With the deep foundation pit of West Railway Station and Tumendun, the settlement deformation law of the surrounding soil and buildings caused by dewatering is obtained through field monitoring. Compared the field monitoring values with the aforementioned calculation results, it shows that both of them are basically coincidence. And the correctness of the aforementioned theoretical algorithm is strongly verified with the field measured data.7、Geotechnical engineering has a strong regional feature. The settlement of soil around caused by dewatering is significantly less than other regions due to the poor gradation and excellent skeleton of large-thickness aqueous pebble layer in Lan Zhou. The settlement of soil caused by dewatering in Lan Zhou is larger when using normal algorithm. The reduction factor ? is put forward based on normal algorithm, which is suitable for Lan Zhou. And the result after reduction is closer to the field measured data.8、Excavation gives rise to the deformation of surround and bottom of the foundation pit soil and retaining structure, which brings the risk to surrounding environment. On the basis of summarizing the existed research results, the M-C model is not suitable for application in the simulation of excavation, which is verified through a large number of numerical examples. The whole process optimized simulation is carried out for the excavation of pit by the FLAC3 D and taking the modified cambridge model as constitutive model. And the values of calculation is basic coincidence with the late measured data, which proves optimized scheme is reasonable. |
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