| With the development of high-rise buildings and the ever-increasing use of urban space,the development of foundation pit projects has been deepened and the environment around the pit has become more complex.At the present stage,considering only the excavation of excavation soil and analyzing the temporal and spatial evolution of the excavation deformation is not enough for all projects.In special circumstances,consideration should be given to the analysis of the spatial-temporal evolution of the foundation pit under different external environmental influences.Combining theoretical analysis,experimental research and numerical simulation,systematically researches the space-time evolution of the foundation pit deformation under complex environmental conditions around the foundation pit.The following work is mainly carried out:(1)Theoretical analysis and calculation of the spatial-temporal evolution of construction seepage caused by the precipitation of foundation pits are carried out.Based on the theory,a time-dependent construction seepage mathematical model was established and the model was used to calculate the engineering water level change.Combined with the actual engineering,the mathematical model of seepage flow established in this paper can simulate and calculate the change of groundwater level drop with time in the construction process,which has a good reference value.And by correcting the ground settlement calculation method generally adopted in the project,the settlement value of the soil after the project rainfall is calculated.Combined with the on-site monitoring data,the calculated settlement value is closer to the surface subsidence value monitored on site.(2)A deeper study was conducted on the effect of surface water infiltration on the deformation of supporting structures,and a model test system was developed on its own.Based on the similarity theory,the conditions of the construction site were reduced to conduct indoor model tests.The test results of the effective infiltration range of different soil layers are analyzed,and the formula for estimating the effective infiltration range of the layered soil is concluded.Combining with actual projects,the effective infiltration impact surface obtained by model calculation is close to the original soil model test and field measurement.At the same time,the deformation test data of the support structure measured by the model test is compared with the on-site monitoring data.The deformation results of the model are close to the measured values,and the rationality of the model test is verified.(3)Movement characteristics of the rail transit load were analyzed and the vibration excitation function was used to simulate the vertical vibration load of the train.Considering the different load types,comparative analysis of the model’s surface settlement,support structure deformation,and anchor cable internal forces and field measured values shows that the calculated value of the equivalent static load model and the bidirectional dynamic load model is larger than the measured value.In this paper,the calculated value of the unidirectional dynamic load model is close to the measured value.It shows that the dynamic load of double-track city trains can be analyzed and calculated by using unidirectional load.(4)By establishing a dynamic three-dimensional analysis model of deep excavation under the influence of complex environmental factors and simulating the space-time characteristics of horizontal displacement,ground settlement,and prestress of anchor cables in the process of excavation of foundation pit under various factors,more systematic numerical values are developed.Simulation study reveals the temporal and spatial evolution of the deformation of the foundation pit supporting structure under special conditions.Combine the actual monitoring data at the site to verify the reasonableness and reliability of the model.(5)Foundation excavation model considering the unloading of soil without consideration of the external force was established,and compared with the deformation of the supporting structure under the influence of various environmental factors respectively,and the influence of various environmental conditions on the stability of excavation support structure of foundation pit was analyzed..Comparative analysis shows that the effect of surface water infiltration has the greatest influence on the stability of the foundation pit supporting structure;the influence of rail traffic load on the foundation pit is limited,and its effect is gradually weakened with the excavation time and depth of the foundation pit;The seepage flow has the tendency of increasing the surface settlement and the displacement of supporting piles.The growth rates of the deformation of the supporting structures under different working conditions are close to each other,indicating that the construction seepage has a long impact on the supporting structure of the foundation pit and the scope of influence More extensive. |
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