Deformation Behavior And Control Of A Deep Excavation Adjacent To Substructures

Deep excavations in congested urbanized areas may cause a significant impact on existing structures.The occurring soil displacements and the related change in forces can cause significant damage to the surrounding environment and structures.Furthermore,the existing structures will also influence the deformation behavior and earth pressures of retaining walls.In order to protect the environment in the close vicinity to excavations,the soil movements should be controlled.Nowadays,numerous protective measures are available but their efficiency can be improved.A good understanding of the soil-structure mechanism is necessary to take appropriate measures,but there is a lack of studies that've investigated this topic.This thesis aimed to improve the understanding of the soil–structure interaction mechanism in case of excavation-induced soil movements and to investigate the efficiency of two optional control measures.The structure-soil-structure interaction mechanism in case of soil confined by an excavation and substructure was being elaborated.This was done by investigating the impact of different substructures on wall deformations.Based on the results,the performance of two measures to control wall deformations and related soil movements was investigated.The first control measure was a pile row placed in the retained soil.The second control measure was a servo strut system which allows to dynamically control wall deformations by varying the strut axial forces.The first part of this thesis focused on the influence of different types of substructures,located closely to a deep excavation,on diaphragm wall deformations and earth pressures.The research was carried out by the numerical software program FLAC~3DD and as basic model the excavation of the Tapei National Enterprise Center(TNEC)was modelled.The substructures are carefully chosen and widely appear in congested urbanized areas.The substructures were(1)a pile foundation,(2)a diaphragm wall and(3)a multi-layered substructure.Under influence of the soil arching effect,diaphragm wall deformations and soil stress were significantly reduced by all adjacent substructures.However,results indicated that a more rigid substructure causes more reduction of deformations and stress.The pile foundation as least rigid substructure also showed some descent reductions because of the combined working of soil arching and soil compression.Based on the findings of the first part,the second part of the thesis investigated whether a pile row can serve as effective control measure for diaphragm wall deformations and soil movements.Numerical simulations were used to compare the basic model(TNEC)to the same model with a pile row placed in the retained soil.Furthermore,a comprehensive parametric study was carried out to investigate the influence of different pile row parameters on wall deformations and ground settlements.The results indicate that the use of a pile row as protective measure is an option that should be considered.Finally,the third part of the thesis investigates a servo strut system as control measure for excavation-induced diaphragm wall deformations by the use of numerical software.Servo struts are struts where the axial force of struts can dynamically be controlled in order to control wall deformations and soil movements better.The axial force can be presented as a function of the retaining wall deformation,a larger deformation asks for a larger axial force.Also,a real case history where servo struts were used was analyzed.The results indicate that servo struts can be an efficient control measure if a good balance between axial force and position of struts on the diaphragm wall is found for the specific case.