Numerical Simulation On Excavation Deformation And Support Optimization Of Utility Tunnel Deep Foundation Pit In Coastal Area

Utility tunnel is an underground structure in the construction process will inevitably involve the excavation problem.Because of it is long span,the project within the scope of the terrain,geotechnical properties have bigger difference,so different stratigraphic structures and different depth come to the main problem of excavation support.At the same time,due to the utility will cross in the space,numerical Simulation on the nodes of foundation pit excavation support,construction sequence has practical significance.In this paper,based on the Hainan international tourism island utility tunnel foundation pit project,the numerical analysis model is established to analyze the two dimensional support type selection of the long strip foundation pit and the three-dimensional space effect of the cross node.The main content of this paper is as follows:(1)Studied and analyzed the typical coastal strata structure of foundation pit excavation deformation characteristics:The soft soil section deformation of soil of foundation excavation is lager,ground settlement curve groove,the maximum deformation of steel sheet pile in excavation face.The fine sand section is a typical coastal sand stratum,foundation pit excavation deformation of the surrounding environment is relatively small,the settlement curve may show a triangle,then the maximum deformation of steel sheet pile at pile top.The sofe soil-fine sand section is a mixed section of soft soil and silty sand,but mainly controlled by the soft soil.(2)Studied and put forward the different depth of deep excavation support optimization approach:5m depth of excavation supporting methods can choose slope excavation,gravity type cement wall and steel sheet pile with supporting.8m depth of pit,steel sheet pile or SMW pile with supporting are available.10m the depth of foundation pit can choose SMW pile support,especially for a formation thick layer of silt clay.(3)Simulation reveals that the utility tunnel excavation construction mechanical behavior,clear its construction safety control points.Steel sheet pile horizontal displacement and bending moment are the largest increase in the last incremental excavation step,the final excavation step is the key and the most dangerous step for the excavation of the comprehensive pipe gallery.The final step is to become the key point of the safety of the foundation pit.(4)Simulation analysis put forward comprehensive utility tunnel crossing node deformation characteristics of the foundation pit.The two intersecting lines of utility tunnel will lead to large disturbance of soil.However,under the support of the steel sheet pile,the displacement of the soil body at the positive corner is deflected,and the large displacement of the steel sheet pile is not at the positive angle but near corner.(5)Comparative studied the intersection node different excavation scheme of foundation pit deformation law of development.It is quite large infuence for the surrounding environment and the wall in different construction sequence.The first node and then both sides excavating coincides with the requirements of step-by-step,symmetrical and balanced excavation of foundation pit,can better control the settlement of foundation pit,reduce formation loss and disturbance.