Study On Seismic Analysis And Design Of Shallow Underground Structures

As an important form of urban public transport, underground mass transit cansolve the urban transport problems effectively and efficiently. Taken Beijing as anexample, total mileage will exceed1000km in the future according to the long-termplanning in2050. Large-scale construction of rail transit lines lead to the occurrenceof large-scale construction of approaching existing building (structures), which willinevitably lead to the appearance of diversity and spatial composition of subwaystructures. The increasing complexity of the subway structures demands higherrequirement of seismic performance. Therefore, seismic performance analysis of thecomplex composite structures, such as extremely close approaching parallel andintersecting subway structures; summary, classification and analysis o f Beijing'sunderground subway structure seismic design methods, of which universal andapplicable laws can be summed up, and these methods are then developed andimproved. Finally, seismic safety of underground complex structures is evaluated incombination with all related standard and guidelines. Therefore, it may have greatsignificance on seismic design and theories of underground structures.This research is supported by National Program on Key Basic Research Project(973Program): Earthquake damage of urban underground infrastructure and seismictheory, supported by Natural Science Foundation: research on urban large-scaleearthquake disaster mechanism of underground structures and process simulation, andsupported by Natural Science Foundation of Beijing: Study on seismic response ofthree-dimensional intersected underground subway structures and its seismic designmethod. Based on strata and underground structures in Beijing, seismic analysismethods of the of subway structures, applicability of seismic design methods ofsubway structures, improved response displacement method, dynamic analysis ofcomplex composition of subway structures and seismic safety evaluation of subwaystructures The principal study contents and results are as follows:(1) Seismic analysis methods of subway structures are introduced and clarifiedwith their calculation procedures, which provide theoretical basis for seismic designmethods.(2) Underground earth pressure and seismic design load conditions are introduced,especially the simplified seismic earth pressure formula, Zhang Jianmin's seismicearth pressure method, and meanwhile seismic design methods for subway structuresare introduced, including dynamic time history analysis method, responsedisplacement method, integrated response displacement method, modified crosssection racking deformation method, the response acceleration method and Pushoveranalysis method, the results of which are compared and analyzed through a instance,providing some reference for the difference law of various design methods'results.(3) Based on the three methods of determining stratum response displacement, an improvement method is proposed which considers the stratum parameters and depthof soil. It can reflect the determination of ground surface peak displacement of groundmotion parameters using equivalent inertia acceleration. Then deformation and stressregularity of underground structures in hard and soft layered strata, near-fault strataand etc. are analyzed, which provide reference for the modification of responsedisplacement method of underground structures in complex strata. Impedancefunction of underground structures obtained by thin layer method (TLM) is applied tothe response displacement method in order to quickly and accurately determines thespring stiffness of the strata.(4) The finite difference procedure FLAC and FLAC3D is used to simulate andanalyze seismic response characteristics of double holes parallel tunnels of differentratio of distance to diameter and different angles. The analytic solutions of the steadyvibration of upper and lower parallel double tunnel are obtained under a moving loadwith uniform velocity. The seismic response characteristics of intersectingunderground subway structures of different spacing and closely-attached intersectingunderground subway structures under vertical strong ground motion are studied inorder to summarize systematically dynamic characteristics of complex composition ofsubway structures.(5) According to <Specific demonstration technical points of earthquakeresistance protection of municipal public facilities (underground engineering)>,<Code for seismic design of urban rail transit structures>(draft-2011),<Seismicdesign of buildings>(GB50011-2010),<Guideline for seismic design and disastermitigation of underground subway works>(draft-2012) and other relevant standardsand research results at home and abroad, a specific subway structure is taken as anexample to identify risk sources. Then according to the typical geological andstructural conditions, seismic response characteristics are analyzed and universal lawis summed up, which has significance and provides a reference for similar projects.