Analysis On Mechanical Characteristics And Cracking Phenomena Of Segment Structure For Shield Tunnel During Construction Period

Currently,the research mainly focuses on the mechanical behaviors of segmental lining during the operation period for shield tunnels,and the influence during construction is minorly taken into consideration.However,segmental lining is subjected to construction loads in the process of shield construction,including jack thrust force,sealing grease pressure,grouting pressure,assembling force,and other sort of loads.Compared to the operation period,the mechanical behavior of segmental lining is more complex in construction stage with a typical feature of three-dimensional stochastic uncertainty.Under the action of various loads,segmental lining will be cracked and damaged more easily during the construction stage,then the waterproof system will be destroyed and the normal usage of the tunnel will be severely affected,and the safety of the tunnel structure may be endangered as well.Therefore,it is of remarkable significance to conduct research and analysis on the mechanical properties of segmental lining in construction stage.The mechanical properties and cracking phenomena of segmental lining considering the impact of construction factors were studied by means of field investigation,numerical simulation,similar model test and in-situ test in this thesis.The main results are as follows:1.Taking a metro engineering as a typical case,cracking and breakage status of segmental lining during construction was collected through field investigation.The results show that,the diseases of lining can be divided into three categories,that is,longitudinal cracks,encircle cracks and corner cracks.The distribution law,morphological feature and damage degree of the three kinds of cracks are revealed,and the damage mechanism regarding segmental lining is discussed.2.A numerical model which can capture the crack propagation was established based on finite element theory.The distribution and propagation of cracks in segmental lining under different conditions(unequal thrust of jack,excessive thrust of jack,eccentricity of jack and sudden failure of jack)are obtained and the main causes of cracking and breakage in lining are revealed.3.Based on the shield tunnel-stratum experimental system,similarity model tests were conducted to reveal the mechanical behaviors of cracked lining.The effects of cracks on the progressive failure process of lining(damage,macroscopic crack propagation and structural instability)are systematically analyzed.The influence of damage degree of cracks on the failure patterns and mechanical responses of linings are discussed as well.4.Field tests were conducted by selecting typical metro section.The results have ascertained the temporal and spatial variations of water and soil pressure during the entire construction period.The variation law of mechanical responses of segmental lining during construction is revealed.The influence of jacking forces on the inner force of segmental lining is analyzed.