Field Test and Analysis of Segment Secondary Stresses in Small Interval Shield Tunnel During Construction

During construction of small interval shield tunnel,the magnitude of the advanced tunnel stresses changed.The magnitude and changing regularity of the advanced tunnel segment secondary stresses were studied by field test on a practical project.By means of steel sting surface strain gages and frequency instrument readings,in-situ monitoring on the circumferential secondary stresses and the longitudinal secondary stresses were carried out in a small interval shield tunnel of Beijing subway.Lasted curves of the circumferential secondary stresses and the longitudinal secondary stresses were given by analysis of the measured data,and a comparative analysis on maximum secondary stresses and stabilized secondary stresses in different monitoring point was made.The analysis results of the measured data show that the circumferential secondary stresses is pressure,their magnitude is greater than those of the longitudinal secondary stresses,and the maximum magnitude takes place in the intersection of horizontal diameter with circumference of the tunnel.The maximum magnitude of all measured circumferential secondary stresses is 12.77 MPa in this project case.The results may be applied to quantificational assessment to the interaction of small interval shield tunnel during construction and conducted as reference material to design,construction and field test of shield tunnel.