RESEARCH ON LINING MECHANICAL BEHAVIOUR OF TWIN TUNNELS WITH A BIG SPAN AND A SMALL SEPARATION BY FIELD TEST

By utilizing an integrated method of field tests and numerical modeling the law of force distribution in second lining,it was studied the effect of the adjacent construction of following tunnel on the existing tunnel with different spacing of a eight-lane twin highway tunnel with a big section and a samll separation on the Shenzhen Nanping Expressway(Stage Ⅱ).The research results showed that the axial force and bending moment values of each measuring point in second lining were much small.It was possible to be a smaller tension in vault,the side wall away from the intermediate rock specimen and the arch foot of the intermediate rock specimen,attention should be paid to preventing the concrete cracking.The influence scope of the following tunnel excavation on the existing tunnel reinforcement force under the condition of 30 m spacing and IV surrounding rock was within 40 m at the rear of the tunnel face,and the better the surrounding rock the smaller the influence scope.Only the principal stress in vault was subjected to tension,and the other parts were under pressure,of which the maximum principal stress was on in the left and right arch foot.With the spacing gradually increasing,the tensile stress and compressive stress values changed little,there was no consistent trend of increase or decrease,the effect of spacing changes on the supporting stress was not obvious.