盾构接收中钢套筒的受力变形特性与实测分析

富水砂性地层中在盾构接收时极易发生涌水、涌砂等事故,是盾构施工过程中的重大风险源之一。以上海轨道交通11号线龙华路站钢套筒接收工法盾构接收的工程实践为依托,首先采用数值模拟对钢套筒在盾构接收施工期间的受力和变形规律进行了分析,然后通过钢套筒变形和防汛墙沉降的现场实测数据验证了钢套筒接收工法的可行性。结果表明,盾构推进使钢套筒结构的最大拉应力由后端板逐渐发展为筒体与地连墙连接部位的底部,筒体结构的环向应力为纵向应力的2~7倍、腰部以下的环向轴力增长明显、腰部累计变形将近10 mm,筒体底部的纵向应力增长明显、腰部的纵向弯矩变化明显。盾构推进导致筒体结构的底部外张、腰部内凹,筒体的径向变形由横鸭蛋变为竖鸭蛋并最终变为8字形,椭圆度达到3‰,但是盾构推进对后端板的应力和位移变化均不明显。筒体与地连墙间的接缝、钢套筒分块间的腰部接缝和底部接缝均是盾构接收中钢套筒结构受力和变形的薄弱部位。盾构完全进入钢套筒后,钢套筒结构的受力和变形最为不利。工程实测表明,采用钢套筒接收工法进行盾构接收安全、可行,但在工程实践中应重视腰部、底部和后端板位移实测数据的大的波动,规范施工操作并加强监控。

Mechanical behaviors and field tests of steel sleeves during shield receiving

Water inrush and gushing can be easily induced during shield receiving in water rich sandy ground. Based on shield receiving practice at Longhua Station of Shanghai Metro Line 11, the rules of stress and deformation of steel sleeves are analyzed by using the FEM numerical method, and the field tests on deformation of steel sleeves and settlement of flood wall are carried out to verify the feasibility. The results show that the maximum tension stress location gradually changes from the back plate to the bottom of connection area between sleeve and diaphragm wall during shield arriving. The circumferential stress is 2 to 7 times the longitudinal stress. The mechanical states at the following locations change obviously: circumferential axial force below the spring, longitudinal axial force at the bottom and longitudinal moment at the spring, and the accumulated deformation at the spring reaches 10 mm. As the shield advances, the bottom will deform outward while the spring inward, therefore, the radial deformation of the sleeve changes from a lying duck egg to a standing duck egg, and finally similar to the shape of 8, with the ovality reaching nearly 3‰. However, the stress and strain have no significant changes at the back plate because of bracing constraint. The joints between the steel sleeve and the diaphragm wall and those at the spring and the bottom of blocks are the weak positions of steel sleeve for stress and deformation control during shield receiving, and the most disadvantage state occurs when the shield is completely into the steel sleeve. The in-situ measurements show that the steel sleeve receiving technology is safe and feasible when adopting the current design parameters. However, the large fluctuations and instability of field data at the spring, bottom and back plate should be paid great attention to, and standard operating