砂土层中隧道漏砂情况下的安全性研究

盾构隧道的漏水漏砂会引起隧道周围土体应力的变化,导致隧道周围局部或者大范围的土体松动,以致改变隧道横向受力与变形模式,影响隧道结构的安全。采用可考虑大变形的颗粒流方法 PFC,研究隧道不同部位发生漏砂时隧道周围土体的应力变化规律及隧道内力、横向变形的发展规律。结果表明:隧道腰部漏砂引起漏砂位置外围土体松动并进而在松动区外围形成土拱区,隧道扁圆化趋势加剧,隧道内力急剧增加;隧道顶部和底部漏砂极易导致顶部和底部弯矩符号发生变化,改变隧道横向受力模式;隧道肩部发生漏砂时,隧道最大弯矩点向漏砂位置转移,危及隧道肩部管片结构的安全。

Safety situation investigation and analysis of the shield tunnels under the condition of the sandy ground leakage

The present paper is concerned with a safety situation investigation and analysis of the shield tunnels under the condition of sandy ground base leakage.What the author wants to do is to predict and assess the likely effects of the leakage development around the tunnel due to the internal force pressure and the deformation mode of the lining structures.In response to the research need,we have introduced the erosion voids around the tunnel lining at different positions (the crown,the springline,the invert,and the shoulder) by deleting the soil particles flowing into the erosion voids in modeling the leakage of the tunnel.For the above mentioned purpose,we have chosen a set of suitable software named PFC (Particle Flow Code) based on the Discrete Element Method released by the Itasca Company,which is capable for modeling large or serious deformation and disaster problems.At the same time,efforts have also been made to acquire the alteration of the soil stresses in the ground,the evolutionary situation both of the internal force and the transverse deformation in case any leakage takes place in the tunnel.The results of our investigation indicate that the leakage at the springline of the tunnel is likely to create a loosening zone and an arch-like zone from the inside to the outside.Meanwhile,the tunnel ovalization trend might also aggravate the lining status,thus leading to costly failure.On the other hand,if the leakage takes place in the crown and the invert,the bending moment may reverse its sign from negative to positive in the counterpart,respectively,which may lead to essential change of the loading mode and result in the crack of the outside of the lining if the tensile strength of the lining material is too large.On the other hand,if the leakage at the shoulder of the tunnel may cause asymmetric change of the internal force,and make the maximum bending momentum displace towards the leaking position,serious damage risk would like to come up to the position.At this point,the PFC software tends to be very useful and effective in modeling the tunnel disaster.Thus,the findings of the present paper is qualified enough to highlight the importance for preventing the leakage in the tunneling project from further deterioration and the likely failure.All the results we have gained can be taken as of theoretical importance in nature,through physical testing is still needed to evaluate the performance of the above calculations.