无衬砌黄土隧道压力拱模型试验及数值模拟

Model test and numerical simulation on pressure arch of unlined loess tunnel

为研究无衬砌黄土隧道压力拱分布及发展规律,开展不同荷载下直墙圆顶隧道开挖物理模型试验,采用微型土压力盒测试围岩变形稳定后的内部应力分布,并利用数值模拟进行对比分析.试验及数值模拟表明,距洞壁约1.5倍洞径范围内,无衬砌黄土隧道围岩存在应力明显增大的区域.当荷载超过一定限值后,洞壁一定范围内的土体应力不再随荷载的增大而增大,出现明显的压力拱边界,黄土隧道围岩表现出一定的压力拱特性.荷载在20kPa以下压力拱范围和边界几乎不变,隧道围岩可以自稳;荷载大于20kPa后,随着荷载增大,压力拱边界及范围逐渐扩大,直墙附近压力拱范围扩展最快,拱肩次之,底板最慢.各级荷载条件下,直墙底部附近压力拱范围最大,拱顶最小,形成了最利于受力的拱脚扩大式压力拱.

To study the distribution and the development law of the pressure arch in unlined loess tunnel, the physical model tests on the excavation of a segmental shape tunnel were carried out under different loads. The miniature soil pressure sensors were used to test the internal stress distribution of surrounding soil after the deformation stability, and the numerical simulations were carried out for comparative analysis. The results of the model tests and numerical simulation show that, within the range of 1.5 times of the tunnel diameter from the tunnel wall, there are areas where the stress increases significantly in surrounding soil of the unlined loess tunnel. When the load exceeds a certain limit, the soil stress in a certain range of the tunnel wall no longer increases with the increase of the load. The obvious pressure arch boundary appears;and the surrounding soil of the loess tunnel exhibits certain pressure arch characteristics. The range and the boundary of the pressure arch are almost unchanged when the load is less than 20 kPa, and the surrounding soil can be self-stable. However, when the load is more than 20 kPa, the boundary and range of the pressure arch gradually expand with the increase of the load. The pressure arch near the straight wall expands to be the fastest, followed by the shoulder, and the bottom is the slowest. Under different load conditions, the pressure arch range near the bottom of the straight wall is the largest, and the crown is the smallest, forming the foot expansion pressure arch that is the most conducive to bearing capacity.