高地应力软岩隧道中型钢与格栅支护适应性现场对比试验研究

RESEARCH ON SELECTION OF STEEL AND STEEL GRID FOR TUNNEL SUPPORT IN SOFT ROCK WITH HIGH GEOSTRESS

结合正在修建的兰新铁路第二双线LXS–7标存在极高地应力的大梁隧道,系统开展型钢钢架与格栅钢架在高地应力软岩隧道支护中适应性的现场对比试验研究。现场设置型钢钢架支护段与格栅钢架支护段各20 m,通过现场试验及三维数值仿真模拟,对施工过程中的围岩位移、初支钢架应力、围岩–初期支护接触压力进行对比分析,结果表明:(1)在高地应力软岩隧道支护中,型钢钢架对沉降及水平位移的约束作用较强,但支护后期变形呈现台阶式增长趋势,支护设立2个月后仍无明显收敛趋势。相应地,支护结构承受了较大的围岩压力,试验断面围岩–初期支护接触压力最大值为336 kPa,钢架应力较大;二衬施作后围岩变形仍在增加,对二衬结构会有一定影响。(2)格栅钢架属于柔性支护,初期支护设立一周后拱顶累计变形达350 mm,可较好地释放高地应力区围岩应力与变形,但支护内力及变形急剧增加无法收敛。(3)为更好地控制围岩变形,在格栅支护设立一周后增设工字钢套拱作为后期刚性支护,围岩变形曲线呈现明显收敛趋势,洞室变形稳定至446 mm。断面围岩–初期支护接触压力实测最大值为190 kPa,有效地控制支护的变形与格栅应力。(4)试验表明,现场采用"先柔后刚"的支护原则,即先架立格栅后加设套拱对高地应力软岩隧道进行支护,可有效控制软岩大变形及支护内力,结构合理。经济性分析也表明,此支护形式具有较好的经济性,是一种可适用于高地应力软岩隧道的支护结构。

The different effects of applying the steel frame and the steel grid frame in high geostress region were investigated during the construction of Daliang tunnel in LXS–7 of Lanzhou—Xinjiang double line Railway. The experimental sections applying the section steel and the steel grid are 20 meters in length each. Numerical simulations were carried out. The settlement of the tunnel crown and the arch foot,the horizontal convergence,the surrounding rock pressure and the stress of initial supporting steel framework were compared through experiments and numerical simulation. The section with the steel frame had the settlement and the horizontal convergence controlled more effectively than the one with the steel grid. But the contact pressure of surrounding rock and steel reached 336 kPa,much higher than the cases of the section with steel grid support. In the section of steel grid,the settlement of tunnel crown reached 350 mm after a week,with the rapid displacement increasing. To control the deformation of the surrounding rock,multiple support including the steel grid and the steel frame were set up. The settlement of tunnel crown reached a stable value of 446 mm and the surrounding rock pressure reached 190 kPa. The deformation of surrounding rocks and the stress of initial supporting steel frameworks were finally effectively controlled,so as to indicate that the multiple support is an effective measure of controlling the large deformation of surrounding rocks.