凝灰岩高边坡二次开挖稳定性分析及防护技术优化

Stability Analysis of Secondary Excavation on Tuff High Slope and Optimization of Protection Technology

凝灰岩具有遇水后易软化、崩解导致的强度大幅度下降性质,施工容易产生坡体局部开裂、溜坍等病害。为解决惠深高速公路加宽改扩建工程中凝灰岩高边坡二次开挖的稳控问题,首先采用有限元软件分析凝灰岩高边坡开挖中失稳机理及影响因素,并提出了高边坡二次开挖加固技术,后结合现场边坡位移和支护结构应力联合监控的方法,评价凝灰岩高边坡加固后的效果。研究结果表明:三级边坡至五级边坡的初次浅层溜坍区,降雨为诱因,开挖卸荷变形为主因;削方卸荷后发生二次溜塌,降雨为诱因,未及时支护为主因。针对病害实况,在三级边坡溜坍区采取“素混凝土护壁+锚杆格梁”支护措施,加固施工完成后,4级平台水平位移测点最大水平速率为0.28 mm/d,平均速率仅为0.02 mm/d,支护结构的应力值亦在预警范围内且无明显波动,加固措施效果明显。

Tuff is softened and disintegrated when contacts with water,resulting in remarkable strength decline.Tuff high slope in construction are prone to cracking and slippery collapses.In order to solve the stability problem in the secondary excavation of the high tuff slope of Huizhou-Shenzhen highway Project,we analyzed the instability mechanism and influencing factors in the excavation of high tuff slope using finite element software,and put forward reinforcement technology for the secondary excavation.Moreover,we assessed the result of reinforcement by joint monitoring of slope displacement and support structure stress.Results unveiled that the excavation-induced unloading deformation was the major cause,and rainfall the inducing factor of the first shallow slide of grade-3 slope to grade-5 slope;the absence of timely support was the major cause,and still rainfall the inducing factor of the secondary collapse after the square cutting and unloading.We propose to apply concrete retaining wall and anchor beam in the collapsed area of grade-3 slope.After the reinforcement construction,the maximum horizontal displacement was 0.28 mm/d at grade-4 platform,averaging only 0.02 mm/d,and the stress of support structure stayed within the early-warning range with no obvious fluctuation,indicating an effective reinforcement.