北石窟寺平顶窟顶板稳定性评价与黏结补强有效性研究

Stability evaluation of the roof of the flat-roof caves and the analysis of the effectiveness of bonding and reinforcement in North Grottoes

顶板岩体层间开裂、崩落是砂岩石窟平顶窟顶板结构失稳的主要病害之一。调查北石窟寺平顶窟顶板发现,地层岩性、岩体层间抗拉强度、剥离体厚度、开口宽度及剥离体与基岩体连通率是影响开裂体稳定性的主要因素。为有效提高平顶板安全储备,增强平顶窟顶板的整体稳定性,根据现场调查和定量计算分析,将顶板开裂岩体划分为低风险、中风险、高风险、极高风险4个等级,抽象简化为“悬臂式折断破坏”和“重力式坠落破坏”两种主要破坏方式,并提出针对北石窟寺顶板开裂岩体稳定性评价的定量计算公式。通过北石窟寺现场注浆黏结试验发现,填充浆液面积覆盖率一般为40%~60%,对剥离体厚度不大于11.4 cm的裂隙岩石进行黏结加固可取得较为理想的效果,考虑8度抗震设防,其有效黏结厚度不大于10.89 cm。

The interlayer cracking and collapse of the roof rock mass is one of the main diseases that cause the structural instability of the roof of flat-top caves in sandstone caves.Investigation on the flat roof caves in Northern Grottoes shows that lithology,tensile strength between rock layers,thickness of stripped body,opening width and connectivity rate between stripped body and bedrock are the main factors affecting the stability of cracking body.In order to effectively improve the safety reserve of the flat roof and enhance the overall stability of the roof,according to on-site investigation and quantitative calculation and analysis,the roof cracked rock mass is divided into four levels:low risk,medium risk,high risk and extremely high risk.According to the force characteristics and deformation failure mode,the roof cracked rock mass is simplified into two main failure modes:“cantilever fracture failure”and“falling failure”.Through the on-site grouting bonding test of the North Grottoes,it is found that the area coverage of the filling slurry is generally from 40%to 60%,and the bonding and reinforcement of the cracked rock with a thickness of no more than 11.4 cm can achieve ideal results.Considering of 8 degree for earthquake fortification intensity,the effective bonding thickness is not more than 10.89 cm.