大足石刻北山168窟在多年的风化作用和自重应力的影响下，石窟壁和其顶板位置出现了大量的裂缝现象，导致了洞窟顶部围岩的稳定性变差面临失稳坍塌的危险，为了能够有效对平顶石窟顶板破碎围岩进行加固，本文针对现场的地质情况采用了一种悬吊锚杆的顶板加固方式。首先根据现场调查确定出顶板裂缝的分布规律，总结出石窟顶板开裂的主要原因，然后利用新奥法的思想在考虑最不利围岩受力的情况下计算出锚杆的锚固长度，最后利用数值模拟的手段分析了悬吊梁加固方法在降雨条件下石窟顶板的位移变化情况以及应力情况，结果表明：在悬吊锚杆加固条件下，其顶板各个方向位移均不超过1mm；石窟洞口位置及洞内位置应力较为集中，最大拉应力小于砂岩的抗拉强度值，顶板围岩处于稳定状态；悬吊锚杆支护过程中锚固段承受拉应力，平均所受拉应力为4.3MPa，受力情况较好。从现场加固前后曲线数据可以看出悬吊梁加固工法减少了裂缝的波动值，可以认为在悬吊锚杆加固条件下石窟保持稳定状态，该悬吊锚杆加固方式为类似平顶石窟薄板破碎顶板的稳定性支护提供参考。

Under the influence of years of weathering and self weight stress, a large number of cracks have appeared in the cave wall and its roof of Cave 168, Beishan, Dazu Rock Carvings, resulting in the instability of the surrounding rock at the top of the cave and the danger of instability and collapse. In order to effectively reinforce the broken surrounding rock of the roof of the flat roof grottoes, this paper adopts a roof reinforcement method of hanging anchor bolts according to the geological conditions of the site. Firstly, based on on-site investigation, the distribution pattern of cracks in the roof slab was determined, and the main causes of cracking in the cave roof were summarized. Then, the anchoring length of the anchor rod was calculated using the idea of the New Austrian Method considering the most unfavorable stress on the surrounding rock. Finally, numerical simulation was used to analyze the displacement and stress changes of the cave roof under rainfall conditions using the suspension beam reinforcement method. The results showed that: under the conditions of suspension anchor rod reinforcement, The displacement of its top plate in all directions shall not exceed 1mm; The stress at the cave entrance and inside the cave is relatively concentrated, with the maximum tensile stress being less than the tensile strength value of sandstone, and the surrounding rock of the roof is in a stable state; During the suspension anchor rod support process, the anchoring section mainly bears tensile stress, with an average tensile stress of 4.3MPa, indicating a good stress situation. From the curve data before and after on-site reinforcement, it can be seen that the suspension beam reinforcement method has reduced the fluctuation value of cracks. It can be considered that the grotto maintains a stable state under the conditions of suspension anchor rod reinforcement. This suspension anchor rod reinforcement method provides a reference for the stability support of thin and broken roof slabs similar to flat roof grottoes.

重庆市自然科学资助(cstc2021jcyj-msxmx0903)