为了研究桩端岩溶顶板破坏形态和安全厚度受岩体质量的影响,借助离散元软件,建立含节理裂隙的岩溶顶板承载计算模型,揭示顶板损伤断裂破坏细观机制,明确含裂隙顶板破坏形态,以此为基础提出考虑裂隙影响的顶板安全厚度修正计算法。研究表明:完整岩体岩溶顶板表征出典型的脆性破坏,破坏临界位移仅为较破碎岩体的60%,对应的破坏荷载则大了67.5%,岩体裂隙会明显影响桩基安全冗余度的判断,实际工程应充分考虑;桩基荷载作用下含裂隙岩溶顶板发生渐进破坏,主要经历局部压缩、微裂隙闭合→新裂隙萌生、旧裂隙扩展→形成宏观裂纹并张开→生成贯通破坏面与断口,岩体割裂成块→破坏面发展,岩体割裂加剧→形成滑动带,顶板整体破坏;岩溶顶板因错综复杂分布的节理裂隙,其空间破坏形态并非遵循规则的椎台,也非以特定曲线为母线的旋转体,而是源于裂隙的空间不规则破坏体;提出了考虑岩体节理裂隙和桩基荷载作用的岩溶顶板安全厚度修正分析方法,与模型试验结果对比表明,修正计算具备合理性。
In order to study the influence of rock quality on failure form and safe thickness of karst roof, the bearing calculation model of karst roof with rock fracture is established by discrete element software. The mesoscopic mechanism of roof damage fracture failure was revealed and the failure form of karst roof with fractures was clarified. Based on the above, the correction calculation method of safe thickness of karst roof coupling fractures was proposed. The results show that the karst roof of intact rock characterizes typical brittle failure, in which critical displacement for failure is only 60% of more broken rock, and the corresponding failure load is increasing at 67.5% larger. Rock fractures can obviously affect the judgment of the safety redundancy of pile foundations, so the actual project should be fully considered. The karst roof with fracture occurs progressive failure under the pile foundation load and mainly undergoes local compression, micro-fracture closure→new fracture initiation, old fracture expansion→formation of macro-cracks and opening→formation of penetrating failure surface and breaks, rock fragmentation into blocks→development of failure surface, rock fragmentation intensifies→formation of sliding zone, roof overall failure. Because of the complex distribution of rock fracture in karst roof, its spatial failure form is not a regular vertebral platform, nor a rotating body with a specific curve as the busbar, but a spatial irregular failure body derived from fracture. The correction calculation method of roof safe thickness coupling rock fracture and pile load is proposed. Its comparison with the model test results indicates that the correction calculation is reasonable.
[1]刘汉龙, 赵明华. 地基处理研究进展[J]. 土木工程学报, 2016, 49(1): 96-115. (Liu Hanlong, Zhao Minghua. Review of ground improvement technical and its application in China[J]. China Civil Enginee-ring Journal, 2016, 49(1): 96-115. (in Chinese))
[2]董芸秀, 冯忠居, 郝宇萌, 等. 岩溶区桥梁桩基承载力试验与合理嵌岩深度[J]. 交通运输工程学报, 2018, 18(6): 27-36. (Dong Yunxiu, Feng Zhongju, Hao Yumeng, et al. Experiment on bearing capacity of bridge pile foundations in karst areas and reasonable rock-socketed depth [J]. Journal of Traffic and Transportation Engineering, 2018, 18(6): 27-36. (in Chinese))
[3]张乾青, 乔胜石, 邢宇铖, 等. 穿越无充填溶洞时单桩承载特性研究[J]. 湖南大学学报(自然科学版), 2022, 49(7): 186-196. (Zhang Qianqing, Qiao Shengshi, Xing Yucheng, et al. Study on bearing characteristics of single pile crossing unfilled karst save[J]. Journal of Hunan University(Natural Sciences), 2022, 49(7): 186-196. (in Chinese))
[4]黄明, 付俊杰, 陈福全, 等. 桩端岩溶顶板的破坏特征试验与理论计算模型研究[J]. 工程力学, 2018, 35(10): 172-182. (Huang Ming, Fu Junjie, Chen Fuquan, et al. Theoretical calculation model and model test on the failuer characteristic of karst roof under rock-socketed pile [J]. Engineering Mechanics, 2018, 35(10): 172-182. (in Chinese))
[5]黄明, 付俊杰, 陈福全, 等. 桩端荷载与地震耦合作用下溶洞顶板的破坏特征及安全厚度计算[J]. 岩土力学, 2017, 38(11): 3154-3162.(Huang Ming, Fu Junjie, Chen Fuquan, et al. Damage characteristics of karst cave roof and its safety thickness calculation under the coupling effect of pile-tip load and seismic wave [J]. Rock and Soil Mechanics, 2017, 38(11): 3154-3162. (in Chinese))
[6]张俊萌, 方从启, 朱俊峰. 桩基下岩溶顶板稳定性有限元阶段分析[J]. 工程地质学报, 2014, 22(1): 78-85. (Zhang Junmeng, Fang Congqi, Zhu Junfeng. Finite element phase analysis of karst-roof stability under pile foundation[J]. Journal of Engineering Geology, 2014, 22(1): 78-85. (in Chinese))
[7]赵明华, 雷勇, 张锐. 岩溶区桩基冲切破坏模式及安全厚度研究[J]. 岩土力学, 2012, 33(2): 524-530. (Zhao Minghua, Lei Yong, Zhang Rui. Study of punching failure mode and safe thickness of pile foundation in karst region [J]. Rock and Soil Mechanics, 2012, 33(2): 524-530. (in Chinese))
[8]张永杰, 邓俊强, 杨兴山, 等. 考虑溶洞空间形态的岩溶桩基稳定性分析方法[J]. 中国公路学报, 2019, 32(1): 37-45. (Zhang Yongjie, Deng Junqiang, Yang Xingshang, et al. Stability analysis method of pile foundation in karst area base on cavern spatial form[J]. China Journal of Highway and Transport, 2019, 32(1): 37-45. (in Chinese))
[9]化建新,郑建国. 工程地质手册[M]. 北京: 中国建筑工业出版社, 2021. (Hua Jianxin, Zheng Jianguo. Geological engineering handbook[M]. 4th ed. Beijing: China Architecture & Building Press, 2021. (in Chinese))
[10]宋胜武. 基于稳定性评价的坡体结构统一分类研究[J]. 岩石力学与工程学报, 2022, 41(1): 1-9. (Song Shengwu. Unified classification system of slope structure based on stability evaluation [J]. Chinese Journal of Rock Mechanics and Engineering, 2022, 41(1): 1-9. (in Chinese))
[11]张建华. 基于突变理论的岩溶区路基顶板安全厚度分析[J]. 铁道科学与工程学报, 2009, 6(3): 52-55. (Zhang Jianhua. Analysis of cave roof safe thickness in karst region based on catastrophe theory[J].Journal of Railway Science and Engneering, 2009, 6(3): 52-55. (in Chinese))
[12]赵明华, 朱志仁, 黄明华, 等. 考虑基桩嵌岩段侧阻的岩溶区顶板安全厚度计算[J]. 岩土力学, 2018, 39(11): 4201-4209. (Zhao Minghua, Zhu Zhiren, Huang Minghua, et al. Study on thickness of safety for cave roofs suffered bending failure in karst areas[J]. Rock and Soil Mechanics, 2018, 39(11): 4201-4209. (in Chinese))
[13]柏华军.考虑溶洞顶板自重时桩端持力岩层安全厚度计算方法[J].岩土力学,2016,37(10):2945-2952. (Bai Huajun. A method for calculating the safety rock thickness of pile bearing strata with considering deadweight of karst cave roof [J]. Rock and Soil Mechanics, 2016, 37(10):2945-2952. (in Chinese))
[14]雷勇, 陈秋南, 马缤辉. 基于极限分析的桩端岩层冲切分析[J]. 岩石力学与工程学报, 2014, 33(3): 631-638. (Lei Yong, Chen Qiunan, Ma Binhui. Punching analysis of rock at pile tip base on limit analysis[J]. Chinese Journal of Rock Mechanics and Engineering, 2014, 33(3): 631-638. (in Chinese))
[15]于泽泉.溶洞顶板承载力影响因素研究[R]. 广州:广东省建筑科学研究院集团股份有限公司, 2021. (Yu Zequan. Study on ultimate bearing capacity of upper rock plate of karst cave[R]. Guangzhou:Guangdong Research Institute of Building Science Group Co., 2021. (in Chinese))
[16]中华人民共和国住建部. 岩溶地区建筑地基基础技术标准(GB/T 515238—2018) [S]. 北京:中国计划出版社, 2018. (Ministry of housing of the People's Republic of China. Technical standard for building foundation in karst area [S]. Beijing: China Planning Publishing Press, 2018. (in Chinese))
