【作者】 蒋德松；

【导师】 赵明华；

【作者基本信息】 湖南大学 ， 道路与铁道工程， 2019， 博士

【摘要】 岩溶是一种常见的不利工程地质,其在我国的分布范围十分广泛,占到我国国土面积的1/3,尤其在南方地区分布更为密集,如云南、贵州、广西、湖南和湖北等地。随着我国经济的发展,西部大开发及一带一路战略的实施,大量的基础设施修建在岩溶区。在高速公路修建过程中经常遇到岩溶的情况,如何评价岩溶区路基的稳定性是工程设计与施工的关键技术之一,其关系到整个工程的安全与经济。因此,对岩溶区路基稳定性分析方法进行研究具有重要的理论意义和工程实践价值。本文在前人研究的基础上,综合考虑溶洞截面形状、几何尺寸及分布形态的影响,结合理论和数值分析方法,对路基荷载作用下圆形、马蹄形溶洞的稳定性进行分析,计算考虑溶洞旋转角度和溶洞空间分布的路基极限承载力。在稳定性评价的基础上,考虑工程安全和减小路基沉降,提出桩网复合地基岩溶处治方法,最终形成一套完整的岩溶路基稳定性评价和处治方法。主要研究内容如下:(1)为研究路基下伏圆形溶洞的稳定性,根据工程的实际情况,将路基荷载及岩层上覆土层荷载作为整体考虑,建立理论分析模型。基于复变函数理论,通过映射函数将分析平面映射到单位圆的外域中,采用保角变换和柯西积分等求解手段,推导得到路基荷载作用下含圆形溶洞地层中的各应力分量表达式。在此基础上,进一步求得溶洞洞边上任意一点的最大、最小主应力,同时引入Griffith强度破坏准则判断各点的破坏状态,从而对溶洞的整体稳定性作出评价。(2)在路基下伏圆形溶洞稳定性分析的基础上,进一步深化复变函数法在岩溶区路基稳定分析中的应用。针对路基下伏马蹄形溶洞稳定性问题,介绍了三种任意截面形状溶洞的映射函数确定方法,包括图解结合法、多角形逼近法和三角插值法。在此基础上,求得路基荷载作用下含马蹄形溶洞地层中溶洞洞边的各应力计算公式,并求得各点的最大、最小主应力。结合Griffith强度破坏准则,对溶洞洞边各点的破坏状态进行判断,得到了路基荷载作用下马蹄形溶洞稳定性评价方法,并采用数值分析和工程实例对所提方法的正确性进行了验证。(3)根据有限元极限分析法的基本原理,将上、下限定理转化为相应的数学规划模型,基于MATLAB平台编制了有限元极限分析程序。该方法结合了极限分析法和有限元法的优点,不需要通过人为构造机动场和静力场,也不需要荷载-位移曲线判断路基的极限承载力,可直接求解得到上限解和下限解,为复杂工况下岩溶路基稳定性分析奠定了基础。开发了自适应的网格划分技术以减小上限解和下限解的相对误差,其能根据能量耗散的不同自动调整网格划分的密度。(4)采用有限极限分析法对路基荷载作用下矩形溶洞的稳定性进行分析。根据工程实际情况,首先建立路基荷载作用下矩形溶洞稳定性数值分析模型。然后对路基的极限承载力进行计算,并将计算结果进行无量纲处理,总结成设计计算表格。详细探讨材料物理力学参数、溶洞跨径、高度和旋转角度对路基极限承载力的影响。(5)将修正的Hoek-Brown准则直接嵌入有限极限分析程序中,对多溶洞地层上方路基的极限承载力进行计算。以单个圆形溶洞上方路基承载力作为参照对象,定义了衡量多溶洞条件下路基承载力的无量纲参数,得到了可供工程实践采用的设计计算表格,并探讨了溶洞大小、溶洞间水平距离、垂直距离和岩体参数对路基极限承载力的影响。(6)对于岩溶区路基容易失稳的工况,综合考虑工程安全和减小路基沉降,提出桩网复合地基处治岩溶的方法。从有无溶洞的工况出发,对不考虑溶洞影响下的桩土应力比进行计算,同时分析桩网复合地基处治溶洞后筋材变形与受力的关系,以指导桩网复合地基岩溶处治过程中筋材的设置。更多还原

【Abstract】 Karst is a common disadvantageous engineering geology,which is widely distributed in China,accounting for 1/3 of China’s land area,es pecially in the southern region,such as Yunnan,Guizhou,Guangxi,Hunan and Hubei.With the development of economy and the development of the western region,and the implementation of the "The Belt and Road" strategy,a large number of infrastructures are constructed in the karst areas.Karst is often encountered in the process of expressway construction.How to evaluate the stability of subgrade in karst area is one of the key technologies in engineering design and construction,which relates to the safety and economy of the whole project.Therefore,the method of the subgrade stability analysis in karst area has important theoretical significance and practice value.Following the previous studies,the effects of section shape,geometric size and distribution shape of the karst cave are considered in this paper.Combining theoretical and numerical analysis methods,the stability of circular and horseshoe-shaped caves under subgrade load is analyzed,and th e ultimate bearing capacity of subgrade is calculated,which has considered the effect of the rotation angle and the spatial distribution of caves.Considering engineering safety and reducing roadbed settlement,A Karst treatment method for pile-net composite foundation is proposed.Finally,a whole set of methods karst roadbed stability evaluation and treatment is formed.The main study contents are shown as follows:(1)To investigate the stability of circular karst cave under subgrade,based on the engineering practice,a theoretical analysis model is established,which considers the load of roadbed and overlying soil layer as a whole.Based on the theory of complex variable function,the analysis plane is mapped to the outer field of unit circle by mapping function.Using conformal transformation and Cauchy integral,the expressions of stress components in the stratum with circular cave under subgrade load are derived.On this basis,the maximum and minimum principal stresses at any point on the cave are obtained,and the Griffith failure criterion is introduced to judge the failure state of each point,so as to evaluate the overall stability of the cave.(2)Based on the stability analysis of circular karst cave underlying subgrade,the application of complex variable function method in stability analysis of roadbed in karst area is further deepened.Considering the stability of horseshoe-shaped karst caves under subgrade,three mapping functions of karst caves with arbitrary cross-section shape are introduced,including graphic combination method,polygonal approximation method and triangular interpolation method.Then,the formulas for calculating the stress at the edge of the cave in horseshoe-shaped cave stratum under subgrade load are obtained,and the maximum and minimum principal stresses at each point are calculated.Based on the Griffith failure criterion,the failure state of each point at the edge of karst cave can be judged,and the stability evaluation method of horseshoe-shaped karst cave under subgrade load is established.The method is verified by numerical analysis and engineering examples.(3)According to the theory of finite element limit analysis,the upper and lower limit theorems are transformed into corresponding mathematical programming models.Based on the platform of MATLAB,the finite element limit analysi s program is developed.This method combines the advantages of limit analysis method and finite element method,which does not need to construct maneuvering field and static field artificially,nor does it need load-displacement curve to judge the ultimate bearing capacity of subgrade.The upper and lower bounds can be obtained directly,which lays a foundation for stability analysis of karst subgrade under complex conditions.An adaptive meshing technique is developed to reduce the relative errors between the upper bound and the lower bound,which can automatically adjust the meshing density according to the different energy dissipation.(4)The stability of rectangular karst cave under subgrade load is analyzed by using finite limit analysis method.According to the engineering practice,the numerical analysis model of rectangular cave stability under subgrade load is established.Then,the ultimate bearing capacity of the subgrade is calculated,and the calculation results are dealt with dimensionless,which are summarized as design tables.The effects of physical and mechanical parameters of materials,the karst cave span,height and rotation angle on the ultimate bearing capacity of subgrade are discussed in detail.(5)The modified Hoek-Brown criterion is directly embedded in the finite limit analysis program to calculate the ultimate bearing capacity of the subgrade above multi-cave strata.Taking the bearing capacity of the subgrade above a single circular karst cave as a reference object,the dimension less parameters for measuring the bearing capacity of the subgrade under the condition of multiple karst caves are defined,and the design calculation tables for engineering practice are obtained.The influence of cave size,horizontal distance between cav es,vertical distance and rock mass parameters on the ultimate bearing capacity of subgrade has also beeb discussed.(6)Considering the engineering safety and reducing the settlement of the subgrade,a method of treating Karst by pile-net composite foundation is proposed for the condition that roadbed is easy to lose stability in Karst area.The pile-soil stress ratio without considering the influence of karst cave is calculated.Meanwhile,the relationship between deformation and stress of reinforcement after treatment of karst cave with pile-net composite foundation is analyzed to guide the setting of reinforcement in the process of treatment of karst cave with pile-net composite foundation.更多还原