广西柳州白云岩强岩溶发育区天然地基稳定性研究

发布时间：2018-03-09 08:09

  本文选题：岩溶　切入点：岩溶地基　出处：《广西科技大学》2015年硕士论文　论文类型：学位论文

【摘要】：论文以广西柳州白云岩强岩溶发育区天然地基为研究基础,以柳州白云岩强岩溶发育区的岩溶塌陷地质灾害为分析对象,分析总结了柳州白云岩强岩溶发育区岩溶塌陷的主要影响因素,通过引入层次分析法对主要影响因素进行分类,在此基础上结合工程实例,运用层次分析法对柳州白云岩强岩溶发育区某一场地岩溶塌陷的危险性进行分区。而后结合柳州白云岩强岩溶发育区岩体力学性能,运用圆板小挠度理论和数值分析软件分析研究了溶洞顶板的稳定性问题;论文考虑人类工程活动对天然地基稳定性的影响,研究了地下水位升降过程中土洞的扩展机理及其周围的应力应变分布规律;在抽水情况下,考虑抽水量对极限水力坡度的影响分析了抽水量的大小对场地稳定性的影响并探讨了场地(土洞)距抽水井的安全距离问题;通过前述研究工作,主要取得了如下认识与成果:(1)柳州白云岩强岩溶发育区岩溶塌陷主要受浅层岩溶发育程度、地形地貌、地层岩性、地下水活动及人类工程活动的影响。其中岩溶发育程度、地形地貌、地层岩性、地下水活动是产生岩溶塌陷的自然因素,而人类工程活动是加快岩溶塌陷的主要诱发因素。(2)厚跨比的不同对溶洞顶板最大拉应力的影响程度差别较大。厚跨比大于0.5时对顶板最大应力的影响较小,但厚跨比小于0.5时对顶板最大应力有显著的影响,且随着厚跨比的减小,最大应力急剧增大。(3)桩径小于溶洞顶板跨度时,除考虑厚跨比对溶洞顶板稳定性的影响外还应考虑跨径比的影响。对于边界固定的溶洞顶板,跨径比对其弯矩和拉应力的分布影响较显著,当跨径比小于2.2时,顶板弯矩及拉应力的最大值均在边界处取得。当跨径比大于2.2时,弯矩及拉应力最大值则于顶板中心取得;边界简支时弯矩及拉应力均在其中心有最大值。但最大剪应力则与跨径比无关,都于顶板外边缘处取得最大值。(4)地下水活动对土洞的扩展表现出一系列影响,地下水位的升降直接导致土洞周围土体塑性区与弹性区范围发生改变,并导致土体应力应变及变形不断变化,于弹塑性交界面附近形成松动圈促进土洞的扩大。(5)当桩径大于或等于溶洞顶板跨度且溶洞顶板岩体基本质量级别为Ⅱ、Ⅲ级时,把厚跨比大于1.0的溶洞顶板判定为稳定,其安全系数大于1.4,此时溶洞顶板有足够的安全储备。
[Abstract]:This paper takes the natural foundation of the strong karst development area of Liuzhou dolomite in Guangxi as the research foundation, and takes the karst collapse geological hazard in the strong karst area of Liuzhou dolomite as the analysis object. This paper analyzes and summarizes the main influencing factors of karst collapse in the strong karst area of Liuzhou dolomite, classifies the main influencing factors by introducing the analytic hierarchy process (AHP), and on this basis combines with an engineering example. The risk of karst collapse in a site in a strong karst area of Liuzhou dolomite is divided by analytic hierarchy process (AHP), and then combined with the mechanical properties of rock mass in the strong karst area of Liuzhou dolomite. The stability of cavern roof is studied by using circular plate small deflection theory and numerical analysis software, and the influence of human engineering activities on the stability of natural foundation is considered in this paper. In this paper, the spreading mechanism of soil tunnel and its stress and strain distribution in the process of groundwater level rise and fall are studied, and in the case of pumping water, Considering the influence of pumping capacity on the limit hydraulic gradient, this paper analyzes the influence of pumping quantity on site stability and discusses the safe distance between site (earth hole) and pumping well. The main achievements are as follows: (1) Karst collapse in the strong karst area of Liuzhou dolomite is mainly affected by the degree of shallow karst development, topography, stratigraphic lithology, groundwater activity and human engineering activity. Topography and landform, stratigraphic lithology and groundwater activity are the natural factors that cause karst collapse. However, human engineering activity is the main inducing factor of accelerating karst collapse. The difference of thickness span ratio on the maximum tensile stress of karst cavern roof is great. When the thickness span ratio is greater than 0.5, the influence of thickness span ratio on the maximum roof stress is relatively small. However, when the ratio of thickness to span is less than 0.5, it has a significant effect on the maximum stress of the roof, and with the decrease of the ratio of thickness to span, the maximum stress increases sharply when the diameter of the pile is smaller than the span of the roof of the cavern. In addition to considering the influence of thickness to span ratio on the stability of the roof of a karst cave, the influence of span ratio on the distribution of bending moment and tensile stress is significant for the roof of a karst cave with fixed boundary, when the span ratio is less than 2.2, The maximum values of bending moment and tensile stress are obtained at the boundary. When the span ratio is greater than 2.2, the maximum value of bending moment and tensile stress is obtained at the center of the roof. When the boundary is simply supported, the bending moment and tensile stress have the maximum value in the center of the boundary, but the maximum shear stress is independent of the span ratio and reaches the maximum value at the outer edge of the roof. 4) the groundwater activity shows a series of effects on the expansion of the soil tunnel. The rise and fall of groundwater level directly change the plastic zone and elastic zone of soil around the soil tunnel, and cause the continuous change of stress, strain and deformation of soil. When the diameter of pile is greater than or equal to the roof span of the karst cave and the basic quality grade of the rock mass of the karst cave is grade 鈪，

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