白鹤滩柱状节理玄武岩几何结构特征分析及其几何模型构建

Geometrical characteristic investigation of the Baihetan irregular columnar jointed basalt and corresponding numerical reconstruction method

柱状节理岩体具有独特的几何和地质构造特征,其源于基岩冷凝收缩而形成的横截面为不规则多边形的柱体结构,是自然界存在的独特几何构造奇观。在白鹤滩水电站左岸坝基开挖过程中,出露了大面积的不规则柱状节理玄武岩,给大坝基础安全建设带来不均匀沉降变形破坏等隐患,为此本文对其几何结构特征进行了大量的现场调查研究并开展相应的力学机理分析。现场调查表明,白鹤滩柱状节理玄武岩主要由5边、6边和7边柱组成,柱状节理截面呈不规则的多边形裂隙形式。在总结柱状节理岩体横截面多边形的尺寸和形状的定量测量方法基础上,提出了柱状节理截面多边形的不规则程度的评定方法,进而针对柱状节理的不规则多边形节理模式并基于随机Voronoi算法,提出了一种改进的Voronoi多边形(MVP)生成方式。用MVP方法得到的多边形模式包含大量不规则多边形,可以实现随着不规则程度的增加,多边形模式从初始理想的正六边形到最终实际存在的不规则多边形模式的快速演化过程,不同规则度下柱状节理岩体的压缩试验表明,几何不规则性对其力学特性产生较大的影响。该数值重构方法可为构造具有特定多边形特征的柱状节理岩体提供了一种可靠的几何建模方法。

Columnar jointed rock mass with unique geometric and geological properties is one spectacular example of geometrical order in nature.Columnar joints are generally accepted to be formed by spatially uniform volume contraction during cooling.In this paper,substantial field work was performed to study the geological characteristics of irregular columnar jointed basalt on the left bank dam foundation in the Baihetan Hydropower Station,where the columnar jointed rock mass is extensively exposed due to excavation.The quantitative measurements of the sizing of polygonal crack pattern of columnar joints and assessment of their degree of irregularity were summarized.Considering the irregularity of polygonal crack pattern,a modified Voronoi polygon(MVP)method was developed to model the special polygonal crack pattern of columnar joints.The new polygonal pattern obtained by the MVP method consists of a large number of irregular polygons,of which the degree of irregularity is consistent with the field measurement results.This method can reproduce the rapid evolution from an initial ideal regular hexagonal pattern to a final actual irregular polygonal pattern as the degree of irregularity increases.The compression tests of columnar jointed rock mass with different irregularity show that the geometric irregularity has a great influence on its mechanical properties.This numerical construction method provides a reliable way to reconstruct columnar joint structure with specific polygonal crack pattern,which is consistent with onsite columnar jointed basalt.