岩体结构不平衡力的实验研究

The deformation reinforcement theory states that the residual unbalanced force is the dominating source of structural failure, whose counterpart is just the required reinforcement force to stabilize the structure. Therefore, the distribution of unbalanced forces are fatal to the stability monitor and control of lager-scale geotechnical structures. In elastoplastic finite element analysis, the unbalanced forces are just pseudo variables, whose objectivity and measurability have not yet been investigated so far. This proposal starts from the proposition that unbalanced forces are the driving forces of the time-dependent deformations, or the visco-plastic deformations. This proposition combines the design and monitor analysis of structural stability and provides theoretical basis for unbalanced force measurements: unbalanced forces can be indirectly determined by the measured visco-plastic rates with giving rate equations. In the project, the measurements are carried out on geomechanical model test. The strain gauges are attached on the blocks made of test materials, which are stacked to form the model by means gluing. Constant loads are exerted on the model and the strains measured by the internal strain gauges can be transformed to the visco-plastic strain rates. The unbalanced forces are calculated from the visco-plastic strain rates based on Perzyna equation with associated flow rule, in which the material parameters are calibrated beforehand. Rock matrix and structural surfaces are handled in different ways. The rock matrix is considered within classical visco-plasticity theory while the structural surfaces are measured and analyzed individually on their own orientations, where the Perzyna equation and yield function are all recast to vector forms on that orientation. Finally, an integrated system is established for monitoring and analyzing the unbalanced forces inside the structures, which can display the unbalanced force distributions of the high-stress-gradient zones and reveal the unloading and relaxation mechanisms of rock masses.

根据变形加固理论，结构残余不平衡力就是结构所需加固力，故确定不平衡力分布对实施大型岩土工程的准确而有效的稳定控制至关重要。但不平衡力作为弹塑性有限元分析中的中间虚拟变量，其在实际结构中的存在性、可测性问题从未被探索研究过。本申请首先从理论上提出并阐明了"不平衡力就是时效变形的主要驱动力"的学术思想。该学术思想使稳定设计分析和监测分析有机地结合起来，并为不平衡力测量奠定了理论基础。本研究拟在地质力学模型试验的基础上测定不平衡力：在相似模拟材料小块体上贴上应变片，岩体结构由大量小块体粘接砌置而成后，在恒载作用下，这些内部应变片即可反映出黏塑性应变率，再以Perzyna关联黏弹塑性模型为基础即可推求岩体结构的不平衡力。本研究最终将构建成套的监测理论、系统、方法以测定岩体结构内部的不平衡力分布，在此基础上论证并确立该学术思想，并展示高梯度应力区内不平衡力的分布以探索岩体卸荷松弛的内在动力机制。

根据变形加固理论，岩体结构残余不平衡力就是结构所需加固力，故确定不平衡力分布对大型岩土工程实施准确而有效的稳定控制至关重要。但不平衡力作为弹塑性有限元分析中的中间虚拟变量，其在实际结构中的存在性、可测性问题从未被探索研究过。本项目对已有的三维非线性有限元程序TFINE程序进行版本升级，实现了基于OPENMP的并行计算，计算最大单元规模由十万级升至百万级，速度也大大加快；研制了保压作用的长期伺服加载系统，为岩体结构的非平衡演化实验提供保障。基于流变模型指出不平衡力是推动岩体结构产生非平衡演化的内在作用力，证明了最小塑性余能原理，进一步完善岩石蠕变松弛的热力学基础，搭建了相对完整的不平衡力与松弛、破坏的理论框架，通过小块体试件流变实验验证流变模型。通过预制裂纹试块开裂试验、高拱坝坝踵开裂模型试验、水压致裂破坏研究等实验验证了不平衡力与开裂良好的相关性，并成功在锦屏一级、白鹤滩、孟底沟等高拱坝超载破坏过程分析中应用。针对高坝库区蓄水期谷幅收缩现象，提出了裂隙岩体的有效应力原理，指出蓄水期基础中孔隙水作用使岩体的有效应力变化产生的塑性变形是库区谷幅收缩的主要原因，该成果在锦屏一级、白鹤滩水库蓄水期边坡稳定分析中得到应用。