DDA模拟岩体张拉破坏的精确性研究

Investigating the accuracy of DDA to simulate tensile failure of rock masses

准确分析岩体结构面张拉破坏状态,对于正确处理岩质工程问题极为重要。DDA已经广泛应用于岩土工程领域,然而针对准确分析岩体结构面张拉破坏状态研究较少,为此开展DDA分析张拉破坏状态准确性研究。以经典倾斜台上块体张拉破坏以及倾倒破坏离心机物理模型试验为模拟对象,对原DDA(O-DDA)以及引入二相接触本构关系的DDA(T-DDA)分析张拉破坏状态准确性比对校核。结果表明:DDA计算张力时会出现震荡现象,即初始会出现偏离理论值的峰值计算张力,随后慢慢收敛至理论值,这一现象主要受DDA控制参数中罚弹簧和时间步长影响。为降低计算张力震荡程度,提出了两种参数的优化选择方案。然而,即便在合理选择两种参数情况下,O-DDA分析结构面张拉破坏状态准确性严重依赖于峰值计算张力,误差较大;相比之下,T-DDA克服了依赖峰值张力判断张拉破坏缺陷,在一定程度上降低震荡现象导致的误差,并且软化系数的合理选择也有助于改进DDA模拟张拉破坏的精度。研究成果对改进DDA分析岩土工程中倾倒破坏类问题具有重要意义。

It is very important to analyze the tensile failure state of the rock mass discontinuity.DDA has been widely used in the field of geotechnical engineering.However,there are few researches on the accurate analysis of the tensile failure state of rock mass.In this study,the accuracy of DDA analysis of tensile failure state is investigated.Taking the classical theoretical model of block tensile failure on the tilting table and the toppling failure centrifuge test as simulation objects,the accuracy comparison of the original DDA(O-DDA)and the DDA with the two-phase contact constitutive relation(T-DDA)is checked.The results show that the vibration phenomenon will occur when DDA calculates the tension,that is,the initial peak value of the calculated tension will deviate from the theoretical value,and then slowly converge to the theoretical value.The vibration phenomenon is mainly affected by the DDA control parameters,i.e.,the penalty value and time step.In order to reduce the degree of calculated tension oscillation,the optimization schemes of two parameters are proposed.However,even when two parameters are reasonably selected,the error is still large O-DDA,because the accuracy depends heavily on the peak calculated tension.By contrast,T-DDA overcomes the defect of judging tensioning failure by relying on peak tension,reduces the error caused by oscillation to some extent,and the reasonable selection of softening coefficient is also helpful to improve the accuracy of DDA s simulation of tensioning failure.The research results are of great significance for improving DDA analysis of toppling failure problems in geotechnical engineering.