Characterization of clastic rock using a biconcave bond model of DEM

This paper presents a biconcave bond model to investigate the effect of the cementation between grains on the mechanical behavior of rock. The proposed model considers the shape of the bonds among particles that have a biconcave cement form, based on observations of microscopic rock images. The general equations of the proposed model are based on Dvorkin theory. The accuracy and efficiency of the bond model is improved in three ways. After the biconcave bond model is implemented in the discrete element method software Particle Flow Code in 2 Dimensions, a series of numerical uniaxial compression tests were performed to investigate the relationships between the micro‐ to macro‐parameters. The simulations revealed that the biconcave bond model reflects the effect of micro‐parameters, such as the elastic modulus and Poisson's ratio of the cement, on the macroscopic deformation of cemented granular material. Variations in the bond geometry caused extremely diverse macro‐mechanical behaviors. Experimental results concerning rock demonstrate that the biconcave bond model accurately captures the mechanical behavior of intact rock and supports an innovative method for investigating the relationships between the micro‐ and macro‐parameters of cemented granular material. Copyright © 2016 John Wiley & Sons, Ltd.     

盘形滚刀破岩过程的数值研究

为了研究全断面岩石掘进机盘形滚刀的破岩过程以及盘形滚刀的结构参数（刀刃宽、刀刃角）对滚刀破岩特性的影响,利用离散元方法建立岩石与盘形滚刀的二维数值模型,研究了滚刀侵入岩石过程中贯入度、切削力以及裂纹数三者的关系,在此基础上通过仿真得到滚刀结构参数与岩石破碎特性的规律。研究结果表明：裂纹的扩展与滚刀受到的切削力密切相关;破岩过程中切削力先增大后减小的循环模式,证实了岩石跃进破碎特性。在盘形滚刀作用下,岩石中的应力是向下、向四周无限扩展的对称的应力泡。滚刀刀刃作用区域,应力值最高,随着滚刀贯入度增加,最大应力减小;远离滚刀刀刃区域,应力呈应力泡形式逐层降低至0。选择滚刀刀刃宽在10～15 mm之间,既避免滚刀受到的推力过大,又能提高滚刀的破岩效率;岩石破碎以滚刀刀刃下方向下发展裂纹的扩展为主,刀刃角在10°～20°之间,既能减少滚刀的磨损又能提高破岩效率。     

Displacement‐controlled method and its applications to material non‐linearity

For the analysis of non‐linear problems, the displacement‐controlled method (DCM) has a more extensive application scope and more powerful abilities than the load‐controlled method (LCM). However, difficulties of the DCM's procedure not amenable to most finite element implementations of the conventional LCM have restricted its applications in geomechanics. By means of Sherman–Morrison's theorem, the solution of DCM is improved. The improved procedure is characterized by high efficiency, good numerical stability and a programme structure similar to LCM. Two aspects of applications of DCM are illustrated. The first application is to compute the response of a structure under a given load level like the conventional finite element analysis. The second application is to trace the equilibrium path of a structure under a given load distribution type. A simple but effective algorithm is presented for automatically adjusting the step length in tracing the equilibrium path. Examples illustrate that the proposed procedures are suited for modelling complicated non‐linear problems in geomechanics. Copyright © 2005 John Wiley & Sons, Ltd.     

Evaluation of excavation‐induced relaxation and its application to an arch dam foundation

Based on the damage mechanism of rock during excavation, the maximum tensile strain criterion for pinpointing relaxation region or excavation‐disturbed (damage) zone (EDZ) is introduced. To simulate the deformation and stress redistribution caused by the deterioration of the deformation and strength parameters in the EDZ, the ‘restraint‐relaxation’ finite element algorithm is formulated using the deformation and strength parameters of pre‐and post‐relaxation. The Xiaowan arch dam project (292 m high) is studied by the proposed method, in which the permissible tensile strain and fluidity parameter are evaluated using back analysis. The computation results have good agreement with the field monitoring. An important inference from the study is the necessity of considering the relaxation effects on the dam/foundation system during the construction and operation period. Copyright © 2011 John Wiley & Sons, Ltd.