شبيه سازي ناهمساني در سنگ نرم با استفاده از يك مدل

Simulation of Anisotropy in Soft Rock

به خاطر ساختار ذر هها فرايند رسوبگذاري و بارگذاري هاي متعاقب، مصالح ژيوتكنيكي از خود رفتار ناهمساني نشان مي دهند. در اين مقاله تاثير ناهمساني در رفتار برشي توده سنگ نرم بررسي م ي شود . ازين رو مدلي در چارچوب مد ل هاي چندصفحه ارايه شده است كه رفتار تغيير شكل توده را به وسيله ي پاسخ روي چندين صفحه تماسي بيان م يكند. سطح تسليم، قانون جريان و سخت شوندگي، روي صفح هها فرمول بندي شده و ناهمساني مواد رسوبي با در نظرگرفتن ويژگي هاي مقاومتي مختلف، روي صفحات فرضي مدل چن دصفحه، شبيه سازي مي شود. اگر تعداد صفحات از حدي كمتر باشد، از مدل ارايه شده مي توان براي شبيه سازي توده سنگ درزه دار بهره برد. درحالي كه با ارايه توابع تسليم متفاوت روي تعداد زيادي از صفحات با پخش يكنواخت ، اضافه شده و پس از Flac رفتار سنگ نرم رسوبي، ناهمسان است. مدل چند صفحه به صورت مدل رفتاري به نر مافزارتفاضل محدود بررسي درستي آن با روش حل بسته، از آن براي شبيه سازي رفتار ناهمسان يك نوع سنگ رسوبي استفاده شده است . در نهايت، شبيه سازي پايداري شيرواني از مصالح ناهمسان ارايه است.

Due to sedimentation process, structure of particles and subsequent loading history, most of the natural soil and rock deposits, tend to be highly anisotropic, which manifests itself in the directional dependence of deformation and strength characteristics. Also, existence of discontinuities such as joints and faults cause anisotropic behavior in the rock mass. Different constitutive models have been introduced by researchers to simulate the inherited or induced anisotropy in geo-materials. Due to the concept of the multi-laminate framework, in which yield and plastic potential functions are defined on a number of independent acting planes, plastic flow is developed independently on different planes. Therefore multi-laminate models are able to simulate induced anisotropy, intrinsically. In this study, a constitutive model based on multi-laminate framework with Mohr-Coulomb failure criterion for modeling the anisotropy is written and added to a two-dimensional explicit finite difference program, FLAC. In this model, anisotropy of geo-materials can be modeled in tow different ways; the first way is used to model jointed rocks with the assumption that a pronounced anisotropy of rock can be described by introducing a certain number of planes of weakness and behavior of rock mass can be determined from interaction of the joint planes and the intact rock. In the second way, anisotropy of sedimentary materials can be introduced in a straightforward manner by varying model parameters over the sampling planes that obtains by the parameters in the vertical and horizontal direction. When the number of plans is less than 5, geo-material is considered as the jointed rock mass with those number of joint sets, otherwise, geo-material considered as the sedimentary rock or soil mass; so application of different yield strength in numerous contact plane with uniform distribution, enable the model to simulate anisotropy in intact samples. For each contact plane, two failure criteria are considered associated with two potential functions. In fact non-associated flow rule and associated flow rule are applied to simulate plasticity formulations in shear and tensile mode of failure, respectively. Strength parameters of each contact plane are calculated based on its dip angle and the strengths of the intact soft rock in the direction of parallel and vertical to the sedimentation.The capability of the model is demonstrated by numerical simulation of uni-axial tests on jointed rock mass and the results are compared with those from analytical closed form solutions. The effect of anisotropy in friction angle and cohesion are investigated through the model in order to present sensitivity of the model to anisotropy ratio and angle of sedimentation. Finally the proposed model is used to simulate stability of a slope in the sedimentary domain; the results show that with a constant sedimentation angle, increase in anisotropy ratio will increase the differences of the safety factor of the slopes with isotropic and anisotropic behavior.