基于Griffith断裂准则的根系固土力学模型

A root-reinforced soil mechanics model based on the Griffith fracture criterion

【目的】土体抗剪强度增量ΔS是衡量植物根系固土效果的重要指标,针对目前计算ΔS的力学模型精度不高、计算过程复杂等问题,本论文对根系固力学模型进行改进,以期提高生态边坡稳定性分析的准确性。【方法】本文运用断裂力学与功能原理,探究植物根系破坏失效模式,提出基于Griffith断裂准则下的根系固土力学模型。选用寒旱环境下代表护坡植物霸王Zygophyllum xanthoxylon、柠条锦鸡儿Caragana korshinskii根-土复合体的直剪试验数据,采用回归分析方法分析其根径与抗拉指标间的相关性,验证根系固土力学模型的合理性、有效性。【结果】理论分析表明,植物根系对土体抗剪强度增量与根系断裂韧性G_(p)决定,可表示为ΔS=kG_(p),其中G_(p)由植物根径、根系弹性模量及土体横截面积等参数决定。直剪试验数据分析结果显示,植物根径与抗拉力呈线性关系,与抗拉强度呈幂指数关系。根系在剪切破坏失效过程中,表现为断裂、拔出及滑移3种状态,其中断裂主要发生在根径较小的侧根处。【结论】直剪试验数据验证的结果表明,构建的根系固土力学模型简便可靠,土体抗剪强度增量的预测误差值保持在15%左右,精度较高,可为根系固土力学效应预测及生态边坡稳定性评价提供理论依据,具有广泛的应用前景。

【Objective】The increase in shear strength of the soil(ΔS)is an important index to measure the effect of root system soil consolidation.Aiming at the problems of low precision and complex calculation process of the mechanical model for calculatingΔS,this paper improves the mechanical model of root system in order to improve the accuracy of ecological slope stability analysis.【Method】Fracture mechanics and functional principles was used to explore the failure mode of plant root failure,and proposes a root soil consolidation mechanics model based on Griffith fracture criterion.Using direct shear test data of root-soil complexes of Zygophyllum xanthoxylon and Caragana korshinskii,which are representative of slope protection plants under cold and drought conditions,the regression analysis method was used to determine the root diameter and tensile strength of the two plants.The strength correlation relationship verifies the rationality and validity of the root soil consolidation mechanics model.【Result】Theoretical analysis shows that the increase in shear strength of the root system to the soil is mainly determined by the fracture toughness(G_(p))of the plant,which can be expressed asΔS=kG_(p),where G_(p) is determined by the plant root diameter,root elastic modulus and soil Parameters such as cross-sectional area are determined.The analysis results of the direct shear test data show that the root diameter of the plant has a linear relationship with the tensile strength and a power exponential relationship with the tensile strength.During the shear failure process of the root system,there are three states of fracture,pull-out and slip.Among them,the fracture mainly occurs at the lateral root with smaller root diameter.【Conclusion】The results of direct shear test data verification show that the constructed root soil consolidation mechanics model is simple and reliable,and the prediction error value of the increase in soil shear strength is maintained at about 15%.The accuracy is high.It can be used to predict the mechanical effect of root consolidation and ecology.The slope stability evaluation provides a theoretical basis and has a wide range of application values.