溶蚀作用下层状灰岩力学模型研究

Study on mechanical model of layered limestone under dissolution

【目的】层状灰岩的不同层面会表现出不同的力学特性,为了研究溶蚀作用下不同层面倾角的层状灰岩力学特性影响规律,确立溶蚀作用下横观各向同性应变软化模型对溶蚀作用下层状灰岩力学特性进行描述。【方法】首先,采用横观各向同性应变软化模型来描述无溶蚀作用下层状灰岩平行和垂直层面的力学特性,并结合对0°、30°、60°和90°四个层面倾角的层状灰岩单轴压缩试验结果的整理分析,得到无溶蚀作用下平行和垂直层面的层状灰岩核心参数,即弹性模量、黏聚力和内摩擦角等;然后,基于溶蚀作用下层状灰岩力学发生改变机制分析,确定溶蚀作用下层状灰岩的塑性力学模型;最后,结合溶蚀作用下层状灰岩单轴压缩力学试验结果,采用FLAC—强度折减法联合求解确定溶蚀作用下层状灰岩力学模型中力学参数(弹性模量、黏聚力)随溶蚀作用的变化规律。【结果】结果显示,溶蚀等效时间和卸载应变(裂纹发育程度处卸载应变)对不同层面倾角层状灰岩力学特性影响不同,溶蚀等效时间对层面倾角为0°的层状灰岩参数影响最大,卸载应变对层面倾角30°时的层状灰岩参数影响最大。表现为溶蚀等效时间对基质黏聚力c2的影响大于层面黏聚力c1,卸载应变对c1影响大于对c2的影响。【结论】结果表明,横观各向同性应变软化模型能较准确地获取层状灰岩不同层面倾角力学强度参数与溶蚀作用之间的变化关系式,较好地表征溶蚀作用下不同层面倾角层状灰岩力学特性,可为岩溶地下洞室围岩稳定性分析提供理论基础。

[Objective]Different layers of layered limestone show different mechanical properties.In order to study the influence law of mechanical properties of layered limestone with different dip angles under dissolution,a transverse isotropic strain softening model under dissolution is established to describe the mechanical properties of layered limestone under dissolution.[Methods]Firstly,the transverse isotropic strain softening model is used to describe the mechanical properties of parallel and vertical bedding planes of layered limestone without corrosion.Combined with the analysis of the uniaxial compression test result of layered limestone with four bedding angles of 0°,30°,60°and 90°,the core parameters(elastic modulus,cohesion and internal friction angle)of parallel and vertical bedding planes of layered limestone without corrosion are obtained.Then,based on the analysis of the mechanism of mechanical change of layered limestone under dissolution,the plastic mechanical model of layered limestone under dissolution is determined.Finally,combined with the uniaxial compression mechanical test result of layered limestone under dissolution,the FLAC-strength reduction method was used to determine the variation of mechanical parameters(elastic modulus and cohesion)with dissolution in the mechanical model of layered limestone under dissolution.[Results]The result show that the dissolution equivalent time and unloading strain(unloading strain at crack development degree)have differ-ent effects on the mechanical properties of layered limestone with different dip angles.The dissolution equivalent time has the greatest influence on the parameters of layered limestone with a dip angle of 0°,and the unloading strain has the greatest influ-ence on the parameters of layered limestone with a dip angle of 30°.The effect of dissolution equivalent time on matrix cohesion c2 is greater than that of layer cohesion c1,and the effect of unloading strain on c1 is greater than that on c2.[Conclusion]The transversely isotropic strain softening model can accurately obtain the relationship between the mechanical strength parameters of different dip angles of layered limestone and dissolution,and better characterize the mechanical properties of layered limestone with different dip angles under dissolution,which can provide a theoretical basis for the stability analysis of surrounding rock of karst underground caverns.