软硬互层状反倾岩质边坡倾倒变形离心模型试验研究

Centrifuge model test study on toppling deformation of anti-dip soft-hard interbedded rock slopes

针对软硬互层状反倾岩质边坡倾倒变形演化模式尚不明确的问题,基于相似原理以及地质资料,以水泥、石膏等作为相似材料建立3组边坡物理模型:一组为单一硬岩层状反倾岩质边坡,另外2组为不同层厚比的软硬互层状反倾岩质边坡。通过离心模型试验,运用图像量测技术,探究软硬互层状反倾岩质边坡与单一硬岩层状反倾岩质边坡倾倒变形破坏模式的差异性,分析不同软硬岩层厚比中软岩对于边坡整体倾倒变形程度以及边坡极限承载力的影响。研究表明:(1)软硬互层状反倾岩质边坡倾倒变形模式与单一硬岩层状反倾岩质边坡倾倒变形模式存在差异。前者在倾倒变形过程中产生两级破裂面:主破裂面与次级破裂面,次级破裂面首先贯通,其上浅层岩体失稳,进而深部不连续弯折带相互贯通,主破裂面形成,边坡整体失稳,向下垮落。(2)倾倒变形过程中主破裂面以下岩体几乎未发生倾倒,可将该面定义为倾倒-未倾倒岩体的分界线;次级破裂面发育深度与主破裂面相比更浅,但是其上浅层岩体倾倒变形程度更大,且更易发生失稳破坏,该面为边坡倾倒变形的最危险破裂面。(3)由于软岩强度较弱的影响,软硬互层状反倾岩质边坡其破裂面形态呈弧线形,与单一硬岩层状反倾岩质边坡不同。(4)软岩的存在对于边坡的极限承载力与倾倒变形程度也有影响,且软硬岩层厚比不同,影响不同。相比于单一硬岩层状反倾岩质边坡,软硬岩层厚比为1∶1的软硬互层状反倾岩质边坡,其极限承载力提高,倾倒变形程度减小;而软硬岩层厚比为2∶1的软硬互层状反倾岩质边坡,其极限承载力降低,倾倒变形程度增大。

In view of the lack of understanding of the toppling deformation of anti-dip soft-hard interbedded rock slopes,based on similarity principle and geological data,three groups of slope physical models were established with cement and gypsum as similar materials,among which one group is an anti-dip layered rock slope with hard rock and the other two groups are soft-hard interbedded rock slopes with different layer thickness ratios.By carrying out centrifugal model tests and using image measurement technology,the differences of toppling deformation and failure modes between the anti-dip soft-hard interbedded rock slopes and the anti-dip layered rock slopes are studied,and the influence of the layer thickness ratios of soft rock to hard rock on the overall toppling deformation degree and the ultimate bearing capacity of the slope is analyzed.The following conclusions are obtained by the tests:(1)The pattern of toppling deformation of the anti-dip soft-hard interbedded rock slope is different from the anti-dip layered rock slope with hard rock.The former has two fracture surfaces including the primary fracture surface and the secondary fracture surface.The secondary fracture surface is first formed and the upper rock mass has an instability.Then,the deep discontinuous bending zones coalesce with each other,and finally the main fracture surface is formed and the slope fails as a whole collapsing downward.(2)Almost no toppling occurs in the rock mass below the primary fracture surface during toppling deformation,so the primary fracture surface can be defined as the boundary line between the toppling and non-toppling rock masses.The development depth of the secondary fracture surface is shallower than that of the primary fracture surface,but the shallow rock mass above the secondary fracture surface has a greater toppling deformation degree and is more prone to failure.The secondary fracture surface is the most dangerous fracture surface during the process of slope toppling deformation.(3)Due to the weak strength of the soft rock,the fracture surface of the anti-dip soft-hard interbedded rock slope is arc-shaped,which is different from that of single lithology layered anti-dip rock slope.(4)The existence of the soft rock also has influence on the ultimate bearing capacity and the toppling deformation degree of the slope,varying with the layer thickness ratio of the soft rock to the hard rock.Compared with the single hard rock layered anti-dip rock slope,the ultimate bearing capacity of the soft-hard interbedded rock slope with a thickness ratio of 1∶1 increases and the toppling deformation degree decreases,while for the soft-hard interbedded rock slope with a thickness ratio of 2∶1,the ultimate bearing capacity decreases and the toppling deformation degree increases.