Research on relationship between rock block proportion and shear strength of soil-rock mixtures based on digital image analysis and large direct shear test

Abstract

With the development of geomechanics and the requirements of many large-scale engineering projects, soil-rock mixtures (SRM) have been regarded as a special type of soil and rock materials which are substantially different with the general soils and rocks in geotechnical engineering. In a large extent, the proportion and distribution of the rock block sizes control the physico-mechanical properties of SRM. Using digital image processing, rock block sizes in SRM samples are identified from the soil matrix. The proportion and distribution of the rock block sizes are then obtained quantitatively. Then the results are used for the sample preparation of the large scale direct shear tests, which cuts a new method for the test study of SRM. According to the results of the large scale direct shear tests, as a whole, the rock block size proportion controls the deformation and fracture mechanism of SRM. The shape of the shear stress versus the horizontal displacement curve and the vertical displacement versus the horizontal displacement curve of the remolded SRM samples are different from the general soils and rocks. With the increase of the rock block proportion, the shear band of SRM increased. When the rock block proportion lied in the range of 25% to 70%, the increment of the internal frication angle increased linearly with the increase of the rock block proportion. And the cohesion of the SRM decreased largely from the soil matrix. When the rock block proportion is large than 30%, however, there is only a little decrease in the cohesion with the increase of the rock block proportion.

隨著現代巖土力學的發展及各類大規模工程建設的需要,土石混合體已經逐漸被作為一種有別于常規的土體及巖石的特殊巖土材料受到國內外研究者的高度關注。土石混合體內部的塊石含量及粒度組成很大程度上控制了其相應的物理力學性質。基于現代數字圖像處理技術,通過對土石混合體內部塊石的形態分析,獲取其相應的粒度組成及塊石含量,并將其作為土石混合體大尺度直剪試驗的制備試樣的基礎,為這類巖土體的試驗研究開辟了新的思路。通過大尺度直剪試驗的研究結果表明,土石混合體的內部塊石含量特征在很大程度上控制了其變形破壞機制,其剪應力–水平位移曲線及垂直位移–水平位移曲線均較常規的土體及巖石有很大的差別。土石混合體的剪切帶將隨著塊石含量的增加而變寬,其內摩擦角增量與塊石含量(25%～70%)近似成線性增長的關系,黏聚力較相應土體有很大程度的降低,但當塊石含量大于30%時,其黏聚力隨著塊石含量的增加而緩慢降低。