Effects of block shape and inclination on the stability of melange bimrocks

Abstract

A wide range of heterogeneous geological units composed of strong rock blocks enclosed in a bonded matrix of fine texture exists worldwide. Such geomaterials belong to geotechnically complex formations and are often referred to as bimrocks (block-in-matrix rocks) or bimsoils (block-in-matrix soils), as a function of their matrix characteristics and the interface strength between the matrix and blocks. Stability problems occurring in such complex geomaterials have been analysed almost exclusively by means of deterministic approaches and with the aim of investigating the effects of variable block contents on their mechanical behaviour. However, bimrocks and bimsoils can present very different internal block-in-matrix arrangements and properties according to their forming process and, consequently, significantly dissimilar mechanical behaviours. Therefore, the aim of this paper was to statistically investigate and compare the stability of theoretical slopes in the most widespread bimrock formations, i.e. sedimentary and tectonic melanges. These formations are characterised by substantial differences in their rock inclusion geometry. To this aim, a great number of 2D slope models were generated to enclose blocks with variable shapes, dimensions, arrangements, inclinations and contents. To obtain statistically based results, fifteen configurations were analysed for each block content and geometrical configuration considered. The results obtained indicate that block shapes and orientations significantly affect the stability of slopes in bimrocks only when the block contents are greater than 40%. Moreover, it is demonstrated that blocks inclined 0° to the horizontal provide the most tortuous and irregular failure surfaces and, consequently, the highest safety factors.

Research Progress on the Geomechanical Properties of Block-in-Matrix Rocks

“…Medley and Sanz [ 94 ] and Minuto and Morandi [ 95 ] developed a simple two-dimensional model simulating blocks with a horizontal rectangle, stating that a three-dimensional model is needed for Monte-Carlo-type random simulations to better approximate real-world conditions. Montoya-Araque et al [ 96 ] and Napoli et al [ 23 , 25 ] utilized the finite element method (FEM) and Limit Equilibrium Method (LEM) to simulate the uncertainty of actual block distributions, emphasizing the crucial role of random methods in Bimrock simulations.…”

“…Due to the prevalence of Bimrock belts in tectonically active regions, secondary disasters such as landslides are likely to occur. The complex lithology, structure, geological hydrology, and geomechanical characteristics of Bimrock pose significant challenges to engineering projects involving underground structures, tunnels [ 20 , 21 , 22 ], and slopes [ 23 , 24 , 25 ]. Notable incidents include the Bai Ge landslide in Changdu City, Tibet, and the Temigu landslide in Batang, which dammed the Jinsha River, leading to substantial downstream losses [ 26 , 27 ].…”

An Experimental Investigation of the Effects of Block Proportion on Bimrocks, Considering Different Block-to-Matrix Strength Ratios

“…Bimrocks are complex geological materials composed of rock blocks and matrices with different mechanical properties, and have obvious inhomogeneity and anisotropy. These materials such as mélange [ 1 , 2 ], fault breccia [ 3 , 4 ], conglomerate [ 5 ], and lithified colluvium [ 6 ] are inevitable to encounter in engineering. Therefore, it is necessary to understand their strength characteristics and failure behaviors.…”

The relict landslide in bimsoils in downtown Genova, Italy: a new modeling approach

“…[2][3][4][5]. Therefore, in order to take all these characteristics into full account and perform an accurate stability assessment, stochastic instead of deterministic analyses should be used [6][7][8].…”