Abstract
Abstract. The widespread availability of soft rocks and their increasing use as cheap rockfill material is adding more to geotechnical hazards because time-dependent granular decomposition causes significant damage to their mechanical properties. An experimental study was conducted through monotonic torsional shear tests on crushed soft rocks under fully saturated and dry conditions and compared with analogous tests on standard Toyoura sand. Due to the sensitivity of material to disintegration upon submergence, saturated conditions accelerated granular decomposition and, hence, simulated loss of strength with time, whereas, dry test condition represented the response of the soil with intact grains. A degradation index, in relation to gradation analyses after each test, was defined to quantify the degree of granular decomposition. Possible correlations of this index, with strength and deformation characteristics of granular soils, were explored. Enormous volumetric compression during consolidation and monotonic loading of saturated specimens and drastic loss of strength parameters upon submergence were revealed. It is revealed that the observed soil behaviour can be critical for embankments constructed with such rockfill materials. Moreover, the enhanced ability of existing soil mechanics models to predict time-dependent behaviour by incorporating water-induced granular decomposition can simplify several in situ geotechnical problems.
Highlights
While dealing with a variety of non-conventional complex geomaterials, engineering structures are exposed to increased geohazards with intensive developments in hilly areas
Keeping all the initial conditions similar for position on geotechnical properties of the materials were two comparative tests, one specimen was consolidated and explored by comparing the experimental results between the sheared under dry conditions, whereas, the other was satu- crushed soft rocks and Toyoura sand
On the basis2 of maximum evolution potential of the initial grain size distribution (GSD) of a material, a degradation index, ID, was defined, as shown in Fig. 7,3 to quantify the accelerated negative ageing of crushed rocks mainly due to water-induced granular decomposition. Such an index was perceived from grading index (IG), defined by Wood and Maeda (2008), and relative breakage index (Br) by Hardin (1985)
Summary
While dealing with a variety of non-conventional complex geomaterials, engineering structures are exposed to increased geohazards with intensive developments in hilly areas. A typical example of geotechnical hazards, caused directly by the phenomenon of negative ageing mainly due to water-induced granular decomposition of crushed rocks, is reported by Asada (2005). The conditions under which soft rocks are degraded due to physical or chemical decomposition are well established (Hawkins et al, 1988) and efforts are made towards constitutive modelling of degradable geomaterials by Pinyol et al (2007), Yuan and Harrison (2008), and Castellanza and Nova (2004) They concluded that granular decomposition affects the mechanical behaviour due to progressive degradation of bonding and loss of soil structure. The gap between geology and geotechnical engineering needs to be bridged for successful realization of engineering problems faced in complex geology, as well as for efficient use of cheap rockfill materials
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