Bulletin of Engineering Geology and the Environment

The mechanical properties of clays are highly dependent not only on the stress/strain ratio to which the material is subjected but also on the chemistry of the pore fluids which in turn affects the intergranular or the effective stresses. Atterberg limits and vane shear tests were performed with different pore fluids in order to observe how the fine-grained material mechanically responded. The diffuse double layer theory has been used to interpret the data of vane shear tests in order to explain the variation of geotechnical responses with the different clays. Van der Waals forces and double layer forces were obtained and capillary forces calculated. The results show that while for kaolinite and illite the chemistry of the pore fluids has no influence on the water content and hence on the mechanical behaviour of the material, Na-smectite shows a strong correlation between the dielectric constant of the pore fluids and an increase in undrained shear strength. The data obtained extends an understanding of the influence of the dielectric constant (ε) of the pore fluids on the geotechnical properties of fine-grained materials.

Recent researches indicated that the topography is one of the factors affecting the wave propagation pattern (i.e., the amplification or de-amplification). In recent years, many researchers investigated the effect of the tunnels on the wave propagation pattern in the free-field. Although in the construction of the roads in mountainous areas, tunneling for passing through slopes is unavoidable, the role of the tunnel in seismic behavior of slopes has been less concerned. In this study, the structural behavior of the tunnel lining and the amplification pattern in slopes in the presence of horseshoe tunnels, subjected to Ricker incident in-plane shear wave (SV), has been evaluated using the ABAQUS software. Several parameters affecting this phenomenon are accounted for such as the overburden, the distance of tunnels from the slope surface, and the dip angle of slope and bedrock. Results show that the presence of the horseshoe tunnels has a significant effect on the seismic response of the slopes. In comparison to the free-field, the amplitude of the seismic response was increased approximately 30 and 70% for the upstream and the inclined surface of the slope, respectively.

 This paper discusses the method of evaluating the shear strength of a rock mass for the Baoquan Pumped Storage Power Station project. Formulae are presented from which numerical characteristics of the shear strength can be derived. The results are compared with those obtained by the centre point of group and least squares methods. The random-fuzzy method is shown to be the more realistic and appropriate approach, allowing for fluctuations of the parameters and corresponding well with the test values.

The degradation of rock masses making up carbonate slopes within water-level fluctuation zones after the impoundment of reservoirs is in some cases very intense. This has attracted widespread concern because such degradation can result in evolving geological hazards. Quantitative characterization of carbonate rock degradation is the key to the study of this phenomenon and its subsequent impacts. In this article, a meter-scale representative observation plane (body) is selected as the research object. The continuous medium mode is used to describe a carbonate rock mass with evenly distributed degradation quantitatively by way of a rock mass degradation variable (De), which is the relative area ratio or volume ratio of new macroscopic defects (bedding planes, joints, cracks, pores, holes, etc.) that form in a representative rock mass within a period of time. For carbonate rock with nonuniform degradation, a further rock mass degradation variable, DeA, is developed, which represents the relative area ratio or volume ratio of the new defects within a discontinuous surface or body within a period of time. Direct and indirect methods and formulae for acquiring these values are presented, dependent upon the degradation process involved, such as mechanical erosion, dissolution, and fissure development or expansion. The De value is established based on the measurement of area, volume, trace length, aperture, eroded depth, and acoustic wave velocity. The resulting formulae are used to analyze the degradation of typical rock masses in the Wu Gorge in the Three Gorges Reservoir area quantitatively. From 2010 to 2013, the De value increased continuously from 0.18 to 0.42 in Maocaopo and showed an accelerating trend. For the Qingshi 6# slope, for the period from 2017 to 2019, the De value showed an overall decreasing trend with increasing depth based on acoustic wave velocity data. The De value of the rock mass underground is greater than 0.2 for eight sections and reaches a maximum of 0.69. The degradation of the rock mass presents structural and zonal characteristics in the depth direction. In Jiandaofeng, the De value is calculated to be 0.0041 for the period from 2012 to 2017, while, at the Sunjiawan cliff, the DeA value of a large structural plane reaches to 1.03 after 10 years of impoundment. This research forms a foundation for the measurement of the degradation of rock masses in the Three Gorges Reservoir area and provides basic technical support for the subsequent study of rock degradation and hazard prevention in the area. Furthermore, it also provides a reference for assessing the degradation of rock masses within the water-level fluctuation zone for other areas around the world.

Gujarat is one of the western states of India. The workable sand deposits are available in shoals along number of rivers in the state. Since 1980 to 1982, 150 sand samples from 100 different rivers in the state have been collected and petrographically examined. The paper described the classification of the sand deposits into four different groups viz., (i) Kachchh Group (ii) Saurashtra Group (iii) North Gujarat Group (iv) South Gujarat Group. This classification is based upon the variation in percentage of various contituents and their physical as well as chemical properties. The authors have established the relationship of the sand deposits with provenance and the geomorphology of the area through which the rivers flow. They have recommanded the suitability of sand deposits of the above four groups based on physical and chemical properties of the constituents.

Variability in the nature, over a small area, of soils derived from coarse-grained rocks have been widely reported. Such reports concerning soils from fine-grained rocks are however sparse. Some geotechnical properties of a laterite soil derived from a fine-grained amphibolite have been investigated with a view to ascertain its variability. Samples of the soil were taken from the same horizon within an area of about one square metre. The basis index properties, chemistry, mineralogy and microstructure of the sol samples have been investigated. Despite the similarities in the grain-size distribution. Atterberg limits and chemistry of the samples, large variations were obtained in the mineralogy as evidenced by the goethite content, as well as in the micro-structure. The variation in the microstructure is attributed to the inconsistent cementation of the soil particles by non-uniformly distributed goethite which itself is believed to be a result of the variations in the Eh-pH conditions within the soil. The implications of this microstructural variation on the geotechnical properties of the undisturbed soil is assessed.