The combined effect of clay and moisture content on very small strain stiffness of compacted sand-clay mixture

The very small strain shear modulus (stiffness) of soils, Gmax, is one of the most important parameters for predicting ground movements and dynamic responses of geo-structures. In this study, the combined effect of clay fraction and moisture content on shear stiffness of an unsaturated sand-clay mixture at very small strains was investigated using bender elements. Compacted soil specimens were prepared at three different clay contents of 10, 20, and 30%, and at four different initial moisture contents of 3, 6, 9 and 12%. Bender element tests were carried out under isotropic and constant moisture content conditions and inside a modified triaxial testing system equipped with a pair of piezoelectric bender-extender elements. Gmax was calculated based on the velocity measurement of shear waves propagated through the specimen. The tests results showed that Gmax decreases approximately linearly with an increase in moisture content, and non-linearly with an increase in clay content. A basic empirical equation was derived from an examination of trends in evolution of Gmax with clay and moisture content. Additional empirical correlations were also derived for estimation of moisture content and degree of saturation based on the compression wave velocity measurements

Reliability of HCT-based Soil Water Retention Curves

The measurement of SWRCs using HCTs has been the subject of several recent studies. Consequently, there have been several design and experimental procedures developed. However, despite these developments, the accuracy, range and duration of HCT-based measurement is still largely characterized by uncertainties and inconsistencies, thereby, reducing the reliability of the obtained SWRCs. In this work, an experimental program is designed to address these uncertainties. SWRCs of reconstituted London clay were measured using the continuous drying method with evaporation rate control. The obtained SWRCs were analysed based on the maximum suction value recorded by HCTs (sₘₐₓ), the obtained air-entry value (sₐₑᵥ), the suction at inflection point (sᵢ), the water content at inflection point (wᵢ), and the slope of tangent to inflection point (mᵢ). A percentage uncertainty of ±4% was obtained for the saev and si values. Similarly, percentage uncertainties of ±6% and ±0.5% were obtained respectively for the mᵢ and wᵢ values. These results were further compared with parametric analysis of the reported SWRCs of the same soil in the literature. Given the observed tolerance ranges, cautions must be taken in selecting values for these parameters e.g. as input values in mathematical curve fitting equations for prediction of the entire SWRC, or in unsaturated constitutive modelling, to enhance reliability of the outputs

An Introduced Methodology for Estimating Landslide Hazard for Seismic andRainfall Induced Landslides in a Geographical Information System Environment

The demand for estimating landslide hazard has evolved during the last decade. Landslides are characterised among the most severe natural hazards, which can cause casualties, fatalities, harm or detriment in natural and man-made environment. In the first part of this paper the results of the research conducted on slope deformation due to seismic loading are presented. According to field observations deformation and displacement of natural and man-made slopes in strong earthquakes are common phenomena, even though they are associated to moderate magnitude seismic events. These permanent displacements are due to seismic loading, and are produced because the material, through which acceleration pulses have to travel before reaching the ground surface, has a finite strength, and stresses induced by strong earthquakes may overcome this strength limit and bring about failure. Many methods were developed in order to assess the earthquake induced ground displacements due to seismic energy flow. We applied the simplified Newmark’s model, in order to study the problem of slope stability estimation and induced permanent deformations. In the current paper, the outcome of the studies attached to slope stability estimation under static and dynamic conditions considering the factors controlling safety conditions is introduced. These principal factors were first introduced to an artificial neural network and the estimated factor of safety and displacement were subsequently implemented in a geographical information system. A software tool was developed in order to produce landslide hazard maps due to static and dynamic loading, implementing failure criteria. In the second part, the results of the investigation of slope hydrology conditions in slope stability are presented. In these cases the factor of safety decreases due to prolonged precipitation and eventually the slope may fail. A parametric study of the effect of suction zone in slope stability of unsaturated soils is examined. This study focuses on slope behaviour under rainfall conditions