Volume change behaviour of a compacted scaly clay during cyclic suction changes

The research presented in this paper focuses on the investigation and modelling of the volume change response of compacted tectonised clay samples subjected to several wetting and drying cycles in controlled-suction oedometers. Oedometer tests were carried out under different values of constant vertical net stress, and wetting and drying cycles were performed varying applied matric suction between 10 and 800 kPa. The investigation was complemented with a study of the material microstructure to support the interpretation of the overall mechanical response. At a microscopic level, the material is characterized by different types of particle assemblages, scales, and clay aggregates. One of th…

Experimental study of a naturally weathered stiff clay

Studying the shear strength of a naturally weathered clay is important to understand rain-induced slope failures in weathered soils. However, experimental studies on naturally weathered soils are limited. The paper focuses on the laboratory experimental investigation carried out to analyse the shear strength of a naturally weathered stiff clay that can be found in unsaturated conditions in situ. This has an important practical relevance in the evaluation of the stability conditions of natural slopes at clay outcrops. Different experimental techniques of suction measurement were used to obtain the soil-water retention curve of the clay over a wide range of suctions. Scanning electronic micr…

Shear Strength of a Compacted Scaly Clay from Suction-Controlled Triaxial Tests

The paper presents the results of an experimental research aimed at investigating the shear strength characteristics of an unsaturated compacted scaly clay. Shear strength was investigated by suction-controlled triaxial compression tests on dynamically compacted samples. Collected results point out that suction effects on stiffness and shear strength can be very different for suction values applied lower or greater than air entry value (AEV), corresponding to the material void ratio.

Mechanical behaviour of compacted scaly clay during cyclic controlled-suction testing

Scaly clays are stiff and highly fissured soils due to their complex geological history. Owing to these characteristics, they may be placed and compacted as excavated, to obtain a material with adequate engineering properties, suitable as core material in earth dams and in waste isolation fills. With reference to these engineering applications, an exhaustive experimental programme is developed to characterise the hydro-mechanical behaviour of this compacted material under a variety of controlled-suction paths. This paper presents selected test results, focusing on the interpretation of specific behavioural features of the volume change of this complex material; namely, the strain accumulati…

Volumetric Behaviour of Lime Treated High Plasticity Clay Subjected to Suction Controlled Drying and Wetting Cycles

The paper presents some experimental results collected on samples recovered from an experimental embankment obtained by compacting a lime-treated clay. Samples were collected soon after the in situ compaction and they were cured in controlled environmental conditions for at least 18 months. Mercury intrusion porosimetry tests (MIP) were carried out on freeze-dried specimens to characterize the microstructure of the material. In order to assess the durability of the improved material, laboratory tests focused on the effects of cyclic variations of the degree of saturation on the water retention properties and the volumetric behaviour of the stabilized clay. Collected results show that the li…

On the reactivation of a large landslide induced by rainfall in highly fissured clays

Abstract The paper discusses the field investigations, geotechnical characterization and time evolution of horizontal displacements in a wide landslide. The latter, triggered by an earthquake occurring in September 2002, is located in Sicily and involves a thick body of stiff and highly fissured clays belonging to a Varicoloured Clay formation. In order to characterise the reactivation of landslide mechanisms induced by rainfall, a three-year monitoring programme (2008–2011) was implemented to measure rain, pore water pressures, and deep and superficial displacements. The monitoring data made it possible to recognize three distinct landslides, which evolve at variable rates in different dir…

Shear strength of a compacted scaly clay in variable saturation conditions

Scaly clays are stiff and highly fissured clays often used as construction materials. This paper presents the results of triaxial compression tests carried out on saturated and unsaturated samples of a compacted scaly clay. Complementary investigation on the microstructural features and their evolution with the amount of water stored into the material are also presented in order to shed light on the evolution of the micro- and macroporosity with suction. The water retention behaviour of the compacted scaly clay is also addressed. The results from the controlled suction triaxial tests are used to discuss the applicability of a single-shear strength criterion to compacted double-structured cl…

Modeling Round Robin Test: An Uncoupled Approach

Abstract The solution of the modeling test presented in the paper is based on an uncoupled hydro-mechanical approach. Firstly, the controlled infiltration process is modeled by a finite element transient groundwater seepage software. Afterwards, calculated pore water pressures at successive instants are used for the slope stability analysis. Time evolution of the slope stability is analysed by using the infinite slope model, according to the classical limit equilibrium method.

Modelling the Water Retention Domain of a Compacted Scaly Clay

A body of experimental data on the water retention behaviour of compacted samples of an Italian scaly clay is analysed. The mechanical and the hydraulic behaviour of compacted samples of this clay are governed by multi-scale arrangement of scales and aggregates, which characterises the compacted clay fabric. At least two different pore networks, namely intra-aggregate and inter-aggregate, may be identified, which interact one with the other along coupled hydro-mechanical paths. The retention behaviour is interpreted in the framework of a comprehensive multi-scale modelling approach recently proposed for compacted clays of low and medium activity, which proves to be able to account for the i…

Suction controlled drying and wetting cycle effects on the volumetric behaviour of a lime-treated high plasticity clay

The paper presents some experimental results collected on samples recovered from an experimental embankment obtained by compacting a lime-treated clay. Samples were collected soon after the in situ compaction and they were cured in controlled environmental conditions for at least 18 months. Mercury intrusion porosimetry tests (MIP) were carried out on freeze-dried specimens to characterize the microstructure of the material. In order to assess the durability of the improved material, laboratory tests focused on the effects of cyclic variations of the degree of saturation on the water retention properties and the volumetric behaviour of the stabilized clay. Collected results show that the li…

Soil slope consolidation processes induced by drainage galleries with drainholes

Microstructure Characteristics of Unsaturated Compacted Scaly Clay

Microstructure characteristics of unsaturated compacted scaly clay are investigated by MIP tests on freeze dried samples and observation of SEM photomicrographs. Effects of scale microstructure and increasing compaction stresses, and microstructure changes induced by loading and unloading paths and clay saturation are analysed.