Determination of consistency limits of clay by means of extrusion tests

The liquid limit of clay is commonly determined through the Casagrande test or the fall-cone test, while the plastic limit is determined through the hand rolling method. The greatest issue with some of these techniques is their low repeatability and operator dependency. In order to minimize those issues, an indirect-extrusion based technique was evaluated as an alternative method to determine both consistency limits. The experimental work was carried out on mixtures of kaolin and bentonite to cover a wide range of plasticity. The results suggested that there is a specific extrusion pressure linked to each consistency limit and that the results are repeatable. The liquid limit obtained through the extrusion method closely matches the results of the fall-cone test. Similarly, the plastic limit out of extrusion closely matches the results of the hand rolling method

Wet and dry effect on the hydraulic conductivity of polymer treated GCL prototype

Geosynthetic clay liners (GCLs) are widely used to isolate pollutants because of their low hydraulic conductivity to water. However, the performance of clay barriers may be impaired by prolonged exposure to electrolytic liquids which may lead to the compression of the diffuse double layer. The consequences are the increase of permeability and the loss of self-healing capacity. Moreover, the efficiency of the liners can further deteriorate by repeated wet and dry cycles, which may lead to desiccation of the bentonite and associated cracking. Modified bentonites have been introduced to improve the resistance of clay barriers to aggressive solutions. This study deals with a polymer-amended clay, HYPER clay. HYPER clay is treated with an anionic polymer and dehydrated and it shows enhanced performance in presence of electrolyte solutions. The effect of wet and dry cycles on the hydraulic conductivity to seawater of needle-punched GCLs prototypes of treated and untreated bentonite was investigated. The prototype samples containing HYPER clay 8% showed lower permeability compared to those containing untreated bentonite. However, the temperature suggested from the standard used in this study is extremely high and it does not represent the temperature in the field

Small-strain shear modulus and strength increase of cement-treated clay

A simple nondestructive technique was used as an alternative method to monitor the hardening of cement-treated clay as a function of time. The principle of this monitoring technique is based on the use of bender elements to measure the small-strain shear modulus (G0) at various time intervals. The strength increase was monitored by conventional unconfined compression testing. Experimental work was carried out on Kaolin clay treated with Portland cement and blast furnace slag cement at different dosages. The results showed that G0, as well as strength, of cementtreated samples increases logarithmically with time. However, blast furnace slag cement produces a slower hardening rate early after mixing. It was found that for each binder type, the G0 increase and the strength increase, when normalized, follow a common trend. Such a hardening function may be used as the basis of a strength prediction rule. The functions obtained are in good agreement with data on other cement-treated inorganic clays published in the literature

Monitoring the impact of sulfate attack on a cement-clay mix

Cement-clay mixtures are regularly employed as cut-off walls to isolate polluted soils or in ground improvement technologies. In this research, an alternative method to monitor the mechanical and hydraulic behavior of cement-clay mixtures is proposed. Bender elements were installed in a hydraulic conductivity cell, to monitor simultaneously the small-strain shear modulus (G0) and the hydraulic conductivity of a cement-treated kaolin clay mixed with blast furnace slag cement. During permeation with deionized water, an increase of G0 with time was observed, due to cement hydration (hardening). Conversely, after permeation with a sulfate solution, a sudden decrease of G0 and a gradual increase of the hydraulic conductivity were noticed. The interparticle cementation of the mixture was probably affected by contact with sulfates, which are particularly aggressive to cement. Monitoring of G0 was shown to provide valuable additional information to study the impact of sulfate attack on the mechanical and hydraulic behavior of cement-clay mixtures

Stress-strain behavior of artificially cemented Kaolin clay

In this paper, the strength and compressibility of a reference material such as Kaolin clay after treatment with binders was studied with the aim of identifying key behavior features and differences with respect to noncemented Kaolin clay. The water content of the soil was fixed at a high value to represent a very soft consistency. Portland cement was used as binder at dosages varying from 5% to 20%. A number of samples were prepared in the laboratory and were allowed to cure under controlled conditions. The shear and compression behavior of natural and cement-treated kaolin clay samples was assessed by triaxial compression testing and oedometer tests. The results demonstrated that cemented samples show initially much higher stiffness and strength than noncemented samples. But as the stress level increases a yielding state is encountered where interparticle bonding begins to break intensively. Before yielding (at low stresses), the strength is governed by the cement dosage and the one-dimensional compression is almost negligible. Beyond yielding (at high stresses) the strength is governed by the stress level just like for any frictional material. Under onedimensional compression, a clear collapse is observed; the compression lines tend towards the compression line of the noncemented clay with a gradient that lightly steepens with increasing cement dosage