Martin D. Liu

Strength development in blended cement admixed saline clay

Abstract Cement stabilization is extensively used to improve engineering properties of soft saline clays. The effect of salinity, which is modified by geological and climate changes, on the strength development in cement admixed saline clay is investigated in this paper. For a particular curing time and salt content, the strength development in saline clay admixed with cement is governed by the clay-water/cement ratio, w c / C . The strength increases with the decrease of w c / C . The increase in salt content for a particular water content decreases the inter-particle attraction of the clay and the cementation bond strength. Hence, for the same clay-water/cement ratio, the strength of the cement admixed saline clay decreases with increasing salt content. In order to increase strength, and improve the economic and environmental impact, fly ash (FA) and biomass ash (BA) can be used to substitute Portland cement. The influence of FA and BA on the strength development of cement admixed saline clay was investigated with unconfined compressive (UC) test and thermogravimetric (TG) analysis. FA and BA were dispersing materials, increasing the reactive surface of the cement grains, and hence strength increases as well. The clay-water/cement ratio hypothesis was used successfully to analyze and assess the strength development of blended cement admixed saline clay at various salt contents. An addition of 25% ash can replace up to 15.8% of cement.

REVIEW OF THE STRUCTURED CAM CLAY MODEL

The Cam Clay model and most models subsequently developed within the critical state framework are normally formulated to represent the behaviour of soils reconstituted in the laboratory, where the soil structure, if present, is standardised by the sample preparation method. However, as seen from both laboratory and in situ tests, soil behaviour may depend significantly on its structure. The structures of soils found in situ vary greatly, depending on their formation processes and their mechanical, electro-chemical and biological histories. The authors have proposed a relatively simple predictive model, known as the Structured Cam Clay (SCC) model, for solving practical geotechnical problems. In this paper a review of the performance of the Structured Cam Clay model is presented. The paper contains the following four parts. (1) A summary is made of the generalisation of the critical state framework into a new four dimensional space, consisting of the current stress state, stress history, the current voids ratio, and the current soil structure. The key assumption of the theoretical derivation is that both the hardening and destructuring of natural clays are dependent on plastic volumetric deformation. (2) The main concepts and the formulation of the Structure Cam Clay model are introduced within the generalized framework and an explicit stress-strain matrix is obtained for SCC. (3) The capacity of the model for describing laboratory single element tests is evaluated and the main features of the model are summarised. (4) Techniques for refining the Structured Cam Clay model are also discussed.

General Strength Criterion for Geomaterials Including Anisotropic Effect

The strengths of geomaterials and their variation under different factors are investigated in this paper. First, a general isotropic variation of a strength criterion is proposed for describing the critical state and peak strengths of geomaterials. Second, the proposed criterion is extended to describe the effect of anisotropy on the peak strength. After an analysis of experimental data, the hypothesis is made that the failure of an element of geomaterial generally occurs in a particular plane when the applied shear stress in that plane reaches the shear resistance of the material. Therefore, the variation of the peak strength of anisotropic materials should be described in terms of the stress tensor applied, a vector parameter defining the position of the potential failure plane of the material, and the material properties. A general failure criterion for geomaterials with cross anisotropy is obtained then from the proposed isotropic strength criterion. The proposed criterion is demonstrated to well represent both the isotropic and anisotropic strengths of various geomaterials. Finally, a general anisotropic criterion is introduced.

Physical, Hydraulic, and Mechanical Properties of Clayey Soil Stabilized by Lightweight Alkali-Activated Slag Geopolymer

AbstractLightweight cement materials are extensively used in the infrastructure construction. Geopolymer is a low-carbon and environmentally friendly cementitious material. This paper presents an investigation on the physical, hydraulic, and mechanical characteristics of lightweight geopolymer stabilized soil (LGSS) and a comparison with lightweight cement stabilized soil (LCSS). Measurements of volumetric absorption (VA) of water, hydraulic conductivity (k), and unconfined compressive strength (qu), scanning electron microscope (SEM) observation, mercury intrusion porosimetry (MIP) test, and thermogravimetric analysis (TGA) are conducted. The results show that LGSS has higher VA than LCSS. The k of LGSS is one order of magnitude higher than that of LCSS. The qu of LGSS is 2–3.5 times of that of LCSS. Microstructurally, the VA and k of LGSS are found to be positively correlated with the volume of large air pores (>10  μm). Higher qu of LGSS than LCSS is attributed to more hydration products that fill up t...

Complete Compression Curves of Reconstituted Clays

AbstractUnlike that adopted in most existing compression models, the complete compression curve of reconstituted clays in the e − lnp′ space is S shaped. In this paper, an accurate S-shaped equation is proposed that is suitable for describing the complete compression behavior of reconstituted clays with p′ ≥ 0.01 kPa. The proposed equation is an elementary function and is ready for implementation into general stress and strain models. The proposed compression equation is validated by simulating the compression behavior of a variety of reconstituted clays.

Simulating the stress and strain behavior of loess via SCC model

The behaviour of collapsible soils (loess) is studied in this paper. Simulations of the stress and strain behaviour of the soil are made via the theoretical framework of Structured Cam Clay, with the effect of glutinous ingredient in loess suggested to be modelled as cementation effect. Based on the simulations, the capacity of the model for representing the behaviour loess is investigated, and discussions on modelling the behaviour of collapsible soil in general are given.

Numerical modelling of soft ground improved with cement

This paper examines the undrained bearing capacity of shallow circular foundations on soft ground improved with cement by using a numerical model based on the finite element method. Guidelines are given to identify the importance of the degree of cementation for assessing the bearing capacity of foundations. Using a bearing capacity improvement factor, influence of the extent of the cemented region on bearing capacity has been investigated. Finally the performance of deep mixed cement columns has been investigated using the numerical model. The results indicate that there exists an optimum length to diameter ratio for the deep mixed cement columns and this value depends on the degree of cementation of the soil.

Effect of KMP Stabilization on Chemical Properties of a Heavy-Metal Contaminated Site Soil

This paper presents a comprehensive investigation of chemical properties, including soil pH, acid neutralizing capacity, metal leachability and chemical speciation, of a Zn, Pb and Cd contaminated site soil stabilized by KMP. The results show that the KMP stabilized soils have lower pH and higher resistance to acid attack than the untreated soil; the KMP is effective in reducing the metal leachability and changing the metal speciation, and the corresponding leached concentrations significantly below their regulatory limits; furthermore, lower acid soluble fraction contents contributes to the lower metal leachability in contaminated soils.

Stress-Strain Relation and Strength Prediction Method of a KMP Stabilized Zn, Pb and Cd Contaminated Site Soil

This paper presents a systematic laboratory investigation of the effects of KMP content and curing time on the mechanical properties of a Zn, Pb and Cd contaminated site soil. Some basic parameters quantifying the stress-strain relation and strength properties of KMP stabilized site soils are evaluated. They are the values of unconfined compressive strength (qu), failure strain (ef), and Young’s modulus (E50). Furthermore, some empirical equations are proposed, which are useful for engineering applications.

A New Equation for SWCCs of Unsaturated Soils

In the current geotechnical engineering practice, soil-water characteristic curves (SWCCs) are essential for quantifying the mechanical responses of unsaturated soil. The SWCC can be measured from laboratory or estimated from some empirical equations. Measured SWCCs are usually conducted for drying curve by using Tempe cell or pressure plate device. Because of the time consuming associate the absorption, the wetting SWCC can be approximated by estimating the magnitude of the hysteresis loop at the inflection point on the drying SWCC. The SWCC is commonly plotted as a curve between (gravimetric or volumetric) water content and and the logarithm of soil suction. The general shape of the SWCC looks similar to the S-shaped function. An accurate mathematical modelling of the S-shaped curve is usually required for engineering computation such as numerical analyses. In this paper, a new method to quantifying the SWCC, i.e., via the S-shaped equation proposed by Liu et al. (2013), is employed to represent the SWCC. Comparisons between the equation simulations and experimental data are made. Discussions on the equation simulations and characteristics of the mechanical properties of unsaturated soils are also presented.