24 research outputs found
Optimising the Performance of Bentonite in Geosynthetic Clay Liners
Geosynthetic clay liners (GCLs), developed over the last quarter century, are innovative
composite matting comprising of bentonite with two covering geosynthetics. The three-layered (2:1)
clay mineral montmorillonite forms the dominant (approximately 75-90% by weight) clay mineral in
the bentonite that is used in its manufacture. Quantitative mineralogical analyses with an assessment
of the adsorbed cation regime need to be normally carried out as part of performance appraisal. The
mineralogical and geotechnical differences between the preferred sodium and the less effective
calcium montmorillonite are presented in the paper. The liners with its encapsulated high active clay
minerals depend on the water balance between the sealing element and the surrounding soil layers.
Assessment of long term hydraulic conductivities and clay-leachate compatibility assessment is also
deemed necessary and the derogatory factors affecting the performance of the bentonite in GCLs
placed in difficult construction and hostile chemical environments are discussed. The performance
specifications for GCLs are identified in this paper and the need to enhance its cation exchange
capacity with polymer treatment coupled with the need for factory prehydration of the untreated
sodium bentonite is emphasised
Geotechnical Characteristics of Peat
Peat soil is encountered in many areas and generally originates from plant/animal remains and is
considered partly as decomposed biomass (Adnan and Wijeyesekera, 2007). Due to this composition, the
structure of this soil is very different when compared with inorganic soils like clay, sand and gravel. Peat
has a high compressibility, low shear strength, high moisture content and low bearing capacity (Bujang,
2004, Adnan et al., 2007). The behaviour and composition of peats in different geographical areas are
different from one another, accentuating the need in soil engineering for a useful geological classification
of peat soils. This paper focuses on presenting a comparative overview of the characteristic geotechnical
properties for these soils. It also examines and discusses the effects of composition on the basic properties
and behaviour of each soil, supported by case studies from Malaysia
Rocker Pipe Solution to Alleviate Settlement Induced Distress in Flexible Pipes
Soil-pipe interaction studies generally recognise the significance of deformations in the
pipe due to soil loading, but not differential ground and structure movements, which can induce
excessive stress concentrations in the pipeline. Plastics pipes can suffer failure due to such
movements, though their flexibility makes them less vulnerable than rigid pipes. This paper examines
the settlements and how the redistribution of the soil sub grade reactions caused by the installation of
a pipeline within a soil mass, can then be estimated by treating the pipeline as a beam on elastic
foundation. Various case histories are summarised, demonstrating these effects, and pointing the way
to possible solutions, which could be incorporated at the project design stage
Shear Modulus and Damping Properties of Peat Soils
Soils are subjected to dynamic loading of various forms. Some of these result from sources
such as earthquakes, traffic loads and tidal action. To assess the level of the consequent ground
motion of the soil, two parameters those are vital in dynamic analysisÍŸ shear modulus (G) and
damping ratio (D) properties (Adnan et. al, 2007, Adnan and Wijeyesekera, 2008). Dynamic
properties of soils such as sand, silt and clay have been studied for more time in the past (Chen et al.,
2007, Hyde and Ward, 1985). However only a insignificant amount of work has been done on the
dynamic properties of peat. This paper presents experimental results based on the undrained cyclic
tests on different peats. Samples were collected from Holme Fen Post, Cambridgeshire and Solway
Post, Carlisle. VJTech Cyclic Triaxial Testing Apparatus was used to measure these parameters. The
significance of peat type, microstructure, loading frequency, confining pressure and index properties
are also discussed
Geotechnical Challenges with Malaysian Peat
Malaysian peat is a tropical peat (Andriesse, 1988). This peat has unique characteristics,
which makes it significantly different from other peat. In its natural state, this soil is normally dark
reddish brown to black in colour and consists of partly decomposed leaves, branches, twigs and tree
trunks with a low mineral content. These are formed through accumulation of disintegrated plant
remains, which have been preserved under conditions of incomplete aeration and high water content.
Hobbs (1986) stated that it was important to include and recognise the peat by not only its
morphology but also by its basic engineering properties. The âspecialâ characteristics for this soil are
a high water content (>200%), high compressibility, high organic content (>75%), low shear strength
(5-20kPa) and low bearing capacity (<8 kN/m2). These geotechnical characteristics make any form of
construction on this soil very challenging in Malaysia (Zainorabidin and Bakar, 2003). This paper
presents an overview of previous research carried out on peat soils (Mutalib et al, 1991; Jarrett, 1997;
Bujang, 2004; Zainorabidin and Bakar, 2003). Edil (2003) demonstrated the variability of the peat
properties even within a single sample, leading to it being far from homogeneous, which is a prime
requirement in engineering soil mechanics. The compressibility of the individual peat particles
invalidates one of the prime assumptions of particle incompressibility adopted in soil mechanics This
paper also discusses the challenges that geotechnical engineers have faced in Malaysia when
designing and managing construction on this soil
Mathematical and Physical Study of Pipe Lines Subjected to Differential Ground Movement
Soil-pipe interaction studies leading to the laboratory observations of the effects of
differential ground movement between a heavy yielding structure and a pipeline firmly connected to
it is presented in this paper. Such differential movements induce excessive stress concentrations on
the pipeline. Plastics pipes fail as a consequence of such movements, though their flexibility should
make them less vulnerable than rigid pipes. In order to evaluate the displacement, bending moment,
shear force, vertical soil resistance at soil pipe interface under these conditions, innovative
experimental techniques were developed and these are described in this paper. The soil resistance on
a pipe section is characterised by the load-displacement behaviour of the embedded pipe section
subjected to lateral displacement, vertical displacement, axial displacement along the axis of the
pipe and rotation about the pipe axis. A mathematical analysis to complement the laboratory studies
is developed and presented by treating the pipelines as a beam on elastic foundation. The magnitude
and location of the maximum bending moments arising from yielding of the heavy structure is
examined. The experimental observations of the behaviour of pipes subjected to such differential
ground movement are compared with the results from the theoretical predictions. The provision of
rocker pipe joints that entertain a permitted rotation helps to redistribute the adverse bending
moments to acceptable levels and thereby alleviate distress in the pipeline. The paper gives results
that demonstrate theoretically and experimentally the appropriateness of the use of flexibly jointed
rocker pipes to prevent such failures. Field examples of the adoption of such joints is also presented
and discussed culminating with the expression of the need for rational design procedures for
pipeline foundations including rocker pipes to be incorporated into codes of practice such as EN
1295 is emphasised
Drying Kinetic of Prehydrated and Extruded Clay Mat
The isothermal drying of prehydrated and extruded clay mat was investigated on a
laboratory scale over a temperature and relative humidity range from 20°C to 40°C and 15% to 70%
respectively. Two sets of polymer enhanced clay mats were used in this study. By measuring the mass
loss of the samples during the isothermal drying process basis dependencies necessary to describe the
kinetic drying process was obtained. The most commonly used model, Page, Wang & Singh,
Henderson & Pabis and Thin layer equation were used to fit experimental data using a nonlinear
regression analysis. The fit quality of the proposed model was evaluated by using the standard error of
estimate, relative percent error and coefficient of correlation. Results probed that the Page model was
more appropriated to predict prehydrated and extruded clay mat for the range of temperatures and
relative humidity studied. Applied model analysis enabled evaluation of the main transport properties:
drying constant, drying rate, effective diffusion coefficient and exponential model parameter. It was
found that the drying condition and type of polymer incorporated in the clay mat strongly influenced
the drying kinetic and transport parameters
Moisture Desorption Isotherms and Thermodynamic Characteristic of Prehydrated and Extruded GCL
An experimental investigation into the drying of pre-hydrated and extruded GCL is
presented in this paper. Moisture desorption isotherm at temperature from 20 to 40°C and water
activity from 0.20 to 0.70 were determined using the static gravimetric method. The moisture
isotherms were sigmoid shaped and were influenced by the thermal environment. The Guggenheim-
Aderson-DeBoer (GAB) was used to fit experimental values using a non-linear regression analysis.
GAB model was appropriate to predict the desorption equilibrium moisture content of pre-hydrated
and extruded GCL for the range of temperatures and water activities studied. Finally, an expression
for predicting the thermal property was developed
Flexibility of âClay Matsâ
This paper presents a scientific development to addressing the current absence of a
convenient technique to identify the ductile to brittle transition of clay mats. The applicability of
clay mats can be brought into question if they become brittle due to drying in hot weather / tropical
climates. Bentonite clay mats produced with different liquid polymers and at different moisture
content were used in the study. The dependence of flexural stiffness on moisture content is
presented. All the specimens showed that the flexibility of the clay mat declined exponentially with
decreasing moisture content. Often one would adopt the feeling from a finger pressure test to give a
perception of the softness / stiffness of the material. The paper also presents an extension of this
concept to adopt an appropriately modified Brinell hardness test for the clay mats. Concurrently, 3
point bending tests were carried out on samples of the clay mat to obtain a value for the elastic
structural stiffness (EI). The paper further confirms a strong correlation between Brinell Hardness
Test and the structural stiffness. This study helps to assess the performance of clay mats with
different proportions of additives that have been introduced in the mat manufacture to delay the
inevitable drying characteristics of the mat, when exposed to hostile thermal environments
Experimental investigation of hydrodynamic erosion of soils
Recent research studies revealed that most bridge piers and other hydraulic structures such
as levees and embankments adopted in flood protection schemes in maritime environment have
collapsed due to the failures attributed to scour associated with a soilâhydrodynamic interaction
phenomenon (e.g. Shirole and Holt, 1991). Though erosion characteristics of coarse sands and gravels
are relatively well known, soil-hydrodynamics interaction for finer sands such as silts and clays is not
fully investigated. A series of small-scale laboratory experiments were conducted in a moveable
sediment tank to investigate scour characteristics under various flow and soil conditions. The present
paper discusses preliminary experimental observations and the analysis of hydrodynamic erosion of
soils in line with the extensive research project âMathematical and Physical Modelling of
Hydrodynamic Erosion of Soils (HES)â carried out under the âUEL Promising Researcher Fellowship
2009-2010â funded by the University of East London (UEL)