Environmental Geotechnics Ltd.

Adderbury, United Kingdom

Environmental Geotechnics Ltd.

Adderbury, United Kingdom
Time filter
Source Type

Meggyes T.,University of Wolverhampton | Jefferis S.A.,Environmental Geotechnics Ltd
Geotechnical Special Publication | Year: 2012

Tailings slurries are suspensions in water of the fine-grained residues of the milling process by which raw materials are extracted from mined rock. Deposition of these slurries in ponds or lagoons, usually confined by man-made dams, can present serious safety and environmental risks, especially if there is inappropriate handling or management. In contrast thickened paste technology using very lowmoisture thickened tailings, has made rapid progress from 1995 onwards, and offers significant economic incentives and environmental benefits. No particle segregation takes place during the thickening process; the paste material exhibits much greater stability than conventional tailings; there is no need for a pond on top of the deposit; which itself forms a gently sloping surface which promotes runoff of rain water; and the overall costs are lower than for conventional slurry technologies. © 2012 American Society of Civil Engineers.

Lam C.,University of Manchester | Jefferis S.A.,Environmental Geotechnics Ltd. | Jefferis S.A.,University of Oxford
Geotechnical Testing Journal | Year: 2015

This paper was concerned with the physical properties of polymeric excavation-support fluids during use and reuse in the field and the techniques for their measurement. Synthetic polymer fluids were used as replacements for conventional bentonite clay slurries for the construction of bored piles (drilled shafts) and diaphragm walls since the early 1990s. They are used, in part, because of their rheological properties, especially their shear-thinning behavior, but to date research has focused on clean fluids and little also has been reported on the effects of reuse under field conditions and on the suitability of viscosity measurement devices. To fill this knowledge gap, the properties of polymer fluids were measured on a construction site in London, UK, over the entire construction period of 52 days. It was found that the density of the fluid and hence other properties were highly dependent on the decisions made by the contractor and that a well-designed tank system could offer considerable benefits in terms of fluid maintenance. Regarding the monitoring of fluid viscosity, the Marsh funnel was, unsurprisingly, found to be unsuitable for detailed analyses; although it did provide some useful information about the overall fluid condition. However, with a direct-indicating viscometer, it was possible to characterize the shearthinning properties of the fluids over a range of shear rates and stages of fluid use. From the test results, it was concluded that the effect of reuse was to increase in the overall fluid viscosity but at the same time to enhance the shear-thinning behavior. © by ASTM Int'l (all rights reserved).

Lam C.,University of Manchester | Jefferis S.A.,Environmental Geotechnics Ltd | Jefferis S.A.,University of Oxford | Martin C.M.,University of Oxford
Geotechnique | Year: 2014

Support fluids are widely used for the construction of deep bored piles and diaphragm walls. Specifications for the use of these fluids vary, and a thorough understanding of their effect on pile shaft resistance has not yet been developed. This paper presents the results of a set of concrete-sand interface shear tests carried out using both polymer and bentonite support fluids, with water as a reference fluid. It was found that polymer fluids had little effect on the interface shear strength when compared with water. Furthermore, in contrast to the results of earlier studies, concrete curing time was found to have little effect on the results. However, when bentonite slurry was used, the interface shear strength was found to decrease approximately linearly with the square root of the filtration time, until the strength of the pure filter cake was reached. This was due to the development of a bentonite filter cake at the interface so that only aggregate protruding through the filter cake made contact with the sand. It was found that the full concrete-sand shearing resistance could be mobilised when the concrete-sand contact area was greater than about 50% of the total area.

Lam C.,University of Manchester | Martin P.J.,University of Manchester | Jefferis S.A.,Environmental Geotechnics Ltd. | Goodhue Jr. K.G.,University of Oxford
Geotechnical Testing Journal | Year: 2014

This paper is concerned with the properties of synthetic polymer fluids used for the temporary support of excavations, such as pile bores and diaphragm wall panels. These fluids can be used as alternatives to bentonite slurries and may influence the performance of the foundation elements formed under them. During the excavation process, polymers tend to be sorbed onto the soil and they may be degraded by the shearing in pumps, etc. It follows that a controlling parameter for these fluids is the residual concentration of active polymer in the fluid, and this paper considers test methods that may be used for its determination. Three different measuring principles, namely, total organic carbon, UV light absorption, and viscosity, were investigated for their suitability for site use. Their performance was compared in a series of polymer-clay sorption experiments-the clay sorbing the polymer, therefore reducing the residual concentration in solution. A method based on the measurement of viscosity of centrifuge supernates was found to have the best overall performance. A comparison with current assessment criteria based on Marsh funnel viscosity and density measurements confirmed the superiority of the proposed method for detecting polymer loss by sorption. Further evaluations showed that the proposed method is not limited to any specific combinations of polymers and soils. The proposed method will allow site engineers to have greater control over the properties of the fluids on site. © ASTM Int'l.

Lam C.,University of Manchester | Martin P.J.,University of Manchester | Jefferis S.A.,Environmental Geotechnics Ltd. | Jefferis S.A.,University of Oxford
Journal of Materials in Civil Engineering | Year: 2015

Synthetic polymer fluids are becoming a popular replacement for bentonite slurries to support excavations for deep foundation elements. However, the rheological properties of the polymer fluids used in excavation support have not been studied in detail, and there is currently confusion about the choice of mathematical models for this type of fluid. To advance the current state of knowledge, a laboratory study has been performed to investigate the steady-shear viscosity and transient viscoelasticity of a polymer support fluid. It is found that over the shear-rate range measurable with the Fann viscometer, an industry standard instrument, the power-law model can be used to represent the results, whereas the Bingham plastic model will significantly overestimate the viscosity at low shear. When evaluated over a much wider shear-rate range with a cone-and-plate rheometer, the polymer fluids show signs of approaching limiting viscosities at the very low and high shear rates, and for this behavior the Carreau model is more appropriate. From a series of oscillatory tests, the viscoelastic properties of the polymer fluid have been shown to be very different from those reported for their bentonite counterparts. The key engineering implications of the rheological results have been discussed.

Lam C.,University of Manchester | Jefferis S.A.,Environmental Geotechnics Ltd. | Jefferis S.A.,University of Oxford
Journal of Performance of Constructed Facilities | Year: 2016

Solutions of synthetic water-soluble polymers have been used for the construction of bored piles (drilled shafts) since the early 1990s. These engineered fluids are very different from conventional bentonite slurries but there is currently a serious lack of industry guidance. Despite their advantages over bentonite, performance issues have arisen in the past and foundation engineers remain wary of their use. To help practicing engineers avoid past pitfalls and to promote best practice, this paper presents a critical reappraisal of selected European case histories of bored piles constructed using polymer fluids. A collective reassessment is necessary in order to provide an overall picture of the situation as individual cases may show conflicting results. It is found that the completed piles can have excellent load-movement characteristics if polymer behavior is understood and respected. Conversely, excavation instability, structural defects, and poor pile performance can result if the special properties of these fluids are not fully appreciated and as a result they are not properly maintained. The findings presented in this paper will be useful for consultants and contractors when designing and constructing piles and diaphragm walls utilizing polymer fluids in the future. © 2015 This work is made available under the terms of the Creative Commons Attribution 4.0 International license,.

Lam C.,University of Manchester | Jefferis S.A.,Environmental Geotechnics Ltd | Jefferis S.A.,University of Oxford
Proceedings of the Institution of Civil Engineers: Geotechnical Engineering | Year: 2014

This paper is concerned with the use of polymer fluids for the construction of bored piles in silty fine sand, a situation which has been found to significantly increase the risk of ‘soft toes’ and concrete contamination due to the settling of the suspended soil particles in the fluid. To illustrate how these problems can be avoided by adopting a simple fluid-testing regime and improved construction practice, this paper presents a case history of polymer use at a site in Glasgow where the ground conditions consist of silty fine sand. Fluid testing showed that the used polymer fluid was heavily laden with soil particles and that cleaning using chemical additives alone was not sufficient to reduce the amount of suspended solids to an acceptable level. The pile bores were therefore left open overnight to allow the particles to settle out of suspension, the effect of which was confirmed by further fluid testing. The settled solids were removed with a base cleaning bucket. Structural integrity tests conducted on over 50 working piles constructed using this method showed no sign of defects. High-strain dynamic loading tests on two completed piles also confirmed their performance despite the extended pile bore open period. © 2014, Thomas Telford Services Ltd. All rights reserved.

Jefferis S.,Environmental Geotechnics Ltd.
Geotechnical Special Publication | Year: 2012

Mixtures of clay and lime or clay and natural pozzolans are possibly some of the most ancient construction materials, and yet there is still much that we do not know about the properties of clay-binder systems. There has been an enormous amount of research on cements and also on clays, but curiously there has been little systematic research on combined cement-clay systems. This paper provides an overview of the properties of clay-cement systems in their many applications, but is focused on the cement-bentonite clay slurries used in slurry trench cut-off walls. It particularly considers areas where it is believed that more research is required; but it also briefly reviews the basic behaviour and properties of cement-bentonite systems including some of the lesser studied aspects of the materials and recent developments. © 2012 American Society of Civil Engineers.

Laver R.G.,Golder Associates | Soga K.,University of Cambridge | Wright P.,Halcrow Group Ltd. | Jefferis S.,Environmental Geotechnics Ltd | Jefferis S.,University of Oxford
Geotechnique | Year: 2013

Prediction of the long-term settlement of clay soils over tunnels requires a knowledge of the permeability of the soil and of the tunnel lining; however, determination of the lining permeability in the field is difficult. An important contributor to this problem is the lack of knowledge concerning the permeability of the grout between the lining and the soil. This paper presents the results of tests to characterise the properties of grout samples from London Underground tunnels, investigating permeability, porosity, micro structure and composition. The tests revealed that the newer grout was impermeable relative to the surrounding clay. However, the older samples showed much greater permeabilities and an altered grout composition, suggesting that degradation had taken place. Exposure to groundwater appeared to have caused carbonation and sulfate reaction. The combination of chemical reaction and leaching of cementitious and degradation products appears to have made these grouts more permeable, so that the grout could act as a drainage path rather than a barrier. This challenges the typical assumption that the grout acts as an impermeable barrier.

Lam C.,University of Oxford | Jefferis S.A.,University of Oxford | Jefferis S.A.,Environmental Geotechnics Ltd
Canadian Geotechnical Journal | Year: 2011

The elastic modulus of a concrete pile is an important parameter for the interpretation of load test results. This paper summarizes and assesses the methods available for its determination. Ten methods have been identified of which four are based on laboratory tests and the remainder on in situ pile instrumentation. Six of the methods have been used to interpret the modulus of a concrete pile subject to an axial load test. From the analyses, it was found that creep strains that developed during load-holding periods can have a significant effect on the modulus value if not allowed for when assessing the measured strain values. Based on a comparison of the derived pile loads the secant modulus method was found to be the most satisfactory. The tangent modulus method was also found to be a useful tool for investigating the effect of a partial steel casing - a feature of the method that has not been discussed before. Surprisingly, the theoretically correct transformed area equation had the worst performance, probably because of the chosen method for obtaining the concrete specimens on site.

Loading Environmental Geotechnics Ltd. collaborators
Loading Environmental Geotechnics Ltd. collaborators