GROUP A - Geotechnical and Environmental
REFERENCE: A-AAT1
TITLE: Permeable active containment materials for groundwater remediation
SUPERVISOR: Dr A. Al-Tabbaa
EMAIL: aa22
ROOM: 223
INDUSTRIAL: Of interest to manufacturers of the materials used
DESCRIPTION: Active containment is a buzz word in contaminated land remediation. Active containment combines containment with remediation and hence offers a long-term effective treatment of the contaminated ground. There are permeable and low permeability active containment systems and this project will concentrate on the former. Active containment systems are walls installed around a contaminated site which contain additives to remove certain contaminants from contaminated groundwater as it flows through the wall. Additive materials which have been used or tested include iron filings, activated carbon, engineered bacteria, granulated tyre, sawdust and peat. The first three have been shown to be effective but are costly. The latter three are waste material and are therefore far more cost effective and conform with sustainable development requirements.
This project will therefore concentrate on the latter three materials i.e. granulated tyre, sawdust and peat and examine their effectiveness in the removal, mainly by adsorption, of certain contaminants. These materials are usually applied as a mixture with soil (sand or clay). The effectiveness of combining additives will also be investigated. The investigation will be carried out in terms of the permeability and leachability of the soil-additive mixture under different contaminant conditions. The variables considered will be the type of additive used and its content, the contaminant type, including heavy metals, inorganic and organic compounds, and concentration, flow rate.
Equipment: Constant head permeability column set-up and batch test set-up.
Pre-requisites: Part IIA Papers G1: Soil Mechanics, G3: Environmental Engineering
REFERENCE: A-AAT2
TITLE: Accelerated long-term behaviour of cement-treated soils
SUPERVISOR: Dr A. Al-Tabbaa
EMAIL: aa22
ROOM: 223
INDUSTRIAL:Of interest to cement manufacturers and those involved in cement-treatment of soils.
DESCRIPTION: The long-term behaviour of treated soils is essential in the validation of the treatment. Soils are commonly treated with cement whether they are contaminated or uncontaminated. Cement-treatment of uncontaminated soil is usually applied to strengthen soils and that of contaminated soils is to reduce the permeability and immobilise certain contaminants.
In order to assess the long-term behaviour of treated soils at design stage laboratory tests have been developed which are assumed to simulate long-term conditions. There is no validation of such correlation. A new way of assessing the long-term behaviour in the short-term is to accelerate the ageing and weathering of cement-treated soils. This can be carried out using elevated temperatures. Such behaviour has been developed to some degree for cement-treated uncontaminated soils.
The project will look at the application of elevated temperatures to cement-treated contaminated soils in developing a correlation between real-time and accelerated ageing.
Hence different soil-cement mixes will be made and tested. The variables will be the soil type, cement content, contaminant type and concentration, temperatures and exposure duration. The behaviour will then be compared with samples which were allowed to cure in real-time. The comparison will be carried out using unconfined compressive strength, durability (soaking in different leachates), leachability and leachate pH.
Equipment: Compactor, oven, uniaxial loading machine, leaching facilities, atomic absorption spectrophotometer.
Pre-requisites:Part IIA Papers G1 Soil Mechanics, G3 Environmental Engineering.
REFERENCE: A-AAT3
TITLE: In-situ soil mixing of contaminated ground
SUPERVISOR: Dr A. Al-Tabbaa
EMAIL: aa22
ROOM: 223
INDUSTRIAL: Of interest to contractors, consultants and owners of contaminated land interested or involved in soil mixing
DESCRIPTION: Soil mixing is a technology with numerous applications in uncontaminated ground, particularly in the USA and Japan, and has recently been applied to in-situ remediation of contaminated ground. The technology is carried out using mixing auger through which a grout, usually cement-based, is introduced and mixed with the soil resulting in overlapping columns of solidified soil-grout material. A number of different auger designs are commercially available. Much validation work for use in contaminated ground is still lacking and this is preventing the wide spread use of this specific application.
A laboratory-scale model auger will be manufactured allowing different blade consifuration. It will allow the use of different number of blades and at different inclinations. The project will examine the relative effectiveness of different blade geometry combined with different installation methods. Different grouts will be introduced through the auger and mixed with different soil types to form soil-grout columns. The different resulting columns will be compared by loading the columns to failure followed by investigation of the failure mode and physical examination of the homogeneity of the mixing within the column. The load carrying capacity is also applicable to possible reuse of the site and hence reuse of the columns as part foundations.
Equipment: Auger set-up, flow pump, pile loading system.
Pre-requisites: Part IIA Papers G1: Soil Mechanics, G3: Environmental Engineering
REFERENCE: A-AAT4
TITLE: Effective immobilisation of contaminated ground
SUPERVISOR: Dr A. Al-Tabbaa
EMAIL: aa22
ROOM: 223
INDUSTRIAL: Of use to contractors involved in contaminated ground remediation.
DESCRIPTION: Immobilisation of contaminated ground using solidification and stabilisation processes is increasingly being utilised. Solidification provides physical encapsulation by reducing the permeability and is usually carried out using cement-based grouts. Stabilisation provides chemical encapsulation and is hence used to provide longer term effectiveness and to deal with many organic contaminants which retard the hydration of cement. Lime is commonly used for the stabilisation of heavy metals and organically modified bentonite clays for organic compounds. The effectiveness of the treatment using various additives is usually assessed by a combination of physical, mechanical, chemical and environmental criteria. Additives are usually included in dry or slurry form. The two most commonly imposed design criteria are strength and leachability. Before adding a treatment additive it is important to investigate any attenuation by the soil and the additives.
The project will examine the effectiveness of various natural soils, various additives e.g. cement, pfa, lime and natural and modified bentonite in dry and slurry forms in immobilising a number of different contaminants and their effect on the resulting unconfined compressive strength of the treated soil. Variables will include soil type and water content, additive type, form and amount, type and concentration of the contaminant including the presence of multi-contaminants and final density of soil-additive material.
Equipment: Loading frame, leaching facilities, atomic absorption spectrometer, spectrophotometer.
Pre-requisites: Part IIA Papers G1: Soil Mechanics, G3: Environmental Engineering
REFERENCE: A-AAT5
TITLE: Design charts for the durability of immobilised contaminated soils
SUPERVISOR: Dr A. Al-Tabbaa
EMAIL: aa22
ROOM: 223
INDUSTRIAL: Of use to contractors involved in contaminated ground remediation.
DESCRIPTION: Immobilisation of contaminated ground using solidification and stabilisation processes is increasingly being utilised. Solidification is usually carried out using cement-based grouts. Stabilisation is used to provide longer term effectiveness and to deal with many organic contaminants which retard the hydration of cement. Lime is commonly used for the stabilisation of heavy metals and organically modified bentonite clays for organic compounds. The effectiveness of the treatment using various additives is usually assessed by a combination of physical, mechanical, chemical and environmental criteria. One very important criterion is the long- term durability of the treated soil under repeated cycles of freeze-thaw and wet-dry conditions. The current problem is the absence of British standard tests and the American ASTM test methods are usually used instead. However, the durability conditions specified in those tests are found to be severe for most practical applications and most treated soils fail this test. Therefore modification to those test conditions are being suggested to relate specifically to the environmental conditions being investigated.
The project is a laboratory treatability study to examine the effect of different contaminants on the freeze-thaw durability of treated soils with the aim of producing design charts relating various variables. The variables will include, soil type, contaminant type and concentration, treatment additive used, freezing temperature and rate of freezing conditions. The unconfined compressive strength of the material will also be tested.
Equipment: Freezer with thermostat, uniaxial compression machine
Pe-requisites:Part IIA Papers G1: Soil Mechanics, G3: Environmental Engineering
REFERENCE: A-AAT6
TITLE: Low permeability cement-waste barrier materials
SUPERVISOR: Dr A. Al-Tabbaa
EMAIL: aa22
ROOM: 223
INDUSTRIAL:
DESCRIPTION: There is always interest in the development of wider applications and new mixtures for commonly used materials such as cement and clays particularly if the mixture includes the use of waste materials which makes it cost-effective and in line with sustainable development.
This project will examine the effectiveness of cement-waste and clay-waste mixtures as low permeability barrier material for the containment of pollutants and the treatment of contaminated groundwater. Waste materials to be tested will include granulated tyre, peat and sawdust. These materials are selected because they have been or are being tested for absorption of certain contaminants.
Properties investigated will be strength, permeability and leachability. Variables will include density, ratio of different constituents and leachate type.
Equipment: Compactor, triaxial sample formers, uniaxial loading machine, leaching facilities, atomic absorption spectrophotometer.
Pre-requisites: Part IIA Papers G1 Soil Mechanics, G3 Environmental Engineering
REFERENCE: A-MDB1
TITLE: The “undrained” strength of clay
SUPERVISOR: Dr M.D. Bolton
EMAIL: mdb
ROOM: 221
INDUSTRIAL:
DESCRIPTION: The best geotechnical laboratories go to considerable trouble to retain or reproduce the effective stress history of a sample of clayey soil prior to testing. They also go to some trouble to saturate it, and to test it under back-pressure to attempt to keep the pore water from cavitating. These expensive tests equate “undrained” with “constant volume”. More rough and ready engineers often perform cheaper “unconfined compression” tests on samples recovered from cores but not reconditioned, and their undrained strength estimates are generally lower.
Real clay soils may not be saturated in the field, and may contain sand or silt layers which readily permit cavitation if the pore water pressure falls below atmospheric. If the soil cavitates due to a fall in pore pressure, the subsequent shearing may be “undrained” but not of “constant volume” due to the expansion of gas or vapour bubbles. Perhaps unconfined tests do not suppress cavitation and therefore give more appropriate answers; it is at least questionable practice to get the effective stresses “right” and the pore pressure “wrong” on purpose, when undrained strength depends on both.
Engineers engaged in construction activities such as tunnelling, basement excavation, or embankment compaction in stiff clays usually rely on undrained strength in the short term. How should their tests be performed? One approach is to study the influence of gassing on the undrained strength of stiff clays by preparing samples in a repeatable way and then treating them variously prior to, and during, shearing – with and without a saturation phase, with various confining pressures, etc. Triaxial tests can be conducted in the Geotechnical and Environmental Laboratories.
Equipment: consolidation/compaction equipment, extraction of sample, triaxial cell and back-pressure system.
Pre-requisites:G1
REFERENCE: A-MDB2
TITLE: Press-in pile-driving
SUPERVISOR: Dr M.D. Bolton
EMAIL: mdb
ROOM: 221
INDUSTRIAL: sponsored by Giken Seisakusho
DESCRIPTION: (pre-assigned to Haramrita Sidhu) Perform model tests on pile driving at the Schofield Centrifuge Centre in order to recommend improved methods to predict and ideally minimise driving forces, while minimising collateral damage to the soil and surroundings.
Equipment:
Pre-requisites:
REFERENCE: A-MDB3
TITLE: Tests on pipe upheaval resistance
SUPERVISOR: Dr M.D. Bolton
EMAIL: mdb
ROOM: 221
INDUSTRIAL:
DESCRIPTION: Sub-sea oil pipelines often need to be trenched and backfilled to protect them from fishing gear, and to keep them thermally insulated. Pipelines are laid cold, warm up in service, and then tend to buckle upwards through their backfill. A system has been developed for pulling 1/10 scale pipes through scaled soil backfills in the mini-drum centrifuge at the Schofield Centre. The soil resistance against pipe upheaval can be measured. This has been used to offer advice to the constructors of four pipelines in the last three years.
In many ways this issue is characteristic of a variety of sea-bed geotechnical problems. However, there are some unresolved questions regarding soil preparation and scaling. In clays, the degree to which the backfill has been liquefied seems to have a highly significant effect on its performance. In sands, there is a question of the effect of particle size in relation to the distance the pipe must move in order to develop its full resistance. These two issues are also quite general in geotechnical failure analyses, the first relating to the influence of soil compressibility, and the second relating to progressive failure.
The scope of the project is to perform model tests on a variety of soils, prepared in a variety of ways, which sheds light on these issues.
Equipment: mini-drum centrifuge
Pre-requisites:
REFERENCE: A-RJL1
TITLE: The control of pollution plumes using air sparging.
SUPERVISOR: Dr R.J. Lynch
EMAIL: rjl1
ROOM: 225
INDUSTRIAL:
DESCRIPTION: The presence of air in the pores of soil is often shown to drastically inhibit the flow of groundwater. In this project we intend to use compressed air to create localised areas of low permeability in the soil, so that a spreading plume can be controlled. Examples could be to throw a ring fence around a spill, to funnel a pollutant so that it is refocussed and can then be removed by pumping, or to direct a plume towards an active barrier. The project will attempt to simulate such operations on a laboratory scale.
Equipment: Sand tank (existing); air spargers( some available).
REFERENCE: A-RJL2
TITLE: Investigation of electrokinetic clean-up of soils
SUPERVISOR: Dr R J Lynch
EMAIL: rjl1
ROOM: 225
INDUSTRIAL: AEA Technology, Dr D J Ilett
DESCRIPTION: The process of electrokinetic remediation - the passage
of electric current through soil to mobilise pollutants such as heavy
metals, is limited by the evolution of a high pH region or front which
moves out from the cathode. In this project we aim to find ways of
improving the process. Two lines of improvement are envisaged: 1.
Moving the electrodes so that we can drive the contamination into a
small area to be removed effectively. 2. Various flushing methods
will be tried to enhance and improve the process.
The project will involve a combined experimental/modelling approach.
AEA Technology has developed computer programmes that can model the
behaviour of pollutants in aqueous systems and can model the evolution
of the system during electrokinetic treatment. These models can be
used to guide experimental technique by simulating a number of
possible scenarios e.g. changing chemistry, varying current and then
selecting the most promising for experimental study. The experimental
results can be compared with the prediction to provide refinement of
the understanding of the process.
A third possibility is to test the operation of an electrokinetic
fence to keep out pollutants. Such a fence has been mentioned as a
possibility in connection with the protection of a natural site from a
large plume from mine tailings, in Southern Spain.
Equipment: Experiments will be carried out in a flat tank of
soil (existing). The modelling will use PC-based computer programs supplied by AEA
Technology. An atomic absorption spectrometer will be used for measuring concentrations of pollutants (existing).
REFERENCE: A-RJL3
TITLE: The prediction of pollutant retention in soils using chromatographic techniques.
SUPERVISOR: Dr R.J. Lynch
EMAIL: rjl1
ROOM: 225
INDUSTRIAL:
DESCRIPTION: The aim of this project is to develop an accelerated laboratory test for predicting the breakthrough time for a pollutant through soils. When there is significant pollutant-soil interaction it can take a prohibitively long time to measure breakthrough in a permeameter. To be able to accelerate the process, one can apply a greater hydraulic gradient (higher pressure) but this applies a compressive stress to the soil so the permeability will be changed, apart from any retention behavior. But if we can establish how to use this accelerated test data for a series of compounds with different retention characteristics then it should be possible to make predictions at normal pressures. The technique of HPLC (high performance liquid chromatography) uses a very high pressure of about 400 bars to force liquid through porous material contained in a small tube. This project will use standard chromatography kit. A high pressure pump applies the pressure, the soil will be contained in a chromatography column, and we can use a normal chromatography optical detector at the outlet. We shall measure retention for a range of pollutants for a range of soils, and use these data to make predictions of breakthrough time.
Equipment: liquid chromatography pump, injection valve, steel tubes with high pressure fittings, UV/visible detector. data logger (all existing, apart from extra steel tubes).
Reference: A-SPGM1
TITLE: Measurement of soil stiffness before and after a liquefaction event during earthquake loading
SUPERVISOR: Dr S.P.G. Madabhushi
EMAIL: mspg1 or mspg1@cus
ROOM: 235 or Schofield Centrifuge Centre
INDUSTRIAL:
DESCRIPTION: Centrifuge modelling offers the geotechnical engineer the possibility of recreating prototype stresses and strains in small scale models. Often the strength profile of the soil model is obtained by pushing into soil, a miniature cone penetrometer, inflight (i.e. while the centrifuge is spinning). This technique has been used by many researchers before. However, we can obtain only limited information on soil strengths this way. The cone penetrometer will measure the strength along one vertical line in the model and at any one given time only (i.e. we can push the cone only once in for a given test).