Oxford University
Civil Engineering
Department of Engineering Science
Environmental Soils Research Group
Home | In Situ | Gassy Soils | Soft Soils | Flocculation | E-Kinetic remediation
The Environmental Soil Mechanics Research group is led by Prof. Gilliane Sills, supported by Chris Waddup.
A brief descriptions of past research topics are found below. Where links are shown, further detail is available on research project pages:
| Seabed soil behaviour | Seabed pore pressure measurement, scour and pipeline stability |
| In situ instrumentation | Joint piezocone research programme with Sheffield University |
| Consolidation of gassy soils | EPSRC: Consolidation of gassy soils |
| Strength of gassy soils | Undrained cyclic loading of marine clay containing gas |
| Soft soil consolidation | Self weight and higher stress consolidation behaviour |
| Sediment flocculation and consolidation | MAST III COSINUS |
Application of electrokinetics and bioremediation
to contaminated soils |
Applications
of electrokinetics to enhance bio-remediation, Electrokinetics and bioaugmentation to optimise the remediation of PCP contaminated soil |
 Gilliane Sills |
 Chris Waddup |
Triaxial testing
Undrained Cyclic Loading of a Marine Clay Containing Gas
Contacts: Scott Munachen, Prof. Gilliane Sills, Dr Dongqing Li
Funding: EPSRC
Description : The undrained strength of a gassy seabed can be significantly lower than that of the same soil in a saturated condition, with the reduction dependent on factors such as the gas content, the consolidation stress level and the depth of overlying water. A method has been developed in which methane saturated zeolite is introduced into a soil slurry to produce a soil sample in the laboratory with a uniform distribution of gas voids. Scanning electron microscope examination of samples produced in this way shows that the structure is similar to that of samples recovered from the seabed. A state of the art cyclic loading facility and triaxial cell have been developed by Scott Munachen, who has completed a programme of cyclic testing of gassy samples consolidated to 400kPa. His conclusions provide a new insight into the behaviour of saturated soils subjected to a cyclic loading as well as to gassy ones. A further project is now under way with Dongqing Li to examine the behaviour of softer gassy soils under similar cyclic loads.
Oedometer Consolidation
The Consolidation of Naturally Gassy Soils;
Contacts: Prof. Gilliane Sills, Dr Ian Richardson
Funding: EPSRC
Description: Differences in structure between naturally and artificially gassy soils (where the gas is produced by the action of bacteria and using the zeolite technique) appear significant at low stress levels. The present research is investigating whether these differences influence the engineering behaviour of soils consolidated to higher stress levels. A specially designed oedometer has been developed, in which gas can be produced naturally using temperature as a control mechanism. Load and back pressure are increased steadily together to simulate increasing depth. This is important in a gassy soil where the gas behaviour is influenced by total stress levels.
Electrokinetic consolidation
Electrokinetics, the application of a direct electric current, causes
movement through soil by a number of different mechanisms.
Electrolysis (EL) of water at the
anode and cathode generates hydrogen and hydroxyl ions, respectively,
which move through the soil matrix towards their poles of opposite charge
by
electromigration (EM). Metal ions and anions (e.g. SO42-) also
move by EM. Dipolar interactions between water molecules and the
negatively charged surfaces of
soil particles lead to the transport of water towards the cathode by
the process of electroosmosis (EO). Charged particles, such as
colloidal clay particles and
bacteria, will be affected by two processes: electrophoresis (EP) will
move negatively charged cells towards the anode, and EO will move the
cells towards the
cathode. The movement of hydrogen and hydroxyl ions through the
soil generates a pH gradient.
Current and previous research projects include:
- Consolidation by electroosmosis
- Nitrate flow by electromigration
Electrokinetic
bioremediation
Electrokinetics to enhance biodegradation of organic contaminants in
soil
Contacts: Michael Harbottle, Prof. Gilliane Sills
Funding: EPSRC Waste and Pollution Management Programme
Description: The aim of the study is to investigate the potential for remediating soil pollution by moving organic contaminants and bacteria by electrokinetics. Initial studies will define the movement of a model organic(pentachlorophenol) in an electric field in different soil types under various conditions. The movement of a range of bacteria, selected for their different morphological characteristics, will be similarly assessed. Marked degradative bacteria will then be introduced into soil which has been contaminated by PCP, and an electric field applied. The electrokinetic conditions will be correlated with bacterial degradation of the organic in order to understand the fundamental underlying interactions. Extending the process into aged and historically contaminated soils will provide information about influences on bioavailability and the constraints upon real contaminated sites.
Current and previous research projects include:
- The Use of Electrokinetics to Enhance the Degradation of Organic Contaminants in Soil
- Nitrate flow by electromigration
Seabed and insitu research
Instrumentation has been developed for seabed use, with an emphasis on
differential piezometers to record pore pressures in the seabed close
to the bed surface and up to 1500mm beneath it. Laboratory experiments
have been used to examine the behaviour of seabed soils.
Current and recent programmes include:
- Wave induced pore water pressures in the seabed.
- Scour around breakwater elements.
- Stability of buried pipelines
- Joint piezocone research programme with Sheffield University
X-ray density and consolidation investigations
Oxford's x-ray / consolidation laboratory has been a main stay of this
research group for over 20 years. The behaviour of soft soils deposited
through water is important in such areas as dredging programmes, reservoir
and estuary siltation, slurry waste disposal and land reclamation.
The fundamental behaviour is being examined by introducing soil slurries
into 2m high, 100mm diameter acrylic settling columns, and allowing them
to settle and consolidate. Accurate, non-destructive measurements of
density are made using X-rays transmitted through the soil, detected
by a scintillation crystal and photomultiplier assembly. Measurements
are also made of pore water pressure by transducers, of shear stiffness
by shear wave transmission and of shear strength by a sleeved
sensitive shear vane and by fall cone. The stress range is extended by
applying a surcharge loading using a piston, or by the use of oedometers
designed for soft soils. Field instruments include in-situ densimeter
and coring equipment.
Previous research programmes have examined the effects of rate of deposition of sediment, initial density and pore water chemistry. The results show that soft soils exhibit creep and time dependent strength increases. The rate of sedimentation has a significant effect on the structure, with a low rate producing a less dense soil than a fast one. Comparisons have been made with field measurements in the bed of the Irish Sea and laboratory simulations.
Recent research includes electrokinetics, the application of a direct electric current, which causes movement through soil by a number of different mechanisms. Electrolysis of water at the anode and cathode generates hydrogen and hydroxyl ions, respectively, which move through the soil matrix towards their poles of opposite charge by electromigration. Metal ions and anions (e.g. SO42-) also move by electromigration. Dipolar interactions between water molecules and the negatively charged surfaces of soil particles lead to the transport of water towards the cathode by the process of electro-osmosis. This process causes consolidation of the soil, which can be significant if the pore water is not replaced at the anode. Charged particles, such as colloidal clay particles and bacteria, will be affected by two processes: electrophoresis will move negatively charged cells towards the anode, and electro-osmosis will move the cells towards the cathode. The movement of hydrogen and hydroxyl ions through the soil generates a pH gradient, and this may affect the soil characteristics and behaviour. Electrokinetics has applications in soil improvement and remediation of contamination.
The current research projects taking place in this area include:
