GROUP A - Geotechnical and Environmental

REFERENCE: A-AAT1TITLE: Permeable active containment materials for groundwater remediationSUPERVISOR: Dr A. Al-TabbaaEMAIL: aa22ROOM: 223INDUSTRIAL: Of interest to manufacturers of the materials usedDESCRIPTION: 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-AAT2TITLE: Accelerated long-term behaviour of cement-treated soilsSUPERVISOR: Dr A. Al-TabbaaEMAIL: aa22ROOM: 223INDUSTRIAL: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-AAT3TITLE: In-situ soil mixing of contaminated groundSUPERVISOR: Dr A. Al-TabbaaEMAIL: aa22ROOM: 223INDUSTRIAL: Of interest to contractors, consultants and owners of contaminated land interested or involved in soil mixingDESCRIPTION: 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-AAT4TITLE: Effective immobilisation of contaminated groundSUPERVISOR: Dr A. Al-TabbaaEMAIL: aa22ROOM: 223INDUSTRIAL: 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-AAT5TITLE: Design charts for the durability of immobilised contaminated soilsSUPERVISOR: Dr A. Al-TabbaaEMAIL: aa22ROOM: 223INDUSTRIAL: 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 machinePe-requisites:Part IIA Papers G1: Soil Mechanics, G3: Environmental Engineering

REFERENCE: A-AAT6TITLE: Low permeability cement-waste barrier materialsSUPERVISOR: Dr A. Al-TabbaaEMAIL: aa22ROOM: 223INDUSTRIAL: 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-MDB1TITLE: The “undrained” strength of claySUPERVISOR: Dr M.D. BoltonEMAIL: mdbROOM: 221INDUSTRIAL:

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-drivingSUPERVISOR: Dr M.D. BoltonEMAIL: mdbROOM: 221INDUSTRIAL: sponsored by Giken SeisakushoDESCRIPTION: (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-MDB3TITLE: Tests on pipe upheaval resistanceSUPERVISOR: Dr M.D. BoltonEMAIL: mdbROOM: 221INDUSTRIAL: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 centrifugePre-requisites:

REFERENCE: A-RJL1TITLE: The control of pollution plumes using air sparging.SUPERVISOR: Dr R.J. LynchEMAIL: rjl1ROOM: 225INDUSTRIAL: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-RJL2TITLE: Investigation of electrokinetic clean-up of soilsSUPERVISOR: Dr R J LynchEMAIL: rjl1ROOM: 225 INDUSTRIAL: AEA Technology, Dr D J IlettDESCRIPTION: 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 ofthe understanding of the process.

A third possibility is to test the operation of an electrokineticfence to keep out pollutants. Such a fence has been mentioned as apossibility in connection with the protection of a natural site from alarge plume from mine tailings, in Southern Spain. Equipment: Experiments will be carried out in a flat tank ofsoil (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-RJL3TITLE: The prediction of pollutant retention in soils using chromatographic techniques.SUPERVISOR: Dr R.J. LynchEMAIL: rjl1ROOM: 225INDUSTRIAL: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-SPGM1TITLE: Measurement of soil stiffness before and after a liquefaction event during earthquake loadingSUPERVISOR: Dr S.P.G. Madabhushi

EMAIL: mspg1 or mspg1@cusROOM: 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).

A more elegant and effective method of measuring small-strain stiffness of the soil is by measuring the Shear wave velocity in the soil. Shear waves are generated by applying an electric pulse to a Bender element akin to a Bi-metallic strip. The twitch of the bender element sets off a shear wave. A receiving bender element will convert the shear wave pulse to a electrical signal. Knowing the distance between the emitter and receiver, and the time of arrival of the shear wave at the receiver, we can determine the shear wave velocity. This shear wave velocity can be related, quite easily, to the small-strain shear modulus of the soil.

This technique of using the bender elements is used in triaxial test set-ups. This project offers the chance to extend this technique to dynamic centrifuge modelling. The main objective of this project will be to measure the initial stiffness of a saturated sand specimen in the mini Electro Magnetic earthquake actuator. The post earthquake stiffness of the soil specimen is measured by firing earthquakes of different strengths. The loss of soil stiffness owing to partial or full liquefaction will be determined.

This project will be continuation of the work that was carried out last year. It would benefit from the experience as well as hardware developed during that period. The work carried out so far concentrated on modelling of stress wave propagation in sands at 1-g. During this project, work will be carried out on the centrifuge ie the bender elements will be used in-flight while the centrifuge is spinning.

REFERENCE: A-SPGM2TITLE: Uplift resistance of an under-reamed pile foundationSUPERVISOR: Dr S.P.G. MadabhushiEMAIL: mspg1 or mspgl@cusROOM: 235 or Schofield Centrifuge Centre INDUSTRIAL:DESCRIPTION: Pile foundations are extensively used for most land based structures in the UK and around the world. It is normal to test some of the driven piles to failure in axial compression. Under certain conditions, where uplift loads are expected on the piles, a pile pull-out test is carried out.

Undrained conditions prevail around the pile, if the pull-out load is applied rapidly. The capacity of the pile to pull-out loads is governed by the friction on the pile surface as well as the suctions generated around the pile in saturated soil. The main objective of this project will be to

determine the magnitude of the pull-out resistance of a pile driven in dense soil stratum.

Dense sands dilate on shearing and under ‘undrained conditions’ this is translated into pore water suctions. Clearly, the rate at which the pile is subjected to pull-out governs the ultimate pull-out resistance. In this project, the rate dependency of the ultimate resistance, will also be investigated.

This project will be carried out using the 10m beam centrifuge in which the soil stratum and the model pile will experience the same stresses and strains as in the field. For example at 100 gravities, a 30 cm pile will behave identical to a 30m long pile.

In previous years, work was carried out on simple piles without any under-reaming. This project would benefit from the hardware already developed.

REFERENCE: A-SPGM4TITLE: Finite Element analyses of a quay wall subjected to earthquake loadingSUPERVISOR: Dr S.P.G. MadabhushiEMAIL: mspg1 or mspg1@cusROOM: 235 or Schofield Centrifuge Centre INDUSTRIAL:DESCRIPTION: Finite element analysis in the time domain is carried out to study the seismic behaviour of soil-structure systems. Commercial packages like ABACUS can be used to this effect. Also research software codes like SWANDYNE are available for more specific problems which need sophisticated constitutive models for the soil component.

The National Science Foundation, USA, sponsored a program to verify numerical codes using dynamic centrifuge test data called VELACS program. A large body of data exists on several bench mark problems, which can be used to verify and compare various numerical codes.

Earthquake accelerations are applied to the base nodes of the FE mesh as input motion. Parameters that will be investigated will include mesh size, speed of convergence in each time step, as well as the prediction of the centrifuge test data. Useful comments can be made by the end of the project, by comparing the two numerical codes and their ability to predict known benchmark centrifuge test results for a quay wall problem.

This project will involve use of two finite element packages to study the seismic response of a quay wall problem with dry back-fill. The first package will be ABAQUS with simple soil models. The numerical predictions made by this program will be compared with the centrifuge results. The second FE program that will be used is called SWANDYNE which is a specialised program developed to tackle the problems in geo-mechanics. SWANDYNE has the more recent soil models which can model the cyclic behaviour of the soils subjected to earthquake loading. At the end of the project, a summary of the performance of these finite element programs in predicting the results from a known centrifuge test (quay wall with dry and saturated back-fills) will be established.

REFERENCE: A-SPGM5TITLE: Construction process induced vibrations on underground structuresSUPERVISOR: Dr S.P.G. Madabhushi,Professor R. J. MairEMAIL: mspg1 or mspg1@cusROOM: 235 or Schofield Centrifuge CentreINDUSTRIAL:DESCRIPTION: Construction processes involve use of heavy machinery and earth-moving equipment. The operation of these equipment or the effect they produce (for example driving of piles into ground) can induce severe vibrations in existing structures. The effect of these vibrations need to be considered seriously especially on underground structures such as tunnels, gas or water pipes and other utilities.

It is possible to study the effect of vibrations on under ground structures using the technique of centrifuge modelling. Centrifuge modelling has the advantage of testing scaled model tunnels under prototype stresses and strains experienced by tunnels in the field. Consequently the behaviour of these model tunnels can be related to the field tunnels

At the Schofield Centrifuge Centre, routine experimentation is undertaken to study the effect of earthquake loading on structures. Experimental facilities to detect vibrations such as accelerometers are in existence.

The project will involve development of an eccentric mass vibrator which when placed on the surface of soil will produce harmonic vibrations. The amplitude of vibration can be increased by increasing the eccentric mass. The frequency of vibration can be changed by altering the frequency of the rotor driving the eccentric mass.The effects of the vibrations induced by the vibrator will be investigated first in terms of wave propagation in soil detected by placing miniature accelerometers buried in the soil model at different levels. Also a model tunnel will be placed in the soil (with instrumented tunnel lining) which will detect the additional stressed induced in the tunnel due to the ground vibrations. The schematic diagram of the proposed model is seen below.

There is a possibility of some industrial collaboration for this project.

REFERENCE: A-SPGM6TITLE: Failure of slopes near vertical barrier systemsSUPERVISOR: Dr S.P.G. MadabhushiEMAIL: mspg1 or mspg1@cusROOM: 235 or Schofield Centrifuge CentreINDUSTRIAL:DESCRIPTION: Vertical barriers such as slurry walls are used to prevent contaminant from land-fill sites from migrating. Following the construction of a slurry wall, at certain sites, waste is deposited to large heights and at steep slopes (upto 70o), to maximise the space available for land-filling the waste. Slip surfaces can develop at such sites causing the slurry wall to shear, thereby, ‘breaching’ the barrier system and allowing the contaminant to migrate.

This project will be carried out using the mini-drum centrifuge at the Geotechnical Centrifuge Centre on Madingley Road. In the centrifuge

model, slurry walls can be constructed by cutting a trench in the soil stratum and filling it up with bentonite slurry. The model waste is then deposited on one side of the slurry wall until the soil slip occurs. One of the advantages of performing a centrifuge test is that, you can test your model to failure, which will be very expensive exercise to conduct at the full scale in the field!

Coloured dye will be injected to simulate the contaminant and its migration through the ruptured slip surface will be monitored. The safe height to which the waste can be deposited near a slurry wall may be suggested based on the experimental results. These can be verified by simplified slope stability calculations.

REFERENCE: A-SPGM7TITLE: Seismic behaviour of rock-fill dams with clay coresSUPERVISOR: Dr S.P.G. MadabhushiEMAIL: mspg1 or mspg1@cusROOM: 235 or Schofield Centrifuge CentreINDUSTRIAL:DESCRIPTION: Loose, saturated sand deposits ‘liquefy’ when subjected to the cyclic shear stresses induced by earthquakes. When the soil suffers partial or complete liquefaction, any structure founded on such soil undergoes severe settlements. Rock-fill dams with clay cores are particularly vulnerable as one of the following failure modes can take place;

a) The cyclic stresses due to the earthquake loading may crack the clay core causing a breach;b) The rock-fill dam body can suffer settlement leading to the overtopping of the reservoir.

This project will be a continuation of the work carried out on settlement of rock-fill dams in the year 1997-8. The fourth year project in the previous years studied the seismic behaviour of a dam with a reservoir held by a ‘model clay core’. It was observed that when the loose sandy deposits form the foundation the settlement of the dam led to overtopping of the dam, following earthquake loading. On the other hand, the when the foundation soil was dense, lateral spread of the embankment left the clay core exposed with no lateral support.

The mini Electro-Magnetic shaker can fire model earthquakes while the centrifuge is spinning. The centrifugal acceleration provides correct prototype stresses and strains in the model. The E-M shaker imparts the lateral shaking which simulates the earthquake loading. It is possible to use ‘realistic’ earthquake motions recorded during the Northridge Earthquake of 1994 near Los Angeles and the Kobe earthquake of 1995 in Japan.

This project will involve use of the E-M shaker on the 10 m beam centrifuge at the geotechnical centrifuge centre on Madingley Road. Typical tests will be carried out at 50 times normal gravity. The results from the project will help to identify the failure mechanisms of Rock-Fill dams with clay cores subjected to earthquake loading.

REFERENCE: A-SPGM8TITLE: Response of tower structures to seismic loadingSUPERVISOR: Dr S.P.G. MadabhushiEMAIL: mspg1 or mspg1@cusROOM: 235 or Schofield Centrifuge CentreINDUSTRIAL:DESCRIPTION: Soil-Structure Interaction plays an important role in determining the seismic behaviour of a structure. One can imagine, simplified discrete models with springs, masses and dashpots to represent the soil and structural components. The ‘soil spring’ is non-linear and its stiffness can deteriorate with strain, pore water pressure build up. The complex behaviour of such soil-structure systems can be studied using dynamic centrifuge modelling.

The main objective of this project will be to study the dynamic response of a short tower structure founded on saturated sand bed and compare it to the response of a tall tower structure. Interpretation of the results will lead to identification of important parameters like damping in the system, resonant frequencies and other dynamic characteristics.

The mini Electro-Magnetic shaker can fire model earthquakes while the centrifuge is spinning. The centrifugal acceleration provides correct prototype stresses and strains in the model. The E-M shaker imparts the lateral shaking which simulates the earthquake loading. It is possible to use ‘realistic’ earthquake motions recorded during the Northridge Earthquake of 1994 near Los Angeles and the Kobe earthquake of 1995 in Japan. Further, model earthquakes of the form of simple sine waves at any chosen frequency can be fired in the range of 30 Hz to 150 Hz. Also, swept sine wave input motions can be used to identify the resonant frequencies. Also the response of the soil-structure system to realistic earthquake motion such as the one recorded at Port Island site during the Kobe earthquake will be investigated.

This project will involve use of the E-M shaker on the 10 m beam centrifuge at the geotechnical centrifuge centre on Madingley Road. Typical tests will be carried out at 50 times normal gravity.

REFERENCE: A-RJM1TITLE: Evaluation of compensation grouting case recordsSUPERVISOR: Professor R.J. MairEMAIL: rjm50ROOM: 222INDUSTRIAL: Geotechnical Consulting Group, London; DESCRIPTION: Tunnelling beneath cities is becoming increasingly important as the need for metro systems and other underground space increases with the demand for environmentally acceptable infrastructure development. The construction of tunnels in soils inevitably causes ground movements and in urban areas such movements may adversely affect buildings above the tunnels. Prediction of ground movements and assessment of risk of damage is an essential part of the planning, design and construction of any tunnelling project in the urban environment. If it is found that buildings are at risk of unacceptable damage from the proposed tunnelling, appropriate protective measures must be designed to ensure that the project can proceed without causing damage.

Compensation grouting is a powerful new technique for controlling settlements and potential damage to buildings during tunnelling. It was conceived for the first time in the UK relatively recently and has since been used extensively with considerable success on the £2.5 billion Jubilee Line Extension project (which has involved the construction of 11.5km of tunnels and 11 stations beneath central London). The technique is now being used on a number of international tunnelling projects.

Compensation grouting involves the injection of grout, which is usually a fluid mixture of water and cement, into the ground between the tunnel and an overlying building. The aim is to compensate for the ground deformations occurring as a result of the tunnel excavation and limit the movements of the building to acceptably small values. The injection of grout is in effect replacing the volume of ground which deforms towards and into the tunnel excavation. Comprehensive instrumentation, monitoring and interpretation are of fundamental importance to the success of the technique. Each grout injection is undertaken in a strictly controlled manner in response to observed ground and building movements.

If the grout injection is undertaken too close to the crown of the tunnel, there is a risk of causing unacceptable deformations and stresses in the tunnel lining. Research on this subject is already in progress within the CUED Geotechnical Group for Nishimatsu Construction of Japan; this is involving evaluation of measurements made on a recent tunnelling project, centrifuge model tests and finite element analysis. This 4th year project will involve evaluating data from extensive measurements made at three different locations on the Jubilee Line Extension project where compensation grouting has been undertaken in close proximity to tunnels of different diameters and in different ground conditions – and in some cases resulted in unacceptably large deformations of the tunnel linings. The evaluation will lead to an assessment of this problem and will provide an important basis on which a design approach can be established for future uses of the technique in close proximity to tunnels.

The opportunity may arise for the student to obtain vacation work in the offices of the Geotechnical Consulting Group (GCG) in South Kensington, London for a period during the summer of 1999, although this is not essential for the 4th year project.. It is envisaged that some visits will be made to GCG’s offices during the course of the project, and there will be opportunities to work with engineers at GCG.

REFERENCE: A-RJM2TITLE: Bury St Edmunds Cathedral – tower constructionSUPERVISOR: Professor R.J.MairEMAIL: rjm50ROOM: 222INDUSTRIAL: Geotechnical Consulting Group; Alan Baxter and AssociatesDESCRIPTION: Suffolk is the only county in England waiting for its cathedral to be completed. In Bury St Edmunds, close to Cambridge, the Church of St James was designated to be the Cathedral for Suffolk in 1914 but it does not have a tower. The existing Cathedral building is a mixture of old and new (the nave was built in 1503, some of the Cathedral has been built in the 1960s). The foundations for the tower have already been

constructed but the tower was never built. Recently, money from the Millennium Commission has been provided to partly fund the construction of the tower.

Construction of the tower will not commence until about the end of the year 2000. A site investigation has recently been undertaken, revealing the ground conditions to be glacial sands with lenses of silt, and a silty band of up to 1m in thickness at 5m depth. There are concerns about the effects of construction of the tower on the adacent Cathedral buildings – the stress induced by the tower in the underlying ground is an order of magnitude larger than the stress imposed by the existing buildings. How much movement of the existing Cathedral (some of which is very old) will be caused by construction of the Tower? This 4th year project will involve researching the history of the site (the existing buildings and their foundations), and undertaking a series of parametric calculations to assess the potential settlements and possible damage to the existing Cathedral that could be caused by construction of the tower. The calculations will involve the use of simple hand calculations and some computer software.

The student will have the opportunity of working with engineers at Geotechnical Consulting Group and Alan Baxter and Associates, who are the Consulting Engineers for the project; both companies are based in London.

REFERENCE: A-ACP11TITLE: Shear zones in geotechnicsSUPERVISOR: Professor A.C. PalmerEMAIL: acp24ROOM: 220INDUSTRIAL:DESCRIPTION: Soil deformations are often characterised by irregular ‘brittle’ behaviour, in which much or all of the deformation is confined to thin shear zones. These shear zones are a dominant influence in landslides, in flow in silos, and in soil cutting processes such as ploughing trenches for pipelines. They are characteristic of strain-softening behaviour, in which the stress level required to produce continuing deformation falls as the deformation continues. Just as the critical material parameter in fracture mechanics applied to metal objects is the fracture toughness rather than the yield stress, so it appears that in brittle geotechnics the fracture toughness may be the important factor. If so, the implications are very wide indeed.

This objective of this project is to attempt to measure the fracture toughness of heavily overconsolidated clay. It will take as its starting point some experiments carried out here by Dr. John Cuckson (who now has a senior engineering position with Shell). Whereas most soil mechanics experiments try to force the soil to deform homogeneously, John set out to create inhomogeneous deformation, and reached some interesting conclusions.

REFERENCE: A-KS1TITLE: Numerical simulation of the performance of improved groundSUPERVISOR: Dr K. SogaEMAIL: ks

ROOM: 227INDUSTRIAL: Raito Kogyo, Japan DESCRIPTION: In recent years, a number of special techniques have been developed to “manufacture” predictable and dependable ground material in-situ, either in preparation for new construction or to correct problems that threaten existing structures. Raito Kogyo is a soil improvement specialist company and it is the largest one in Japan. They specialise in various ground improvement techniques (such as deep jet mixing, cement columns and slurry walls), which are available to densify or otherwise improve the ground as an integral part of the construction.

This project involves a summer job in Tokyo, Japan. The student will stay in Japan for two months (mid-July to mid-September) at company’s expense (including air ticket and living expenses). The company is interested in conducting computer-based research on the following topics.(1) 2D dynamic analysis of buried structures subjected to an earthquake.(2) 2D axi-symmetric FE stability analysis of ground improved by the Jet-mixing method(3) 3D stability analysis of grouped piles supported by improved ground.

The student can pick the topic of interest. The Project continues at Cambridge after October.

REFERENCE: A-KS2TITLE: Laboratory investigation of grouting in transparent claySUPERVISOR: Dr. K. SogaEMAIL: ksROOM: 227INDUSTRIAL: European Commission Project led by Soletanche-BachyDESCRIPTION: When grout is injected into clayey ground, the soil around the grout injection point expands. This type of grouting is often done when large ground movement is expected to happen during tunnel construction and excavation. The grout injection can ‘compensate’ for stress relief and associated ground settlement. This operation is called compensation grouting.

The actual behaviour of grout displacing the surrounding soil is a very complicated one. Initially, a coherent bulb will form around the point of injection. However, as the injection volume increases, the soil around the grout deforms plastically due to large injection pressure. Subsequently, this plastic deformation may accelerate locally or hydraulic fracturing may suddenly occur, leading to penetration of grout in fingers, thin sheets or lenses pattern.

This project will investigate the behaviour of grout injection in the laboratory. Grout will be injected into a Perspex soil column filled with a novel transparent synthetic clay. This will allow observation of the dynamic motion of grout displacing the clay in real time.

REFERENCE: A-KS3TITLE: Comparison of contaminated land risk assessment softwareSUPERVISOR: Dr. K. SogaEMAIL: ksROOM: 227

INDUSTRIAL: Chemix International Ltd.DESCRIPTION: Recently the importance of (human) risk assessment for making decisions about the need for remediation activities in situations dealing with serious soil pollutant has grown considerably. There are several computer software available for the assessment of human exposure risks to soil contamination. Different software uses different assumptions and models to calculate the risk of contaminated sites.

This Project will compare the results obtained by two risk assessment packages: (1) Risc Human, developed by Van Hall Institut in the Netherlands and is used mainly in Europe, and (2) RBCA, developed by American Society for Testing and Materials (ASTM) and is used mainly in the US. The advantages/limitations of the two packages will be investigated. The project follows the last year’s project, which assessed the former program.

The opportunity may arise for the student to obtain vacation work in the office of Chemix International Ltd at Bar Hill (north of Cambridge) during the summer of 1999, although this is not essential for the Project. REFERENCE: A-KS4TITLE: Laboratory investigation of capillary barrier to prevent contaminant migrationSUPERVISOR: Dr. K. SogaEMAIL: ksROOM: 227INDUSTRIAL: Relevant to environmental engineering companiesDESCRIPTION: A capillary barrier is a layer of fine soil overlying a layer of coarser material. When the layers are fully saturated with water, the coarser material with large pore space has a larger permeability than the fine one. However, when the layers becomes unsaturated, the fine layer retains more water due to capillary action between the grains and water and, consequently, the unsaturated hydraulic conductivity of the coarser layer can be smaller than the fine one. Therefore, as long as the coarse layer is in unsaturated condition, the coarser layer can act as a barrier preventing infilteration of contaminants coming from above in the fine layer.

As part of the last year’s 4th year project, laboratory investigation was conducted to investigate this capillary barrier phenonemon using a soil column of 20cm diameter and 1 metre height. This Project will continue the work searching for a suitable combination of two layers for a contaminant migration barrier.

REFERENCE: A-KS5TITLE: Measurement of electrical properties of oil contaminated soilsSUPERVISOR: Dr. K. SogaEMAIL: ksROOM: 227INDUSTRIAL: Relevant to site investigation companiesDESCRIPTION: Traditional methods of site characterisation of contaminated sites involve soil sampling and chemical analysis, which are costly, destructive and time-consuming process. There is a need for new techniques, which can provide non-destructive and in-situ measurements.

Measurements of electrical properties such as resistivity and conductivity have been used in the past to qualitatively detect contamination in soils. The theoretical basis of this approach is that the bulk electrical conductivity of the soil-fluid system is dependent on the electrical conductivity of the pore fluid and the porosity. However, the bulk conductivity of the soil-fluid system also depends on the chemical composition, grain size and shape. Therefore, quantifying the degree of contamination is not very easy.

In search for a method to overcome this problem, measurement of the dielectric properties of contaminated soil-fluid system has been received attention as a potential method of site characterisation and contaminant detection. The value of dielectric properties of soil-fluid system depends on the frequency of the electrical current applied. The data of the frequency dependent dielectric constants can be used to assess the degree of contamination.

This Project will measure the dielectric properties of oil contaminated soils using the available Impedance analyser and dielectric probe. The system measures the capacitance and conductance of the material and the measurements can be converted to the dielectric properties. The soil will be mixed with at different oil/water/air ratios and measurements will be taken. The project will investigate the potential and limitation of the proposed method.

REFERENCE: A-KS6TITLE: Investigation of drilling fluid filter cakes failure modesSUPERVISOR: Dr K. SogaEMAIL: ksROOM: 227INDUSTRIAL: Schlumberger Cambridge ResearchDESCRIPTION: Modern drilling muds are complex, carefully engineeredslurries designed to perform several tasks at the same time: the mud must help reduce friction and wear on the drilling bit, it must carry to the surface the solids cut by the advancing bit, it must maintain a favourable pressure difference betweenthe wellbore and the rock formation in order to avoid blow-outs and wallcollapse and it must generate a thin but impermeable coating, known as a

filtercake, on the wall of the well to minimise infiltration of drilling fluids into

theformation. The filter cake grows on the wall in a process similar to simplesoil consolidation: the overbalance pressure will initially force some mudfluid into the formation, the solids present in the mud accumulatingagainst the wall. As the process goes on, the tighter packing of solid

particleswill reduce the permeability of the growing cake and hence reduce the

fluidinvasion. Once the drilling phase is complete and oil production can bestarted, this filtercake must be removed or by-passed, in order tore-establish the virgin reservoir permeability; this can be done by cementing the wall and perforating small apertures into the formation, deep enough to reach beyond the filtercake and possibly damaged rock

zone, or by treating the wellbore with acids to break the filtercake. These operations are costly and especiallydifficult in the case of long horizontal wells. Depending on the reservoirpressure, it is sometimes preferable to simply drop the wellbore pressuresufficiently to initiate oil flow (backflow) by letting the filtercakerupture spontaneously. It appears that the filtercake can rupture in twodissimilar fashions: either it detaches in large slabs from the rocksurface, or it "pinholes", essentially remaining in place but developing

many smallerosion channels through which the oil can flow.

This project will address the mechanisms by which these two failure modes

occur and will involve either laboratory work to determine characteristicfiltercake mechanical properties or computer simulations (using FE

packagessuch as SAGE CRISP) aiming at recreating the backflow conditions, based

on asmall perturbation analysis.

REFERENCE: A-JRS1TITLE: Investigating the behaviour of a compacted residual soilSUPERVISOR: Dr J.R. StandingEMAIL: j.standing@ic.ac.ukTELEPHONE: 0171 594 6072INDUSTRIAL: DESCRIPTION: Residual soils exist in many of the areas undergoing rapid development (e.g. South America, Africa and Far East). These soils are used in various applications such as forming embankments, dams and roads. They are often removed from borrow areas and then recompacted. Their behaviour is complex as they are generally partly-saturated (in-situ as well as after compaction) and also some of their characteristics (e.g. plasticity limits) change with drying.

The study would initially involve a literature review of previous well documented construction case histories and studies where typical characteristics of residual soils have been investigated.

An experimental investigation would then be carried out on samples of residual soil. It is intended that samples be obtained from a source such as South America or the Far East (e.g. Hong Kong or Malaysia). The samples would be tested in a triaxial apparatus where overall sample volume change could be measured along with the flow in and out of the sample. Samples will generally be formed by compaction but if block samples are available they will be trimmed and tested in an intact state for comparison. The samples would be isotropically and possible K0-consolidated. Effects such as stress level, water content and degree of saturation on the consolidation characteristics will be investigated. The consolidation behaviour will then be compared to that given by Terzaghi’s one-dimensional consolidation theory and the influencing factors identified where possible.

Characterisation of the soil will also be necessary by performing Atterberg limits and determining specific gravities and grading curves.

Equipment: Consolidation triaxial cell for 100mm samples, pressure transducers and volume gauges. Fall-cone, sieves and hydrometer, picnometers. Transducer logging facilities and computer resources. Pre-requisitses: G1

REFERENCE: A-JRS2TITLE: Investigating aspects of behaviour of particulate assembliesSUPERVISOR: Dr J.R. StandingEMAIL: j.standing@ic.ac.ukTELEPHONE: 0171 594 6072INDUSTRIAL:DESCRIPTION: Effects such as arching and restrained dilation occur in geotechnical situations such as within hoppers and around inclusions installed in the ground (e.g. anchors, nails, piles) but are not easy to identify or quantify.

The project would initially involve a literature review to identify cases where the behaviour of particulate assemblies has been controlled by phenomena such as arching or restrained dilation. Previous studies of these phenomena would also be assessed.

An experimental programme of element tests will then be undertaken using granular assemblies formed from varying particle sizes constrained within different boundary conditions (e.g. stress-controlled and displacement-controlled) and with different sized inclusions within the assembly (e.g. to represent a soil nail or a pile). Other variables could also be considered such as changing the constituent materials of the particles and the effect of wet or dry surfaces.

The tests will be performed under conditions of plane strain where one or both of the out-of-plane confining faces is clear so that marker beads and possibly localised densification of the particle assembly can be observed. The use of methods of photo-elasticity is to be investigated to allow regions where there are concentrations of stress to be identified, e.g. within arching structures or at rigid boundaries.

Another aspect of the study could involve the measurement of normal stress at either the confining boundary or the interface of the inclusion. This would necessitate the development of instrumentation.

The results from the study would provide a very useful parametric study at a comparatively small scale. Such information is invaluable for experimental model testing where scale effects govern behaviour. The possibility of extrapolating of the results to scales encountered in civil engineering practice should then be considered. Depending of the observed behaviour, the potential of formulating simple mathematical models to check for the potential of say arching in engineering situations could also be investigated.

Equipment: Purpose-made confining stress chamber with rigid/flexible boundaries. A set-up for photo-elastic analyses. Transducer logging facilities and computer resources.Pre-requisites: G1