Dr. Brendan O'Kelly

My research can be categorized in three main themes, as follows: . NANOPARTICLES, BIOPLOYMERS, MICP, POLYELECTROLYTES, CEMENT AND LIME: 1) Experimental investigation of the strength/stiffness improvements achieved for clean and kerosene-contaminated clay using nanoclay and nanosilica as additives; 2) Guidelines presented for selecting potentially useful natural polymers (biopolymers) as environmentally friendly and sustainable grouting chemicals for strengthening sand; 3) Microbial-induced carbonate precipitation (MICP), including laboratory investigations of different injection strategies and using different concentrations of bacterial cell and urea-calcium chloride solutions for the strength/stiffness improvements in loose sand; 4) Using dilute polyelectrolyte solution in combination with aluminium sulphate as soil improvement measure for organic residues and ultra-soft organic clay; 5) Improvement of phyllite clays using cement and lime for various construction material applications. . GRANULAR COLUMNS AND ANCHORS, GEOSYNTHETICS AND EMBEDDED PILE WALLS; 1) Granular columns, including laboratory model studies on (a) settlement performance of single long floating granular columns and end-bearing column groups installed using displacement and replacement methods in soft clay beds and (b) settlement performance of pad footings bearing on reinforced loose and dense sand beds under the influence of fluctuating groundwater table; 2) Granular anchor performance insitu (lodgement till and made ground), including numerical modelling, development of a new method of analysis for the determination of ultimate pullout capacity and novel modification of the anchor's conventional flat baseplate presented for enhanced performance ; 3) Enhancement in short-term shear strength for embankments constructed from marginal fill achieved using dual-function geosynthetics (reinforcement and local in-plane drainage functions); 4) Embedded pin pile walls for slope stabilisation/rehabilitation; 5) Model studies performed to demonstrate the novel use of concentric rings of small diameter displacement piles around central monopile to limit its lateral displacement (rotation) under long-term cyclic lateral loading. . GROUND IMPROVEMENT FOR PEAT DEPOSITS: 1) The vacuum consolidation technique applied to peat, including heavily instrumented field trial on a 10m x 10m x 4m deep fibrous peat deposit; 2) For fibrous/hemic peats, laboratory trial demonstrating osmosis effect achieved by addition of salt grains to accelerate the rate of primary consolidation and reduce creep rate; 3) Stimulated decomposition in peat for engineering applications, including feasibility trial undertaken regarding the ability to artificially stimulate and pre-decompose a bearing peat stratum prior to the main construction works towards mitigating against unacceptable compression rates occurring over the design life.

This project comprises experimental investigations and theoretical work on the geotechnical behaviour/properties of biosolids, sewage sludge and water-treatment residue materials, which are by-products of municipal wastewater treatment and water treatment processes. Topics covered include their physical, geotechnical index, compaction, undrained strength and effective-stress strength properties, compressibility, consolidation and permeability, and the effects of oxidation, biodegradation, the viscous gel-like pore fluid for biosolids/sewage sludge material, and chemicals added during the treatment processes. The project addresses various geotechnical issues pertinent to landfill (monofill) disposal of these materials, including undrained strength requirements, design strength, on-site and laboratory strength measurements and water content-strength correlations.

This project involved a comprehensive experimental program of 1g repeated lateral load tests performed on scaled rigid monopiles installed in sand beds. Firstly, a new mechanical loading system was developed to apply many thousands of repeating cycles of lateral load in different forms to the 1g model, with full control provided over the loading direction (i.e. one-way or two-way lateral loading), amplitude, frequency and waveform shape (sinusoidal, square or haversine). Novel techniques to limit the lateral displacement (rotation) of the monopile under long-term cyclic lateral loading were investigated including: 1, use of concentric rings of small diameter displacement piles around the monopile; 2, installation of four shorter piles, arranged in a cruciform, which attach to the head of the central monopile by way of a grillage. Lateral soil resistance profiles were determined from measured pile bending strain data. Further, an experimental model that takes into account various basic characteristics of the applied lateral load cycles was developed for estimation of the pile's accumulated rotation.

This project involved axial loading of reduced scale piles and footings on sand beds insitu. For closed-ended piles in dense sand, static and cyclic axial compression and tension load testing was performed to study the causes of friction fatigue. For open-ended piles in loose and medium-dense sand, the effects of installation method, soil-core development and cyclic loading on shaft resistance mobilisation were investigated. A new design method for estimating the shaft capacity of piles in sand was proposed and compared with measurements made on prototype field-scale piles. Eccentric load testing was performed on model footings having different aspect ratios and embedment depth in dense sand to study the factors affecting the bearing resistance of shallow footings in sand.