Geotechnical Engineering

Geotechnical Engineering is the branch of civil engineering associated with the behaviour of earth materials, including soil and rock. Geotechnical engineers use theories of soil and rock mechanics, allied with testing and experience, to help understand how earth materials respond to various construction activities such as the formation of foundations, embankments, excavations and tunnels.

Geotechnics is a challenging discipline due to the variability of the ground (as it is a natural material) and its complex behaviour compared to other engineering materials. The research carried out by the Geotechnical Engineering Research Group at NUI Galway, led by Dr. Bryan McCabe, is contributing to national and international knowledge in a number of areas.

(i) Ground Improvement
Vibro stone columns are commonly used to increase the strength and stiffness of various soil types so that simpler foundation solutions can be implemented. Vibro stone columns nowadays have increasing application to soft/marginal ground conditions. At NUI Galway, the behaviour of small footings supported by stone columns (an area not well served by existing theory) is under investigation using Finite Element analyses and an original analytical settlement design method has been developed. The ability of stone columns to reduce consolidation settlements in fine soils is well known; research is also underway at NUI Galway to establish the contribution of stone columns to the arrest of secondary settlement (creep) in organic soils. Dry soil mixing is an alternative ground improvement technique used in soft soils. Experimental research is underway in the laboratory to improve our understanding of the proof tests (PORT/PIRT) used in the field to confirm stabilised strengths. The testing is being carried out on stabilised organic silt and a stabilised peat.

(ii) Piling
The research group is working in conjunction with a UK based geotechnical contractor to examine locked in stresses associated with Driven Cast in Situ (DCIS) piles. In addition, new techniques are being developed to allow real-time estimates of static pile capacity to be derived (during pile installation) from drive records arising from new rig instrumentation. In another project, the area of pile to pile interaction is being revisited; finite element analyses is being used to help refine our understanding of the factors influencing pile group response

(iii) Microtunnelling
The use of microtunnelling has spiralled in Ireland in the last 2-3 years as a means of installing utility pipelines. The research group at NUIG is working closely with a Galway-based microtunnelling specialist to interpret jacking force and settlement data recorded in a variety of ground conditions in Ireland and beyond.

(iv) Expansive Pyritic Fill
The presence of expansive pyrite in fills used for numerous housing developments in the North Leinster area has emerged as a major issue in recent years, with thousands of houses likely to be afflicted with damage due to the expansion. Recent controlled experiments on ‘active’ fill at NUI Galway, the first of their kind in Ireland, have successfully measured pyritic expansion and have identified some factors on which the expansion depends. This work is carried out in conjunction with a specialist Irish consultant and in parallel with work at the University of Sheffield.

(v) Stabilised soil blocks (SSBs)
A construction technology used for houses in developing countries that has very low impact on the environment is stabilised soil blocks (SSBs), which are formed by compressing a mixture of soil, cement and water. The blocks are low-cost as their main component, the soil, is usually sourced locally, often directly from the site of construction. Further, these blocks can be produced on site, saving in transportation costs. The main stabilisers used in their manufacture are cement, lime or a combination of both stabilisers. Experimental studies are being undertaken at NUIG to determine the performance of SSBs. In particular, the main objectives were to identify suitable soil, to investigate the variation in the performance of blocks in terms of strength and durability with varying cement content and alternative stabilisers, and to highlight the effects of different curing methods on the strength of blocks.