Determination of Peat Strength

Environmental considerations frequently prevent the removal of weak compressible peat beneath highway structures. Therefore the assessment of the undrained shear strength (s u ) of the peat is essential to design safe and economic infrastructure. In Ireland this is typically carried out using the in-situ vane test. While this test is very useful in clay soils, it can be directly misleading in peat. Laboratory assessment of s u is not without its difficulties. The high compressibility and water content make peat a difficult soil to sample and prepare for laboratory testing. In addition to this, many laboratory testing devices are unable to simulate the low in-situ stresses of peat. Fibres in peat also present problems for triaxial testing due to the retraining effect of horizontally aligned fibres. Research at UCD is being carried out to determine the in-situ shear strength using full flow penetrometers, including the T-bar and ball. In contrast to the vane test results, the T-Bar penetration resistance shows a smooth, consistent and repeatable profile.

Fig. Cone and full flow penetrometers

Contact: mike.long@ucd.ie

Shear Wave Velocity Monitoring Of Ground Improvement Works

In many types of ground improvement there may be some uncertainty regarding the effectiveness of the ground improvement method. Shear wave velocities obtained in-situ from Multichannel Analysis of Surface Waves (MASW) testing are used for monitoring ground improvements as they provide a rapid and direct measure of improvement during the treatment process. Improvement may be quantified in terms of small strain shear stiffness (G max ).

Fig. MASW monitoring of ground improvement works

Clients: CON-FORM, Apex Geoservices

Contact: shane.donohue@ucd.ie

Smart Asset Management Tools – Real time monitoring of Infrastructure for Safety Evaluation

We have developed numerical techniques to predict the rate of infiltration of rainfall into slopes and probabilistic design tools to measure the reliability (in terms of slope stability) of these embankments and natural slopes. The key input parameters for these models are the in-situ water content of the soil and rainfall intensity. The development of low-cost sensors which measure in-situ water content, the data from which can be accessed remotely in conjunction with rainfall measurements from a given site allows real-time assessment of slope stability to be performed. In this way remedial action, such as temporary covering of sections of the slope with impermeable sheeting could be adopted to prevent failures. Sponsor: Irish Rail

Contact: kenneth.gavin@ucd.ie kenneth.gavin@ucd.ie

Effect of Cyclic Loading on the Performance of Offshore Structures

This project is examining the most efficient type of foundation system for offshore wind and/or wave power platforms. This assessment will include use of geophysical techniques to characterize the soil and will then be continued to do the more experimental prototype testing. The prototype experiments use highly instrumented piles developed at UCD to perform cyclic load tests at two test sites. The test results in conjunction with laboratory soil tests and numerical modelling will allow extension of the static design methods to properly model cyclic response.

Contact: kenneth.gavin@ucd.ie

Reliability Analysis of Offshore Foundations

Because of the natural variability of wind loading, reliability analysis, where the soil properties and external loading are treated as random variables rather than discrete values would be a powerful tool for offshore foundation designers. In this research project an analysis approach developed by the UCD geotechnical research group will be applied to the offshore foundation problems, whilst a serviceability limit state model for static loading of foundations will be expanded to account for cyclic degradation of soil stiffness.

Contact: kenneth.gavin@ucd.ie