Forecast climate change impact on pore-water pressure regimes for the design and assessment of clay earthworks

Understanding and mitigating the impact of climate change on the built environment is becoming increasingly important worldwide. Earthworks (embankments and cuttings) supporting road and rail transportation networks often have direct contact with the atmosphere and are therefore influenced by extreme weather events and seasonal weather patterns. Atmospheric wetting and drying alters pore-water pressures (PWP) within earthworks, potentially contributing to the deformation and failure of earthwork slopes. Consequently, it is essential to understand the influence of climate change on PWPs within earthwork slopes, to inform strategies for their design, assessment and maintenance. Extensive one-dimensional seepage analyses were carried out for typical railway embankments in the London area. The analyses showed that forecast hotter, drier summers will increase the water storage capacity of earthworks. This will lead to increased net infiltration in the winter months due to both a forecast increase in rainfall, and a longer time being required to saturate the soil pores and bring the water table back to the slope surface. Hence, despite the forecast increase in winter rainfall, this will not lead to higher design PWP regimes. The analyses were conducted for the London area, but the methodology and conceptual framework can be readily adapted for other locations

Failures in transport infrastructure embankments

To ensure that road and rail transport networks remain operational, both highway and railway embankments require continual maintenance and renewal to mitigate against ongoing deterioration and repair any sections damaged by realised failures. This paper provides a review of recent developments in the understanding of highway and railway embankment degradation and failure. Failures due to pore water pressure increase, seasonal shrink-swell deformation and progressive failure are considered. The material composition and construction of highway and railway embankments differ, which influences the dominant type and timing of embankment failure. There is evidence for highway embankment failures induced by pore water pressure increase, but not seasonal deformation and progressive failure. Some railway embankments are susceptible to pore water pressure increase, seasonal shrink-swell deformation and progressive failure due to the age and nature of the dumped clay fill used in their construction. The approaches used to measure and explore embankment failure mechanisms are compared and discussed. Field observations have been used to understand pore water pressure increase and seasonal shrink-swell deformation in embankments, while the investigation of progressive embankment failure has mainly utilised physical and numerical modelling approaches. Further field and laboratory investigation is required before the rigorous analysis of embankment failure can be routinely undertaken. However, progress is being made to empirically identify and evaluate the various risk factors affecting transport infrastructure embankment failure

Thermal conductivity of soils by the needle probe method, for energy foundation applications

Soil thermal conductivity is an important parameter in the design of ground source heat pump and energy foundation systems. One laboratory method for measuring the soil thermal conductivity is the needle probe method. Previously, analysis of the needle probe test data has been simplistic, relying heavily on human judgment and rules of thumb. This paper presents an alternative method of analyzing the needle probe data with the aid of a MATLAB program. Four agar-kaolin specimens of varying densities were prepared to resemble simple soils. These were tested using the needle probe for a range of heating times and heating powers, to see what effect these parameters would have on the results. The repeatability when keeping the heating time and heating power constant was within ±2%. When the heating time and heating power were varied, the variation in results from the average for a given specimen ranged from ±4% to +10%/-8%. This range is significantly higher than the repeatability. Possible reasons for this are discusse

Assessing the applicability of thermal response testing to energy piles

Deep foundations are increasingly being used, not just to carry structural loads, but also to act as heat exchangers as part of a ground source heat pump system. Such foundations, often called energy piles, have the potential to make signific ant contributions towards meeting the heating and cooling demands of buildings, thus reducing the overall energy consumption and carbon dioxide emissions during their lifespan. To ensure that the available energy from these systems is maximized, it is important to determine the thermal conductivity of the surrounding soils, a key design input parameter. In situ thermal response tests are commonly used to carry out this task for small diameter borehole heat exchangers. However, there has been debate over the applicability of these tests to energy piles due to their larger diameter and the consequent increased influence of the pile thermal properties on the test outcome. This paper examines the results of three thermal response tests carried out on piles of different diameters and thermal properties installed at the same site in Texas. Transient analysis of the test results, combined with comparisons to laboratory testing of soil samples from the site, is used to given an indication of the applicability of the thermal response test over different timescales for the different piles. It is concluded that the test is most suited to smaller diameter piles constructed with lower thermal diffusivity materials. Recommendations are given for the conduction of pile thermal response tests and interpretation of test data

Stabilisation of a landslide on the M25 highway London's main artery

This paper describes the lessons learnt in the assessment, stabilization and subsequent monitoring of a landslide, which mobilized over 90,000 m3 of material and threatened to completely close England’s busiest highway, the M25 around London. The wedge shaped slide occurred on the 19th December 2000 and extended some 80m up the slope with a slip surface up to 10 m below the ground surface. Due to the strategic importance of the M25, the design and construction was fast tracked to be completed before the fall rains when further movements would be inevitable. The adopted solution used a combination of 1050 mm diameter augered piles, a deep cutoff trench and counterforts at the toe and was extensively instrumented.The collected data for the winter 2001/02 demonstrates that not only were the remedial works successful in stabilizing the slope but that the proposed design method can accurately predict the bending moments and forces produced in the pile