F.A. Loveridge

The impact of climate and climate change on infrastructure slopes, with particular reference to southern England

Abstract Climate interacts with infrastructure slopes and their associated vegetation to cause changes in porewater pressures and shear strength with time. Extreme events may ultimately lead to slope failure as a result of increases in porewater pressure and/or decreases in strength. In addition, certain weather conditions may also cause serviceability problems owing to excessive movements. This paper uses network-level studies of infrastructure earthwork performance, site-specific data and numerical modelling to explore the relationships between climate, geological conditions and the performance of the UKs earthworks. Key factors for understanding earthwork behaviour are identified, including plasticity and permeability. How climate change may affect UK infrastructure slopes is then considered, assessing how different failure mechanisms may become more prevalent in the future and hence the relative risk at different sites may change.

The Thermal Behaviour of Three Different Auger Pressure Grouted Piles Used as Heat Exchangers

Abstract Three auger pressure grouted (APG) test piles were constructed at a site in Richmond, Texas. The piles were each equipped with two U-loops of heat transfer pipes so that they could function as pile heat exchangers. The piles were of two different diameters and used two different grouts, a standard APG grout and a thermally enhanced grout. Thermal response tests, where fluid heated at a constant rate is circulated through the pipe loops, were carried out on the three piles, utilising either single or double loops. The resulting test data can be used to determine the surrounding soil thermal conductivity and the pile thermal resistance, both essential design parameters for ground source heat pump systems using pile heat exchangers. This paper uses parameter estimation techniques to fit empirical temperature response curves to the thermal response test data and compares the results with standard line source interpretation techniques. As expected, the thermal response tests with double loops result in smaller thermal resistances than the same pile when the test was run with a single loop. Back analysis of the pile thermal resistance also allows calculation of the grout thermal properties. The thermally enhanced grout is shown to have inferior thermal properties than the standard APG grout. Together these analyses demonstrate the importance of pile size, grout thermal properties and pipe positions in controlling the thermal behaviour of heat exchanger piles.

Building codes, green certification and implementation issues, market challenges

Abstract The purpose of this paper is to provide a current state of affairs regarding the existing building codes in relation to thermoactive foundations, if any exist at all. This paper also explores regional incentives in the form of energy and carbon requirements for new structures as a potential driver for thermoactive foundation implementation. Two Green Certification programs, LEED and BREEAM, are discussed which both offer credit for shallow geothermal energy systems. The actual implementation of thermoactive foundation technology has proved to be challenging due to the complications arising out of the concept development stage and the coordination required among the various parties involved in the design stage. A discussion of these challenges and an outline of the deliverables needed of those in academia and industry in order to progress is included.

Environmental impact calculations, life cycle cost analysis

Abstract This session explored the evaluation and characterization of the sustainability of thermoactive geotechnical systems. Thermoactive geotechnical systems take advantage of shallow geothermal energy by using the foundation of a structure as a heat source and sink for use with a ground source heat pump. Methods for their evaluation within a sustainability framework still need to be developed. This can be done within larger regulatory frameworks such as the Code for Sustainable Homes. The Life Cycle Analysis methodology has been used to examine non-thermoactive geotechnical systems using both embodied carbon and embodied energy as metrics. Life Cycle Analyses have also been performed on ground source heat pumps and can provide valuable insight into the indirect operational environmental impacts of thermoactive geotechnical systems.

Identifying best practice, installation, laboratory testing and field testing

Abstract This paper summarizes recommendations for best practice associated with the installation of geothermal loops within foundations to form thermopiles, based on experience gained over the past 10 years in the UK. The issue of paramount importance in constructing a successful thermopile installation is the early stage coordination with all parties that will encounter, install or test the geothermal loops. Several lessons learned from the installation and construction of thermopiles are described to help ensure a smooth installation process. As long as there is early coordination, the installation of geothermal heat exchange tubing is relatively simple and will have very little or no impact on typical deep foundation installation procedures. This, coupled with the fact that there are additional costs and implications associated with other geothermal heat exchange approaches, implies that thermopiles are an ideal economic solution to access a renewable energy source.

Design tools for thermoactive geotechnical systems

Abstract This paper presents a review of current design tools used for thermoactive geotechnical systems, along with validation efforts. The capabilities of available analytical methods used for the thermal and thermomechanical design of these systems are evaluated and shortcomings of the existing methods are identified. Although the analytical methods permit accurate prediction of the thermal stress and strain response of thermoactive piles from readily available soil and concrete properties, current shortcomings consist of the ability of the methods to simulate cyclic heating and cooling effects, transient pore water pressure generation and dissipation, and the effects of radial stress changes. Recommendations are provided on how to properly address the current design requirements and the efforts to overcome shortcomings with the development of constitutive relationships from further full scale and laboratory scale experimental studies on thermoactive piles. Furthermore, the need for the development of both simplified analytical tools and advanced finite element models is emphasized. In addition, the existing analytical tools should be validated using field data from recently available case studies of thermoactive piles in varying soil deposits. An urgent need for an extensive design guide for energy geostructures was identified. The guidelines should be targeted towards practitioners and include field observations and measurements, as well as laboratory and numerical studies.

In situ measurements of near-surface hydraulic conductivity in engineered clay slopes

In situ measurements of near-saturated hydraulic conductivity in fine-grained soils have been made at six exemplar UK transport earthwork sites: three embankment and three cutting slopes. This paper reports 143 individual measurements and considers the factors that influence the spatial and temporal variability obtained. The test methods employed produce near-saturated conditions and flow under constant head. Full saturation is probably not achieved owing to preferential and bypass flow occurring in these desiccated soils. For an embankment, hydraulic conductivity was found to vary by five orders of magnitude in the slope near-surface (0–0.3 m depth), decreasing by four orders of magnitude between 0.3 and 1.2 m depth. This extremely high variability is in part due to seasonal temporal changes controlled by soil moisture content, which can account for up to 1.5 orders of magnitude of this variability. Measurements of hydraulic conductivity at a cutting also indicated a four orders of magnitude range of hydraulic conductivity for the near-surface, with strong depth dependence of a two orders of magnitude decrease from 0.2 to 0.6 m depth. The main factor controlling the large range is found to be spatial variability in the soil macrostructure generated by wetting–drying cycle driven desiccation and roots. The measurements of hydraulic conductivity reported in this paper were undertaken to inform and provide a benchmark for the hydraulic parameters used in numerical models of groundwater flow. This is an influential parameter in simulations incorporating the combined weather–vegetation–infiltration–soil interaction mechanisms that are required to assess the performance and deterioration of earthwork slopes in a changing climate.

Site investigation for energy geostructures

Energy geostructures are structure or infrastructure foundations used as heat exchangers as part of a ground source heat pump system. Although piles remain the most common type of energy geostructure, increasingly infrastructure projects are considering the use of other buried structures such as retaining walls and tunnels for heat exchange. To design and plan for construction of such systems, site investigations must provide appropriate information to derive analysis input parameters. This paper presents a review of what information regarding the ground, and also the structures themselves, would be required for the ground energy system design process. Appropriate site investigation methods for energy geostructures are reviewed, from desk study stages through in situ testing to laboratory testing of samples recovered. Available methods are described and critically appraised and guidance for practical application is given.

The Average Temperature of Energy Piles

The geotechnical design of energy piles requires confirmation that the foundations can continue to carry safely the required load from the overlying structure and that no detrimental effects from the additional imposed temperature changes will occur. These additional design checks require assumptions to be made about the temperature changes within the pile. However, there is no universal approach for determining these, and routine application of over-conservative pile temperatures can lead to unrealistically adverse geotechnical design scenarios. This paper considers how the average temperature of a pile can be determined based on the analysis steps already carried out for the thermal design. The aim is to be able use the calculated fluid temperatures, along with readily available pile and ground parameters, to provide better assessments of the actual pile temperature so that the outputs of the geotechnical design can be improved. Two dimensional numerical simulations are used to determine the average pile temperature for different pipe, pile and concrete properties. The results of the simulations are compared with analytical approaches, allowing these to be validated for use on a routine basis. It is shown that the temperature of the center of the pile, which can be determined easily by analytical methods, can be used as a proxy for the average pile temperature.

New technologies and applications: materials and equipment in near surface geothermal systems

Abstract This paper presents an overview of new technologies and applications on thermoactive geostructures. A discussion session on issues involved with near surface geothermal systems is presented, focusing on opportunities for developing new technologies to address these issues. In addition, opportunities for new applications of geothermal heat exchange in geotechnical engineering were discussed. Progress on the development of new materials and equipment that may be used to enhance the rate of heat transfer or heat storage capacity was discussed.