Geothermal energy pile foundation, soil-structure interaction, coal seam gas (CSG), wind farm collector system, gas/liquid permeability characteristic of cement bentonite used in cut-off walls and borehole walls, unsaturated geosynthetic clay liner (GCL), barrier design for nuclear waste, suction measurement techniques, thermo-hydro-mechanical (THM) behavior of soils and geosynthetics, modification of bentonite to improve its retention capacity.
Monash University, Australia
Queen's University, Canada
Cardiff University, UK
UPC Barcelona, Spain
IIT Guwahati, India
University of Sydney, Australia
Energy Geotechnics ENGM270
Surveying ENG1074, ENG2105
Engineering Geology ENG1075
Mathematics 1 ENG1084
• Ground Engineering Group ICE Wales
• Institute of Ground Source Heat Pump Association (IGSHPA)
• Institute of Engineers India (IEI)
• Australian Geomechanics Society (AGS)
Find me on campus Room: 24 AA 02
9:00 - 17:30
A gas flow unified measurement system (UMS-G) for sequential measurement of gas diffusion and gas permeability of geosynthetic clay liners (GCLs) under applied stress conditions (2 to 20 kPa) is described. Measurements made with the UMS-G are compared with measurements made with conventional experimental devices and are found to give similar results. The UMS-G removes the need to rely on two separate systems and increases further the reliability of the gas properties’ measurements. This study also shows that the gas diffusion and gas permeability reduce greatly with the increase of both gravimetric water content and apparent degree of saturation. The effect of applied stress on gas diffusion and gas permeability is found to be more pronounced at gravimetric water content greater than 60%. These findings suggest that at a nominal overburden stress of 20 kPa, the GCL used in the present investigation needs to be hydrated to 134% gravimetric water content (65% apparent degree of saturation) before gas diffusion and gas permeability drop to 5.5 × 10−11 m2·s−1 and 8.0 × 10−13 m·s−1, respectively, and to an even higher gravimetric water content (apparent degrees of saturation) at lower stress.
Geothermal energy piles utilize the almost constant ground temperature at shallow depths below the ground surface to heat and/or cool built structures. Heat is extracted from and/or injected into the ground through the use of a heat carrier fluid that flows in pipes attached to the reinforcement cage of the pile foundations. The performance of the energy piles can be improved by enhancing the heat exchange between the heat carrier fluid and the ground. The purpose of this paper is to provide evidence from literature on multidisciplinary methods to improve the thermal properties of elements in a geothermal energy pile. Geometrical optimization such as the number of pipes and their arrangement can be done to reduce the total pile thermal resistance. Nanofluids can be used as the heat carrier fluid to enhance the fluid conductive and convective heat transfer. Highly thermally conductive fillers can be mixed with the pipe material to enhance its thermal conductivity. The thermal properties of the concrete can also be enhanced by adding highly thermo-conductive materials to the concrete mix.
Field observations from a heating test conducted on a geothermal energy pile, containing two Osterberg cells, installed in a dense sandy material are reported. An instrumented pile and two boreholes were installed for this purpose. The pile was heated for various time intervals and the ground heat response was observed via thermocouples installed at various depths in the two boreholes. A time lag in the diffused heat wavefront arrival was consistently observed in the borehole farthest from the heat source (i.e. pile). This suggests heat diffused slowly in the ground and its intensity reduced with distance from the heat source. Heat transfer was affected by the ground stratigraphy. The pile and the ground were allowed to cool by letting heat dissipate naturally once the heating test was completed. It was found that both the pile and the ground required at least more than twice the heating time to have full thermal recovery from the heating process. A constant heat exchange rate (or heat rejection rate) of 100–125 W/m2 was achieved, despite continuous rise in temperature of the pile and the ground.
Super-saturated salt solutions are used to control relative humidity (RH) and to infer the hydration (water uptake and loss) behaviour of three needle-punched geosynthetic clay liners (GCLs) with respect to time under conditions of both free swell and 20 kPa applied stress. It is shown that RH and applied stress play a key role in the hydration behaviour with time when GCL specimens were in equilibrium with water vapour. It was also observed that water uptake and loss was affected by the bentonite form (powdered or granular) and mineralogy of the bentonite. However, the effect of GCL structure (i.e. difference in geotextiles and bonding of needle-punched fibres to the carrier geotextile) on their hydration behaviour for GCLs with similar form of bentonite was not significant for RH ≤ 97.7%. The effect of GCL structure became more apparent at 100% RH (for all GCLs). The results presented in this study can be used to better assess the hydration of GCLs in field applications such as waste containment liners and cover systems at different RH and overburden stress conditions.
An initially wet contact filter paper test (IW-CFPT) and an initially dry contact filter paper test (ID-CFPT) were used to examine the wetting paths of geosynthetic clay liners, including non-contact filter paper tests for comparative purposes. The CFPTs were applied to both geosynthetic clay liner faces to examine the effect of geotextile type on capillary contact. The non-woven geotextile face was found to be more likely to cause capillary breaks than the woven geotextile face. Both IW- and ID-CFPTs were found to be applicable to geosynthetic clay liners within their accurate upper matric suction measurement limits of 146 kPa and 66 kPa, respectively.
Heat exchanger pile foundations have a great potential of providing space heating and cooling to built structures. This technology is a variant of vertical borehole heat exchangers. A heat exchanger pile has heat absorber pipes firmly attached to its reinforcement cage. Heat carrier fluid circulates inside the pipes to transfer heat energy between the piles and the surrounding ground. Borehole heat exchangers technology is well established but the heat exchanger pile technology is relatively new and requires further investigation of its heat transfer process. The heat transfer process that affects the thermal performance of a heat exchanger pile system is highly dependent on the thermal conductivity of the surrounding ground. This paper presents a numerical prediction of a thermal conductivity ground profile based on a field heating test conducted on a heat exchanger pile. The thermal conductivity determined from the numerical simulation was compared with the ones evaluated from field and laboratory experiments. It was found that the thermal conductivity quantified numerically was in close agreement with the laboratory test results, whereas it differed from the field experimental value.
Shallow geothermal heat exchangers integrated in structural pile foundations have the capability of being an efficient and costeffective solution to cater for the energy demand for heating and cooling of built structures. However, limited information is available on the effects of temperature on the geothermal energy pile load capacity. This paper discusses a field pile test aimed at assessing the impact of thermomechanical loads on the shaft capacity of a geothermal energy pile. The full-scale in situ geothermal energy pile equipped with ground loops for heating/cooling and multilevel Osterberg cells for static load testing was installed at Monash University, Melbourne, Australia in a sandy profile. Strain gauges, thermistors, and displacement transducers were also installed to study the behavior of the energy pile during the thermal and mechanical loading periods. It has been found that the pile shaft capacity increased after the pile was heated and returned to the initial capacity (i.e., initial conditions) when the pile was allowed to cool naturally. This indicated that no losses in pile shaft capacity were observed after heating and cooling cycles. A variance in average vertical thermal strains was observed along the upper section of the pile shaft at the end of the heating periods. These were almost fully recovered at the end of the cooling periods, indicating that they are of an elastic nature. Pile average circumferential strains were found to be relatively uniform at the end of the heating and cooling periods and did not change with depth. They, also, were fully recovered during the cooling period. It was also observed that the increase of temperature during the heating periods prompted the pile shaft to expand radially. Subsequently, as the pile cooled down, the pile shaft slowly contracted and returned closely to its original condition, suggesting a thermoelastic behavior.
Movement of fluids in the unsaturated zone plays an important role in many geoenvironmental engineering problems. Examples include cover and basal liner systems for waste containment facilities where geosynthetics are widely used, amongst many other examples. This paper highlights the importance of assessing the unsaturated characteristics of geosynthetics and their influence on the behaviour of engineered systems where soils and geosynthetics interact under unsaturated conditions. It includes information on the water retention curve and hydraulic conductivity function of geosynthetics such as geotextiles and geosynthetic clay liners (GCLs) with particular focus on capillary barriers, liner performance under elevated temperatures, and interface friction respectively. Mechanisms involved in the development of capillary barriers are evaluated to explain the storage of water at the interface between materials with contrasting hydraulic conductivity (e.g. a fine-grained soil and a nonwoven geotextile). Potential desiccation of GCLs is explained in the light of an application in a liquid waste impoundment.
The thermal conductivity of soils and rocks is an important property for the design of thermally active ground structures such as geothermal energy foundations and borehole heat exchange systems. This paper presents the results of a laboratory study of the thermal conductivity of soils and rocks from around Melbourne, Australia. The thermal conductivity of six soils and three rock types was experimentally measured using both a thermal needle probe and a divided bar apparatus. Soil samples were tested at a wide range of moisture contents and densities. The results demonstrated that the thermal conductivity varied with soil moisture content, density, mineralogical composition and particle size. Coarse grained soils were observed to have a larger thermal conductivity than fine grained soils. In addition, the thermal conductivity of soils increased with an increase in dry density and moisture content. Siltstone, sandstone and basalt rock samples were tested dry and water saturated. They demonstrated an increase in thermal conductivity with an increase in density when dry. However, when water saturated, siltstone and sandstone showed no significant correlation between density and thermal conductivity; whereas a linear increase in thermal conductivity with density was observed for the saturated basalt samples. These differences were attributed to both variations in mineralogy and anisotropy of each sample. The thermal conductivity data obtained from this study provides an initial database for soils and rocks from the Melbourne (Australia) region which can serve for the design of thermo-active structures installed locally and in locations with similar ground conditions.
Thermal conductivity is a key property that controls heat migration in a variety of applications including municipal solid waste and/or mining/industrial containment facilities. In particular, heat may be encountered in cases where geosynthetic lining systems are exposed to elevated temperatures due to either waste biodegradation, solar radiation, or mining processes. This paper presents the results of an experimental investigation on thermal conductivity of nonwoven geotextiles, geosynthetic clay liners and an HDPE geomembrane. A steady state method was used to measure the thermal conductivity of a selected number of these materials. The thermal conductivity of the HDPE geomembrane was found to be consistent with the thermal conductivity of HDPE polymer. On the other hand, the thermal conductivity of the nonwoven geotextiles depended on water content and whether they are hydrophobic or hydrophilic. The form of bentonite, its mass per area and water content affected the thermal conductivity of GCLs. The results presented in this paper provide a lower bound of thermal conductivities of geosynthetics routinely used in waste containment facilities.
Non isothermal moisture movement in unsaturated kaolin is investigated in a series of experiments. Vapour transfer is then empirically quantified, and its theoretical representation considered. A thermo-hydraulic cell is used to apply thermal and hydraulic gradients to confined specimens in a number of thermal gradient, thermal-hydraulic gradient, and isothermal-hydraulic tests. Transient measurements of the thermal regime are made, and end of test measurement of moisture content, porosity, and chemical composition from a number of identical tests run for different durations allow pseudo transient variations of these parameters to be established. In each of the tests, where a thermal gradient is applied, the accumulation of chloride ions in the hottest regions indicates a cyclic movement of vapour and liquid moisture. Estimated vapour fluxes are determined by consideration of overall moisture and conservative ion movements in the sealed thermal gradient tests. These vapour fluxes are then compared to those predicted by an established vapour flow theory, and a modification to this theory is proposed based on a variable enhancement factor.
Incorporation of heat exchangers into pile foundations is a relatively novel sustainable technology for the intermittent storage of energy in soils. Energy can be utilised in this way for space heating and cooling of buildings by means of suitable systems integrated into buildings. This paper relates to an ongoing study on the impact of coupled thermo-mechanical loads on heat exchanger pile foundations. This study evaluates the performance of a laboratory scale energy pile under different vertical stress levels, temperature gradients and heat transfer modes and presents the full-scale in situ energy pile setup equipped with ground loops for heating/cooling and multi-level Osterberg cells for static load testing.
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Page Created: Thursday 8 January 2015 13:16:09 by as0033
Last Modified: Wednesday 8 June 2016 17:35:44 by rs0051
Expiry Date: Friday 8 April 2016 13:15:23
Assembly date: Tue May 21 00:32:27 BST 2019
Content ID: 138514