Hydraulic and thermal conductivities of soils

Abstract

The aim of this research is to investigate the hydraulic and thermal conductivities of different types of soils. These two parameters are the main ones controlling the heat flow in the ground beneath a building. Therefore in this thesis, a system, including a testing and analysis methodology has been designed that will allow the construction of new laboratory apparatus in order to determine the required thermal parameters and thus reduce the uncertainty in the design of energy piles. This thesis presents and discusses the effects of physical properties on determining both the hydraulic and thermal conductivity of soils. Two flexible wall permeameters using the constant rate of flow technique were used to determine the hydraulic conductivity of two types of clayey soil. This technique proved to be accurate and produced results in a relatively short time. One of the, aims of this research was to develop a better technique for testing coarse soils; therefore these permeameters were developed to work using falling head technique. The falling head technique proved to be accurate and produced results in relatively shorter time than the constant flow technique. Tests at low and high hydraulic gradient and over a range of effective stress show the hydraulic conductivity varies with these two parameters. A part of the thesis describes the methods of interpreting the results from both the constant flow and falling head techniques, also it describes how the falling head tests can be interpreted as a constant head test for clayey soils. A comparison between the results showed the advantages of using the new systems. It is also demonstrated how the new system can determine the hydraulic conductivity of a soil in a relatively short time of one hour. The second aim of the research was to design a simple device to determine the thermal conductivity of soils. Two thermal conductivity cell devices were designed. A test procedure and its method of interpretation are discussed and presented. The thermal conductivity results were compared with the published results and proved to be within the same range (0.15 to 4 W/m.°C). These experimental results were also compared and discussed with the predicted results produced by different thermal conduction models.The thermal results for deferent types of soils can be used to model the heat transfer between the ground and the energy piles, in which the ground can be used as a heat sink or source. It is believed that the water content of the soils together with their mineralogical constituents can be particularly valuable, not only as a basis for understanding the behaviour of the soils but also to enable a reasonably good estimate of the thermal conductivity using the thermal conduction models.