Th gme 10: A numerical model to capture the geotechnical response to coal combustion at an underground coal gasification site

A detailed numerical modelling study was carried out to represent geotechnical aspects of the Wieczorek underground coal gasification (UCG) site in Poland. A coupled thermos-mechanical numerical model was created to represent a single coal burning panel. The coal burning proceb was simulated by modifying the energy balance equation with an additional term related to the calorific value of coal as a source. Temperature dependent material properties were abigned to the coupled thermal-mechanical model according to published data. In the model, the burning zone spread about 7.5m laterally after 20 days of burning. Results from the coupled model were used to gauge a worst-case scenario in terms of the potential size of a formed cavity. This data was used within a leb computationally expensive mechanicalonly numerical model in order to evaluate the ground subsidence caused by the worst-case scenario for single and multiple UCG burning panels. The single panel burning resulted in 23mm of ground subsidence at the top of the model after long term coal burning. The ground subsidence measured at the top of the model, at the center point of the gasification arrangement, was approximately 72mm when five panels were burnt with an edge to edge panel distance of 5m; this was increased to 85mm for seven panels. The numerical modelling results have implications to the industrial application of UCG

Application of roller compacted concrete for road pavements in Sri Lanka

There is a great need to construct more durable roads such as concrete roads in Sri Lanka since the government is spending a considerable amount of money every year to maintain the national road network which has been constructed using with either conventional asphalt concrete or bituminous paving materials. This research was carried out mainly to explore the possibility of introducing more durable and cost effective Roller Compacted Concrete for road pavements in Sri Lanka. The structural behavior of Roller Compacted Concrete pavement (RCCP), which is a rigid pavement, is completely different from conventional asphalt pavements which are designed as flexible pavements. Since RCCP is not currently used in Sri Lanka there is no local standards available for design and construction of RCCP. An extensive literature review was carried out regarding the design of rigid pavements practiced in other countries. The rigid pavements can be designed using different types of design methods for given conditions. However, out of those methods, American Association of State Highway Traffic Organization method (AASHTO) and Portland Cement Association (PCA) method are popular in the countries where rigid pavements are used. Out of these two methods AASHTO method uses more parameters in designing the pavement thickness. Therefore, parametric study was carried out to investigate the effect of each parameter used in AASHTO method. And also a computer program was developed based on PCA method to carry out the thickness design procedure effectively, as it is more suitable for low volume traffic conditions. An experimental investigation was carried out to formulate a mix design procedure for RCC using local materials. Since the thickness of RCCP depends on the flexural strength of RCC, tests were carried out to investigate the factors affecting the flexural strength of RCC and also other properties such as wet density, compressive strength and drying shrinkage. New test methods were developed to measure these properties specially the flexural strength and wet density incorporating actual conditions of RCC such as actions of static and vibrating rollers. A new apparatus was developed to measure the wet density by modifying the conventional V-B apparatus where vibration as well as known static pressure can be applied to compact concrete. Furthermore, use of chemical and mineral admixtures to improve the properties of RCC was also investigated. Based on the results of experimental investigations a mix design procedure for RCC was proposed

Design of roller compacted concrete mixes for road pavements

This paper presents some guidelines to carry out mix design for Roller Compacted Concrete (RCC). In order to propose a mix design method for RCC, an experimental investigation was carried out to study the properties of RCC such as wet density and flexural strength under different cement contents. A new test method was proposed to measure the wet density of RCC considering the action of a vibrating roller. The test results of wet density show that the behaviour of RCC is similar to soil with respect to optimum density. And also it was found that the flexural strength depends not only on the water cement ratio but also on the cement content. An approximate relationship was obtained for the flexural strength combining the water cement ratio and cement content

Numerical modelling of ground subsidence at an underground coal gasification site

A detailed numerical modelling study was carried out to represent geotechnical aspects of the Wieczorek underground coal gasification (UCG) site in Poland. A coupled thermos-mechanical numerical model was created to represent a single coal burning panel. The coal burning process was simulated by modifying the energy balance equation with an additional term related to the calorific value of coal as a source. Temperature dependent material properties were assigned to the coupled thermal-mechanical model according to published data. In the model, the burning zone spread about 7.5m laterally after 20 days of burning. Results from the coupled model were used to gauge a worst-case scenario in terms of the potential size of a formed cavity. This data was used within a less computationally expensive mechanical-only numerical model in order to evaluate the ground subsidence caused by the worst-case scenario for single and multiple UCG burning panels. The single panel burning resulted in 23mm of ground subsidence at the top of the model after long term coal burning. The ground subsidence measured at the top of the model, at the center point of the gasification arrangement, was approximately 72mm when five panels were burnt with an edge to edge panel distance of 5m; this was increased to 85mm for seven panels. The numerical modelling results have implications to the industrial application of UCG