Planning and evaluation of landfill at Nideng in Klæbu

Abstract

A landfill is to be established at Nideng in Klæbu which is a municipality within the sør- trøndelag region in Norway. The landfill composed of mass deposit of peat which is characterised by fibrous and organic materials. The topography of the project site is primarily ridges with valleys and stream passing through the site. The quaternary geological map shows mountains and weathering material at the project site as well as thick marine deposit. The site has undergone landslide activities in the past and is believed that the ridges left by the slides consist of clay, sand and gravel. Plans for developing the area have been launched, which means that proper stability evaluations have to be carried out.The primary objective of the study is stability evaluation of the peat mass deposit.The slide software based on limit equilibrium methods and plaxis which is based on finite elements method were employed for the slope stability evaluation.The factor of safety based on undrained conditions estimated by the slide software for profiles A, B, C are 0.25, 0.26 and 0.43 respectively. The calculated safety factor for the undrained condition has not satisfied the minimum safety factor required.The presence of the peat layer which is characterised by high in-situ void ratio, high water content and high values of compression index presents a pre-existing sliding surface causing instability of the peat mass embankment.The existence of the peat layer controls the shape of the failure surface. An employment of a berm composed of gravel with a modification of the actual embankment height and placing of layers of sand material of thickness 1m each in the peat embankment help to increase the factor of safety of the embankment for the undrained case significantly. The factor of safety for profile A increases from 0.25 to 1.2, profile B also increase from 0.26 to 1.1 and profile C also increases from 0.43 to 1.1.The factor of safety based on drained conditions estimated by the slide software for profiles A, B, C are 1.44, 1.53 and 1.51 respectively and the plaxis are also 1.33, 1.44 and 1.66 respectively. Using geogrid with tensile stiffness of EA=50 kN/m with lengths varying from10m to 130m and a spacing of 2m in the peat layer at Profile A for the drained case, the factor of safety increases by almost 21% decreasing the horizontal displacements of the embankment and there by increasing the stability of the peat embankment.