Browsing by Author "Collins, Niamh"
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Item Support and sealing at the toe of a retaining wall extending to bedrock; theory and practice(Aalto University, 2011) Collins, Niamh; Heikkilä, Jaakko; Rakennustekniikan laitos; Department of Civil Engineering; Insinööritieteiden korkeakoulu; School of Engineering; Korkiala-Tanttu, LeenaThe issue of providing lateral support to the toe of a retaining wall arises in supported excavations extending to the bedrock. During the excavation phase lateral support is most commonly provided by rock dowels drilled into the rock along the toe of the wall. Inclined toe bolts and a toe beam are later installed to provide final support at the toe when the excavation has reached bedrock. Problems relating to the use of rock dowels have been encountered in Finland, in particular problems relating to the incorrect positioning of the rock dowels. A large gap between the wall and the rock dowel allow excessive displacement to occur at the toe. Another practical problem frequently encountered in deep excavations extending to bedrock where the base of the excavation lies below the groundwater level is the provision of a water tight seal along the base of the wall. This particularly becomes an issue in conditions of high groundwater flow at the level of the bedrock. Solutions must be found to adequately control the flow of groundwater in the region of the toe of the wall. This thesis aims to address the practical problems relating to the provision of lateral toe support and sealing at the toe through an examination of current practice. This was done by carrying out a series of interviews with experienced engineers and contractors. The interviews were carried out from November 2010 to May 2011 and sought to gain an understanding of the concepts, attitudes and processes used in practice. It should be noted that this thesis is based in Finland and hence focuses on the situation in Finland. The theory presented in this thesis is mainly based on European literature but attention is drawn to those parts which are particularly relevant for use in Finland. The interviewees consisted of Finnish professionals. It should also be noted that results of the interviews are based solely on the opinions and experiences of the interviewees. Problems involving the positioning of the rock dowel relate to the method of installation used. Inaccurate positioning of the dowel is associated with the use of bored installation tubes. Installation of the rock dowels through casings attached to the wall eliminates this problem. However pre-attached casings are not always favoured in practice due to the difficulties in ensuring the casing is not damaged during driving. Additionally pre-attached casings are a more expensive method. The solution for sealing at the toe depends on the site conditions. A toe beam is suitable for conditions of low groundwater flow where the occurrence of some seepage beneath the toe is allowable. For conditions of higher groundwater flow or conditions very sensitive to lowering of the groundwater grouting techniques must be employed. Jet grouting is considered the most dependable technique and therefore is highly recommended where sealing at the toe is critical.