Q1 An excavation is required close to BH2 (Figure Q1) to construct a building with basement levels. The foundation is intended to be constructed on the sand soil layer. The groundwater level is marked on BH1 and BH3 logs as illustrated in the cross section below. The groundwater mark however is missing on BH2 log. To deliver the earthworks economically, the client has queried whether the foundation level can be reached via battering to a safe angle (without using any temporary excavation support such as sheet piles). Assume there is enough space for battered excavation and a planned exposure time of less than 6 days before foundation installation. Briefly write your advice to the client. Can the client save money, and reach the bed of foundation by battered excavation and a safe slope?
Water strike: the level at which water is first encountered
Standing water level: depth water rose toFigure Q1 – Cross section showing the exploratory borehole logs
Q2 A construction site for a bridge over the River Orwell in Ipswich extends over an area of 200x80m, with a complete layer of drift deposits (sand with some gravel, clay and silt) on a sloped terrain, and therefore no bedrock exposure. Sixteen boreholes were excavated. A chalk rockhead (top of bedrock) was found at 5-10m depth. Boreholes are mostly positioned across lower terrains. A walk-over survey reveals a number of small valleys across the region. Available geological maps show a number of major folds – that is when a layer of rock under earth pressures has bent upwards and downwards, forming depressions and hills (Figure Q2). The geological map of the area and a cross section along the proposed bridge alignment is shown in Figure Q2. Briefly discuss the probable risk(s) that need to be taken into account in design when the data from the 16 borehole logs only are used. Underpin your answer with proper reasoning and through commenting on the landform formation mechanisms.
Figure Q2 –geological map and cross section: River Orwell crossing, Ipswich (generated by LithoFrame v2.0
Q3 The town of Bicester lies approximately 24km to the north east of Oxford and 28km to the south east of Banbury, approximately 3 km from the town centre. You are commissioned to study the ground conditions for development of the Bicester Eco-Town, which will comprise approximately 5,000 homes with supporting employment and education infrastructure. The new town will be situated on the north-western periphery of Bicester, as depicted in the OS map in Fig. Q3-1. The whole of the development site is sized appx. 350 ha and comprises Grade 3 agricultural land with a number of farmhouses and other buildings.
Figure Q3-1 – Ordnance Survey 1:25,000 map and location of the proposed new eco-town
[1] Comment on the solid and superficial geology of the east, west and middle of the project site;
[2] Comment on the strength of the topsoil layer across the project site;
[3] Comment on any possible pockets of problematic soils across the project site; briefly explain the nature of hazards (if any).
Q4 A two-storey residential building is to be constructed on a riverside plot (protected by a river wall) in South Downs, East Sussex. The ground consists of a top 0.1m dark grey spongy-like soil over 3.9m thick made ground, overlying a 5m-thick river alluvium layer (granular sand and gravel) on chalk bedrock. The alluvium layer contains a lenses of silty soils which seems to be loess. A plan view of the site and a longitudinal cross section through the site are illustrated in Figure Q4. The residential building is shown as Block H on the plan drawing. With proper reasoning, recommend a foundation solution (shallow or pile) and comment on the possible design/construction challenges.
Figure Q4 Layout of residential block H and existing defence wall and geological cross section through the site