Geological description of Core log of M2 motorway By Peshawa Mahmod ď‚ˇ Introduction Core drilling log is very important in construction properties, spatially, in tunnel construction. North Downs Tunnel on M2 motorway was built in Kent County and core bore hole was drilled along the tunnel way. In this report describe the geology of the area with properties, lithology and stratigraphy of the core rock that drilled in this area.
ď‚ˇ Purpose of the drilling core The core log has been a part of investigation to build North Downs tunnel on M2 motorway in (Kent). They start on working in October 1998 by two major engineering companies; Eurolink JV has been worked in this tunnel. They started with drilling core well in North Downs Tunnel in Bluebell Hill. Rotary core drilling method has been used in the investigation. The M2 motorway was come to an end in August 2001(Glasspool, 2009).
ď‚ˇ Geology of the area The area is laid on recent deposit flowed by deposition of Chalk group (British Geological Survey, 1974) (see fig 1); the group deposited in late cretaceous age and it made a North Downs outcrop in South East of UK (Sumbler, 1996). The Chalk group is a famous physiogrphical features in the North Downs outcrop (Adams, 2008). It extended from coast of Kent in east to Hog Back in west. The North Downs Chalk outcrop forms the northern limbs of the Wealden anticline (Wood et al, 2000) (see fig 2).
ď‚ˇ Geological description of core sample The core was from box NO.1, bore hole NO.327, and the total core recovery was 1.85m. According to lithological and stratigraphical description the core are divided in to 6 beds. 1- Pure soft white Chalk of medium density could be robbed by thumb. Structure less of coarse fragments and highly fractured to cobble and pebble size Chalk. Contain shell of Inoceramid fossils and dark to dark brown colour of sub-rounded pebble size flints. The thickness of 30cm. 2- White milky colour Chalk of Medium density of highly fractured and structure less of
course fractures and there is no dissolution features; contain shell of Inoceramid fossils. Of 24cm thickness. 3- Whit smoky colour Chalk of mediam to high density, highly fractured and structur less with no observation of disolution features and no filling in the fractures. contain Inoceramid shell. The thickness is 58cm. 4- Light gray colour Marl of low density and Structural lessof 18cm thickness.
5- White milky colour Chalk of mediam density, highly fractured and structure less. Contanin gravel and pebble size Flint of dark brown colour and yellow sand particals. No dissolution feature and no filling of the fractures, of 28cm thickness. 6- White milky colour Chalk of medium to high density of highly fractured with no dissolution feature and no filling of the fractures. Contain yellow and gray colour sand partials of organic and nonorganic origins. The Inoceramid the abundant fossils, the thickness is 27cm.
ď‚ˇ Stratigraphical and Lithological description Typically, Chalk is pure white Limestone of biogenic origin (Brenchley and Rawson, 2006); contain more than 98% of calcium carbonate (Sumbler, 1996). The Chalk is divided in to three sub-groups, Lower, Middle and Upper Chalk (Young and Lake, 1988) (Wood et al, 2000); in the North Down it is not so simple to apply this classification on the Chalk (Bristow et al, 1997). The abundant future that saw in the core sample is the presence Inoceramid fossils of bivalve family. This family reach global distribution during Cretaceous age spatially in (Cenomanian -Turonian) (Harries et al, 1992). According to the white colour and presence of flint, marl bed and Inoceramid fossils the core could be returned to the Upper Chalk of late Turonian stage. Furthermore, it might be from Lewes Nodular Chalk Formation. This formation according to (Bristow et al, 1997) is of white Chalk, gray marl bed, dark brown flit and abundance of Inoceramid fossils.
ď‚ˇ Discussion It is not easy to correlate this small depth core sample with a hole stratigraphical unite of the Chalk groups. However, according to the physical properties of the core rocks and fossils contains the core rock is from Upper Chalk of late Turonian stage of Lewes Nodular Chalk Formation. In general, the rocks are highly weathering with occurrence of marl bed in the depth 2.42m that might lead to accumulation of water in the above death and cause series engendering preleases.
ď‚ˇ Bibliography -
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Geological Survey of Great Britain (England and Wales) (1974), sheet 272, Map scale 1:50000. 6