Geotechnical Desk Study - Islington Council

Geotechnical Desk Study
7. Fieldwork
7.1 Walkover Survey
A walkover survey was carried out by a geotechnical engineer on 16 February 2009 and the
findings are given in Appendix C and summarised below.
The tarmac or concrete surfacing, in particular near to the Youth and Community Centre is uneven
and cracked. There is an area along the length of the west side retaining wall that has been
fenced off and has pronounced cracking approximately parallel to the wall. The west side retaining
wall only retains a small height of fill (less than 0.5m), although the wall is around 2m high. A
telegraph pole within this area close to the wall is leaning towards the cutting.
The east side retaining wall is greater than 2m in height, is cracked and leaning and has been
buttressed. This wall retains the gardens of the properties along Battledean Road; assumed
retained height of 1.5 to 2m.
The condition of the retaining walls is discussed further in Section 7.3.
The Youth and Community Centre shows signs of cracking in the walls which is likely to be as a
result of subsidence. Trees are located immediately adjacent to the west wall of the Centre along
the top of the railway cutting.
The walls of No. 1 Whistler Street, No. 71 Ronalds Road and the railway tunnel have all been
anchored or tied back as a result of structural displacement.
The railway cutting has a gradient of between 1:2.5 and 1:3. The surface of the cutting slope is
cohesive with evidence of a small amount of orange-brown granular fill below the west side
retaining wall. No evidence of slope instability was observed. An embayment has been cut into the
slope for a seating area below the west side retaining wall. The slopes are covered with semimature
trees. The toe of the cutting is supported by a sheet piled retaining wall.
A greenhouse has been constructed on a terrace cut into the slope near to the top of the sheet
piled wall. The brick wall retaining the cut is cracked and is displaced towards the railway.
A new brick wall is currently under construction along the west side of Whistler Street which ends
at the north side of the Youth and Community Centre.
7.2 Topographical Survey
A topographic survey of the site has been carried out excluding the area above the tunnel. The
survey plan is given in Appendix E.
7.3 Condition Survey of Retaining Structures
The site consists of an area of land at the top (crest) of the D/S railway cutting slope, known as
‘Highbury Roundhouse’, the graded cutting slope down to the railway line (Olden Gardens) and
area of land of the over the CE of Canonbury Tunnel (between Ronalds Road and the CE tunnel
portal) – refer to site plan in Appendix A.
Within the site are a number of retaining wall structures, which provide support to the cutting
slope material, allowing the development of the land at the top of the slope for commercial
premises, and later use by the local community.
The retaining wall structures inspected as part of this desk study are:
West Side Retaining Wall – Formed of mass brickwork construction with flat concrete coping
stones, approx 2.2 metres in height, with an approx. thickness of 330mm (above retained ground
5044006/002 Geotechnical Desk Study (2).doc 15