July/August 2021 - 94
From left, the backside of the façade of 71-81 Whitfield Street, structural reuse at No. 67-69, and 65 WS
residential use; so, new cores and
surrounding bays were proposed as
new build.
Ongoing desk study failed to provide
any reliable information on the mid1900s
foundation design and construction
at either building.
Extensive Site Investigation
In 2012, a structural and geotechnical
investigation was carried out on site
that eventually involved three phases.
The investigations of existing foundations
were carried out within the
basements of the occupied buildings.
They involved pits adjacent to the
existing foundations to locate the pile
caps, piles and pad foundations, together
with boreholes and parallel seismic
testing to investigate pile length, and
cores into the foundations to investigate
strength and durability of the concrete.
Additional deep boreholes were also
carried out in external areas to
supplement the internal boreholes.
They provided stratigraphy and soil
parameters for design - in particular,
for the Terrace Gravels, which were the
bearing stratum for the 1930s pads at 65
94 * DEEP FOUNDATIONS * JULY/AUG 2021
WS, and the London Clay, which was
the main bearing stratum for existing
and new piled foundations. The
extensive Phase 1 geotechnical
investigations identified variations in
levels of stratigraphy and existing pile
lengths across the site, which resulted
in a lack of clarity in the assumed
design philosophy of the existing
foundations. Therefore, a second phase
of investigation was specified and
carried out in 2013. This involved
further pits, boreholes and probing to
map the foundations, together with an
Stratum
Made Ground
River Terrace Deposits
London Clay
Lambeth Group & Thanet Sands
Chalk
attempt to map the foundations at 65
WS using ground radar penetration.
The structural investigations
broadly confirmed the expected superstructure,
as well as the need for
strengthening works to columns and
some beams on 65 WS, and remedial
works to some columns on No. 67-69.
The structural investigations also
found some areas of slab on 65 WS that
were unable to take new loads and had
to be replaced.
The first two geotechnical investigations
broadly confirmed expected
Thickness at location
investigated (m)
0.6 to 6.5
1.3 to 5.0
15.6 to 16.0
21.7
unproven
Stratigraphy from Phase 1 and 2 geotechnical investigations
Top surface at location
investigated (mOD)
+25.2 to +27.5
+19 to +23.9
+18.1 to +20.6
+2.8 to +3.0
-18.7
July/August 2021
Table of Contents for the Digital Edition of July/August 2021
July/August 2021 - Intro
July/August 2021 - 1
July/August 2021 - 2
July/August 2021 - 3
July/August 2021 - 4
July/August 2021 - 5
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