July/August 2024 - 92

Where PPDTs were performed in the
lower sand and gravel layer, the
potentiometric surface of the groundwater
was calculated to be approximately
8-16 ft (2.4-5 m) below ground
surface. The higher readings indicated
the groundwater in the lower sand
layer was under artesian pressure.
Geotechnical Challenges
Site location map
The alluvial clays encountered have
various amounts of sand and gravel and
are generally medium stiff to hard. The
alluvial clays are generally slightly to
moderately overconsolidated, with
overconsolidation ratios greater than
1.1. Also, where tested, the shear
strengths of the clays range from about
920-4,000 psf (4,500-19,500 kg/sq m).
According to observations and the
results of laboratory testing, the clays
are typically moderately compressible
and moderately corrosive.
The sands and gravels encountered
between depths of approximately
35-65 ft (11-20 m) are designated as the
upper sand and gravel layer. These
layers are saturated and have various
amounts of fines and are generally
medium dense to very dense. The lower
sand and gravel layer was encountered
at depths of approximately 85-125 ft
(26-28 m) and is generally dense to very
dense and relatively incompressible.
Groundwater Conditions
Groundwater was measured in the
borings during drilling and in pore
pressure dissipation tests (PPDTs) performed
during the CPTs. The groundwater
levels measured during drilling
ranged from about 19-30 ft (6-9 m)
below ground surface. The PPDTs con92
* DEEP FOUNDATIONS * JULY/AUG 2024
ducted at the CPTs were performed at
depths ranging from approximately
34.5-160 ft (10.5-49 m) below ground
surface. Where PPDTs were performed
in the upper sand and gravel layer, the
potentiometric surface of the groundwater
was calculated to be approximately
15.5-25 ft (5-7 m) below
ground surface.
Approximate locations of exploration points on site
As previously discussed, construction
of the basement for the building
required an excavation of about 54-58
ft (16-18 m) below the adjacent
sidewalk's existing grades. During the
excavation of the basement, the
adjacent property and streets needed to
be supported by temporary shoring.
Several key issues were considered
while selecting a suitable shoring
system for the project. These included:
* Rigidity of the shoring system to
limit the potential for ground
mo v eme n t a n d d ama g e t o
sur round ing improvement s ,
including roadways, utilities and
adjacent structures.

July/August 2024

Table of Contents for the Digital Edition of July/August 2024

TOC
July/August 2024 - Intro
July/August 2024 - 1
July/August 2024 - 2
July/August 2024 - TOC
July/August 2024 - 4
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