EI 02C097
01 Jul 97
Other important data include type of excavation (e.g., dry,
(d) The bottom of the excavation should be checked
cased, or slurry), time of initiation and completion of the
before placement of the reinforcement cage and concrete to
boring, estimates of location of changes in the soil strata, and
ensure that all loose soil is removed, water has not collected
description of each soil stratum. Determine any evidence of
on the bottom of open boreholes, and the soil is in the correct
pervious lenses and groundwater, problems encountered
bearing stratum. Depth of water in an open borehole should
during excavating (e.g., caving, squeezing, seepage, cobbles,
be less than 2 inches. Casing should be clean, smooth, and
or boulders), and the location of the bearing stratum. A
undeformed.
small diameter test boring from the excavation bottom can
be made and an undisturbed sample recovered to test the
(2) Placement of reinforcement. The reinforcement cage
bearing soil.
should be assembled prior to placement in the excavation
with the specified grade, size, and number of bars. The cage
(b) The excavation should be checked for proper length,
should be supported with the specified horizontal stirrups or
diameter, and underream dimensions. Any lateral deviations
spirals either tied or welded in place as required to hold bars
from the plan location and unintentional inclination or batter
in place and prevent misalignment during concrete
should be noted on the report and checked to be within the
placement and removal of casing. The minimum spacing
required tolerance. Provided that all safety precautions have
between bars should be checked to ensure compliance with
been satisified, the underream diameter can be checked by
specifications for adequate flow of concrete through the
placing the underream tool at the bottom of the excavation
cage. The cage should be checked for placement in the
and comparing the travel of the kelly when the underreamer
specified position and adequately restrained from lateral
is extended to the travel when it is retracted in the barrel of
movement during concrete placement.
the underream tool. Electronic calipers may be used if the
excavation was made with slurry or the hole cannot be
(3) Concrete placement. The properties of the concrete
entered for visual inspection. Extreme safety precautions
mix and placement method must be closely monitored to
must be taken if an inspector enters an excavation to ensure
avoid defects in the shaft. A record of the type of cement,
no fall-in of material, and he should be provided with
mix proportions, admixtures, quantities, and time loaded on
adequate air supply, communications and lifeline, and
the truck should be provided on the delivery ticket issued by
hoisting equipment. In the event of entry, a liner or casing
the concrete supplier. The lapse of time since excavation of
should be in place to protect against fall-in. Fresh air may be
the borehole and method of concrete placement, including
pumped through hoses extending to the bottom. Minimum
details of the tremie used to place the concrete, should be
diameter of casing for personal inspection is 2 feet. An
recorded. Concrete slump should be greater than 6 inches
alternative to downhole inspection is to utilize ADSC drilled
and the amount of concrete placed in the excavation for each
shaft inspectors manuals.
truck should be recorded. A plot of the expected quantity
calculated from the excavation dimensions and the actual
(c) Slurry used during excavation should be tested for
quantity should be prepared to indicate the amount and
compliance with mix specifications after the slurry is mixed
location of the concrete overrun or underrun. Excessive
and prior to placing in the excavation. These tests are
overruns or any underruns observed during concrete
described in Table 6-3 and should be performed by the
placement will require an investigation of the cause. Any
Government and reported to construction management and
unusual occurrence that affects shaft integrity should be
the designer.
described.
6-9
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