Page 409 - Trenchless Technology Piping Installation and Inspection

Inspection and QA/QC for Trenchless Installation and Replacement Methods 359

8.10 Groundwater Control

1. Dewatering must be conducted whenever there is a high
groundwater table level to prevent flooding and facilitate
the operation. The water table elevation must be main-
tained at least 2 ft below the bottom of the casing at all
times. When needed, dewatering may be initiated prior to
any excavation.
2. Minor water seepage or pockets of saturated soil may be effec-
tively controlled through bailing or pumping. This control
must be accomplished without removing any adjacent soil
that could weaken or undermine any access pit, its supports,
or other nearby structure.
3. Larger volumes of groundwater must be controlled with one
or more well points or with staged deep wells. Well points
and staged deep-well pumping systems must be installed
and operated without damage to property or structures, and
without interference with the rights of the public, owners of
private property, pedestrians, vehicular traffic, or the work of
other contractors. Any pumping methods used for dewater-
ing and control of groundwater and seepage must have prop-
erly designated filters to ensure that the adjacent soil is not
pumped along with the water. Well diameter, well spacing,
and the pump’s pumping rate must provide adequate draw
down of the water level. Wells must be located to intercept
groundwater that otherwise would enter the access pit exca-
vation and interfere with the work. On removal of a well, the
borehole must be filled and grouted according to the specifi-
cations identified in DOT’s flowable fill special provision,
and DOT’s plugging drill holes special provision.
4. Existing storm sewers must only be used to discharge water
from the dewatering operation in accordance with a permit
obtained from the appropriate storm sewer owner. Filters or
sediment control devices must be required to ensure that the
existing system is not adversely affected by construction
debris or sediment.
5. If grouting is used to prevent groundwater from entering
the area of the access pit, the grouting must be installed
without damage to property or structures and without inter-
ference with the rights of the public, owners of private prop-
erty, pedestrians, vehicular traffic, or the work of other con-
tractors. The material properties of the grout must conform
to the specifications identified in DOT’s flowable fill special
provision.