Page 203 - Urban Construction Project Management

158 Chapter Six
Initial Layout

The site engineer indicates on the site plan the boundary of the area to be excavated.
The subcontractor responsible for the excavation checks the layout that was initially
created by the CM/GC’s surveyor. Once the layout is confirmed, a fence is established
around the site (with access gates for equipment), so the public is protected from the
excavation. In addition, the CM/GC is protecting the site for security reasons and for
possible intrusion from unauthorized personnel. The CM/GC has to be concerned about
injury to unauthorized people who may enter the excavation for whatever reason (van-
dalism, burglary, or just for fun).

The Equipment
Heavy equipment is brought in to start the removal work. This can consist of bulldozers,
rock crushers, trucks, backhoes, compressors, tunnel drills (for any required tiebacks), or
even a crane with a scope bucket attached. Trucks will need access to the site for removal
of the dirt. In order to protect the public, when equipment enters or leaves the site a flag
person is stationed at the access gates stopping pedestrians from crossing in front of the
equipment that may be arriving or leaving the site. When the excavation is completed, the
equipment is removed from the bottom of the excavation by the use of a crane.

Excavation Stability
When the excavation reaches a certain elevation below the initial grade level and the
point at which the sides of the excavation may become unstable, then some retaining
system is required. The side of the excavation may become unstable because the soil
cannot maintain a 90° cut or the pressure being exerted by the soil from street traffic
loads or other conditions becomes too great. When this condition exists then the meth-
ods outlined in the section on sheeting will have to be implemented. If an existing
building is close to the excavation, then shoring and underpinning may be required.
Exhibit 6-37 is a photograph of a building being braced due to adjacent excavation.
Exhibit 6-38 is a photograph of a typical urban site where contiguous buildings are very
close together to the proposed building site. See the section on shoring and underpin-
ning for the methods used to stabilize the existing structure. In addition, a ramp has to
be created so that the trucks are able to climb out of the excavation. If water is found
when excavation continues, then some form of dewatering process will be required. See
the section on dewatering for the methods used to contain or divert water.

Rock Excavation
At one time, rock was removed by blasting with dynamite. In order to protect the pub-
lic, metal mats were placed so that the rock pieces would not fly into the air and injure
someone. Now, in most urban situations, blasting is not allowed due to the potential
dangers, dust, vibration, and noise. Rock crushing and drilling machines are now used
to break up the rock. Exhibits 6-39 and 6-39A are photographs of a drilling machine
and rock crusher. After the rock is crushed, the heavy equipment is brought in for plac-
ing the rock onto the trucks. This excess excavation material is sold to a third party for
use in another project or process (sea walls, road and railway beds, etc.).