Page 9 - Moving the Earth_ The Workbook of Excavation

LAND CLEARING AND CONTROLS

LAND CLEARING AND CONTROLS 1.9

Detection The use of trenchless technology can be helpful in locating the extent of contamina-
tion. Compact directional drilling equipment is used to reach areas of the underground that are
inaccessible under a building or other obstruction. Refer to Fig. 20.60.
As stated for the National Ground Water Association in the United States, “horizontally”
drilled wells have been installed to perform remediation of subsurface groundwater and soils with
pump and treat systems, such as by air spraying, soil vapor extraction, and bioremediation.
Horizontal wells also are used to prevent contaminant migration and for characterization, i.e., taking
samples for evaluation, under buildings and other areas where surface conditions prevent drilling
of vertical wells. Because underground plumes often spread horizontally, fewer horizontal wells
are required to treat a site than the numbers of vertical wells that would be needed. The EPA
believes horizontal well technology has the potential for significant cost saving on site remediation
projects.
The success of horizontal directional drilling (HDD) depends on the drilling machine’s elec-
tronic guidance system and its correct use. Currently there are two types of systems: (1) the walk-
over system and (2) the wireless system. The wireless guidance system uses computers to calculate
information necessary to steer the directional bore. This system is generally used for long, deep
installations.
The majority of horizontal directional installations use the less expensive walk-over electronics
system. There are two basic components: (1) a radio transmitter mounted in the drill head and (2)
a handheld receiver operated by a crew member, who walks on the ground surface directly above
the drill head as the pilot hole progresses. The transmitter sends signals to the receiver which
processes the information and displays it on the receiver. This tells the drill head location and
depth, roll angle of the drill head slanted face, and the pitch or horizontal inclination of the drill
head. This information is transmitted to the drill machine operator by two-way radio so that he or
she can make adjustments in the drilling process.
The use of vacuum excavation or potholing has been useful in locating underground pipelines
that could be damaged by HDD running into them. Vacuum excavation, described in Chap. 5, is
used to protect against damage to underground utilities when excavating.
Immobilization is a process in which a binding agent, such as cement, fly ash, kiln dust, or
asphalt, is mixed with the soil to physically or chemically immobilize contaminants. This method
could be called solidification, while chemical treatment is more stabilization. Dechlorination is a
chemical remediation technique used with soils to react with chlorine in such compounds as poly-
chlorinated biphenyls (PCBs), creating by-products that are less toxic than the original contaminants.
Among remediation methods that rely on heat are the in situ vitrification, incineration, and
thermal desorption. Incineration is the most frequently used of any soil treatment method at fed-
eral cleanup sites, according to the EPA in 1992. A thermal desorption system puts the contami-
nated soil through a heated, rotating drum as in an asphalt plant. The temperatures in the drum are
sufficient to vaporize the contaminants for collection and treatment.

BRUSH CLEARING

Dozer. Dozers and loaders are basic machines for clearing, both with regular blades or buckets
and with special attachments. They work best when the ground is firm enough for support, and
where they are not hampered by holes, gulleys, sharp ridges, and rock. These forms of equipment
are described in Chaps. 15 and 16.
Uneven surfaces make it hard to keep the blade in contact with the ground, and lead to burial
rather than removal of vegetation in hollows. However, there are few places where a dozer cannot
aid hand-clearing crews, by clearing areas where it can work, moving logs and cut brush, cutting
roads for supply trucks, or firebreaks.
Dozers have a particular advantage over hand crews where briars and vines are abundant, as
these are very tedious to cut but can be readily stripped off by the blade, provided the operator
does not take too long a pass and get caught in the tangle.