Page 315 - Moving the Earth_ The Workbook of Excavation

LANDSCAPING AND AGRICULTURAL GRADING

LANDSCAPING AND AGRICULTURAL GRADING 7.9

designed by someone familiar with the work. If this is not possible, pipe size should be figured in
the same manner as culvert capacity, according to the maps and tables in Chap. 5.
If land tile is used, it will also function as a subdrain. However, care must be taken not to allow
more surface water to enter it than it can easily handle, as the hydraulic pressure resulting from
water standing in or over the inlets may force channels outside the tile, which will undermine or
misalign them, with resultant impairment or destruction. If the important problem is surface
water, concrete pipe or sewer tile with mortared joints is preferable.
All inlets should be protected with gratings firmly set in masonry. Lack of these may permit
entrance of large objects or masses of material which will plug the drain. Gratings are usually larger
in area than their pipe, to allow for partial clogging with leaves. The vertical or steeply sloped pipes
up to the catch basin should have tight joints.
If backfill is not tamped in the trench made for the drain, it may settle and leave the grating
standing up above the sod. This is unsightly, makes it vulnerable to breakage, and interferes with
reception of water.
If a garage is below ground level, a catch basin in the driveway just outside it is necessary. This
drain must be adequate, as its failure in a heavy storm will flood the garage and perhaps the basement.
Subdrainage. Land tile subdrains may be installed under lawns and gardens to correct saturated
or oozing conditions, to speed up drying after rain, or to provide better growth conditions for plants.
Subdrains may be tied in with the tiling around the basement and with catch basin systems for
surface runoff. They should drain to low areas when possible, as opening into storm water drains
exposes them to damage from backed-up flood water.

FINISHING OFF

Topsoil. Topsoil which has been salvaged in advance of digging may be spread as soon as the fill
is graded off, or left piled until the building is finished. Immediate spreading provides a cleaner
appearance, which is of particular value to buildings built for sale, but the topsoil is liable to
become mixed with various sorts of waste, and to be severely packed by supply trucks.
Two-ton “toy” dozers or small compact loaders are good spreaders, as they are so light that they
leave average topsoil in condition to be finished off by hand, where heavier machines compress
it so that machine tillage is required. They also can maneuver among trees, retaining walls, and
other obstacles with less danger of damage and far less loss of time than larger dozers.
A light wheel tractor with a front bucket or rear grader blade can do light grading.
Freshly spread topsoil or undisturbed field sod which is to be reworked into lawn is often loosened
up with a rotary tiller. This machine leaves it soft and easy to work, and if the topsoil is thin will
increase its usefulness by mixing in some subsoil.
It is not possible to state a general rule for the amount of topsoil needed around a building.
Good topsoil has three important characteristics: it contains humus which absorbs water and doles
it out to plants in dry weather, it contains a supply of available fertilizer, and it has a grain size
and arrangement that is favorable to plants.
A lawn made with poor or too thin topsoil may be persuaded to grow vigorously by proper fer-
tilizing. However, it will tend to burn out during dry spells unless it is shaded. It will dry out more
readily if it is over gravel or sand subsoil than over fine-grained soil. The minimum topsoil depth
for a lawn under most conditions is 2 inches, and 4 inches is safer. However, benefits are obtained
from greater depths, and it is common practice to use up whatever piles are around. If the original
soil was thin, or had been lost, more must be trucked in.
Gardens, flowerbeds, and shrubs like to have about 8 inches, and depths up to 2 feet are rec-
ommended for some species.
If peat (humus) is obtainable locally at a low price, it may be spread on subsoil and mixed in by
hand or machinery. With the addition of lime and fertilizer it may serve well as topsoil and might
be much cheaper.
Converting Field to Lawn. The original lawn made around a new building may be partly or
wholly at the grade of an existing field supporting a growth of mixed grass, wild flowers, and weeds.