Soil Survey of Dallas County, Texas Page: 46
vii, 153 p., 70 fold. p. of plates : ill., maps ; 29 cm.View a full description of this book.
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SOIL SURVEY
they have been adequately designed and carefully in-
stalled. The extent to which a soil will change in volume
as moisture content changes is the shrink-swell potential
of the soil (see table 18).
The soils that are most susceptible to shrinking and
swelling are Branyon, Burleson, Ferris, Heiden, Houston
Black, Ovan, Trinity, and Vertel soils. Other soils in the
county that have lower layers that are high in montmoril-
lonite are Axtell, Crockett, Dalco, Mabank, Normangee,
and Wilson soils.
The soils that are likely to swell and shrink enough to
damage foundations are those that have a high liquid
limit and high plasticity index. These soils are classified
as CH in the Unified soil classification system. The Uni-
fied classification for each soil in the county is given in
tables 17 and 20.
Other soils that can cause damage to foundations are
those that are subject to flooding and ponding, are
poorly drained, have low strength, have high corrosivity,
or are unstable on the steeper slopes.
Underground utility lines
Water mains, gas pipelines, communication lines, an-
chors, and sewer pipes that are buried in the soil can
corrode and break unless they are protected against
certain electrobiochemical reactions that result from in-
herent soil properties.
All metals corrode to some degree when buried in the
soil, and some metals corrode more rapidly in some soils
than in others. The corrosion potential of a soil depends
on the physical, chemical, electrical, and biological char-
acteristics of the soil. For example, concentrations of
oxygen, concentrations of anaerobic bacteria, the con-
tent of moisture, and external factors, such as manmade
electrical currents, influence corrosion potential. Design
and installation of utility lines also have an influence. In
some cases, corrosion is intensified by connecting two
dissimilar metals, by burying metal structures at varying
depths, and by extending pipelines through different
kinds of soils.
Although electrical resistivity is only one factor in cor-
rosion, a measurement of that property is a fairly accu-
rate reflection of the corrosion potential of a soil. Electri-
cal resistivity measures the resistivity of a soil to the flow
of an electrical current when the soil is wet to field
capacity. It is measured in ohms per cubic centimeter. A
low value indicates low resistivity, or high conductivity,
and thus a high corrosion potential.
An earth resistivity meter was used to measure the
resistivity of the soils in Dallas County. A four-electrode
configuration was used, in which four probes are driven
into the ground along a straight line and equidistant from
each other. An alternating current was passed into the
ground through the outer two probes, and the potential
appearing across the inner two probes was measured.
The instrument thereby measured the resistance of the
soil mass under test.Because the depth of the measured soil mass is di-
rectly proportional to the probe spacing, a record of
electrical conductivity of the subsurface layer was ob-
tained to the desired depth as the probe spacings were
increased. These values were then converted into units
of resistivity. As different kinds of soil exhibit different
values of apparent electrical resistivity, the surface layer
and lower layers of selected kinds of soil in the county
were readily classified.
The values of resistivity obtained with the earth resis-
tivity meter have been rounded off to the nearest 100
ohms per cubic centimeter. The ranges in resistivity have
been translated into categories of corrosion potential as
follows- high, less than 2,000 ohms per cubic centi-
meter; moderate, 2,000 to 5,000 ohms per cubic centi-
meter; and low, more than 5,000 ohms per cubic centi-
meter.
In table 12, the electrical resistivity and the corre-
sponding corrosion potential are given for each kind of
soil tested. They are given for each soil layer, to a depth
of 10 feet.
in soils that have a high shrink-swell potential, stress
caused by volume changes can break cast-iron pipe. In
these soils, it may be necessary to cushion pipes with
sand to prevent damage. Table 18 gives the estimated
shrink-swell potential of each soil in Dallas County.
Controlling runoff and erosion
During urban construction, the natural vegetation gen-
erally is removed from the soil, and large areas are left
bare. On construction sites, the amount and rate of
runoff generally increase, and the natural pattern of
runoff changes. After a heavy rain, runoff generally is
much greater than it was when the land was used for
farming. The runoff concentrates in streets and gutters
instead of flowing into natural waterways. This causes
flooding, erosion, and deposition of sediment in lower
lying areas. See table 11 for limitations and features of
the soils that affect water management.
Planning and design for controlling erosion and runoff
should take place before construction begins. With a
good development plan, the problems brought on by
erosion, runoff, and sedimentation generally can be
avoided or lessened. Two general kinds of erosion- and
sedimentation-control measures can be used -mechani-
cal and vegetative.
Some of the mechanical measures that can be used
to control erosion and runoff are:
Land grading-Only those areas to be used immedi-
ately for construction should be graded, not the entire
site. Large areas should not be left bare of vegetation.
Bench terraces-Bench terraces should be construct-
ed across the slope to fit the natural terrain. They are
useful to break up long slopes and to slow runoff.
Subsurface drains-If the natural drainage channels
need to be filled in during construction, subsurface
drains can be installed to help remove excess ground
water.46
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General Soil Map, Dallas County, Texas (Map)
Map displays soil types along with creeks, towns, schools, churches, power transmission lines, oil and gas pipelines, roads, and railroads. Includes legend and symbols. Scale 1:253,400
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Coffee, Daniel R. Soil Survey of Dallas County, Texas, book, 1980; Washington D.C.. (https://texashistory.unt.edu/ark:/67531/metapth130211/m1/56/: accessed July 16, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu; crediting UNT Libraries Government Documents Department.