Fountain Park 1-SY 930824GEO -
TECHNIQUE
INc.
CONSULTING SPECIALISTS IN:
Environmental Assessments
Environmental Engineering
Soils & Foundation Engineering
Construction Materials Testing
Commercial & Industrial Inspection
"Excellence by Experience"
August 24, 1993
Legend Construction, Inc.
P.O. Box 606
Euless, Texas 76039-0606
Attn: Mr. David Chaney
Re:
Utility Trench Design
Water & Sewer Improvements
Fountain Park Addition
Coppell, Texas
93-922
Dear Mr. Chaney:
In accordance with your request, we have reviewed soil core borings
and summary of tests, performed by others, which are incorporated
into a previously submitted sub-surface soils investigation. These
borings and test results are adequate for this report. The Boring
Logs and Test Summaries are a part of project specifications.
The purpose of this examination was to study the sub-surface soil
stratigraphy along the proposed utility lines in order to properly
design an open trench to be used in utility construction.
Examination of the test results and the boring logs revealed that
these sub-surface soils are typical of the Woodbine Geological
Formation and locally non-uniform. Generally, from the surface
down, we encountered varying thicknesses of stiff to hard dark
brown, brown, tan and gray clays, sandy clays or clayey sands
underlain by very dense tan fine to medium cemented sand. The
underlying primary (rock) formation, sandy shale, was not
encountered in any of the borings.
The borings were advanced dry to allow for extremely accurate water
table measurements. After a twenty-four (24) hour period, no
ground water was in evidence in any of the borings.
-1-
1939 East Continental Boulevard · Southlake, Texas 76092
(817) 329-0281 · (800) 348-6308 · Fax (817) 488-1866
Considering the non-existence of a shallow water table, we do not
expect groundwater to influence the deeper excavations on this
project.
In order to determine a safe open trench configuration, we referred
to a bulletin on "Excavating and Trenching Operations", published
by the U.S. Department of Labor Occupational Safety and Health
Administration, July 1975, revised December 1987 and Federal
Register, Part II, Department of Labor, 29 CFR Part 1926, dated
October 31, 1989. The angles of repose from our enclosed typical
trench cross-sections were taken from Table B-i, titled "Maximum
Allowable Slopes", referenced Federal Register, Vol. 54, No. 209,
Rules & Regulations 45965.
The project comprises approximately 1,880 feet o~ 8 inch PVC water
transmission main, 1,574 feet of 8 inch PVC sanitary sewer main,
and 377 feet of 21 inch to 36 inch R.C.P. storm sewer main. A
great majority of the excavation will require cuts between four (4)
and ten (10) feet. A small segment will require cuts in excess of
ten (10) feet, but in no case will the excavation be deeper than
twelve (12) feet.
From the enclosed table B-l, "Maximum Allowable Slopes", it becomes
evident that OSHA allows trenches cut into stable rock to be cut
vertically (90 degrees) from the trench bottom to the top of the
stable rock. Where rock is not encountered, the maximum vertical
cut is limited to three and one-half (3.5) feet. Examination of
the boring logs reveals no stable rock is reached throughout the
depths investigated (15.0 feet).
At the top of vertical excavations, where necessary, the trench
walls should be sloped back on varying angles of repose up to the
existing ground surface, as shown on the enclosed typical trench
slope configuration diagrams.
Notes from
excavation.
Table B-1 allow steeper slopes for "short
Short term is generally defined as 24 hours.
term"
on all vertical excavations adjacent to existing roadways or where
sloping is not practical, the contractor may elect to utilize a
sliding trench box in all cuts deeper than three and one-half (3.5)
feet in order to prevent caving or sloughing of the trench walls.
This method is acceptable by the OSHA regulations.
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The foregoing recommendations are based on the analyses which
presume the condition of soil properties between the borings to
have a normally uniform variation of conditions revealed by the
borings. Should any unusual conditions be encountered during
construction, this office should be contacted immediately so that
further investigation and supplemental recommendations can be
given.
Further, since we are not actively engaged in any phase of trench
excavation, Geo-Technique, Inc., or any of its employees accepts no
responsibility for the safety of these operations.
I trust this is the information you desire; and if we can be of
further service, please call on us.
Respectfully submitted,
Louis L. Hargis, P.E.
President
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TABLE B-1 - MAXIMUM ALLOwABLE SLOPES
(REFERENCE= FEDERAL REGISTER, VOL. 54, NO. 209
RULES & REGULATIONS 45965)
SOIL OR ROCK TYPE
STABLE ROCK
Type A
(see Footnote 2)
Type B
Type C
MAXIMUM ALLOWABLE SLOPES (H:V){1}
SHORT-TERM
EXPOSURE
(DEGREES)
VERTICAL (90)
LONG-TERM
EXPOSURE
(DEGREES)
VERTICAL (90)
~/2 : ~ (63)
3/4 : ~ (53)
I ~/2 : 1 (34)
3/4 : i (53)
1 : 1 (45)
2 .- ~ (27)
{1} Numbers shown in parentheses next to maximum allowable slopes
are angles expressed in degrees.frOm the horizontal. Angles
have been rounded off.
{2} A short-term maximum allowable slope of 1/2 H:IV is allowed in
excavations that are 12 feet (3.67m) or less in depth. Short-
term maximum allowable slopes for excavations greater than 12
feet (3.67m) in depth shall be 3/4 H:IV (53 degrees).
OSI-IA SOl L CATEGORIES
STABLE'
ROCK
DECP~"" ~ "S
TYPE A" "TYPE B't
ORDER OF STAP_,ILITY
"TYPE
Slope Configuration
Unsupported Vertically Sided Lower Portion
Maximum Depth - Ei§ht (8) Feet
Type A Soil
Slope Configuration
Unsupported Vertically Sided Lower Portion
Maximum Depth - Twelve (12) Feet
Type A Soil