Northlake 1nd Park-SY 890719Trench Excavation Plan
NORTHLAKE BELTLINE LIMITED PARTNERSHIP
Offsite Sanitary Sewer
Northlake Industrial Park
Coppell, Texas
Report to
Northlake Beltline Limited Partnership
c/o Nathan D. Meier Consulting Engineers, Inc.
Dallas, Texas
By
Hooper Engineering Laboratories,
2870 Walnut Hill Lane
Dallas, Texas 75229
Tel 214/351-6419
Inc.
HEL Job No. 88.229A
July 19, 1989
TABLE OF CONTENTS
INTRODUCTION .
FIELD EXPLORATION
LABORATORY TESTING .
GENERAL CONDITIONS
Topography .........
Geology of the Site .
Soil/Rock Profile
Groundwater
RECOMMENDATIONS
Trench Methods
Slopes for Trenching a~d'E~clvltio~s'
LIMITATIONS .
RECOM/~ENDED ALLOWABLE CONFIGURATIONS
SUMMARY OF LABORATORY TEST RESULTS
BORING LOCATIONS
LOG OF BORINGS
TABLE 1. CUT SLOPES FOR UTILITY TRENCHES
7
7
8
9
11
12
13
16
INTRODUCTION
This investigation was conducted to determine the
geotechnical engineering characteristics of the subsurface
soil/rock profile at the proposed location for a new eight inch
sanitary sewer line to tap the existing eight inch sanitary sewer
line at Creekview Estates to future sanitary sewer lines at the
Northlake Industrial Park in Coppell, Texas. The subsurface
conditions were evaluated in order to formulate recommendations
for excavation of open cut trenches for utility systems at this
site.
One
excavation
test boring had been drilled for the trench
plan for the Creekview Estates Addition and an
additional boring was made where more subsurface information was
necessary. These test borings were used in the evaluation for
open cut trenches that will be used in the installation of the
eight inch sanitary sewer lines. Each of these test borings was
drilled to a depth below the anticipated depth of the proposed
new utility lines.
A drawing is included in this report that notes the
boring locations referenced to the existing streets and property
lines shown on the site plan furnished to the geotechnical
engineer by the civil engineer.
FIELD EXPLORATION
The test boring was advanced with a truck mounted rotary
drill using a continuous flight, hollow stem auger. Since this
method of drilling does not require the use of water, there was
87.229A 1
no moisture contamination of the subsurface soils that were
sampled.
Undisturbed samples of the subsurface cohesive soils were
obtained through the hollow stem auger using a thin wall Shelby
tube sampler, and the samples were ejected in the field to
examine for sample quality and testability. Disturbed samples
of harder subsurface clays and shale were obtained with a thick
wall tube sampler for visual identification.
The shale found in the subsurface profile at this site
was tested in place using the Texas Cone Penetrometer. This test
consists of driving a three inch diameter cone into the soil or
rock stratum with blows from a 170 pound weight dropped with a
24 inch free fall. The number of blows required to drive the
cone 12 inches or the distance penetrated with 100 blows is a
value that can be correlated to allowable bearing capacity for
the soil or rock stratum. The blow count penetration is
recorded on the boring log at the test depth.
Each soil and rock sample was sealed in a polyethylene
bag to maintain the in-place moisture content, and packed in a
protective wooden box for transporting to the laboratory.
L~BORATORY TESTING
Each soil sample was visually examined by an experienced
soils technician, and classified according to the Unified Soil
Classification System.
Undisturbed soil samples were trimmed to required testing
dimensions, and were tested for in-place water content, dry unit
87.229A 2
weight and unconfined compressive strength. The results of these
tests give the normal engineering characteristics required for
evaluating the shear strength and consistency of fine grain soils
found in the subsurface profile.
Soil or rock samples obtained at the time of the Texas
Cone Penetration Test are disturbed from their in-place condi-
tion, and tested in the laboratory for in-place moisture only.
Representative samples of each fine grained soil type
found in the subsurface profile were tested for Atterberg Limit
values. These index values give an indication of the potential
soil volume change that might occur when there are changes in the
soil moisture content.
GENERAL CONDITIONS - TopoqraDh¥
The ground surface at this site is flat to gently sloping
terrain.
Geoloq~ of the Site - Terrace Deposit/Eagle Ford Shale
This site is located in an area of Dallas County where
the primary geological formation, the Eagle Ford Shale, is
overlain by a thick deposit of alluvial terrace materials. The
alluvial soils are thoroughly mixed during the transporting of
the materials, and the alluvial deposit normally consists of all
soil sizes, including clay, silt, sand and gravel. The terrace
deposit varies laterally, changing from fine grain soil to coarse
grain soil in very short distances. Normally, the surface soil
is a high plasticity clay or silt that may be subject to sig-
87.229A 3
nificant shrink/swell volume changes with seasonal changes in
soil moisture content.
The Eagle Ford Shale formation is of Cretaceous Age was
formed by the buildup of clay at the bottom of a shallow inland
sea approximately ninety million years ago. The formation is
predominately shale, normally varying in consistency from a soft
to medium hard rock, and there are thin lenses of limestone found
at various depths in the formation.
bentonitic clay is another variable
formation.
An occasional thin layer of
feature of the Eagle Ford
Long term weathering of the Eagle Ford Shale results in
a residual soil that is notorious for the amount of shrink/swell
volume changes that occur with changes in soil moisture content.
Clay minerals in the residual soil are highly expansive, and
ground surface movements on the order of two to six inches are
not unusual for the residual clay soils as the soil moisture
content changes with the seasons. Changes in soil moisture
content extend to a depth of ten to twelve feet below the ground
surface in this area, and below this depth, the soil moisture
content is considered to be relatively stable from year to year.
The unweathered shale is usually found below depths of
fifteen feet, and there is some variability in the hardness of
the successive layers in the shale. For this reason, straight
shaft drilled piers are normally used for foundations that are
based in the shale. Allowable bearing capacities are moderate
to low for the base of the piers in the unweathered shale, but
side resistance capacities can provide additional support for
87.229A 4
piers that penetrate into the shale, and the formation is used
for the support of single story to high rise structures.
Soil/Rock Profile
Samples obtained from the test borings show the surface
soil is a brown clayey sand to sandy clay fill. The clayey sand
to sandy clay fill is dense to stiff in consistency, moist in
water content, and extended to depths of six inches and one foot
at the test boring locations.
Below the clayey sand to sandy clay fill is a layer of
brown to tan clayey sand to orange sandy clay that has iow to
moderate plasticity characteristics (PI = 13 to 24). The clayey
sand to sandy clay is stiff to hard in consistency, moist in
water content and extended to depths of six feet and seven feet
at the test boring locations.
A layer of tan and grey clay to brown and grey shaley
clay with very high plasticity characteristics (PI = 40 to 45)
is found below the clayey sand to sandy clay. The clay to shaley
clay is very stiff to hard in consistency, moist in water
content, and extended to depths of twelve feet and nineteen and
one half feet at the test boring locations.
Below the clay to shaley clay is a grey shale. In-place
penetration test results indicate the shale is a medium hard rock
in consistency. The grey shale is moist in water content and
extended to the termination depth of the test boring s at twenty
feet.
87.229A 5
The boring logs show each soil type at the test boring
locations, but in areas between the test borings, the soil will
vary in thickness and order of occurrence.
CLAYEY SAND FILL is a soil that has been brought to the
site from another location. The clayey sand fill has low
cohesion, and is classified as a Type C soil. A Type C soil is
stable on a cut slope of one and one half horizontal to one
vertical for trenches less than twelve feet deep that are left
open less than twenty four hours. For trenches that are deeper
than twelve feet, but less than twenty feet deep, slopes should
be cut at two horizontal to one vertical.
SANDY CLAY, CLAY, SHILEY CLAY, and SHALE are soils that
have good cohesion, and are classified as a Type A soil when
pocket penetrometer values are greater than 1.5 tsf. These soils
are stable on a cut slope of three quarter horizontal to one
vertical for slopes less than twelve feet deep left open for less
than twenty four hours. For a trench that is deeper than twelve
feet and less than twenty feet deep, slopes must be cut at one
horizontal to one vertical.
GROUNDWATER
Groundwater was found in one of the two test borings, at
a depth of six feet below the existing grade. Due to the heavy
rains that we have experienced in the area, it is suspected that
this is a perched water table and may be limited to a small area.
Any soil encountered below the water table, however, is to be
considered a Type C soil and open cut excavations should be cut
87.229A 6
to the slopes recommended in the Table below.
RECOMMENDATIONS
Trench Methods
Several trenching methods are available to the utility
contractor including open cut sloped excavation, spaced sheeting,
trench boxes and shoring. The scope of this report does not
include specifications for shoring or trench boxes. Proposed
shoring or trench box design must be submitted and approved prior
to use on this jobsite. The table below provides equivalent
fluid pressures, we, for use in design of these systems.
The recommended trench method at this site is the open
cut sloped excavation, and this method can be used for the
proposed sanitary sewer line at this site.
SIODeS for Trenchinq and Excavations
There are three soil types found in the subsurface
soil/rock profile at this site, and each soil or rock will be cut
at a different allowable slope for utility trench excavations.
The following table outlines the different soil and rock types
with the allowable cut slopes for open utility trenches.
Type Description we steepest Allowable Slope
Horizontal : Vertical
pcf Depth 0-12 ft Depth 12-20 ft
C Clayey sand fill 40 1-1/2 : 1 2 : 1
A Clay, Shaley Clay 40 3/4 : 1 1 : 1
A Shale 20 3/4 : 1 1 : 1
C Submerged Soil 80 1-1/2 : 1 2 : 1
87.229A 7
Notes:
1. If there is any indication of general or local instability,
slopes should be cut back at least 1/4 horizontal : 1 vertical
flatter than the stable slope.
2. Trenches 0-12 feet will be open less than 24 hours. If open
longer than 24 hours, use the 12-20 feet values for cut slope.
3. Soil beneath the water table is classified as Type C.
4. Profiles with two or more soil types should be classified in
accordance with the weakest layer.
soils.
Spaced sheeting is permitted only in Type A cohesive
The drawing on the following page shows allowable
configurations for sloped excavations, and the maximum height of
vertical cuts in soil. The utility contractor can use any of the
configurations that are desirable for his operations, but the
slope of the cut will be in accordance with the above table of
values. Additional notes and classification criteria are
presented in Table 1, page 16.
Daily inspection of all excavations shall be made by a
competent person, with periodic inspections by a representative
of the geotechnical engineer. Ail OSHA recommendations should
be followed by the contractor.
LIMITATIONS
Every effort has been made to properly evaluate the
subsurface conditions at this site based on the samples recovered
87.229A 8
h
-- = Steepest allowable sideslope
V
1 ft = 0.30m
Case l
max.
Case
a d
__'/h
3
f~
max.
Slope 1: 1 or less ----
A~ < Az A~ A~
Case III
Case I - Ordinary slope
Case II - Compound slope with bench no more than 3 ft. high
Case Ill - Configuration must meet following criteria:
1. No vertical hank to exceed 5 ft, the bank adjacent to the
work area not to exceed 3 ft
2. Imaginary slopes ab and cd not to exceed max. allowable.
If steps are used [left side of ]1]) imaginary slope [ab)
not to exceed 1: 1
3. Excavated area equal to or greater than area within abcda
RECOMMENDED ALLOWABLE CONFIGURATIONS
OF SLOPED EXCAVATIONS*
ADAPTED FROM NATIONAL BUREAU OF STANDARDS,NBS SERIES 127
87. 229A 9
from the test borings and the results of laboratory tests on
these samples. However, it must be recognized that the con-
clusions reached in this report were based on the conditions at
the two test boring locations. Our professional services were
performed, our findings were obtained, and our recommendations
prepared in accordance with generally accepted engineering
principles and practices.
Should any unusual conditions be encountered during
construction of this project, this office should be notified
immediately so that further investigation and supplemental
recommendations can be made.
Engineering Analysis by:
David Hooper, M. Engr.
Geotechnical Engineer
Reviewed by:
C. Darrow Hooper, M. Engr., P.E.
Consulting Geotechnical Engineer
Texas 18137
87. 229A 10
SUMM~RY OF LABORATORY TEST RESULTS HEL Job No. 87.229A
Date: 07/17/89
goring Depth Soil Description ~ater
Ho. Feet Content
Class
lA 2 CLAYEY SAND, brown,
SC 15.3
lA 4 CLAYEY SAND, tan,
SC 15.0
lA 9 SHALEY CLAY, brown & grey,
41.6
lA 14 SHALE, grey,
Sh 17.7
lA 19 SHALE, grey,
Sh 17.8
Dry Liquid Ptasticity Unconfined Unit
Unit Limit lr~dex Cc.~pressive Strain
~eight Strength
pcf % % ksf %
117 21 7
120 44.6% Minus 200 Mesh
87.229A 11
Proposed
BETHEL
ROAD
I
Boring
Locat ions
Project, NORTH LAKE INDUSTRIAL
COPPELL TEXAS
Client = NORTHLAKE BELTLINE
Job No= 87. 229A
PARK
LIMITED
19
St. Louis ~
Southwestern
RailroadL
PART.
dULY 89
87. 229A 12
LOG OF BORINGS
The boring logs and related information depict sub-
surface conditions at the specific locations and at
the particular time designated on the logs. Soil
conditions at other locations may differ from the
conditions found at these boring locations, and with
the passage of time, soil conditions at these boring
locations may change.
87.229A 13
Log of Boring
PROJECT: Northlake Industrial Park BORING NO: lA
CLIENT: Northlake Beltline Limited LOCATION: Coppell, Texas
JOB NO: 87.229A SORINGTYPE: Hollow Stem Auger
BATE: 7/11/89 DRILLER: Hooper GROUND ELEVATION:
· ,, ~=~. LEGENB; B--BAG~
3 ~ ~ P -- STD PEN TEST X -- NO RECOVERY ~
grown sandy clay, stSf~ fi moSst
[fill) 1.5'
S 1.25 Brown clayey sand~ stiff & moist 3.5'
S 1.25 Tan clayey sand, stiff & moist
~ 6.0'
Brown & grey shaley clay, very
stiff & moist
~,~'
~o S 3.75 Bentonite clay, very stiff & moist 10.0'
Browa ~ gr~y shaley clay, very
st~~ moist 12.
0'
Grey shale, medium hard & moist
~ T S0/1 25"
~o T 50/1.0" End of Boring 20'
30
87.229A 14
Creek Vie,, Addk q of Boring
PROJECT: Residential Development BORING NO: 8
CLIENT: Mr. Bill Thompson, Trustee LOCATION: Coppell, Texas
JOB NO: 87.229A EORINGTYPE: Hollow Stem Auger
DATE: 12/9/87 DRILLER: Wigington GROUND ELEVATION:
~. m m U-~ ~~g LEGEND: S ~ BAG
~ ~ > m ~ ~ ~ P-- STD PEN TEST X-- NO RECOVERY
~ 2 ~ 0 ~ T -- THD CONE TEST ~-- WATER TABLE
~ Z ffi ~ DESCRiPTiON OF STRATUM
z*~'~:~ S 3.50 Brown clayey sand~ dense ~ moist 0.5'
S 4.5+ Orange sandy clay, hard & moist
.e S 4.5+
7,~'
~ Tan & grey clay, very stiff & moist
9.8'
~o ,// S 3.50 Tan & orange bentonite clay, very
stiff ~ moist ~.5'
Tan & grey shaley clay, hard & moist
19.5'
.~o T 50/1. 25"
Grey s~ale, medium hard & dry
End of Boring 20'
87.229A 15
TABLE 1. CUT SLOPES FOR UTILITY TRENCHES
Type Description
Steepest Allowable Slope
Horizontal: Vertical
Depth 0-12 ft Depth 12-20 ft
A Intact Hard Soils 3/4 : 1 1 : 1
B Medium Soils 1 : 1 I 1/2: 1
C Submerged Soils 1 1/2: 1 2: 1
1. Intact Hard Soils (Type A) include stiff clays and cohesive or cemented sands and
gravels above the water table which have no fissures, weak layers, or inclined layers that dip
into the trench. Stiff clays have an unconfined compressive strength (pocket penetrometer
reading) qu = 1.5 tsf or more. Intact hard soils subject to vibration by heavy traffic, pile
driving or similar effects are Type B.
2. Medium Soils (Type B) are all soils which are not Type A or Type C.
3. Soft Soils (Type C) include cohesive soils with an unconfined compressive strength
(pocket penetrometer reading) of 0.5 tsf or less and soils that cannot stand on a slope of 3
horizontal: 1 vertical without slumping (muck).
4. Submerged Soils (Type C) are assumed whenever water drains into the trench from the
soil forming the bank or where there is a possibility that the trench may be fully or partially
flooded before workers leave it or may be entered by workers within 5 hours after more than
half of its depth was flooded and pumped out.
5. Granular Soils Gravels, sands and silts that can stand on a slope steeper than 3
horizontal: 1 vertical without spalling or slumping should be classified as Type B.
6. Fractured Rock shall be considered Type B when it is dry and Type C when it is
submerged, Fractured rock has cracks or fissures with a spacing less than 24 inches.
Unfractured rock is exempt from sloping requirements.
7. Layered Systems (two or more distinctly different soil or rock types or micaceous seams
in rock) which dip toward the trench wall with a slope of 4 horizontal: 1 vertical or steeper
are considered Type C. Layered soils are classified in accordance with the weakest layer.
8. Instability If there is any indication of general or local instability, slopes shall be cut back
to a slope that is at least 1/4 horizontal: 1 vertical flatter than the stable slope.
9. Short Term/Lon~ Term Trenches 0-12 feet will be open for less than 24 hours, If open
longer than 24 hours, use 12-20 feet values for cut slopes.
87. 229A 16