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I GENERAL INFORMATION
The data presented herein were collected to help develop designs and cost
estimates for this project. Professional judgements on design alternatives and
criteria are presented in this report, These are based on evaluation of technical
information gathered, partly on our understanding of the characteristics of the
proposed 95 +/- lot subdivision, and partly on our experience with subsurface
conditions in the area. We do not guarantee the performance of the project in
any respect, only that our engineering work and judgements rendered meet the
standard of care of our profession.
The test holes drilled were spaced to obtain a reasonably accurate picture of
subsurface conditions for design purposes. Vonarions rrom me cunU111U1 s
portrayed frequently occur. These variations are sometimes sufficient to
necessitate modifications in design.
We recommend that construction be continuously observed by a qualified soils
technician trained and experienced in the field to take advantage of all
opportunities to recognize different conditions and minimize the risk of having
some undetected condition which might affect the performance of the
foundation elements.
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PAVEMENT THICKNESS DESIGN
In conjunction with the subsurface soils investigation, this office also performed
pavement thickness designs for the streets within the site. These designs have
been performed in accordance with the A.A.S.H.T.O. Guide For Design of
Pavement Structures. Eleven (11) roadway boring samples were obtained (see
map) and classified according to ASTM classification procedures. Two (2) soil
types emerged; a clayey sand (SC) and sandy lean clay (CL). An R-value of 37
for the sand and 8 for the clay was determined. Using these figures along with
on EDLA of 70, on overall Standard Deviation (50) of 0.44, a reliability of 70% and
a design serviceability loss of (e P.S.I.) of 2.5, structural number (SN) of 1.4 and 2.3
were obtained from the Nomograph. Using these numbers as a solution in the
equation SN = a,D, + aaD�2 the pavement thickness sections of Hot Bituminous
Pavement (H.B.P.) and Class V Aggregate Base Course (A.B.C.) are listed in the
tables below. These thicknesses are based on the H.B.P. having on R-value of 95
or better and the A.B.C. having an R-value of 78-83. The M2 factor is based on
a value of 1.0.
Streets Encompassing Borings 8R thru 11 R 11 R thru 9R 9R thru iR and 4R thru 5R
(R-Value = 37, SN = 1.4)
H.B.P. (inches) A.B.C. (inches) Total Thickness (inches)
3 4 7
3-112 - 3-112
Remainder of Streets
(R-Value = 8, SN = 2.3)
H.B.P. (inches) A.B.C. (inches) Total Thickness (inches)
3 8 11
4 4.5 8-1/2
5-112 - 5-112
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SITE GRADING LANDSCAPING & DRAINAGE
Every precaution should be taken to prevent wetting of the subsoils and
percolation of water down along the foundation elements. Water infiltrating
along side the foundation may result in architectural or structural damage due
to consolidation or swelling at the subsoils. Bockfili around the outside perimeter
of the structure should be compacted at optimum moisture, or above, to at least
90 percent of Standard Proctor Density as determined by ASTM Standard Test D-
698. A suggested specification for placement of backfills is included as Appendix
A. Bockfill material should be relatively impervious and non -swelling. The backfil!
should be free of frozen soil, large dried clods, and organic matter. Backfilling
should only be accomplished when concrete strength and adequate support to
foundation walls are applied and acceptable to the Foundation Engineer. It is
our opinion that the natural soils at the site could be used for backfil) material.
Finished grades should be sloped away from the structure on all sides to give
positive drainage. A minimum of 6 inches fall in the first 10 feet is recommended
and should be maintained throughout the life of the structure. Sprinkling systems
should not be installed within 10 feet of the structure. Downspouts are
recommended and should be arranged to carry drainage from the roof at least
5 feet beyond the foundation walls. Should landscaping plants be located next
to the structure, we recommend the use of varieties of plant life which require
little watering.
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7. It is recommended that a backhoe excavator be utilized for all foundation
excavation. A rubber tired front end loader tends to pump moisture up to
the surface, while reducing the bearing capacity of the soil.
FLOOR SLABS
The slabs placed on the natural ground at the site should be anticipated to
heave or settle depending on type of soil to some degree due to wetting of the
subsoils. Therefore, slabs should be constructed to be "free-floating", isolated from
all bearing members, utilities, and partitions so that the slab can move unimpaired
without producing architectural orstructural damage. Slobs should be underlain
with a four -inch (40) layer of washed rock to help distribute floor loads, provide a
capillary break, and provide a pathway for potential infiltrating water to be
directed toward sump areas. Positive drainage should be provided for the
excavation subgrode to prevent pooling of water beneath the slab. The slabs
should be reinforced with wire mesh, or equivalent. The slabs should be jointed
to a depth of at least one -quarter (1/4) of the slab thickness in dimensions not to
exceed fifteen feet (15) or 225 square feet and at areas of potential cracking.
Exterior slabs exposed to de-icing chemicals or extreme weathering should be
constructed using Type 11 cement with higher air contents and higher compressive
strengths.
BASEMENTS
Basement construction is feasible if a vertical separation of 2 feet or more exists
between high ground water level and bottom of footing. A perimeter drain is
also required for all below grade habitation.
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IThe following recommendations should be followed in the design of the
foundation system:
1. All footings, pads or caissons should bear on or in the some type of soil.
Foundation components bearing on the earth should not be placed on
frozen ground, topsoil, or inadequately compacted or unsuitable fill
material.
2. Areas where habitable space will be located below finished grade should
be protected by a perimeter drain system.
3. Partition walls should not be placed directly on concrete slabs. They should
be hung from the floor joists, or other approved method which will allow the
slab to have unimpaired for a vertical distance of 1-1/2 inches.
Foundations shall be provided for all bearing walls.
4. Laboratory test results indicate that soluble sulfates are > 800 parts per
million. Therefore, a Type V cement should be used for all concrete
exposed to the soils or rock.
5. The bottom of all foundation components (except piers) should be placed
at least two feet (2) above subsurface water levels.
6. The completed open excavation should be inspected by an experienced
soils engineer or technician to confirm the subsurface conditions described
in this report and observe any variations which may affect construction at
the site.
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l 1. Piers should be designed for the maximum end bearing pressure and skin
friction specified in this report.
2. All piers should be designed for the minimum dead load pressure specified
in this report.
3. All piers should penetrate a minimum of 4 feet into the firm bedrock
stratum, with a minimum length of 10 feet (10') and a minimum diameter
of 12 inches (12").
4. All piers should be reinforced for their full length to resist tension. We
recommend the use of at least two (2) Grade 60 05 bars.
5. A minimum of 4 inch air space should be provided beneath all grade
beams to insure the concentration of dead load pressure on the piers.
6. All piers should be carefully cleaned and dewatered before placing
concrete. In our opinion, casing and/or dewatering probably will be
required in most locations.
7. Most of the bedrock at the site can be drilled with normal heavy
commercial size pier drilling rig. Some or the oearocx is very nuru UIIU
problems may arise if the contractor attempts to drill the pier holes with
small drill rigs. in case drilling refusal is encountered, the depth of
penetration into bedrock may be reduced if design criteria are adjusted
accordingly.
8. All pier holes should be inspected during construction by a competent soils
engineer or technician to insure that penetration is started at the proper
Idepth and no loose material remains in the holes.
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Where the foundation will be placed on the natural, undisturbed silty sandy clays
and 2 feet above the water table, the foundation should be a narrow footing or
a grade beam and void foundation designed for a maximum allowable bearing
capacity of 3000 pounds per square foot (dead load plus full live load) and a
dead load of at least 1000 pounds per square foot to help counteract swelling
should the subsoils become wetted. All pads shall be a minimum of thirty inches
(30) below finished grade for frost protection. Grade beams should be reinforced
I to span unsupported lengths between pads as determined by the Design
Engineer. Four inch (40) void form shall be located under the grade beams,
between pads, so that no part of the grade beam will bear on the soil, bearing
only on the pads.
Drilled Pier (Caisson) and Grade Beam Foundations
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If higher bearing capacities are needed and bedrock is relatively shallow, the
foundation could be a drilled pier (caisson) and grade beam foundation. The
piers should be designed for a maximum end bearing of 70,000 pounds per
square foot (dead load plus full live load), side shear of 500 pounds per square
foot for that portion bearing in the firm siltstone, and a minimum dead load of
' 1,500 pounds per square foot.
' Difficulty is sometimes experienced in achieving the desired minimum dead load.
If this occurs, we suggest the piers be reinforced full length to take the different
Ibetween the "desired" and the "obtainable' dead load in tension. The side shear
value given above may be used in uplift provided the sides of the hole are
Igrooved or roughened.
In drilling the piers the following design and construction details should be
observed.
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testing. The ultimate bearing capacity of the foundation soil depends upon the
size and shape of the foundation element, the depth below the surface, and the
physical characteristics of the supporting soil or rock.
This site can generally be divided into two areas, each with its own foundation
design criteria. it should be kept in mind, however, that these are generalizations
and, therefore, all foundations should be verified with an open hole inspection
' prior to construction.
Continuous Spread Footing Foundations
Northern Area - (where silts are encountered at foundation level and/or areas
encompassing Boring No.'s 5A, 6A, 3A & 9.
Where the foundation will be placed on the natural undisturbed clayey/sandy
silts, and least 2 feet above the high water table, the foundation could be a
continuous spread footing foundation designed for a maximum allowable bearing
capacity of 500 pounds persquare foot (dead load plus full live load). If the entire
footing rests on the siltstone bedrock, the maximum capacity can be increased
to 5,000 maximum (dead load plus fill live load). All footings should be placed a
minimum of thirty inches (300) below finished grade for frost protection.
Foundation walls should be reinforced with rebar to span on unsupported length
of ten feet (10') or as required by the Engineer. Splicing and placement should
' comply with ACi-378 or as required by the Engineer.
' Central and South Area - (Narrow footings or grade beam and void where clays
are encountered at foundation level and/or areas encompassing Boring No.'s 1
' through 8 & 2A, 4A and 7A.)
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water table and in swelling potential of upper level soils, especially across the
Central and Southern portions of the site. It is advisable that each lot be drilled
individually to determine accurately the limits of such variations. The general
recommendations contained below should be regarded as representing a range
of design techniques which may be employed in foundation designs for the area.
In preparing the report we have analyzed test data from several previous reports
by others as well, and have found that data both correlative and helpful.
Narrow footings and pad/grade beam footing systems are simple and effective
design and construction methods used where dead -load pressure requirements
dictate. In all cases it is our recommendation that below -grade habitable space
be protected by a perimeter drain, and that the site grading and landscaping
recommendations be followed and be noted to home buyers. Often the
homeowner can create drainage anomalies which may be detrimental to the
performance of foundation elements.
For normal home construction we do not anticipate the need for caisson -type
foundations on many, if any, of the lots. We have included design
recommendations for that type of foundation, because it is a very acceptable
alternative to the other alternatives listed above, and may be preferred by some
builders, where bedrock is within economical range of depth.
The selection of the foundation type for a given situation and structure is
governed by two basic considerations. First, the foundation must be designed so
as to be safe against shear failure in the underlying soils and/or rock; and second,
Idifferential settlement or other vertical movement of the foundation must be
controlled at a reasonable level.
' Two basic controls ore available to us in selecting the foundation type and
allowable loads. These are the standard penetration test and consolidation -swell
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Topsoil - The entire site is covered by a 8'± layer of organic topsoil. This material
should be stripped away prior to construction and used in landscape areas.
Silty Sandv Clay - Brown to tan in color, dry, stiff to very stiff sulfate evaporites
present. This material offers moderate bearing capacities while possessing low to
moderate swell potentials when wetted. This material was found in all borings
except 5A, 6A, and 9. The thickness ranged from 2 feet to 5 feet.
Cloven/Sandy Silt - Brown to grey in color, loose, moist to wet. This material offers
very low to low bearing capacities and tends to consolidate when loading. Found
in borings 2A thru 7A and 7.
Sandy Gravels & Cobbles - Arkosic sands and gravels, clean, dry in Borings 1, 2 &
5, and wet in Borings 3, 4, and 6. Offers moderate to high bearing capacities.
Siltstone Bedrock - Tan to gray, weathered to firm, iron concretions present, poorly
to moderately cemented, dense to very dense. Encountered in all borings except
1,2&5.
No groundwater was encountered in the extreme Northern borings or Southern
borings. However, throughout the middle portion of the site, groundwater was
found from 4 to 7-1/2 feet below the surface. Groundwater fluctuation
throughout the year can be expected due to the proximity to bedrock.
FOUNDATION RECOMMENDATIONS
Over much of the area, conventional foundation techniques used in the Front
Range area can be employed. Notable variations can occur both in depth to
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As the boring operation advanced, an index of soils relative density and
I consistency was obtained by use of the standard penetration test, ASTM Standard
Test D-1586. The penetration test result listed on the log is the number of blows
required to drive the 2 inch split -spoon sampler twelve inches, or increments as
shown, into undisturbed soil by a 140 pound hammer dropped 30 inches.
Undisturbed samples for use in the laboratory were taken in 3" O.D. thin wall
f samplers (Shelby), pushed hydraulically into the soil and California samplers driven
into the bedrock. Undisturbed and disturbed samples were sealed in the field
and preserved at natural moisture content until time of test.
Complete logs of the boring operation are shown on the attached plates and
include visual classifications of each soil, location of subsurface changes,
standard penetration test results, and subsurface water level measurements at the
time of this investigation.
LABORATORY TESTING
The laboratory testing program was undertaken to determine visual classification,
moisture contents, dry densities, swelling and consolidation characteristics,
gradation and soluble sulfates.
SUBSURFACE CONDITIONS
Subsurface strata consisted of alluvial terrace fill and residual deposits overlying
siltstone units of the Pierre Shale Formation. The depth to bedrock was very near
the surface in the northern portion of the site and greater than 10 feet at the
South portion.
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SCOPE
The following report presents the results of a geotechnical investigation for
Greenbrier Village P.U.D., 2nd Filing. Approximately one half of the site had on
existing soils report performed by C.D.S. Engineering Corporation, Project No. 92-
7441. The data collected from that report along with information obtained from
our investigation will be compiled in this report. All of C.D.S. Engineering's borings
are followed by the letter "A". Please see their report for boring and test data.
The investigation was performed for ZTI Group. The purpose of this investigation
was to obtain the technical information and subsurface property data necessary
for the design and construction of foundations for the proposed subdivision. The
conclusions and recommendations presented in this report are based upon
analysis of field and laboratory data and experience with similar subsurface
conditions in the general vicinity.
SITE DESCRIPTION
The project site is located in N.W. Fort Collins. Willox Lane bounds the property to
the North and Redwood Drive bisects the proposed subdivision, The site slopes
to the South to Southeast at approximately 2% at the North end and less than 1 %
over much of the remainder. Native grasses, weeds and small trees vegetate the
site.
FIELD INVESTIGATION
Our field investigation consisted of 9 borings at selected locations on the site. The
borings were advanced with an Acker AD-11 drill rig utilizing 4-inch diameter
continuous flight augers.
TABLE OF CONTENTS
Page
Letter of Transmittal ........................................ i
Table of Contents ......................................... ii
Scope.................................................. 1
Site Location and Description ................................ 1
Field In vestigotion......................................... 1
Laboratory Testing ........................................ 2
Subsurface Conditions ..................................... 2
Foundation Recommendations .............................. 3
Floor Slabs ............................................... 8
Basements.............................................. 9
Site Grading, Landscaping and Drainage ..................... 10
Pavement Thickness Design ................................ 11
General Information ...................................... 12
Boring Site Plan (Foundations) ........................... Plate 1
Boring Site Plan (Road Borings) ......................... Plate IA
Legend of Soils and Rock Symbols ........................ Plate 2
Boring Logs ...................................... Plates 3 - 11
Consolidation - Swell Tests ........................ Drawings 1 - 7
Summary of Test Results ............................... Table 1
Suggested Specifications For Placement of
Compacted Earth Fills and/or Backfills ................ Appendix A
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Landmark
ENGINEERING Ltd.
June 16, 1993
Project No. ZT1GR-93052H-01-7091713
Zit Group
1220 S. College
Ft. Collins, CO
1%1
Gentlemen:
The enclosed report presents the results of a geotechnical investigation for
Greenbrier Village P.U.D., 2nd Filing, Fort Collins, CO.
if you have any questions or if we may be of further assistance, please feel free
to contact our office.
Sincerely,
Landmark Engineering Ltd.
Larry A48ler
Geologist
LAM/ej
The above has been reviewed and approved under the direct supervision of Dale
D. Olhausen, P.E. 5007 �r,,��Pmm®��B•m,++ ----�
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�'•� e �'v
3521 West Eisenhower Blvd. +wlfi m• ,; ..- Dale D. Olhausen. P.E. & L.S.
Loveland, Colorado 80537 �0++�t�F C1��a�w� President
ENGINEERS •ARCHITECTS •PLANNERS •SURVEYORS -!d�•
Loveland (303) 667-6286 FAX (303) 667-6298 Denver (303) 629-7124
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A
GEOTECHNICAL INVES77GA77ON
FOR
GREENBRIAR VILLAGE P.U.D., 2ND RUNG
FT. COLLINS, COLORADO
f;drw;*:*Jm*qm
ZTi Group
1220 S. Conegre
Ft. Collins, CO
June 16, 1993
Project No.: Z17GR-93052H-01-709/713
LANDMARK ENGINEERING LTD.
3527 W EISEN14OVIER BLVD.
LOVELAND, CO 80537
IV
GEOTECHNICAL INVESUGA77ON
FOR
GREENBOAR VILLAGE P.U.D., 2ND FILING
FT. COLLINS, COLORADO
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Landmark