HomeMy WebLinkAbout1.0 ApplicationIP
PETER JAMAR ASSOCIATES, INC.
PLANNING • DEVELOPMENT ANALYSIS • RESEARCH
October 17, 1994
Mark Bean, Director of Community Development
Garfield County
109 8th Street Suite 303
Glenwood Springs, CO 81601
RE: Rifle Village South Filing Two
Dear Mark,
A
OCT 1 7 1994
ca' i*JcLD GOJNTY
The Rifle Village South Filing Two Sketch Plan proposes a total of 51 single family lots on 14.987
acres of land. The property is located within the existing Rifle Village South Subdivision and is
currently zoned Residential Limited Urban Density. No zone change is required as the Sketch Plan
proposal is in conformance with the existing zoning.
Under cover of this letter please find:
15 sets of the Rifle Village South Filing Two Sketch Plan and Survey
15 sets of the accompanying Rifle Village South Sketch Plan narrative
An executed application form and a check made out in accordance with the Garfield County
Subdivision fee schedule
This sketch plan proposal is submitted for your review and for review by the Garfield County
Planning Commission. If you need additional information or have any questions please feel free to
contact me at 476-7154.
Sincerely,
UM4—)
Rick Pylman
Suite 204, Vail Bank Building
108 South Frontage Road West • Vail, Colorado 81657 • (303) 476-7154 • FAX (303) 476-5143
RIFLE VILLAGE SOUTH
FILING TWO
SKETCH PLAN SUBMITTAL
October, 1994
RIFLE VILLAGE SOUTH
FILING TWO
SKETCH PLAN SUBMITTAL
Prepared for.•
RVS Partners LLC, a Limited Liability Company
PO Box 955
Avon, CO. 81620
Prepared by:
Peter Jamar Associates Inc.
108 South Frontage Road W. Suite 204
Vail CO. 81657
303-476-7154
October, 1994
I . Introduction
The purpose of this report is to provide a comprehensive description and analysis of the proposed
subdivision of 14.987 acres of land located within Rifle Village South Filing One. This report will
address the submittal requirements for a sketch plan subdivision in accordance with Section 3:30 of
the Garfield County Subdivision Regulations.
The property is currently unimproved and is zoned Residential Limited Urban Density. This
application does not require a zone change, as the proposed subdivision is in conformance with the
RLUD Zone District.
The property is bordered to the east by agricultural land and is surrounded on the south, west and
north by the road system and platted lots of Filing One of the Rifle Village South Subdivision.
This report provides a description of the proposed subdivision, outlines existing conditions,
describes potential impacts and suggest measures that can be taken in order to avoid any adverse
impacts.
The goal of the Rifle Village South Filing Two subdivision is to create a high quality subdivision
that is compatible with the existing neighborhood and that utilizes the existing zoning of the land.
II. Project Description
The 14.987 acre parcel was originally zoned as a portion of the Rifle Village South Subdivision.
This parcel was not subdivided and platted at the time of Filing One, however, and remains
unplatted to date.
The Filing Two parcel is bordered on the south by Village Drive. The opposite side of Village
Drive consists of single family lots platted as Rifle Village South Filing One. Several of these lots
have single family homes built upon them. The property is bordered on the west by one row of
platted lots and Shotgun Drive. The north border of the property is adjacent to a row of single
family lots that have not been built upon and do not have improved access or utility infrastructure
in place.
The site slopes to the north at a 2%- 4% grade. Approximately 100 feet north of the property the
grade transitions to a steep bluff which drops approximately 40 feet at a near vertical grade.
Several gullies have eroded into this bluff and extend back into the site. The largest gully
encroaches 300 feet into the property and has a maximum depth of twenty feet.
According to the Federal Emergency Management Agency Flood Insurance Rate Map, Panel 1353,
the entire site is designated as "A0" with a 1 foot flood depth. This Special Flood Hazard Area is
described as a 100 year alluvial flood plain. Development is permitted in these areas with proper
precautions, such as establishing minimum floor elevations 2 feet above the general finished site
grade.
The Filing Two development will utilize the existing RLUD zoning and consist of 51 single family
lots and several open space parcels. The minimum lot size will be 7500 square feet, as allowed by
zoning, and each will be allowed a single family home and accessory uses as described in Section
3.04 of the Garfield County Zoning Code.
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Access to the lots will be provided by a road system to be developed as shown on the
accompanying sketch plan. These roads will be built to Garfield County standards and will be
dedicated to the public. The new road system will connect to the existing Rifle Village South road
system.
The Rifle Village South Subdivision water supply is provided and maintained by the City of Rifle.
The existing water distribution system includes a 10" diameter main line running down Village
Drive. It is anticipated that the Filing Two service will connect to this main in a loop system
configuration. Fire hydrants will be provided along the street system at a minimum spacing of
every 300 feet. The Rifle City Engineer, Tim Moore, has indicated there is adequate capacity to
serve the proposed development.
The City of Rifle also owns and operates the wastewater treatment facility serving the Rifle Village
South Subdivision. The proposed development is bordered on the south and west by existing 8"
diameter collection lines. It is anticipated that this proposed development will utilize the existing
collection and treatment system.
It is our understanding that the wastewater treatment facility does not currently comply with
Colorado Department of Health standards. According to Mr. Moore, Rifle City Engineer, the city
is planning to provide the repairs necessary to bring the plant into compliance by May/June of
1996. Although no phasing plan for this subdivision is currently being contemplated, it may be
necessary to phase Final Plat approvals in order to avoid adverse impact upon the wastewater
treatment system.
Shallow utilities are available within the vicinity of the proposed development and service
providers have indicated capacities are adequate to serve the proposed development.
III. Environmental Conditions
Geology
Hepworth-Pawlak Geotechnical, Inc. has conducted a Geologic Site Assessment of the 14.987
acre parcel. While the conclusion of this study shows that development of the property is feasible
from a geotechnical aspect there are several issues which must be considered during the planning
and design of the proposed development.
The five gullies that encroach onto the property from the north have been created by an active
erosional process. The most severe gully areas have been avoided through the proposed design.
The remainder of the gully areas will require mitigation work as recommended by Hepworth-
Pawlak. The existing gullies will be filled and site grading will be carefully designed to eliminate
any continuance of the erosional process.
In addition to the erosional concerns the soils on site may be moisture sensitive. Further
geotechnical studies will be conducted in conjunction with a preliminary plan and appropriate
mitigation measures will be implemented.
The Hepworth-Pawlak Study is included as an appendix to this report.
IV. Supplemental Information
The following information is submitted in accordance with Section 3:40 of the Garfield County
Subdivision Regulations:
A. The source and amount of water supply will be provided by the City of Rifle. The
existing city water supply system runs adjacent to the proposed development and
will be extended to provide service to each lot.
B . Sewage disposal will be provided by the City of Rifle. The existing sewage
collection system is adjacent to and is accessible from the proposal development.
C. Refer to Appendix A, Hepworth-Pawlak Geotechnical Study.
D. There are no lakes, streams or defined natural watercourses on the site. Surface
drainage will be carefully controlled and released in a manner that will mitigate
geotechnical concerns. The site topography will be altered as part of an overall
grading plan to mitigate the geotechnical concerns with the existing gullies.
E. There do not appear to be any existing or potential radiation hazards associated with
this site.
F . All parcels created by this proposed subdivision will have access to the public road
system as demonstrated by the sketch plan map.
G. The utility service providers are as follows:
Water: City of Rifle
Sewer: City of Rifle
Electric: Public Service
Natural Gas: Public Service
Telephone: U.S. West
Cable T.V.: T.C.I.
V . Summary
In summary, the Rifle Village South Filing Two Subdivision can be developed in conformance
with the existing RLUD Zone District Designation and with the Garfield County Subdivision
Regulations. The proposed development is in compliance with the Garfield County
Comprehensive Plan and all new roads will be designed and built to Garfield County Road
standards and policies.
APPENDIX
HEPWORTH-PAWLAK GEOTECHNICAL, INC. 5020 Road 154
Glenwood Springs, CO 81601
Fax 303 945-8454
Phone 303 945-7988
GEOLOGIC SITE ASSESSMENT
RIFLE VILLAGE SOUTH DEVELOPMENT
GARFIELD COUNTY, COLORADO
JOB NO. 194 398
OCTOBER 4, 1994
PREPARED FOR:
RVS PARTNERS
LIMITED :LIABILITY COMPANY
P.O. BOX 955
AVON, COLORADO 81620
ATTENTION: MR. MICHAEL THRASH
HEPWORTH-PAWLAK GEOTECHNICAL, INC.
October, 4, 1994
RVS Partners
Limited Liability Company
P.O. Box 955
Avon, Colorado 81620
Attention: Mr. Michale Thrash
Subject:
Job No. 194 398
5020 Road 154
Glenwood Springs, CO 81601
Fax 303 945-8454
Phone 303 945-7988
Geologic Site Assessment, Rifle Village South Development, Garfield County,
Colorado
Dear Mr. Thrash:
As requested, we have conducted a geologic site reconnaissance for the proposed Rifle South
Development. The propose of the study was to review the geologic conditions on the property
and evaluated their anticipated influence on the development of a single-family, residential
subdivision.
This study has shown that it should be possible to develop much of the property without
encountering severe geologic constraints, but severe constraints should be expected near the five
gullies. Development near the gullies should not be done unless mitigation is undertaken to reduce
the potential for foundation problems in this area associated with soil piping. In addition to soil
piping other geologic conditions which should be considered in development planning and design
are moisture sensitive soil, storm water management, and earthquakes.
The report which follows summarizes our findings and presents our conclusions and
recommendations. As planning proceeds, additional geologic and geotechnical engineering studies
should be done to develop site-specific design criteria.
If you have any questions, please contact us.
Respectfully submitted,
HEPWORTH-PAWLAK GEOTECHNICAL, INC.
AcZ"(
Ralph G. Mock
Engineering Geologist
Rev by: SLP
RGM/rgm
cc: Peter Jamar Associates, Inc. (Attn: Mr. Rick Pylman)
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY 1
PROPOSED CONSTRUCTION 1
SITE CONDITIONS 1
GEOLOGIC SETTING 2
GEOLOGIC SITE ASSESSMENT 3
GULLY EROSION AND SOIL PIPING 3
MOISTURE SENSITIVE SOILS 4
STORM WATER MANAGEMENT 5
EARTHQUAKES 5
LIMITATIONS 6
REFERENCES 7
PURPOSE AND SCOPE OF STUDY
This report presents the findings of a geologic site assessment for the proposed Rifle
Village South Development, Garfield County, Colorado. The purpose of the study was to review
the geologic conditions on the property and evaluated their anticipated influence on the
development of a single-family, residential subdivision. The work was preformed in accordance
with our August 18, 1994 Professional Services Agreement with RVS Partners, Limited Liability
Company.
A field reconnaissance of the property was made on August 30, 1994. An assessment of
the geology and its potential impacts on the proposed development was made based on our field
observations, reviews of geologic and topographic maps, and our experience in the area. This
report has been prepared to summarize the data obtained during the study and to present our
conclusions and recommendations.
PROPOSED CONSTRUCTION
At the time of this study, development planning was proceeding towards sketch plan
submittal to Garfield County. The 15 acre parcel will be subdivided into single-family residential
lots. The final number of lots has yet to be determined. It is our understanding that the property
is currently zoned "Residential Limited Urban Density". It is expected that the residences will be
one or two story, wood frame structure With basements, similar to the existing residences in the
area. The development infrastructure will consist of street and utilities.
SITE CONDITIONS
The 15 acre parcel is located on a low terrace on the south side of the Colorado River
about two miles southwest of the Rifle town center. The property is located in the NE 1/4 of the
NW 1/4, Sec. 20, T6S., R.93W. The Colorado River lies about 2,500 feet to the north of the
property and about 40 feet lower in elevation. The terrace at the site is an alluvial fan at the mouth
of Helmer Gulch. The fan surface slopes towards the river with an average slope of about 4%. A
steep bluff located about 100 feet to the north of the northern property line separates the gently
2
slopping fan surface from the Colorado River valley floor. The 40 -foot high bluff is nearly vertical
and has an average slope of about 200%. Several gullies, with nearly vertical sides have been
eroded into the bluff and extend to the south. Five gullies are present on the property and extend
about 300 feet to the south of the northern property line. On the property, the gullies are about 20
feet deep along the northern property line.
Helmer Gulch and it tributaries are ephemeral streams which only have surface flow during
periods of intense precipitation. The gulch and its tributaries drain an area of several square miles
on the mesas to the south of the property. The gullies on the property have formed from the
concentration of local surface runoff with contributory areas not much larger than the property.
Vegetation on the site is sparse and is primarily salt brush with some sage brush. A single-family
residential subdivision borders the property on the west and south. Nineteen residential lots border
the property on the north. None of these lots have been built on.
GEOILOGIC SETTING
The terrace at the site was formed when the old channel of the Colorado River cut into the
Helmer Gulch alluvial fan and formed the steep bluff just to the north of the property. Since
cutting the bluff the river has migrated across the flood plane to the north. The present river
channel lies about 2,000 feet to the north of the base of the bluff Remnants of the abandoned
channel which have been dammed to form a lake can still be seen at the base of the bluff.
Alluvium deposited by Helmer Gulch crops out for the full height of the bluff and is exposed in
the gully sides. The alluvium consists of poorly stratified fine sandy silt with scattered fine gravel.
In a few places the alluvium contained local lenses of rounded, basalt gravel, cobbles and small
boulders in a fine sandy silt matrix. Colorado river alluvium, which usually consists of stratified,
relatively clean, sand, gravel, cobbles, and boulders may underlie the Helmer Gulch alluvial fan at
the site. The depth to the river alluvium is probably greater than 40 feet below the ground
surface..
Formation rock in the area is the Eocene and Paleocene -age Wasatch Formation (Tweto
and Others, 1978). The Wasatch Formation crops out in places along the mesa flanks to the south
3
of the property and underlies the surfical soil deposits at the site. The Wasatch is made up of
varicolored calystone, siltstone, sandstone, and conglomerate. The formation is of fluvial origin
and the different rock types occur as discontinuous lenses throughout the formation. Major faults
have not been mapped in the vicinity of the property (Tweto and Others, 1978).
GEOLOGIC SITE ASSESSMENT
This study has shown that it should be possible to develop much of the property without
encountering severe geologic constraints, but severe constraints should be expected near the five
gullies. Development near the gullies should not be done unless mitigation is undertaken to reduce
the potential for foundation problems in this area associated with soil piping. In addition to soil
piping there are several other geologic conditions which should be considered in development
planning and design. A discussion of these conditions and their anticipated influence on the
proposed development is presented in the following sections. When appropriate, conceptual
remedial engineering to reduce the potential problems is discussed.
GULLY EROSION AND SOIL PIPING
The five gullies which enter the site from the bluff to the north results from headword
erosion caused by surface runoff concentrations. The erosional process is active under current
environmental conditions. Slow, but progressive, gully extension will continue unless stabilization
measures are taken. In addition to gully down cutting and head cutting, subsurface soil erosion
(soil piping) is also occurring near the margins of the gulches where hydraulic gradients are steep.
The piping process can result in relatively large subsurface void which can not always be seen at
the surface. Foundations, street, and utilities placed in the zone of soil piping on the alluvial fan
surface next to the gullies could experience severe differential settlement as a result of void
collapse. Judging from surface observations the piping zone may extend about 50 feet horizontally
beyond the top edge of the gullies. If this is the case, then we estimate that about 5 acres of the 15
acre site (about 30%) would be in the potential hazard zone.
4
Because of the potential for severe differential settlement, we recommend that residences,
street and utilities not be located in the zone where soil piping could be a potential hazard or
remedial actions should be taken. Also, the active gully erosion must be stabilized so that piping
and erosion does not progress into areas not presently in the piping zone. A surface water
hydrologist should be consulted for the best method of gully stabilization of this site and the
proposed development From a geotechnical view point, the potential piping hazard can be
mitigated by (1) not building in the hazard zone, (2) regrading the gullies and adjacent piping zone
to eliminate the subsurface voids, or (3) using a deep foundation system which bears below the
piping voids. The regrading option could have a significant impact on the existing platted lots to
the north. Subsurface exploration should be performed to evaluate the extent of the piping zone
and possible methods of site-specific mitigation.
MOISTURE SENSITIVE SOILS
The Helmer Gulch alluvial fan soils on the property could be moisture sensitive. It has
been our experience that similar soils in the area have a collapse and settlement potential when
subject to increases in soil moisture. The dry soil has a relatively high strength and low
compressibility. When wetted the soil looses strength. This can often result in large settlements
under typical residential foundation bearing pressures and in some cases the soil will collapse when
wetted under its own weight without additional loading. It has been our experience that soil
moisture changes associated with residential landscape irrigation over a period of years is enough
to cause settlement when highly sensitive soil is present.
An assessment of the moisture sensitivity of the on-site soil will require subsurface
exploration, sampling, and laboratory testing. If the soils are moisture sensitive, then engineered
mitigations should be included in the foundation design. Mitigation at moisture sensitive soil sites
may include the following:
• Control of Landscape Irrigation
• Shallow Foundations Capable of Withstanding Large Differential Settlements
• Removal and Replacement of the Moisture Sensitive Soil
• Pre -Wetting of the Site Before Construction
• Deep Foundations which Bear Below the Moisture Sensitive Soil
5
STORM WATER MANAGEMENT
Helmer Gulch is an ephemeral drainage which only occasionally carries surface flow
during periods of intense precipitation. Although dry most of the time a surface water hydrologist
should evaluate the flood potential. Flood water in the gulch could have high sediment loads
which should be considered. The potential for channel blockage and the spreading of flood waters
on the fan surface should also be considered when assessing potential flood impacts.
EARTHQUAKES
The project site could experience moderately strong earthquake ground shaking of
Modified Mercelli Intensity VI during a reasonable service life for the development, but the
probability for stronger ground shaking is low. Intensity VI ground shaking is felt by most people
and causes general alarm, but results in negligible damage to structures of good design and
construction. The residences should be designed to withstand moderately strong ground shaking
with little or no damage and not to collapse under stronger ground shaking. The site is located in
the Uniform Building Code Seismic Risk Zone 1. Based on our current understanding of the
earthquake ha7nrd in this part of Colorado, we see no reason to increase the commonly accepted
seismic risk zone of the area.
6
LIMITATIONS
This study was conducted according to generally accepted engineering geologic
principles and practices in this area and at this time. We make no other warranty either expressed
or implied The conclusions and recommendations submitted in this report are based on data
obtained from a field reconnaissance, review of the published literature and our experience in the
area. The report has been prepared for the exclusive use by our client for preliminary project
evaluations and identification of potential geologic hazards and problem areas. Additional
geotechnical engineering studies should be done to develop specific design criteria for hazards
mitigations and project facilities.
Respectfully submitted,
HEPWORTH-PAWLAK GEOTECHNICAL, INC.
Ralph G. Mock
Engineering Geologist
Review by:
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Steven L. Pawlak,r; r' 1 5 2 2 2
RGM/rgm
7
REFERENCES
Tweto, O. and Others, 1978, Geology Map of the Leadville 1 °X 2 ° Quadrangle, Northwestern
Colorado: U.S. Geological Survey Map I-999.
HEPWORTH-PAWLAK GEOTECHNICAL, INC. 5020 Road 154
Glenwood Springs, CO 81601
Fax 303 945-8454
Phone 303 945-7988
GEOTECHNICAL ENGINEERING STUDY
PROPOSED RIFLE VILLAGE SOUTH, FILING 2
GARFIELD COUNTY, COLORADO
JOB NO. 194 398
NOVEMBER 28, 1994
PREPARED FOR:
RVS PARTNERS, LLC
ATTN: MICHAEL E. THRASH, MANAGER
P.O. BOX 955
AVON, COLORADO 81620
HEPWORTH-PAWLAK GEOTECHNICAL, INC.
November 28, 1994
RVS Partners, LLC
Attn: Michael E. Thrash, Manager
P.O. Box 955
Avon, Colorado 81620
5020 Road 154
Glenwood Springs, CO 81601
Fax 303 945-8454
•Phone 303 945-7988
Job No. 194 398
Subject: Geotechnical Engineering Study For Grading and Preliminary Foundation
Design, Proposed Rifle Village South Subdivision, Filing 2, Garfield
County, Colorado.
Gentlemen:
As requested, we have conducted a geotechnical engineering study for the proposed
Rifle Village South Subdivision. The project area is shown on Figure 1.
Subsurface conditions encountered in the exploratory borings drilled in the proposed
development area consist mainly of sandy silt and clay with scattered gravel layers.
Dense sandy gravel and cobble alluvium was encountered below the silt and clay at a
depth of 62 feet. Groundwater was not encountered in the borings and the subsoils
were relatively dry.
Residences can be founded on spread footings placed on the natural subsoils and
designed for an allowable bearing pressure of 1000 psf. The grading design should not
allow surface water ponding and discharge areas should be protected against erosion.
The proposed grading will include backfilling of the existing gullies and building
setbacks for slope stability concerns will not be required.
The report which follows describes our investigation, summarizes our findings, and
presents our recommendations. During the individual lot development we should
provide consultation and field services for the building foundation design. We should
also review and monitor the implementation of the geotechnical recommendations
presented in this report.
RVS Partners, LLC
November 28, 1994
Page 2
If you have any questions regarding this report, please contact us.
Sincerely,
HEPWORTH-PAWLAK GEOTECHNICAL, INC.
Steven L. Pawlak, P.E.
Rev. By: DEH SJV
SLP/rr
cc: High Country Engineering - Attn: Bruce Lewis
Peter Jamar Associates - Attn: Rick Pylman
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY 1
PROPOSED DEVELOPMENT 1
SITE CONDITIONS 2
FIELD EXPLORATION 2
SUBSURFACE CONDITIONS 3
PRELIMINARY DESIGN RECOMMENDATIONS 3
FOUNDATION BEARING CONDITIONS 4
FLOOR SLABS 5
UNDERDRAIN SYSTEM 5
SITE GRADING 6
SURFACE DRAINAGE 6
PAVEMENT SUBGRADE 7
LIMITATIONS 7
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURES 4 - 7 SWELL -CONSOLIDATION TEST RESULTS
FIGURES 8 - GRADATION ANALYSES TEST RESULTS
TABLE I - SUMMARY OF LABORATORY TEST RESULTS
PURPOSE AND SCOPE OF STUDY
This report presents the results of a preliminary subsoil study for the Rifle Village
South Subdivision, Filing 2, to be located along Village Drive, South of Rifle, Colorado.
The project site is shown on Fig. 1. The purpose of the study was to develop
recommendations for grading and preliminary foundation design. The study was conducted
in accordance with our proposal for preliminary geotechnical engineering study to RVS
Partners LLC, dated November 7, 1994. Hepworth-Pawlak Geotechnical, Inc. previously
conducted a geologic hazards assessment for the Rifle Village South Subdivision under Job
No. 193 398, dated October 4, 1994.
A field exploration program consisting of widely spaced exploratory borings was
conducted to obtain information on subsurface conditions. Samples obtained during the
field exploration were tested in the laboratory to determine compressibility and other
engineering characteristics of the on-site soils. The results of the field exploration and
laboratory testing were analyzed to develop recommendations for the overlot grading design
and for possible foundation types, depths and allowable pressures for the proposed single
family residences. This report summarizes the data obtained during this study and presents
our conclusions, design recommendations and other geotechnical engineering considerations
based on the proposed construction and the subsoil conditions encountered.
PROPOSED DEVELOPMENT
The proposed residential development consists of 53 lots for single family homes.
We assume the single family homes will be 1 to 2 story wood frame structures over
basement or crawlspace. Grading in the northern part of the property will be extensive and
require fill depths up to between about 5 and 15 feet. Grading for the houses is assumed
to be relatively minor with cut depths between about 3 to 8 feet. We assume relatively
light foundation loadings, typical of the assumed type of construction.
2
If building loadings, location or grading plans change significantly from those
assumed, we should be notified to re-evaluate the recommendations contained in this
report.
SITE CONDITIONS
The site is essentially the same as that when observed for the geologic hazards
review. In general, the ground surface slopes down gently from Village Drive to the north
with about 20 feet of elevation difference across most of the lots. The steep sided gulleys
that cut into the north part of the property are typically 10 to 15 feet deep and encroach
several proposed building lots and the on-site roadway. Vegetation on the property
typically consists of sage brush, grass and weeds.
FIELD EXPLORATION
The field exploration for the project was conducted on November 12 and 14, 1994.
Seven exploratory borings were drilled at the locations shown on Fig. 1 to evaluate the
subsurface conditions. The borings were advanced with 4 -inch diameter continuous flight
augers powered by a truck -mounted Longyear BK-51HD drill rig. The borings were
logged by a representative of Hepworth-Pawlak Geotechnical, Inc.
Samples of the subsoils were taken with 1 3/8 -inch and 2 -inch I.D. spoon samplers.
The samplers were driven into the subsoils at various depths with blows from a 140 -pound
hammer falling 30 inches. This test is similar to the standard penetration test described by
ASTM Method D-1586. The penetration resistance values are an indication of the relative
density or consistency of the subsoils. Depths at which the samples were taken and the
penetration resistance values are shown on the Logs of Exploratory Borings, Fig. 2. The
samples were returned to our laboratory for review by the project engineer and testing.
3
SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on
Fig. 2. The subsoils consist of a thin root zone overlying mainly stiff sandy silt and clay
with scattered gravel layers. Dense silty sandy gravel and cobble alluvium was
encountered in Boring 6 below the silt and clay at a depth of 62 feet. The gravel layers
interbedded in the silt and clay soils were about 8 feet thick and found in 3 of the 7
borings.
Laboratory testing performed on samples obtained from the borings included natural
moisture content and density, Atterberg limits and gradation analyses. Results of
consolidation testing performed on relatively undisturbed drive samples, presented on
Figs. 4 to 7, indicate the sandy silt and clay soils have low compressibility under light
loading and low collapse potential (settlement under constant load) when wetted. Two of
the more clayey samples (Boring 3 at 10 feet and Boring 4 at 20 feet) showed a minor
expansion potential when wetted. Results of gradation analyses performed on a small
diameter drive sample (minus 1 1/2 -inch fraction) of the interbedded gravel soils are shown
on Fig. 8. Atterberg limits testing indicates the fine grained soils generally have low
plasticity. The laboratory testing is summarized in Table 1.
No free water was encountered in the borings at the time of drilling and the subsoils
were relatively dry.
PRELIMINARY DESIGN RECOMMENDATIONS
Based on the subsoil conditions encountered in the exploratory borings and our
experience in the area, development of the property as proposed should be feasible with
proper mitigation design. The following recommendations are presented for preliminary
foundation design, overlot grading and drainage.
-4
FOUNDATION BEARING CONDITIONS
The natural soils are hydrocompactive and wetting of the bearing soils could cause
settlement under even light residential loading. The amount of settlement will depend on
the depth and extent of wetting. We expect that settlements due to wetting could be in the
range of 2 to 4 inches. Compacted structural fill beneath the building should reduce the
settlement risk. Shallow spread footings placed on the natural soils or properly compacted
fill and designed for a maximum bearing pressure of 1,000 psf can be used for building
support. Basement level foundations should have lower risk of settlement due to less
potential for wetting of the bearing soils. A structural slab foundation could also be used
to reduce the effects of differential settlement.
The following recommendations are made for preliminary design of shallow spread footings
bearing on the natural soils or properly compacted fill.
1) The footings should have a minimum width of 20 inches for continuous walls and
2 feet for isolated pads.
2) Exterior footings and footings beneath unheated areas should be provided with
adequate soil cover above their bearing elevation for frost protection. Placement
of foundations at least 36 inches below exterior grade is recommended.
3) Continuous foundation walls should be reinforced top and bottom to span local
anomalies such as by assuming an unsupported length of at least 12 feet.
Foundation walls acting as retaining structures should also be designed to resist a
lateral earth pressure corresponding to an equivalent fluid unit weight of 50 pcf
assuming the on-site fine grained soils are used as backfill.
4) The topsoil and any loose or disturbed soils should be removed and the footing
bearing level extended down to the firm natural soils. The exposed subgrade should
be moistened and compacted in footing areas.
5) A representative of the geotechnical engineer should observe the building excavation
to evaluate the bearing conditions.
-5
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded
slab -on -grade construction. There is a risk of some post construction settlement due to
wetting of the subsoils. To reduce the effects of some differential movement, non-
structural floor slabs should be separated from all bearing walls and columns with
expansion joints which allow unrestrained vertical movement. Floor slab control joints
should be used to reduce damage due to shrinkage cracking. The requirements for joint
spacing and slab reinforcement should be established by the designer based on experience
and the intended slab use. A minimum 4 -inch layer of free -draining gravel may be placed
beneath basement level slabs to facilitate drainage. This material should consist of minus
2 -inch aggregate with at least 50% retained on the No. 4 sieve and less than 2% passing
the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95 % of
maximum standard Proctor density at a moisture content near optimum. Required fill can
consist of the on-site soils devoid of vegetation, topsoil and oversized rock.
UNDERDRAIN SYSTEM
Although free water was not encountered during our exploration, it has been our
experience in the area that local perched groundwater may develop during times of heavy
precipitation or seasonal runoff. Frozen ground during spring runoff can create a perched
condition. We recommend below grade construction, such as basement areas more than
4 feet deep, be protected from wetting and hydrostatic pressure buildup by an underdrain
system.
The drains should consist of drainpipe placed in the bottom of the wall backfill
surrounded above the invert level with free -draining granular material. The drain should
be placed at each level of excavation and at least 1 foot below lowest adjacent finish grade
and sloped at a minimum 1% to a suitable gravity outlet. Free -draining granular material
used in the underdrain system should contain less than 2% passing the No. 200 sieve, less
than 50% passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel
backfill should be at least 1 1/ 2 feet deep. An impervious liner such as 10 mil PVC
-6
should be placed in a trough shape beneath the drain gravel and attached to the foundation
wall with mastic to reduce the risk of wetting the bearing soils.
It may be possible to eliminate the underdrain for residences with shallow
crawlspaces provided that good surface drainage as outlined below is maintained around
the house.
SITE GRADING
The gullies on the property will be regraded as mitigation of the piping hazard and
progressive erosion. With proper fill construction, it should be feasible to construct
roadways, utilities and buildings on the backfill areas. Structural fills should be compacted
to at least 95% of the maximum standard Proctor density near optimum moisture content.
In structural fill areas deeper than 5 feet, the fill should be compacted to at least 98 %
standard Proctor density. Prior to fill placement, the subgrade should be careful prepared
by removing all vegetation and topsoil and compacting to 90 % standard Proctor density.
The fill should be benched into side slopes exceeding 20% grade. Any piping voids should
be excavated and backfilled with structural fill.
Permanent unretained cut and fill slopes should be graded at 2 horizontal to
1 vertical or flatter. The risk of slope instability will be increased if slopes are subjected
to prolonged wetting and stream erosion. Revegetation or other means should be provided
to prevent erosion. This office should review site grading plans for the project prior to
construction.
SURFACE DRAINAGE
The silt and clay soils are susceptible to surface and subsurface erosion and
precautions should be taken to control runoff. Ditches or swales with high flow or velocity
may need to be lined. Water should not be ponded, especially near steep down slopes at
the north end of the property. The following drainage precautions should be observed
during construction and maintained at all times after the residences have been completed:
7
1) Inundation of the foundation excavations and underslab areas should be avoided
during construction.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to at
least 95 % of the maximum standard Proctor density in pavement and slab areas and
to at least 90% of the maximum standard Proctor density in landscape areas.
3) The ground surface surrounding the exterior of the building should be sloped to
drain away from the foundation in all directions. We recommend a minimum slope
of 6 inches in the first 10 feet in unpaved areas and a minimum slope of 3 inches
in the first 10 feet in paved areas.
4) Roof downspouts and drains should discharge well beyond the limits of all backfill.
5) Landscape irrigation should be restricted to reduce the potential for wetting
of the bearing soils. Lawn areas should be graded to drain without ponding.
PAVEMENT SUBGRADE
Based on the subsoil profile encountered in the borings and the laboratory test
results, we recommend that a subgrade Hveem ' R' value of 15 be used for pavement
design. Fill will be placed in the northern part of the property to establish design subgrade.
Other areas will generally have shallow stripping. Structural fill placed for the road
subgrade should be compacted to at least 95 % of standard Proctor density at a moisture
content near optimum. The fine grained soils on the site should be suitable for use as
roadway embankment fill.
LIMITATIONS
This report has been prepared in accordance with generally accepted geotechnical
engineering principles and practices in this area at this time. We make no other warranty
either expressed or implied. The conclusions and recommendations submitted in this report
are based upon the data obtained from the exploratory borings drilled at the locations
indicated on Fig. 1, the proposed type of development and our experience in the area. Our
findings include interpolation and extrapolation of the subsurface conditions identified at
-8
the exploratory borings and variations in the subsurface conditions may not become evident
until excavation is performed. If conditions encountered during construction appear
different from those described in this report, we should be notified so that re-evaluation of
the recommendations may be made.
This report has been prepared for the exclusive use by our client for planning and
preliminary design purposes. We are not responsible for technical interpretations by others
of our information. During the individual lot development, we should provide continued
consultation and field services for foundation design. We should also review and monitor
the implementation of our recommendations presented in this report. Testing of structural
fill and observation of excavations and foundation bearing strata should be made at the time
of construction by a representative of the soil engineer.
Sincerely,
HEPWORTH-PAWLAK GEOTECHNICAL, INC.
I.
Steven L. Pawlak, P.E.
Reviewed By:
1,
Daniel E. Hardin, P.E.
DEH/rr
Shotgun Drive
I 1 I I
1 1 I I
Existing Platted Lots 1
1
1 I
1
J
a
—°'
c
X
w
Boring 6
Open Space
Boring 3
• Open Space
0 50 100
Scale In Feet
194 398
HEPWORTH-PAWLAK
GEOTECHNICAL, Inc.
200
Boring 5
•
• Boring 4
Boring 7
•
Village Drive
•Boring 2
Rifle Village South
Boring 1
•
Proposed
Lots and
Roadway
Layout
(Typ.)
Location of Exploratory Borings
Fig. 1
Depth - Feet
0
5
10
15
20
25---
30
350
4021/6
Boring
77
%
�-200=63
/
/
/
/
/�
/
/
/
1
1
/ 25
DD=5104
LL=21
PI=
15/12
WC=5.4
DD=97
19/12.7
-9/6
13/6
13/6
DD=114
zoo=aL
Boring 2 Boring
-7
/ 15/12
, WC=4'3
/ DD=98
,
25/6, 50/1
• WC=3.0
+4=33
; -200=29
o?
f
/� 34/12
'/
16/6
13/6
-200=78
11110/12
11122/12
0
�.21/12
11111/6
!
oll
3
DD=106
200=b7
-200=6
30/6, 50/
55/12
34/12
Boring
-7
/
i
/
.
%18/12
�'
/
/
/
/-120/12
, ,
/
7/7117/6
4
C=7.2
DD/94
-200=72
LL=26
PI=10
18/12
DD=102
>7/12
Boring
-7
/
/
/
,
/
/
%
/ /
/
5 Boring
13/12
WC=4.6
DD=102
-200=68
16/12
X1%12
DD=L11
13/6
11/6
-7
///://13/12
.
/
�
�9C=7,6
/
/
,
%
�DD=DD=107 /
//116/12
/
/��
/,00
'
/
/]23/12
�/
��
6
19/12
DD=105
-200=61—
9/12
17/12
JC=0 Boring
14/20—.II
0
11
• •
PPP
60
_
45
-
50—
55Ill
—
—
60--
—
=
<c____
Boring
o
c
Oi
�5S
!'
1
01
r
0
0
0
7
0 .m--.
23/12 —
WC=4.5
DD=96 —
-200=51
5 ----
—
—
10 --
22/12
—
—
15 —
' 20/6
--1
14/6 25 —
_
—
30 ---
--
35
—
39/12 40
4VC=ti .1
DD=107 =
SS
45
0
194 398
HEPWORTH-PAWLAK
GEOTECHNICAL, Inc.
Rifle village South
Logs of Exploratory Borings
Fig. 2
LEGEND:
SILT AND CLAY (ML -CL); sandy, scattered gravel, stiff, slightly moist, Tight
brown, slightly calcareous and porous.
GRAVEL AND SIT (GM -ML); sandy, cobbles, medium dense, slightly moist,
Tight brown, subangular to rounded rock.
GRAVEL AND COBBLES (GM -GP); sandy, silty, dense, brown.
Relatively undisturbed drive sample; 2 -inch I.D. California liner sample.
Drive sample; standard penetration test (SPT), 1 3/8 -inch I.D. split spoon
sample, ASTM ID -1586.
15/12 Drive sample blow count; indicates that 15 blows of a 140 -pound hammer
falling 30 inches were required to drive the California or SPT sampler 12
inches.
NOTES:
1. Exploratory borings were drilled on November 12 and 14, 1994 with a 4 -inch
diameter continuous flight power auger.
2. Locations of exploratory borings were measured approximately by pacing from
features shown on the site plan provided.
3. Elevations of exploratory borings were not measured and Togs of exploratory
borings are drawn to depth.
4. The exploratory boring locations and elevations should be considered accurate
only to the degree implied by the method used.
5. The lines between materials shown on the exploratory boring Togs represent the
approximate boundaries between material types and transitions may be gradual.
6. No free water was encountered in the borings at the time of drilling. Fluctuations
in water level may occur with time.
7. Laboratory Testing Results:
WC = Moisture Content (%)
DD = Dry Density (pcf)
+ 4 = Percent retained on No. 4 sieve
-200 = Percent passing No. 200 sieve
LL = Liquid Limit (%)
PI = Plasticity Index (%)
194 398FitF4WUH 1 F1-F'AWLAK
GEOTECFINI A , Inc.
LEGEND AND NOTES
Fig. 3
Compression
Compression
0
1
2
3
4
5
6
0.1
APP'_IE: oRESSURE — ksf
Moisture Content = 4.3 percent
Cry Unit weicat = 98 oc'
Sample at: Sandy Silt and Clay
From: Boring 2 at 2 Feet
0.1
Compression
Upon Wetting
1.0 10
APPLIED PRESSURE — ksf
100
HEPWORTH-PAWLAK
194 398 1 GEOTECHNICAL, Inc.
SWELL -CONSOLIDATION TEST RESULTS I Fis 4
Moisture Content = 5.4 pent
Dry Unit Weignt = 97 Pct
Sample at: Sandy Silt and Clay
Fro m: Boring 1 at 5 Feet
Compression
Upon Wetting
n
1
ivC.
0.1
APP'_IE: oRESSURE — ksf
Moisture Content = 4.3 percent
Cry Unit weicat = 98 oc'
Sample at: Sandy Silt and Clay
From: Boring 2 at 2 Feet
0.1
Compression
Upon Wetting
1.0 10
APPLIED PRESSURE — ksf
100
HEPWORTH-PAWLAK
194 398 1 GEOTECHNICAL, Inc.
SWELL -CONSOLIDATION TEST RESULTS I Fis 4
Expansion
1
Compression
Q
1
2
3
4
Moisture Content = 4.7
Ory Unit Weignt = 106
percent
pct
Sample or: Sandy Silty Clay
Front: Boring 3 at 10 Feet
Expansion
Upon Wetting
0.1
1.:
PPPI_:ED °RESSUPE — ksf
10
100
o_i
1.o 10
APPLIED PRESSURE — ksf
194 398
HE''WOATI I-PAVYLAK
GECTECHNICAL
Inc.
SWELL -CONSOLIDATION TEST RESULTS I- 5
I
I
I
Moisture Content = 4.8 aercent
Cr, Unit `Netcnt = 102 oc:
5amoie of: Sandy Silt and Clay
I I
I
I I
From: Boring 4 at 10 Feet
I
II
I
i i i i 1
I
I
s
}
I I
Compression i
Upon Wetting)
I i
j
I
II
H
l
I
II
I
l.
I H
o_i
1.o 10
APPLIED PRESSURE — ksf
194 398
HE''WOATI I-PAVYLAK
GECTECHNICAL
Inc.
SWELL -CONSOLIDATION TEST RESULTS I- 5
Compression
Compression %
0
1
2
3
0
1
2
4P°LE ESSUE — kst
I
I
1
Moisture Content = 7.0 percent
Dry Unit Weignt = 107 pct
sarnote of: sandy silty clay
forn: Boring 4 :' 20 Feet
,
,Moisture Concent =
L'ry Unit weignt = 4.9 percent
111 3C:
Sample or: sandy silt and clay
! i
, .
!
I 1
=rom: Boring 5 c 15 Feet
:
•
i . . i
, . I .
I
•
)
1
I
Upon Wetting, 1 1
I
1 1 I 1 I
1 ; .
! , ;
I I
i
I
i
I
I
1
I
1
,
.N.Expansion
Upon Wetting
I
i
I
I
i I
I i
, 1
I 1
0
1
2
4P°LE ESSUE — kst
01
LQ 10
APPLIED PRESSURE — ksf
100
194 398
HEPWORTH-PAWLAK
GEOTECHNICAL, Inc.
SWELL-CONSOLIDAT1ON TEST RESULTS
6
I
I
1
,Moisture Concent =
L'ry Unit weignt = 4.9 percent
111 3C:
Sample or: sandy silt and clay
! i
, .
!
I 1
=rom: Boring 5 c 15 Feet
:
•
i . . i
, . I .
•
i , 1
i I
Compresson
1
I
Upon Wetting, 1 1
I
1 1 I 1 I
1 ; .
! , ;
I I
i
I
i
I
I
I
01
LQ 10
APPLIED PRESSURE — ksf
100
194 398
HEPWORTH-PAWLAK
GEOTECHNICAL, Inc.
SWELL-CONSOLIDAT1ON TEST RESULTS
6
Compression %
Compression %
0
1
2
3
0
1
2
3
4
,AppLiE2 PPEES.UPE — kst
I
i
1
!
• •
I I 1
I
Moisture Content = 6.1
:Dr! Unit Weient = ::ercent
107 :Ic,
Samote at: sandy silt and clay
• .
i 1
,
;
,
. ,
i
1
1
=ram: Boring 7 @ 40 Feet
, , • ,
i —9'•
Moisture Content . 7.0 percent
Dry Unit Weignt = 105 pct
sample of: sandy silt and clay
;"°r": Boring 6 @ 20 Feet
, .
.
.
ill
.
1
,
. . , .
1 1 compression 1
Upon Wetting i
1
1
1
, I I
i
1 i 1
,
L.
II 1I
Compression
Upon Wetting
I! 1
1 1
I
,
I 1
I
I 1 I
i I
i 1
1
.
. :
. .
. ,
,AppLiE2 PPEES.UPE — kst
I
i
1
!
• •
I I 1
I
Moisture Content = 6.1
:Dr! Unit Weient = ::ercent
107 :Ic,
Samote at: sandy silt and clay
• .
i 1
,
;
,
. ,
i
1
1
=ram: Boring 7 @ 40 Feet
, , • ,
i —9'•
i ,
, .
ill
I
. . , .
1 1 compression 1
Upon Wetting i
i
1 i 1
II 1I
I! 1
1 1
I 1
0.1
1.0
APPLIED PRESSURE — ksf
14EPWORTH-PAWLAK SWELL-CONSCUDAT1CN TEST RESULTS 7
194 398
GEOTECHNICAL, Inc.
HYOROMETER ANALYSIS
24 Hn, 7 Hn.
45 MIN 15 MIN
1001
I IME IIEIAUINGS
RO MIN. 19 MIN. 4 MIN.
SIEVE ANALYSIS
1 MIN. '7171 •1nn
U.S. SIANUMIU SEIIIES
'10
•5n •4(47143 •16 rn
CLEAII SUUANL UVENINGS
n- ,•�- .r
5-3- 5'
!O
20
30
10
1
0 :: 1 r 1 1"1 1T7
.001 .002 .005 .009 .9 9 .03/ .014 .149 .29! „590 1.19 2.0 22 38 4.16 9.52
I 1n0
10
19.1 38.1. 16.1 12T ' 0
152
DIAMETER OF PARTICLE IN MILLIMETERS
CLAY TO SILT
SANT) 1
GHAvI•L
FINE 1
GRAVEL 33 SAND 38
LIOUID LIMIT PLASTICITY IND (
SAMPLE OF silty sand and gravel FROM Boring 2 (@ 5 Feet
MEDIUM 1COA)1SE I FINE { COAN:;E
SILT AND CLAY 29 %
IC000LES
1 HYDROMETER ANALYSIS
r IME i4EAUINGS
74 1111 7 Hn.
45 MIN ,5 MIN 6n MIN. 19 MIN 4 MIN I MIN '700 • inn
100
90
90
70
SIEVE
U.S. ;;IANI)AI11.) Sf:111ES
•+n
•5n • 1n .,n • if x
1NALYSIS
CLEAN SOUAIIE OPENINGS Ij
'.t 't- Y' 1'h' Sr SO
•
J
1
i J l
10
• , 1
v
60
�50
W
rt �0
a30
20
10
•
1
3
4,0
1 ;} 1 i i .1,
1_I +00r(i)
�ti 1
TO
1 1 1
+
0(
.001 .002
r 11r
.005 .009
1 LI
.019 .037 .0/4 .149 .297 500 1.19 7.38
.42 2.0
DIAMETER OF PARTICLE IN MILLIMETERS
4./6
60
1111 lc - 1R1I '100
9.52 19.1 38.1 1fi.2 127 • 200
152
CLAY TO SILT
FINE
GflAVEL
MEOIUM ]COAHSEI firm 1 COARSE
SANO
COBBLES
GRAVEL
LIQUID LIMIT
SAMPLE OF
SANG
HEPWORTH-PAWLAK
194 398 I GEOTECHNICAL, inc.
SILT AND CLAY
PLASTICITY INDEX
FROM
GRADATION TEST RESULTS
I F+9. 8
HEPWORTH-PAWLAK GEOTECHNICAL, INC.
JOB NO. 194 398
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
061
NATURAL
DRY
DENSITY
(pcFl
GRADATION
PERCENT
PASSING
NO. 200
SIEVE
ATTERBERG LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH
(PSF)
SOIL OR
BEDROCK TYPE
BORING
DEPTH
(feet)
GRAVEL
(%)
SAND
(%)
LIQUID
LIMIT
(%)
PLASTIC
INDEX
(%)
1
2
5.5
104
63
21
5
Sandy Silt and Clay
5
5.4
97
Sandy Silt and Clay
25
5.5
114
81
Sandy Silt and Clay
2
2
4.3
98
Sandy Silt and Clay
5
3.0
33
38
29
Silty Sand and Gravel
25
4.8
78
Sandy Silt and Clay
3
10
4.7
106
Sandy Silty clay
15
4.0
105
67
Sandy Silt and Clay
4
2
7.2
94
72
26
10
Sandy Siiity Clay
10
4.8
102
Sandy Silt and Clay
20
7.0
107
Sandy Silty Clay
5
5
4.6
102
68
Sandy Silt and Clay
15
4.9
111
Sandy Silt and Clay
6
5
7.6
105
61
Sandy Silt and Clay
20
7.0
105
Sandy Silt and Clay
7
2
4.5
96
51
Very Sandy Silt with
Gravel
40
6.1
107
Sandy Silt and Clay