HomeMy WebLinkAboutGeotechnical Investigation 06.07.2024Huddleston-Berry
Engineering & Testing, LLC
Jvne7,2024
Project#02850-0001
Joe Reider
1620 County Road 2l
Brighton, Colorado 80603
Subject: Geotechnical Investigation
Parcel 24072300004
Parachute, Colorado
Dear Mr. Reider,
This letter presents the results of a geotechnical investigation conducted by lluddleston-Berry
Engineering & Testing, LLC (IIBET) at Parcel 24A7n00004 in Parachute, Colorado. The site
location is shown on Figure 1. The proposed construction is anticipated to consist of a new
single-family residence. The scope of our investigation included evaluating the subsurface
conditions at the site to aid in developing foundation recommendations for the proposed
construetion.
Site Conditions
At the time of the investigation, tlre investigated area was open. The northwest portion of the site
was fairly flat, and vegetation primarily consisted of grasses and weeds. The center and southeast
portions of the site contained moderate to steep slopes down to the adjacent canyon, and
vegetation consisted of grasseg weeds, and trees. The site was bordered to the north by a vacant
lot and a rural residential property, to the west and south by rural residential properties, and to
the east by Federal Land.
Subsurface Investieation
The subsurface investigation included trvo borings and two test pits as shown on Figure 2 - Site
Plan. The borings were drilled to a depth of 20.0, and the test pits were excavated to a depth of
6.0 feet below the existing ground surface. Typed boring and test pit logs are included in
Appendix A.
As indicated on the logs, the subsurface conditions encountered at the site were fairly consistent.
The borings and test pits encountered 1.0 foot of topsoil above reddish-tan to brown, moist, soft
to very stiff lean clay with sand soils that extended to a depth of 12.0 feet in the borings and to
the bottoms of the test pit excavations. The clay soils in the borings were underlain by brown to
gray and tan, moist, dense silty sand with gravel soils that extended to the bottoms of the borings.
Groundwater was not encountered in the subsurface at the time of the investigation.
2789 RiversidePa*way
Grand Jrmction, Colorado 81501
Phone: 970-255-8005
Info@ltuddlestonberry. com
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Laboratorv Testine
Laboratory testing was conducted on samples of the native soils encountered in the borings. The
testing included grain size analysis, Atterberg limits determination, natural moisture content
determination, and maximum dry density and optimum moisture content (Proctor) determination.
The laboratory testing results are included in Appendix B.
The laboratory testing results indicated that the native clay and sand soils are moderately plastic.
In general, based upon the Atterberg limits and our experience with similar soils in the vicinity
of the subject site, the native clay soils are anticipated to be slightly expansive.
Foundation Recommendations
Based upon the results of the subsurface investigation and nature of the proposed construction,
shallow foundations are recommended. Spread footings and monolithic (turndown) structural
slabs are both appropriate foundation alternatives. However, as discussed previously, the native
soils are anticipated to be slightly expansive. Therefore, in order to provide a stable bearing
stratum and limit the potential for excessive differential movements, it is recommended that the
f,oundationsbe construeted above a minimum of 24-inehesof structural fill.
Due to their plasticity, the native soils are not suitable for reuse as structural fiIl. Imported
structural fill should consist of a granular, non-expansive, non-free drainins material with
greater than l0o/o passing the #20A sieve and Liquid Limit of less than 30. However, all
proposed imported structural fill materials should be approved by FIBET.
For spread footing foundations, the footing areas may be trenched. However, for monolithic slab
foundations, the structural fill should extend across the entire building pad area to a depth of 24-
inches below the turndown edges. Structural fill should extend laterally beyond the edges of the
foundation a distance equal to the thickness of structural fill.
Prior to placement of structural fill, it is recommended that the bottoms of the foundation
excavations be scarified to a depth of 6 to 8-inches, moisture conditioned, and re-compacted to a
minimum of 95o/o of the standard Proctor ma:<imum dry density, within *ZYo of the optimum
moisture content as determined in accordance with ASTM D698. However, as discussed
previously, soft soils were encountered in portions of the subsurface and this may make
iompaction of the subgrade difficulf It may be necessary to utilize geotextile andlot geogrid in
conjunction with up to 30-inches of additional granular fill to stabilize the subgrade. I{BET
should be contacted to provide specific recommendations for subgrade stabilization depending
upon the actual conditions encountered during construction.
Structural fill should be moisture conditioned, placed in maximum 8-inch loose lifts, and
compacted to a minimum of 95o/o of the standard Proctor maximum dry density for fine grained
soils or modified Proctor maximum dry density for coarse grained soils, within *ZYo of the
optimum moisture content as determined in accordance with ASTM D698 or D1557C,
respectively. Structural fill should be extended to within 0.l-feet of the bottom of the
foundation. No more than 0.I-feet of gravel should be placed below the footings or turndown
edge as a leveling co'urse.
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Pwcel 240702300004
#028504001
06107D4
HuddlestorlBerty
For structural fill consisting of approved imported granular materials and foundation building
a maximum allowable beari
pcl may used for imported structural fill
materials. Foundations subject to frost should be at least 36-inches below the finished grade.
Any stemwalls or retaining walls should be designed to resist lateral earth pressures. For backfill
consisting of the native soils or imported granular, non-free draining, non-expansive material, we
recommend that the walls be designed for an active equivalent fluid unit weight of 55 pcf in
areas where no surcharge loads are present. An at-rest equivalent fluid unit weight of 75 pcf is
recommended for braced walls. Lateral earth pressures should be increased as necessary to
reflect any surcharge loading behind the walls.
Water soluble sulfates are common to the soils in Western Colorado. Therefore, at a minimum,
cement adequate for Sulfate Exposure Class S1 is recommended for construction at this site.
Non-structural Floor Slab and Exterior Flatwork Recommendations
In order to reduce the potential for excessive differential movements, it is recommended that
non-structural floating floor slabs be constructed above a minimum of 24-inches of structural fill
with subgrade preparation, structural fill materials, and fill placement be in accordance with the
Foundation Recommendations section of this report. It is recommended that exterior flatwork be
constructed above a minimum of l2-inches of structural fill.
I)rainase Recommendations
Grudins and drainase are uitical for the lons-term oetformnnce of the structure and grading
around the structure should be designed to carry precipitation and runoff away from the
structure. It is recommended that the finished ground surface drop at least twelve inches within
the first ten feet away from the structure. It is also recommended that landscaping within five
feet of the structure include primarily desert plants with low water requirements. In addition, it
is recommended that irrigation, including drip lines, within ten feet of foundations be minimized.
I{BET recommends that downspout extensions be used which discharge a minimum of 15 feet
from the structure or beyond the backfill zone, whichever is greater. However, if subsurface
downspout drains are utilized, they should be carefully constructed of solid-wall PVC and should
daylight a minimum of 15 feet from the structure. In addition, an impermeable membrane is
recommended below subsurface downspout drain lines. Dry wells should not be used.
In order to limit the potential for surface moisture to adversely impact the structure, a perimeter
foundation drain is recommended. In general, the perimeter foundation drain should consist of
prefabricated drain materials or a perforated pipe and gravel system with the flowline of the
drain at the bottom of the foundation (at the highest point). The prefabricated drain materials or
gravel should extend along basement walls to within 36-inches of the finished grade. The
perimeter drain should slope at a minimum of 1.0% to daylight or to a sump with pump. The
drain should also include an impermeable membrane at the base to limit the potential for
moisture to infiltrate vertically down below the foundations.
EnsharhS& T6lhB, t.LC
pad preparation as recommended,
used. In addition, a modulus of
JZ:\2008 A.LL PROJECTSI'02850 - Joe Reider\O2850.0001 Parcel240702300004\200 - Geo\02850.0001 LR06072^1:doc
Paur'el24O7O2300004
#028504001
06107D4 @ Huddleston.Berry
Fn lnarini & IesinS, I.LC
General Notes
The recommendations included above are based upon the results of the subsurface investigation
and on our local experience. These conclusions and recommendations are valid only for the
proposed construction.
As discussed previously, the subsurface conditions encountered at the site were fairly consistent.
Ilowever, the precise nature and extent of any subsurface variability may not become evident
until construction. As a result, it is recommended that IIBET provide construction materials
testing and engineering oversight during the entire construction process. In addition, the builder
and any subcontractors working on the project should be provided a copy of this report and
informed of the issues associated with the presence of moisture sensitive subgrade materials at
this site.
It is imaortant to note thal the recommendations herein are intended to reduce the risk of
structural movement and/or dnmage, to varving desrees. associatedu,ith volutrc change of the
native soils. However. HBET cannot oredict long-term chanses in subsulface ,noisture
conditions and/or the precise mngnitude or utent of volurne chanse in the native soils. Whg'e
significant increases in subsurface moisture occur due to poor gradins. imoroper stormwater
mnntagernent, utilitv line fflilure, ucess irrigation, or other cause, either during construction
or the result of actions of the pronertv owner. several inches,of movement arelossible, In
addition. anv failure to comnlv with the recommendations in this reoort releases Had.d,leston-
Berry Engineerins & Testine, LLC of an! liabilitr with regard ta the structure performnnce.
We are pleased to be of service to your project. Please contact us if you have any questions or
comments regarding the contents of this report.
Respectfully Submitted:
Huddleston-Berry Engineering and Testing LLC
Michael A. Berry, P.E.
Vice President of Engineering
4
3 010
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PR(UECT LOCANONPRCUECT NUMBER
PRG,ECT TIIAME Parel24O7O23fiXlf)4CUENTJoe Reider
Rirrcrside
Engineering & Testing LI.C
97G255-8005
Junctisr, CO 81501
BORING NUMBER B-{
PAGE 1 OF 1
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PAGE 1 OF 1
PRI'ECT LOCANONPROJEGT NUMBER
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APPENDIX B
Laboratory Testing Results
Huddleston-Berry Engin€cring & Testing; LIC
2789 Ri!€rside Parkway
GrmdJunctim,CO 81501
97G25t8005
GRAIN SIZE DISTRIBUTION
CUENT Joe Reider Prc.'EGT II|ATI,IE Paresl2AOT(W3fr)00/
PRO'ECT NUMBER (}2850{too1 PRCUECT LOGAilON Parac
u.s. srEvE opENlrlc lN lt{ctlEs I U.S, SIEI'E NUI'BERS I.IYDROIIIETER
21.5 1V4 6 14 20 1m1{)200
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Specimen ldentification Classification LL PL PI Cc Cu
a B-1, SS-3 5120 STLTYSAND(SM)30 27 3
E coMPoslTE 5120 LEAN cl-AY with sAND(cL)32 18 14
Specimen ldentification D100 D60 D30 D10 ToGravel 06Sand ToSilt o/oClay
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Junctim, CO 81501
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PROIECT NUMBER 028504001 PRO.IECT l.(lq-nON Paraqhde. CO
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Specimen ldentification LL PL PI 1200 Classification
B-1, SS-3 5t20 30 27 3 {o STLTYSAND(SM)
COMPOSITE 5t20 32 18 14 71 LEAN ClAYwith SAND(GL)
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Sample Date:
Sample No.:
Source of Material:
Description of Material:
5t20t202A'
COMPOSITE
145 ClAYwith SAND{CL}LEAN
Test Method (manual):ASTM D698A
140
135 TEST RESULTS
Maximum Dry DensitY llXl:5 FGF
Optimum Water Content 20'O olo
130 GRADATON RESULTS (% PASSING)
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115 Curves of 100o/o Saturation
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