Soils Reportr,
Bob J. Arnold, PE
208-440-6276 biarnoldpe(c~msn.com
April 10, 2012 Page 1 120318001.doc
Mr. Chad S. Kinkela, PE
CK Engineering, PC
860 Headwaters Drive
Eagle, Idaho 83616
Dear Sirs:
As per your authorization, this consultant has prepared the following
Geotechnical Recommendation Report for the proposed Canterbury Commons
Subdivision. This report has been prepared at the request of the client, CK
Engineering who provided the reported design details.
Based upon the subsurface sampling, laboratory test results, and provided
design information, the construction of a residential subdivision is feasible.
Recommendations for site grading, placement of structural fill, stormwater disposal and
pavement sections are provided herein. Preliminary foundation design and
recommendations for home builders are also included.
We appreciate this opportunity to be of service and we look forward to working
with you during the construction of this project. Should you have any questions or
require additional information, please contact our office at your convenience.
Civil Engineering
Geotechnical Engineering
Materials Testing & Inspection Services
Subject: Geotechnical Recommendations
Canterbury Commons Subdivision
Pine Avenue -Meridian, Idaho
tted;
l Dr's/
~I Consultant
Bob J. Arnold, PE
8717 Graydon Drive
Boise, Idaho 83704
Bob J. Arnold, PE Civil Engineering
Geotechnical Engineering
Materials Testing 8 Inspection Services
208-440-6276 biarnoldpe(c~msn.com
April 10, 2012 Page 2 120316001.doc
General
INTRODUCTION
This report presents the results of a geotechnical evaluation performed on a
partially developed lot located on the south side of Pine Avenue, just west of Ten Mile
Road in Meridian, Idaho. The Ada County Assessor website identifies the property as
six tax parcel containing approximately 22.4 acres. The addressed parcels are 2735 to
2985 West Pine Avenue. The property is located within Township 3 North, Range 1
West, Section 11, Boise meridian, Meridian, Ada County, Idaho. Access to the property
is only from West Pine Avenue that borders the property along the north property line.
At the time of our field investigation the property was partially developed as a
multifamily housing complex. It was reported that the property was originally to be
developed with fourplex housing structures. Underground utilities and portions of the
streets and driveways, including curb and gutter, were installed before the project was
abandoned. It is reported that all prior construction is to be demolished and that a new
layout of streets, residential lots and utilities is planned.
Authorization
Written authorization to proceed with this geotechnical investigation was received
from the client, Mr. Chad Kinkela on or about March 15, 2012. Authorization to
proceed, the use of the recommendations provided herein, and payment for the
provided services indicate the client's acceptance of the scope of work, and the
warranty and limitations included in our proposal and herein.
Warranty and Limitations
The exploration and evaluation of subsurface conditions documented herein is
considered sufficient to form a basis for the recommended foundation design. The
provided recommendations are based on the available soil information and preliminary
design details either assumed or furnished by the client. It is warranted that these
recommendations have been promulgated after being prepared in accordance with
locally accepted professional engineering and geotechnical engineering practice. No
other warranties are implied or expressed.
Bob J. Arnold, PE 8717 Graydon Drive Boise, Idaho 83704
Bob J. Arnold, PE Civil Engineering
Geotechnical Engineering
Materials Testing & Inspection Services
208-440-6276 biarnoldpe(a~msn.com
April 10, 2012 Page 3 120316001.doc
RESEARCH & DOCUMENTATION
Field Exploration
An initial site visit occurred on March 20, 2012 during which test pit locations
were marked. Digline was then called and two days time was allowed for utility location.
On April 5, 2012, three test pits were excavated with a track mounted excavator
operated by Sawyer Excavation of Eagle, Idaho. The three test pits were located in
areas identified by the client as possible locations for storm water disposal systems.
The three pits were extended to 12 - 14 feet below the existing ground surface. This
consultant logged and sampled the test pits. The samples were field classified in
general accordance with ASTM D-2488, sealed in plastic storage bags, and transported
to the laboratory for further testing.
Laboratory Testing
In addition to the field investigation, a supplemental laboratory-testing program
was conducted to determine additional pertinent engineering characteristics of the sub-
surface soils. The laboratory-testing program included soil classification and moisture
content determinations on selected samples. In addition, selected samples were
subjected to Atterberg Limits Tests -ASTM designation D-4318, and Grain Size
Analysis -ASTM designation C-117, C-136. All phases of the laboratory-testing
program were conducted in general accordance with applicable ASTM Specifications.
Test results are reported in the Test Pit Logs in the Appendix. Given the high liquid limit
and plastic index results obtained on near surface soils, it was determined not to
perform the proposed R-Value test. Avery low R-Value result can be anticipated
based on the reported Atterberg Limits and Sieve analysis. In accordance with ACHD
policy an R-Value of R=0 has been assumed and is appropriate for this project.
Bob J. Arnold, PE 8717 Graydon Drive Boise, Idaho 83704
BOIJ •.~, Arnold, PE Civil Engineering
Geotechnical Engineering
Materials Testing & Inspection Services
208-440-6276 biarnoldpe(c~msn.com
April 10, 2012 Page 4 120316001.doc
SITE DESCRIPTION /INFORMATION
Observed Conditions
At the time of our field inspection the site was a partially completed multifamily
housing development. Utilities were installed and parking lots and driveways were
completed through base coarse including curb and gutter. The client reported that the
development plan has changed. The plan is now to convert the property to a subdivision
with residential lots for single family homes. The existing curb & gutter and roadway
base courses are to be demolished.
Each of the three test pits was different. In TP-3, the eastern test pit, free
draining sands (Percolation rate P=8) were encountered at approximately four feet
below the existing ground surface. The sand layer was overlain by a one foot thick
hardpan layer and three feet of silty clay or clayey silt. This sand extends to greater
than the 14 feet explored with the retained excavator. Neither gravels nor groundwater
was encountered in this test pit which was extended to the maximum reach (14 feet) of
the retained excavator. A historical piezometer was observed approximately 100 feet
northwest of this test pit. In this well location water was measured at 14.5 feet below
the existing ground surface on April 5, 2012.
Test pit #2 was located on the north side of the property near the bend in the
adjacent drainage canal. 9.5 feet of clayey silt or silty clay was encountered in this
location. The upper five feet appeared to be denser and may possibly be fill placed
during prior development efforts on the property. A cemented layer was observed from
9.5 to 11.0 feet below the ground surface. Groundwater and gravels were both
contacted directly below this hardpan layer. Gravels were free draining by 12 feet.
Test pit #1 was excavated in the far west end of the property. Eleven feet of silty
clay or clayey silts were encountered in this location. Gravels were contacted at 11.0
feet and extended to greater than the 12 feet deep exploration. Groundwater rose to
10.5 feet while the test pit was open.
In each location 4-8 inches of root zone or organic materials were observed.
Near surface soils were tested and confirmed to be elastic silts or low plasticity clays.
Bob J. Arnold, PE 8717 Graydon Drive Boise, Idaho 83704
Bob J. Arnold, PE
Civil Engineering
Geotechnical Engineering
Materials Testing & Inspection Services
208-440-6276 biarnoldpe(a~msn.com
April 10. 2012 Page 5 120316001.doc
CONSTRUCTION RECOMMENDATIONS
General Earthwork
Grubbing or removal of all organic soils is required. Compaction of the exposed
subgrade surface soils is required. subgrade soils are to be brought to proper moisture
contents (± 2% of optimum) and compacted to 95 % of the maximum dry density as
determined by ASTM Method D-698 also referred to as "Standard Proctor" method.
Compaction testing should confirm that the existing subgrade and each lift of structural
fill are properly compacted. Historical construction drawings and compaction tests
performed during prior onsite construction activity should be located and reviewed to
confirm proper compaction of deeper filled areas. As stated above, compaction of the
existing subgrade is to be confirmed prior to the placement of structural fill.
Structural Fill
It is recommended that imported granular materials be used for structural fill. It is
allowed to harvest and reuse the existing onsite base and sub base courses placed
within the previously construction driveways and parking areas. It is also allowed to
utilize crushed concrete (onsite existing curb and gutters) as sub base materials in the
planned street sections. ACRD approval must be obtained before using recycled
materials within their right of ways. Structural fill used within residential lots and future
right of ways are to be compacted to exceed 95% of the maximum dry density as
determined by ASTM Method D-698, Standard Proctor.
Bob J. Arnold, PE 8717 Graydon Drive Boise, Idaho 83704
Bob J, Arnold, PE civil Engineering
Geotechnical Engineering
Materials Testiny & Inspection Services
208-440-6276 biarnoldpeCa)msn.com
April 10, 2012 Page 6 120316001.doc
Foundation System
Based upon observed and reported conditions bearing pressures of up to 1500
psf are allowed for design of residential foundations. Conventional strip foundations and
crawlspaces or slab on grade floor are acceptable. For residences with crawlspaces
proper compaction of foundation wall backfill and utility trenches is critical to prevent
water from entering crawlspaces.
Pavement Design
Since the near surface soils exhibit plastic characteristics, pavement section
equivalent to ACRD maximum requirements are recommended. For residential streets
2.5" of ACP, 4.0" of road base, and 14.0" of subbase are recommended. Along Pine
Avenue ACRD may require matching of the existing pavement section. If a project
specific design is allowed for Pine Avenue, a pavement section of 4.0" of ACP, 4.0" of
road base, and 18.0" of subbase is recommended based upon a Traffic Index of TI=8
and an assumed R-Value of R=O.
Stormwater Disposal
Free draining, granular soils (sands or pitrun) were present in all three test pits at
11.5' below the existing ground surface. A percolation rate of P=8 inches per hour can
be assumed for these soils. It should be confirmed at the time of construction that
percolation facilities extend to free draining materials.
It is noted that this consultant provided similar services for the Courtyard
development located south, across the drainage canal from the west end of the subject
property. Monitoring wells on that property indicate that groundwater was 11-12 feet
below the ground surface in May 2003. This matches well with onsite observations.
Bob J. Arnold, PE 8717 Graydon Drive Boise, Idaho 83704
Bob J , Arnold, PE
Civil Engineering
Geotechnical Engineering
Materials resting & Inspection Services
208-440-6276 biarnoldpe(o~msn.com
April 10. 2012 Page 7 120316001.doc
General Comments
After the plans and specifications are completed it is recommended that this
consultant be provided the opportunity to review the final design and specifications.
This review will confirm that the earthwork recommendations have been properly
interpreted and implemented. At that time, it may be necessary to submit
supplementary recommendations.
Monitoring and testing should also be performed to verify suitability of materials
used for structural fills and to confirm subgrade stability and proper placement and
compaction. Any revision in the plans from those described in this report or deviations
from the noted subsurface conditions should be brought to the attention of this
consultant.
Testing and inspection services are recommended herein. Proper quality control
during construction is required to confirm materials and methods and thereby obtain a
desirable finished product.
This report has been prepared for the exclusive use of the identified client and
other retained design consultants. Findings and recommendations within this report
are for specific application to the proposed construction described here and apply only
to the property identified.
Appendix Follows
Bob J. Arnofd, PE 8717 Graydon Drive Boise, Idaho 83704
Bob J. Arnold, PE Civil Engineering
Geotechnical Engineering
Materials Testing & Inspection Services
__ 208-440-6276 biarnoldpel~msn.com
April 10, 2012 Page 8 120316001.doc
APPENDIX
Aerial Photo (Test Pit Locations)
Test Pit Logs (3 pages)
Soil Log Legend
Pavement Section Calculation Sheet
Abbreviations and Acronyms
Bob J. Arnold, PE 8717 Graydon Drive Boise, Idaho 83704
Bob J. Arnold, PE Civil Engineering
Geotechnical Engineering
Ma'eri~h testing & Inspection Services
208-440-6276 bjarnoldpe(a~msn.com
4pril 10, 2012 Page 9 120316001.doc
Aerial Photo
With approximate test pit locations
(Subject property is six parcels as shown)
Bob J. Arnold, PE 8717 Graydon Drive Boise, Idaho 83704
From Ada County Assessor Website
Bob J . Arnold, PE Civil Engineering
Geotechnical Engineering
Mgt^riais Tssting & Inspection Services
208-440-6276 biarnoldpe(a~msn.com
April 10. 2012 Page 10 120316001.doc
Test Pit #: _ TP-1 File:
Client: _ CK Engineering Date Excavated
Project: Canterbury Commons Subdivision -Meridian Excavator:
Location: West End Logged By:
Test Pit Log
120316001
April 5, 2012
Sawyer/Backhoe
Bob Arnold
Sample # # # #
DEPTH SOILS DESCRIPTION T e 4 10 40 200 M PI LL
0.0-0.8 Root zone /Organic Layer in
Brown, Wet, Clayey SILT or
Silty CLAY
0.0-11.0 Brown, Wet to Saturated, Dry, gag 100 96 84 62.5 17.7
Clayey SILT or Silty "CLAY 3.0
(ML-CL)
Bag 100 99 81 62.8 28.1 7.6 28.9
9.5
11.0 Gravel Contact
11.0-12.0 Tan-White, Dry, Pitrun Type,
Sand and Gravel -Free
draining at 11.5'
12.0 Bottom of Excavation
Sloughing Soils
Groundwater Rose to 10.5'
Bob J. Arnold, PE 8717 Graydon Drive Boise, Idaho 83704
fob J. Arnold, PE Civil Engineering
Geotechnical Engineering
M-~terials Testing & Inspection Services
208-440-6276 biarnoldpeCa~msn.com
April 10, 2012 Page 11 120316001.doc
Test Pit Log
Test Pit #:
Client:
Project:
Location:
Canterbu
TP-2 File:
CK Engineering Date Excavated
Commons Subdivision - Meridian_ Excavator:
South End Logged By:
120316001
April 5, 2012
Sawyer / Backhoe
Bob Arnold
Sample # # # #
DEPTH SOILS DESCRIPTION T e 4 10 40 200 M PI LL
0.0-0.8 Root zone !Organic Layer in
Brown, Wet, Clayey SILT or
Silty CLAY
0.8-5.0 Possible Fill? gag 18.0
Brown, Wet, Clayey SILT or 3.0
Silty CLAY
5.0-9.o Brown, wet to Saturated, gag 100 99 89 74.8 20.0
Sandy Silty CLAY with 5.0
Cemented particles
Bag 100 99 77 63.7 23.7
9.0
9.0-11.0 Tan, Wet to Saturated, gag 26.9
Cemented, SILT & SAND 9 0
11.0 Contact with Groundwater
Contact with Gravels
BELOW HARDPAN
11.0-13.0 White, Saturated, Silty,
PITRUN Type Sand and Gravel
Free Draining at 12.0
13.0 Bottom of Excavation
Sloughing Soils
Groundwater at 11.0'
Bob J. Arnold, PE 8717 Graydon Drive Boise, Idaho 83704
Sob J. Arnold, PE
Civil Engineering
Geotechnical Engineering
Materials Testing & Inspection Services
208-440-6276 bjarnoldpe(c~msn.com
April 10, 2012 Page 12 120316001.doc
Test Pit Log
Test Pit #: TP-3 File:
Client: CK Engineering Date Excavated:
Project: Canterbury Commons Subdivision -Meridian Excavator:
Location: East End Logged By:
120316001
April 5, 2012
_ Sawyer / Backhoe
Bob Arnold
Sample # # # #
DEPTH SOILS DESCRIPTION T e 4 10 40 200 M PI LL
0.0-0.8 Root zone /Organic Layer in
Brown, Wet, Clayey SILT or
Silty CLAY
0.8-2.0 Brown, Moist, Clayey -SILT or
Silty CLAY
2.0-3.0 Brown, Moist, Clayey -SILT Bag 100 98 74 57.9 31.4 15.8 45.8
(ML) 2.5
3.0-4.0 Hardpan Layer gag 29.0 26.3 VNP VNP
3.5
4.0-14.o white, Wet to Saturated, Bag 100 95 82 77.7 4.4 VNP VNP
SAND 4.5
Bottom of Excavation
14.0 Limit of Excavator
No Groundwater Encountered
Bob J. Arnold, PE 8717 Graydon Drive Boise, Idaho 83704
Bob J. Arnold, PE
Civil Engineering
Geotechnical Engineering
Materials Testing 8 Inspection Services
208-440-6276 biarnoldpe(a~msn.com
April 10, 2012 Page 13 120316001.doc
Soil Log Legend
UNIFIED SOIL CLASSIFICATION SYSTEM
(ASTM STANDARD TEST METHOD D 2487 FOR CLASSIFICATION OF SOIL FOR ENGINEERING PURPOSES
DIVISIONS ~ DESCRIPTIONS
COARSE
GRAINED
SOILS
< 50 % - #200 GRAVEL &
GRAVELLY
SOILS
<50% - #4 < 5%- #200 GW Well-graded gravel, gravel-sand mixture, little or no
fines.
GP Poorly-graded gravel, gravel sand mixture, little or
no fines
5-12%-#200 GM Silt gravel, gravel-sand-silt mixtures
> 12% - #200 GC Clayey gravel, gravel-sand-clay mixtures
SAND 8
SANDY SOILS
>50%-#4 < 5% - #200 SW
SP Well-graded sand, gravelly sand, little or no fines.
Poorl - raded sand, ravell sand, little or no fines
>12%-#200 SM Silt sand, sand-silt mixtures
SC Cla a sand, sand-cla mixtures
FINE
GRAINED
SOILS
> 50% - #200 SILTS AND
CLAYS
LL < 50% INORGANIC ML Inorganic silt and very fine sand, rock flour, silty or
clayey fine sand or clayey silt with slight plasticity
CL Lean clay-low to medium plasticity, gravelly clay,
sandy clay, silty clay
SILTS AND
CLAYS
LL > 50% ORGANIC
tNORGANIC OL
MH Or anic silt and organic silty clay of low plasticity
Elastic silt, micaceous or diatomaceous fine sand
or silty soil.
CH Fat cla - hi h lasticit
ORGANIC OH Or anic clay-med. or high plastici : or anic silt
HIGHLY
ORGANIC
SOILS PT Peat, humus, swamp soil with high organic content
Bob J. Arnold, PE 8717 Graydon Drive Boise, Idaho 83704
Bob J. Arnold, PE Civil Engineering
Geotechnical Engineering
Materials Testing 8 Inspection Services
208-440-6276 biarnoldpe(c~msn.com
April 10, 2012 Page 14 120316001.doc
PAVEMENT SECTION CALCULATIONS
(ACRD R-Value Method)
Project: Canterbury Commons -Residential File No.: 12Q316
Meridian, Idaho Caic By: B. Arnold
Client: CK Engineering Date: 04110112
Design Thickness Equation:
T = 0.0032 (TI) (100-R)(12) = GE (inches)
T= Design Thickness TI =Traffic Index = 6 Assumed
GE =Gravel Equivalent R = R-Value = 0 Assumed
GE= 23.5 Inches
ACRD ACP. 3/4" Road Base and Agqreqate Subbase
Actual Thickness Equivalent Thickness
ACRD Asphalt Concrete Thickness = 2.5 Inches ACE= 6.0 Inches
3/4" Road Base Thickness Desired = 4.0 Inches RBE= 4.4 Inches
Calculated Agqreqate Subbase Thickness Equation:
Subbase Thickness=SB=GE-ACE-RBE
SB= 13.1 Inches
CALCULATED DESIGN SECTION
ACRD Asphaltic Concrete= 2.5 inches
3/4" Road Base = 4.0 inches
Aggregate Subbase = 14.0 inches
RECOMMENDED DESIGN SECTION
Asphaltic Concrete = 2.5 inches
3/4" Road Base = 4.0 inches
Aggregate Subbase = 14.0 inches
Bob J. Arnold, PE 8717 Graydon Drive Boise, Idaho 83704
Bob J. Arnold, PE Civil Engineering
Geotechnical Engineering
Materials Testing & Inspection Services
208-440-6276 bjarnoldpe(c~msn.com
April 10, 2012 Page 15 120316001.doc
PAVEMENT SECTION CALCULATIONS
(ACRD R-Value Method)
Project: Canterbury Commons - irr~ .~~r~i~ue File No.: 120316
Meridian, Idaho Caic By: B. Arnold
Client: CK Engineering Date: 04/10f12
Design Thickness Equation:
T = 0.0032 (TI) (100-R)(12) = GE (inches)
T= Design Thickness TI =Traffic Index = $ Assumed
GE =Gravel Equivalent R = R-Value = 0 Assumed
GE= 31.2 Inches
ACRD ACP, 3/4" Road Base and Aggregate Subbase
Actuat Thickness Equivalent Thickness
ACHD Asphalt Concrete Thickness = Inches ACE= 9.6 Inches
3/4" Road Base Thickness Desired = 4.(l Inches RBE= 4.4 Inches
Calculated Aggregate Subbase Thickness Equation:
Subbase Thickness=SB=GE-ACE-RBE
SB= 17.2 Inches
CALCULATED DESIGN SECTION
ACHD Asphaltic Concrete= 4.0 inches
3/4" Road Base = 4.0 inches
Aggregate Subbase = 18.0 inches
RECOMMENDED DESIGN SECTION
Asphaltic Concrete = 4.0 inches
3/4" Road Base = 4.0 inches
Aggregate Subbase = 18.0 inches
Bob J. Arnold, PE 8717 Graydon Drive Boise, Idaho 83704
Bob J. Arnold, PE Civil Engineering
Geotechnical Engineering
Materials Testing S Inspection Services
208-440-6276 bjarnoldpe(a~msn.com
April 10, 2012 PagA 16 120316001.doc
Abbreviations and Acronyms
AASHTO American Association of State Highway & Transportation Officials
ASTM American Society for Testing and Materials
ACP Asphaltic Concrete Pavement
BH Bore Hole
IBC International Building Code
ISPWC Idaho Standard for Public Works Construction
ITD Idaho Transportation Department
NP Non Plastic
PCC Portland Cement Concrete
PCF Pounds per Cubic Foot
TP Test Pit
USCS Unified Soil Classification System
CL Clay
ML Silt
NOTHING FOLLOWS
Bob J. Arnold, PE 8717 Graydon Drive Boise, Idaho 83704
Bob J. Arnold, PG ClvilEngineering
Geotechnical Engineering
Materials Testing & Inspection Services
208-440-6276 bjarnoldpe(a~msn.com
April 10, 2012 Page 17 120316001.doc
RECOMNIE~DAT'IONS FOR HO~IEBUILDERS
Canterbury Commons
Homebuilder is responsible for investigatin~~ onsite soil conditions and elevations prior to acquisition and
prior to construction.
Homebuilder may elect to retain a geoteehnical engineer for asite-specific evaluation of an individual building lot.
If this occurs, all recommendations included herein are supcr,eded by the recommendations of the retained
consultant.
Foundations are to be founded on native, undisturbed soil materials or upon documented structural fill.
Homebuilder must have crawlspace excavations inspected by building department prior to construction of
foundations.
Foundations founded on the native soils or shallow structural fills may assume bearing pressures of up to 1500 psf
are available.
Should homebuilder elect to elevate foundations above the excavation depth indicated above; placement,
compaction, and testing of structural fill is required. This work to be done at contractor expense.
Any such structural fill is to be imported granular (GW, GP, SP, SW, or combination) materials.
Any structural fill placed is to extend to two feet outside the foundations in all directions.
Any required structural fill is to be compacted to 90 percent of the maximum dry density as determined by ASTM
D-]557, Modified Proctor.
Independent compaction testing is required on all structural fill with reports submitted to jurisdictional building
Inspector.
Low-density foundation backfill has been shown to be a major contributing factor to water accumulating in
crawlspaces throughout the Treasure Valley. f lomebuilders are encouraged to properly backfill all foundations.
For homes with a crawlspace, it is recommended that the construction joint between the footing and the stem wall be
sealed with asphalt-based mastic.
For homes with a crawlspace, soils containing, fractured hardpan materials, soils with organic materials or large
clods or chunks of clay and concrete rubble are not recommended for backfill. The use of these materials may result
in voids or flow paths allowing surface water to enter the crawlspace. Clay containing soils may shrink away from
foundation walls.
For homes with slab on grade floors, a building code complying vapor barrier or vapor retarder is required. Some
flooring manufactures may have vapor barrier or vapor retarder requirements more stringent than the building code.
Top of foundation elevation and site grading must promote drainage away from the foundation. Unless the local
code is more stringent, a minimum of Five percent slope for the first ten feet from the residence is recommended.
Compliance with the recommended top of wall elevation, site grading requirement and foundation extending to
acceptable native soils, may require construction of nonstandard foundation walls /foot heights.
Complete roof gutters are recommended with down spouts directed away from foundations and not on to foundation
backfill soils.
Landscaping should be designed to promote drainage away from foundations
Bob J. Arnold, PE 8717 Graydon Drive Boise, Idaho 83704