HomeMy WebLinkAboutWestgate Plaza GI
www.branchengineering.com
June 8, 2023
Westgate Plaza LLC
3700 Coburg Road
Eugene, Oregon
c/o Scott Morris
A&O Engineering LLC
RE: GEOTECHNICAL SITE INVESTIGATION
MAP 17-02-31-00 TAX LOT 00501
SW CORNER OF MAIN STREET & S. 32ND STREET
SPRINGFIELD, OREGON BRANCH ENGINEERING INC. PROJECT NO. 23-109
Pursuant to your authorization, Branch Engineering Inc. (BEI) performed a geotechnical engineering
investigation at the subject site located in Springfield, Oregon for proposed development of the
property. The accompanying report presents the results of our site research, field exploration and
testing, data analyses, as well as our conclusions and recommended geotechnical design parameters
for the project. Based on the results of our study, no major geotechnical/geologic hazards were
identified at the site that would negatively affect development, provided that the recommendations of
this report are implemented in the design and construction of the project.
We appreciate the opportunity to be of service to you. Please contact the undersigned if you have
questions or concerns regarding this report.
Sincerely,
Branch Engineering Inc.
Ronald J. Derrick, P.E., G.E. Matthew Renner, P.E.
Principal Geotechnical Engineer Construction Engineer
Ronald J. Derrick Digitally signed by Ronald J.
Derrick
Date: 2023.06.08 18:47:18 -07'00'
Geotechnical Investigation
Main & S. 32nd Streets, Springfield, Oregon
Project Number: 23-109
Branch Engineering, Inc.
TABLE OF CONTENTS
1.0 INTRODUCTION ....................................................................................................................................1
1.1 Purpose and Scope of Work 1
1.2 Project Location and Description 1
1.3 Site information Resources 1
2.0 GEOLOGIC SETTING .............................................................................................................................2
2.1 Regional Geology 2
2.2 Site Geology 2
2.3 Regional Seismicity 3
3.0 SITE SUBSURFACE CONDITIONS ......................................................................................................3
3.1 Subsurface Soils 3
3.2 Laboratory Testing 4
3.3 Mapped Soils 4
3.4 Groundwater 4
4.0 GEOLOGIC HAZARDS ...........................................................................................................................4
5.0 CONCLUSIONS .......................................................................................................................................5
6.0 DESIGN RECOMMENDATIONS ...........................................................................................................6
6.1 Foundation Subgrade Recommendations 6
6.2 Bearing Capacity 6
6.3 Settlement 7
6.4 Interior Slab-On-Grades 7
6.5 Friction Coefficient and Lateral Earth Pressures 7
6.6 Site Parking and Vehicle Route Subgrade Recommendations 7
6.7 Pavement Design 8
6.8 Structural Fill 9
6.9 Seismic Site Classification 9
7.0 CONSTRUCTION CONSIDERATIONS ............................................................................................ 10
7.1 Wet Weather/Dry Weather Construction Practices 10
7.2 Excavations 10
7.3 Site Drainage 10
7.4 Expansive Soil 10
7.5 Geotechnical Construction Site Observations 11
8.0 REPORT LIMITATIONS ..................................................................................................................... 11
FIGURE 1 – Site Exploration Map
APPENDIX A –USCS Soil Key, Test Pit Summary Logs, OWRD Well Log, NRCS Soil Survey
APPENDIX B – Recommended Earthwork Specifications
Geotechnical Investigation
Main & S. 32nd Streets, Springfield, Oregon
Project Number: 23-109
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1.0 INTRODUCTION
The geotechnical work presented herein was requested by A&O Engineering LLC and field work was
completed on March 24, 2023.
1.1 Purpose and Scope of Work
The purpose of this report is to present geotechnical engineering criteria and recommendations
related to our observed surface and subsurface conditions that may influence the design and
construction of the proposed development. Our scope of work included a field reconnaissance with
subsurface explorations monitored by BEI personnel, an engineering data review of existing geologic
and geotechnical reports in the site vicinity, and other pertinent site research activities resulting in
the preparation of this report in accordance with the 2022 Oregon Structural Specialty Code (OSSC)
Chapter 18 Section 1803. In addition, two site infiltration tests were conducted in locations
recommended by A&O Engineering LLC; the results of these tests are presented in a separate letter
report.
1.2 Project Location and Description
The subject site consists of one Tax Lot approximately 5-acres in size at coordinates of 44.045281°
North Latitude and 122.982358° West Longitude in Springfield, Oregon, see Figure-1. The site is
accessed via a paved road from S. 32nd Street and is currently occupied by a single-story
commercial/retail building and parking lot in the center of the site with underground utilities servicing
the building.
The site topography is relatively flat with swales located on the west side and along the east side of
the existing parking lot for storm water retention. The site is bounded by commercial retail/office
building to the north across Main Street, commercial/residential to the east across S. 32nd Street,
industrial businesses to the west, and Willamalane’s Bob Keefer Center complex to the south. The site
is covered by mown grass, and sparse trees/shrubs.
No specific development plans were provided to BEI; however, we anticipate additional
commercial/retail and/or multi-family residential development to occur.
Review of historical aerial photos available on Google EarthTM show the current site development
having occurred sometime after 2006 with development of the Bob Keefer Center occurring between
2003 and 2005. Prior to this, the subject site and property south to the railroad tracks, appears as
vacant land.
1.3 Site information Resources
The following site investigation activities were performed and literature resources were reviewed for
pertinent site information:
Six exploratory test pits were advanced to a maximum depth of 9.5-feet below ground surface
(BGS) on March 24, 2023.
Review of the Web Soil Survey, United States Department of Agricultural (USDA) Natural
Resources Conservation Service (NRCS) (attached in Appendix A).
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Project Number: 23-109
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Review of Oregon Department of Water Resources Well Logs (attached in Appendix A).
Oregon Department of Geology and Mineral Industries (DOGAMI) web hazard viewer.
DOGAMI Landslide hazard and risk study of Eugene-Springfield and Lane County, Oregon IMS-
60 Interactive Landslide Hazard Story Map, 2018.
Google Earth, earth.google.com
Lane County Maps GIS Mapping
https://lcmaps.lanecounty.org/LaneCountyMaps/LaneCountyMapsApp/index.html
Review of the DOGAMI Digital Map of the Southern Willamette Valley Benton, Lane, Linn,
Marion, and Polk Counties, Oregon, McClaughry, Wiley, Ferns, and Madin, O-10-03, 2010.
Geology of Oregon, sixth edition by Orr, Orr and Baldwin, 2012.
United States Geologic Survey U.S. Quaternary Faults mapping.
(OSSC 2022), applicable building code criteria.
2.0 GEOLOGIC SETTING
The following sections describe the regional and local site geology and a brief discussion of regional
seismicity.
2.1 Regional Geology
The subject site lies within the southern extents of the Willamette Valley Geomorphic Province (WVGP),
east of the Coast Range and west of the Cascade Mountains Provinces. The WVGP is regional lowland
that extends from just south of Eugene, Oregon to Vancouver, British Columbia. In Oregon, this alluvial
plain is approximately 130 miles long and 20 to 40-miles wide (Orr and Orr, 1996). The WVGP is
drained by the north flowing Willamette River. The Willamette River Valley in the area of the subject
site is believed to be underlain by undifferentiated sedimentary rock from the Oligocene and Eocene
epochs (approximately 28 to 37 million years ago).
Approximately 13,500 years ago the Willamette Valley was cyclically flooded by catastrophic breaks
in the ice dams of Lake Missoula. These flood events filled the valley to an elevation of 350 to 400-
feet before retreating, causing sequences of upward fining deposits of silt and clay that may or may
not still be present in areas, depending on erosion by subsequent creek and river actions and
occasionally leaving behind glacial erratics.
2.2 Site Geology
The Geology of the Southern Willamette Valley Map (McClaughry, Wiley, Ferns, and Madin, O-10-03,
2010), as shown in Figure-2, maps the project location as Quaternary age alluvial fan and terrace
deposits (Qtf) described as semi- to unconsolidated lacustrine and fluvial deposits of clay, silt,
sand, and gravels commonly found along major river channels. The observed site conditions are
consistent with the mapped geology of the site and that of the reginal geologic setting described
above.
Below the undocumented fill on the surface and former clay topsoil zone, the site is underlain by a
medium stiff clay with silt, some fine sand and few rounded gravels were observed below a depth of
about 5-feet BGS. Well logs within ¼-mile of site indicate sands and gravels extend to depths over 80-
feet BGS.
Geotechnical Investigation
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Project Number: 23-109
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2.3 Regional Seismicity
Review of available on-line resources show several mapped faults lie within 2-miles from the site;
however, the activity of these faults is not known and are not listed in the online United States Geologic
Survey U.S. Quaternary Faults database. Although usually small in magnitude, earthquakes do occur
in the area (PNSN & DOGAMI) and seismic activity of significance has been felt in the Willamette Valley
area as evidence by the 1993, 5.7 Richter magnitude Scotts Mills earthquake, the 1993, and most
recently a 4.2 magnitude earthquake about 12-miles east of Eugene in 2015.
The greatest source of potential seismicity that would affect the site is the Cascadia Subduction Zone
(CSZ) located off the coast of Oregon, Washington, and the northern portion of California that has the
potential to produce very large earthquakes at intervals of 300 to 500 years—see the published CSZ
timeline below. The last known mega-thrust CSZ earthquake (Magnitude 9.0 +/-) to take place in the
Pacific Northwest occurred in January of 1700.
3.0 SITE SUBSURFACE CONDITIONS
The analyses, conclusions, and recommendations contained in this report are based on site conditions
as they presently exist and assume that the results from the subsurface explorations presented in
Appendix A are representative of the subsurface conditions throughout the site. If, during
construction the subsurface conditions differ from those encountered in the exploratory borings, BEI
requests that we be informed to review the site conditions and adjust our recommendations, if
necessary.
3.1 Subsurface Soils
BEI personnel observed excavation of six (6) exploratory test pits advanced with rubber-tracked mini-
excavator. Our observations at these locations, shown on Figure-1 are:
Previously placed fill appears to be spread across the majority of the site at thicknesses
ranging from 1.5- to 5-feet. The fill is generally comprised of soft/loose to medium stiff organic
silt with fragments of wood and construction debris.
Geotechnical Investigation
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Project Number: 23-109
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Former Topsoil zone that consisted of a moist, stiff dark brown to gray silty clay with organics
(fine roots and decomposed plant material) was found underlying the fill ranging in thickness
from 1- to 1.5-feet.
Silt/Clay, low plasticity clay and silt with traces of sand and gravels in deeper zones. Soils are
slightly moist, brown, and have a medium stiff consistency.
3.2 Laboratory Testing
Representative soil samples were collected at the site for laboratory testing. In-situ moisture contents
varied from 28% to 44%. Free Swell (Holtz and Gibbs) testing indicated shrink/swell potential ranging
from 20% to 30% which is considered to be low to moderate. During our investigation we did observe
areas of clay that may be more expansive than above values. On-site observation during construction
can identify plastic clays that may be expansive. Recommendations to mitigate the shrink/swell
potential of the site soil are presented below.
3.3 Mapped Soils
The USDA NRCS Web Soil Survey of Lane County Area maps the investigation area soil as being Coburg-
Urban land complex, which is described as well drained alluvium formed on stream terraces. A nearby
well log from the Oregon Department of Geology shows clay with gravels to a depth of 6-feet underlain
by mixed lenses of gravels and sands to a depth of 80-feet. This description is consistent with our
findings at prior investigation sites in the general vicinity of the site where ancient stream channels
and flood events have caused varying depths of fine-grain sediments atop gravels and sands.
3.4 Groundwater
Our site investigation took place towards the end of the wet season and no groundwater was observed
in the test pits; however, some standing water less than 1-foot deep was observed in the on-site
stormwater swales on the west side of the site and the east side of the parking lot. The measured static
level in the Oregon Department of Geology boring located across Main Street from the site was
approximately 10-feet BGS in June 1996.
Perched water lenses can be expected in excavations, as soil strata of varying permeability are
encountered. For excavation work at or below 7-feet BGS, taking place in the wet season, generally
October to late May, we expect that groundwater from either perched lenses or static water tables may
be encountered. Conventional dewatering methods are expected to be adequate to mitigate effects
from groundwater and the presence of groundwater is not anticipated to adversely impact the site
development.
4.0 GEOLOGIC HAZARDS
OSSC 2022 (1803.5.11) required criteria for hazards the geotechnical investigation shall address for
seismic site class designations C through F are listed below.
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Project Number: 23-109
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Slope Instability: The site and its local vicinity are relatively flat and DOGAMI geohazard
viewer maps the site has having a low landslide hazard. In our opinion the risk of landslides
impacting the site is low.
Liquefaction: Liquefaction is caused by a rapid increase in porewater pressure within a
saturated soil that reduces the interparticle friction between soil grains that can lead to the
sudden loss of shear strength within the soil. This can cause a loss of bearing capacity,
densification of subsurface soils that can lead to large surficial settlements, and the migration
of soil particles to the surface in the form of sand boils. Loose, granular sands with a low fine-
grained soil content and a recent depositional history are especially vulnerable to liquefaction.
Saturation is required for a soil to experience liquefaction.
Based on the soil observed in our near surface explorations and nearby well log data to 80-feet
BGS, we do not find evidence that the site is susceptible to liquefaction. In our opinion, the
risk of liquefaction occurring on the site is low.
Expected Earthquake Shaking: The site is mapped within the zone of strong shaking that
would typically be associated with very large earthquakes generated from the CSZ off the
Oregon coastline. The neighboring properties to the north are mapped within a zone of very
strong shaking.
Surface Displacement Due to Faulting or Seismically Induced Lateral Spreading or Lateral Flow:
There are no known faults on the site that could cause large surficial displacements. The site
soils are not at risk for liquefaction that would allow for lateral spreading to occur. Surface
displacement or seismically induced lateral spreading is not expected at the site. The nearest
mapped active faults are mapped as being approximately 20-miles southeast and 50-miles
northwest of the site.
Tsunami/Seiche: The distance of the site from a major water body makes impact to the site
from a seismically induced seiche unlikely.
Total and Differential Settlement: See Section 6.3 below for a discussion of settlement risks
Shrink/swell: As discussed in our “Laboratory Testing” section, our testing found the subgrade
soil has a low to moderate shrink/swell potential. Pockets, or areas of more expansive soil may
be encountered on the site. We have provided generalized shrink/swell mitigation strategies
discussed in applicable sections of this report. In areas intended to support foundations,
removal of most, if not all, of the potentially expansive soil is recommended for bearing
capacity issues due to the soft consistency of the soil
5.0 CONCLUSIONS
Based on our field observations, subsurface explorations, and data analyses, we conclude the site is
feasible for development provided the following recommendations are incorporated into the design
and construction of development.
Geotechnical Investigation
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Project Number: 23-109
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6.0 DESIGN RECOMMENDATIONS
The following sections present site-specific recommendations for site preparation. Earthwork shall be
performed in general accordance with the standard of practice as generally described in Appendix J
of the International Building Code, the Oregon Structural Specialty Code, and as specified in this
report. General material and construction specifications for the items discussed herein are provided
in Appendix B.
The subsurface conditions observed in our site investigation explorations only represent specific
locations on the site. Should soft or unsuitable soils extend to a depth or extent greater than that
described herein, or areas of distinct soil variation be discovered, this office shall be notified to
perform site observations and additional excavation may be required.
6.1 Foundation Subgrade Recommendations
All areas intended to directly, or laterally support structures shall be stripped of vegetation, organic
soil, unsuitable fill, and/or other deleterious material such as moisture softened exposed soil. These
stripping’s shall be removed from the site or reserved for use in landscaping or non-structural areas.
In areas of existing trees, vegetation, or previously placed fill the required depth of site
clearing/stripping may be increased.
Soil conditions were relatively consistent across the site, except for variable fill and underlying topsoil
soil thicknesses. The areas of undocumented fill are unsuitable for the support of building foundations
and we recommend their removal to reduce the risk of total and differential settlement. The depth to
suitable subgrade below the fill and former topsoil layer and is expected to vary from 1.5- to 5-feet
BGS based on our test pits observations. The fill appears thickest in the area south of the access road
from 32nd Street as observed in Test Pit TP-4.
Subgrade suitable for the bearing capacities specified in the next section that exceed the required
depth for foundations may have structurally compacted aggregate placed atop the subgrade.
Engineered fill pads should extend at least half the thickness of the aggregate pad beyond the outside
edge of footings, not to exceed 24-inches. Prior to placement of engineered fill materials, a site visit
by the Geotechnical Engineer of Record (GER), or designated representative should be scheduled to
confirm the suitability of the exposed subgrade material.
The structural fill supporting both wall and column footings requires adequate lateral support. In
areas, such as near the stormwater swales where the existing ground surface slopes away, the depth
of footings may be required to increase to maintain at least a downward 1:1 (H:V) bearing splay line
extended outward that does not intersect an open face of a slope, or unsuitable material such as
previously placed fill or organics.
6.2 Bearing Capacity
Based on the anticipated foundation loads, BEI recommends excavation to native, medium stiff, brown
silt/clay subgrade generally expected to be about 2-feet BGS except in the locations such as TP-4, where
undocumented fill was observed to a depth of 5-feet. In the TP-4 area, fill may be removed to a depth
that allows ripping, moisture conditioning and compaction of any remaining fill in-place. Typically
heavy construction equipment can compact a thickness of about 1.5-feet in-place; however, the GER
Geotechnical Investigation
Main & S. 32nd Streets, Springfield, Oregon
Project Number: 23-109
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shall assess conditions in the field at the time of construction. Material containing a high percentage
of organics, debris, or other unsuitable material will require removal and replacement with compacted
aggregate.
A minimum of 12-inches of compacted crushed aggregate is recommend atop all approved subgrade
and will provide an allowable bearing capacity of 1,500 psf that may be increased by 1/3 for short
term loading, such as wind or seismic events.
6.3 Settlement
The estimated settlement of foundation designed for the 1,500 psf bearing is not expected to exceed
1-inch total or ½-inch differentially for equivalently loading column footings a span of at least 20-feet
apart.
6.4 Interior Slab-On-Grades
Interior slabs are not anticipated to be load bearing and therefore excavation to native subgrade is not
required. However, organic topsoil shall be removed and the subgrade ripped, moisture conditioned,
and compacted in-place prior to placement of at least 8-inches of compacted, crushed aggregate. In
areas of potentially expansive soil, or plastic clay, placement of an additional 6-inches of engineered
fill thickness consisting of compacted 3-inch diameter open-graded angular stone is recommended. If
soft or saturated subgrade is encountered, over-excavation and replacement with engineered fill will
be required. As mentioned above, material encountered with a high percentage of organics, debris or
other unsuitable material will require over-excavation to remove the unsuitable material and replace
with compacted aggregate.
The required subgrade preparation for structural slabs is similar to that described in Section 6.2 of
this report.
6.5 Friction Coefficient and Lateral Earth Pressures
Although not anticipated for this project, the following parameters are given based on an internal
angle of friction of 20° for the near-surface soils encountered. These values assume that there are no
hydrostatic pressures or surcharge loads on the walls and the retained soil is not inclined. If these
assumptions change during the course of the project, our office should be notified so we can
reevaluate our recommendations.
1. The coefficient of friction for concrete poured neat against undisturbed native soil is 0.25 and
if poured atop a minimum thickness of 12-inches of compacted aggregate placed on the on-
site material the coefficient is 0.4.
2. The passive earth pressure is 200 pcf.
3. The active earth pressure is 50 pcf unrestrained walls and the at rest earth pressure for a
restrained wall is 70 pcf.
6.6 Site Parking and Vehicle Route Subgrade Recommendations
The depth to suitable subgrade for roadway and parking structural sections is below the topsoil about
2-feet BGS and at least 12- to 18-inches of the subgrade shall be compacted in-place with adequate
equipment after ripping and moisture conditioning as necessary.
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Prior to placing compacted crushed aggregate for the roadway structural section, the exposed
subgrade shall be approved by the GER, or approved representative. Proof-rolling with a loaded 10
cubic yard haul truck, or equivalent vehicle, shall be conducted on the prepared subgrade and any
observed areas of deflection under load shall be corrected prior to placement of aggregate. See Section
6.7 Pavement Design Recommendations for aggregate section and pavement thicknesses
recommendations. Should grading plans require engineered fill, see Section 6.8 for engineered fill
recommendations.
The presence of expansive soil beneath pavements can reduce its life. If encountered in pavement
areas, we recommend that the soils not be allowed to dry out and should be covered with crushed
rock in a timely manner to prevent moisture swings. Soils can be periodically wetted to maintain its
in-situ moisture content if excavation takes place during the drier months. Sources of water should be
prevented from saturating subgrades or becoming trapped below pavement surfaces.
6.7 Pavement Design
Our recommendations for parking and driveway improvements used the guidance of the 1993
AASHTO Guide for Design of Pavement Structures and the 2003 revised Asphalt Pavement Design
Guide, published by the Asphalt Pavement Association of Oregon, and calculated pavement structural
sections based on similar soil profiles. Pavement area subgrade shall be prepared in accordance with
Section 6.6 Site Parking and Vehicle Route Subgrade Recommendations of this report. Our design
assumed a pavement life of 20 years, a resilient modulus of 3,000 psi for unimproved subgrade, a 75
percent reliability, and no growth. Table 1 below, shows the recommended pavement and aggregate
base rock sections for the site. The base rock sections below are for the native clay soil underlying the
topsoil zone on the site, in areas of previously placed fill over-excavation and additional compacted
aggregate thickness should be expected.
Table 1: Recommended Standard Pavement Sections
Pavement Area Asphalt thickness
(in.)
PCC Thickness
(in.)
Aggregate Base Rock Section
(in.)
Vehicle Areas & Parking 4 - 12 (minimum)
Truck Routes 6 8 12 (minimum asphalt)
10 (PCC)
The base rock shall be compacted to at least 90% relative compaction as determined by ASTM
1557/AASHTO T-180 (modified Proctor). Proof rolls with a loaded 10 cubic yard haul truck shall be
observed on the compacted base rock and any areas of deflection under wheel loads shall be corrected
by over-excavation replacing subgrade material with additional compacted aggregate. The compaction
and proof roll testing of the base rock shall be conducted prior to placement of asphalt concrete (AC)
or Portland cement concrete (PCC) pavement (if applicable).
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This recommended section is intended to be the minimum acceptable values. Additional section
thicknesses will be required if construction traffic is allowed to drive on pavements. We can provide
revised pavement section recommendations if the anticipated construction traffic loads and number
of loadings are provided to us.
6.8 Structural Fill
All engineered fill placed on the site shall consist of homogenous material and shall meet the following
recommendations.
The recommended compaction level for crushed aggregate and soil fill is 90% of the maximum
dry density as determined by ASTM D-1557 (modified Proctor).
Prior to placement onsite, the aggregate or soil to be used shall be approved by the GER. If no
recent Proctor curve (moisture-density relationship) is available for the material, a sample will
be required for testing to determine the maximum dry density and optimum moisture content
of the aggregate or fill material. Use of the onsite soils for fill will require careful moisture
conditioning and appropriate compaction equipment selection. Compaction of clayey soils
during the wet season (November through May) will be difficult, if not impossible, to achieve
due to insitu moisture contents being significantly higher than optimum moisture contents.
Compaction shall be measured by on site testing with a nuclear densometer (ASTM D-6938),
or sand cone method (ASTM D-1556) on structural fill with thicknesses in excess of 12-inches.
If compaction testing is not feasible for any onsite or imported material due to factors such
as oversize rock content or variable material, proof rolls with a fully loaded 10 cubic yard
haul-truck or equivalent equipment shall be observed at regular intervals. Any observed areas
of excessive yielding or rutting will require removal and replacement with granular fill or
moisture conditioning and recompaction.
The structural fill shall be moisture conditioned to within +/- 2% of optimum moisture
content and compacted in lifts with loose thicknesses not exceeding 8-inches. Periodic visits
to the site to verify lift thickness, source material, and compaction effort shall be conducted
by the GER, or designated representative, and documented.
Utility trenches excavated to depths below the top of the subgrade elevation shall be
backfilled with approved material and compacted to at least 90% of the maximum dry density.
Controlled Low Strength Material (CLSM) may be used to fill foundation excavations without
requiring aggregate compaction inside excavations. CLSM material shall meet the
specifications in Section 00442 of the 2021 Oregon Standard Specifications for Construction
by Oregon Department of Transportation (ODOT).
6.9 Seismic Site Classification
Based on the soil properties encountered in our explorations and from nearby well logs, we
recommend a Seismic Site Class C (Table 20.3-1 ASCE 7-16) for the design of site structures.
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7.0 CONSTRUCTION CONSIDERATIONS
7.1 Wet Weather/Dry Weather Construction Practices
The near surface soils, if left exposed to prolonged precipitation, will become saturated and soften.
As previously mentioned, expansive soils are present in areas of the site and will need careful
consideration to mitigate their effects. Exposed subgrade soils in structural areas should not be
allowed to dry out, or allow standing water to pool over them. Subgrade soil that will be below
foundations, slabs, and pavements shall be covered with compacted aggregate in a timely manner after
excavation to minimize moisture fluctuations. BEI recommends that foundation subgrade preparation
and general site earthwork be performed during the dry season—generally May through October.
Construction during the wet season may require special drainage considerations, such as covering of
excavations, pumping to mitigate standing water in footing excavations, or over-excavation of
moisture softened soils. Construction traffic should not be allowed to drive directly on exposed
subgrades. Construction traffic routes will also be more susceptible to “pumping” and rutting during
the wet season and will likely require thicker rock sections.
7.2 Excavations
Unsupported trench, or excavation walls will likely stay vertical temporarily, if zones of seepage are
encountered the stability of the vertical walls will decrease. We recommend filling all excavations with
engineered fill, or CLSM as soon as possible following excavation to suitable subgrade. This may
require scheduling and staging of work.
We recommend that shoring or benching be employed for in-ground excavation and utility work.
Utilities deeper than 5-feet BGS will likely require shoring or laying back of sidewalls at a slope of 1:1
(H:V). The site soils are classified as typically OSHA Type A or, B type soils. Heavy equipment or stored
materials should not be stored within 10-feet of open excavations. Permanent slopes (fill or cut) should
not exceed a gradient of 2H:1V unless specifically evaluated for stability.
7.3 Site Drainage
Alteration of existing grades for this project will likely change drainage patterns that should not
adversely affect adjacent properties. Perimeter landscape and hardscape grades shall be sloped away
from foundations and water shall not be allowed to pond adjacent to footings during or after
construction.
7.4 Expansive Soil
Areas of potentially expansive soil, or soil having moderate to high shrink/swell ratings shall be
covered with the recommended engineered fill section in a timely manner following excavation. So
that the moisture content of the subgrade soil is not allowed to fluctuate. Sources of water should be
prevented from saturating subgrades or becoming trapped below pavement surfaces and drainage
structures should also not be located adjacent to pavement or other hardscapes.
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7.5 Geotechnical Construction Site Observations
Periodic site observations by a geotechnical representative of BEI are recommended during the
construction of the project; the specific phases of construction that should be observed are shown in
the following table.
Recommended Construction Phases to be Observed by the Geotechnical Engineer
At completion of subgrade excavation Subgrade observation by the geotechnical
engineer before aggregate placement.
Imported fill material Observation of material or information on
material type and source.
Placement or Compaction of fill material Observation by geotechnical engineer or test
results by qualified testing agency.
8.0 REPORT LIMITATIONS
This report has presented BEI’s site observations and research, subsurface explorations, geotechnical
engineering analyses, and recommendations for the proposed site development. The conclusions in
this report are based on the conditions described in this report and are intended for the exclusive use
of Westgate Plaza LLC and their designated representatives for use in design and construction of the
development described herein. The analysis and recommendations may not be suitable for other
structures or purposes.
Services performed by the geotechnical engineer for this project have been conducted with the level
of care and skill exercised by other current geotechnical professionals in this area. No warranty is
herein expressed or implied. The conclusions in this report are based on the site conditions as they
currently exist and it is assumed that the limited site locations that were physically investigated
generally represent the subsurface conditions at the site.
This report represents our findings and should site development or site conditions change, or if a
substantial amount of time goes by between our site investigation and site development, we reserve
the right to review this report for its applicability and adjust our recommendations. If you have any
questions regarding the contents of this report, please contact our office.
310 5th STREET, SPRINGFIELD, OREGON 9747732nd AND MAIN STREET SPRINGFIELD, OREGONSITE EXPLORATION MAP - MIDTOWN PLAZAFIGURE-1MARCH 24, 2023PROJECT NO. 23-109INDICATES APPROXIMATELOCATION OFTEST PITSCALE: 1:60 (11x17)NOTE: PRELIMINARY SITE PLAN PROVIDED BY A&O ENGINEERING, LLC, 2023LEGENDIT-1INDICATES APPROXIMATELOCATION OF INFILTRATIONTESTTP-1TP-6TP-5TP-1TP-2TP-3TP-4IT-1IT-2
APPENDIXAPPENDIXAPPENDIXAPPENDIX AAAA
Test PitTest PitTest PitTest Pit Log Summaries, Well Logs, and Log Summaries, Well Logs, and Log Summaries, Well Logs, and Log Summaries, Well Logs, and NRCS NRCS NRCS NRCS
SoilSoilSoilSoil SurveySurveySurveySurvey
Depth1
2
3
4
5
6
7
8
9
10
11
12
13
14
15 GraphicMaterial Description
Fill: Medium stiff organic SILT (OL) with rounded gravel and occasional
debris
Medium stiff, dark brown CLAY (CL) with silt, moist
Medium stiff, light brown clayey SILT (ML), moist SamplePocket Pen. (tsf)Free SwellMoisture Content: ⊗PL and LL: ⬤━∎
Borehole ID: TP-1
Sheet 1 of 1
Client:A&O Engineering LLC Project Name:Midtown Plaza
Project Number:23-109 Project Location:South 32nd and Main Springfield, Oregon
Date Started:Mar 24 2023 Completed:Mar 24 2023 Logged By:MWR Checked By:RJD
Drilling Contractor:JT's Bobcat Service Latitude:44.045281 Longitude:-122.982358 Elevation:
Drilling Method:Test Pit Excavation Ground Water Levels
Equipment:Rubber Tracked Mini-Excavator
Hammer Type:
Notes:
10 20 30 40 50 60 70 80 90
Set infiltration test pipe in bottom of excavation
No Groundwater Observed
Depth1
2
3
4
5
6
7
8
9
10
11
12
13
14
15 GraphicMaterial Description
Fill: Medium dense, rounded GRAVEL (GP) with organic silt and wood
fragments
Medium stiff, dark gray CLAY (CL), moist
Medium stiff/dense, silty SAND (SM) and rounded gravel (GP), moist SamplePocket Pen. (tsf)2.50
1.50 Free SwellMoisture Content: ⊗PL and LL: ⬤━∎
Borehole ID: TP-2
Sheet 1 of 1
Client:A&O Engineering LLC Project Name:Midtown Plaza
Project Number:23-109 Project Location:South 32nd and Main Springfield, Oregon
Date Started:Mar 24 2023 Completed:Mar 24 2023 Logged By:MWR Checked By:RJD
Drilling Contractor:JT's Bobcat Service Latitude:44.045281 Longitude:-122.982358 Elevation:
Drilling Method:Test Pit Excavation Ground Water Levels
Equipment:Rubber Tracked Mini-Excavator
Hammer Type:
Notes:
10 20 30 40 50 60 70 80 90
Slight Seepage from 8 to 9.5 feet
Depth1
2
3
4
5
6
7
8
9
10
11
12
13
14
15 GraphicMaterial Description
Fill: Medium dense, 3/4-inch aggregate with 1 1/2-inch stone, rounded
gravel, occasional debris
Stiff, dark brown and gray CLAY (CL) with scattered rounded gravel, moist
Medium stiff, light brown and gray CLAY (CL), with silt, 3-inch piece of
burned wood at 4-feet
Medium stiff, light brown clayey SILT (ML) with scattered rounded gravel SamplePocket Pen. (tsf)3.50
1.50 Free SwellMoisture Content: ⊗PL and LL: ⬤━∎
Borehole ID: TP-3
Sheet 1 of 1
Client:A&O Engineering LLC Project Name:Midtown Plaza
Project Number:23-109 Project Location:South 32nd and Main Springfield, Oregon
Date Started:Mar 24 2023 Completed:Mar 24 2023 Logged By:MWR Checked By:RJD
Drilling Contractor:JT's Bobcat Service Latitude:44.045281 Longitude:-122.982358 Elevation:
Drilling Method:Test Pit Excavation Ground Water Levels
Equipment:Rubber Tracked Mini-Excavator
Hammer Type:
Notes:
10 20 30 40 50 60 70 80 90
Slight Seepage from perched lens at 3 feet
Depth1
2
3
4
5
6
7
8
9
10
11
12
13
14
15 GraphicMaterial Description
Fill: Soft, dark brown organic SILT (OL) with gravel and wood debris,
decrease in gravel content at 2.5-feet
Medium stiff, light brown clayey SILT (ML), moist SamplePocket Pen. (tsf)Free SwellMoisture Content: ⊗PL and LL: ⬤━∎
Borehole ID: TP-4
Sheet 1 of 1
Client:A&O Engineering LLC Project Name:Midtown Plaza
Project Number:23-109 Project Location:South 32nd and Main Springfield, Oregon
Date Started:Mar 24 2023 Completed:Mar 24 2023 Logged By:MWR Checked By:RJD
Drilling Contractor:JT's Bobcat Service Latitude:44.045281 Longitude:-122.982538 Elevation:
Drilling Method:Test Pit Excavation Ground Water Levels
Equipment:Rubber Tracked Mini-Excavator
Hammer Type:
Notes:
10 20 30 40 50 60 70 80 90
No groundwater observed
Depth1
2
3
4
5
6
7
8
9
10
11
12
13
14
15 GraphicMaterial Description
Fill: Medium dense/stiff, brown silt and clay mixed with rounded rock, some
roots
Medium stiff, dark brown SILT (OL) with organics, moist (former topsoil zone)
Medium stiff, light brown clayey SILT (ML), moist, with trace fine grain sand,
sand, moisture content increases with depth SamplePocket Pen. (tsf)Free SwellMoisture Content: ⊗PL and LL: ⬤━∎
Borehole ID: TP-5
Sheet 1 of 1
Client:A&O Engineering LLC Project Name:Midtown Plaza
Project Number:23-109 Project Location:South 32nd and Main Springfield, Oregon
Date Started:Mar 24 2023 Completed:Mar 24 2023 Logged By:MWR Checked By:RJD
Drilling Contractor:JT's Bobcat Service Latitude:44.045281 Longitude:-122.982358 Elevation:
Drilling Method:Test Pit Excavation Ground Water Levels
Equipment:Rubber Tracked Mini-Excavator
Hammer Type:
Notes:
10 20 30 40 50 60 70 80 90
Seepage at 8 feet
Depth1
2
3
4
5
6
7
8
9
10
11
12
13
14
15 GraphicMaterial Description
Fill: Medium stiff organic SILT (OL) with rounded gravel and occasional
debris
Medium stiff, dark brown CLAY (CL), moist with silt
Medium stiff, light brown clayey SILT (ML), moist SamplePocket Pen. (tsf)Free SwellMoisture Content: ⊗PL and LL: ⬤━∎
Borehole ID: TP-6
Sheet 1 of 1
Client:A&O Engineering LLC Project Name:Midtown Plaza
Project Number:23-109 Project Location:South 32nd and Main Springfield, Oregon
Date Started:Mar 24 2023 Completed:Mar 24 2023 Logged By:MWR Checked By:RJD
Drilling Contractor:JT's Bobcat Service Latitude:44.045281 Longitude:-122.982358 Elevation:
Drilling Method:Test Pit Excavation Ground Water Levels
Equipment:Rubber Tracked Mini-Excavator
Hammer Type:
Notes:
10 20 30 40 50 60 70 80 90
Set Infiltration Test pipe at bottom of excavation
No Groundwater Observed
Soil Map—Lane County Area, Oregon
(Westgate Plaza LLC)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
5/25/2023
Page 1 of 3487669048767704876850487693048770104877090487669048767704876850487693048770104877090501070501150501230501310501390501470501550501630501710501790
501070 501150 501230 501310 501390 501470 501550 501630 501710 501790
44° 2' 50'' N 122° 59' 12'' W44° 2' 50'' N122° 58' 38'' W44° 2' 34'' N
122° 59' 12'' W44° 2' 34'' N
122° 58' 38'' WN
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 10N WGS84
0 150 300 600 900
Feet
0 50 100 200 300
Meters
Map Scale: 1:3,440 if printed on A landscape (11" x 8.5") sheet.
Soil Map may not be valid at this scale.
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Map Unit Polygons
Soil Map Unit Lines
Soil Map Unit Points
Special Point Features
Blowout
Borrow Pit
Clay Spot
Closed Depression
Gravel Pit
Gravelly Spot
Landfill
Lava Flow
Marsh or swamp
Mine or Quarry
Miscellaneous Water
Perennial Water
Rock Outcrop
Saline Spot
Sandy Spot
Severely Eroded Spot
Sinkhole
Slide or Slip
Sodic Spot
Spoil Area
Stony Spot
Very Stony Spot
Wet Spot
Other
Special Line Features
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:20,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: Lane County Area, Oregon
Survey Area Data: Version 21, Mar 13, 2023
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Jun 12, 2019—Jun
19, 2019
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Soil Map—Lane County Area, Oregon
(Westgate Plaza LLC)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
5/25/2023
Page 2 of 3
Map Unit Legend
Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI
32 Coburg-Urban land complex 48.8 88.5%
76 Malabon-Urban land complex 6.3 11.5%
Totals for Area of Interest 55.1 100.0%
Soil Map—Lane County Area, Oregon Westgate Plaza LLC
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
5/25/2023
Page 3 of 3
Lane County Area, Oregon
32—Coburg-Urban land complex
Map Unit Setting
National map unit symbol: 2369
Elevation: 100 to 1,300 feet
Mean annual precipitation: 30 to 60 inches
Mean annual air temperature: 50 to 55 degrees F
Frost-free period: 160 to 235 days
Farmland classification: Farmland of statewide importance
Map Unit Composition
Coburg and similar soils:55 percent
Urban land:30 percent
Minor components:4 percent
Estimates are based on observations, descriptions, and transects of
the mapunit.
Description of Coburg
Setting
Landform:Stream terraces
Landform position (three-dimensional):Tread
Down-slope shape:Linear
Across-slope shape:Linear
Parent material:Loamy alluvium over clayey alluvium
Typical profile
H1 - 0 to 18 inches: silty clay loam
H2 - 18 to 53 inches: silty clay
H3 - 53 to 65 inches: fine sandy loam
Properties and qualities
Slope:0 to 3 percent
Depth to restrictive feature:More than 80 inches
Drainage class:Moderately well drained
Capacity of the most limiting layer to transmit water
(Ksat):Moderately high (0.20 to 0.57 in/hr)
Depth to water table:About 18 to 30 inches
Frequency of flooding:None
Frequency of ponding:None
Available water supply, 0 to 60 inches: High (about 11.0 inches)
Interpretive groups
Land capability classification (irrigated): 2w
Land capability classification (nonirrigated): 2w
Hydrologic Soil Group: C
Ecological site: R002XC006OR - Stream Terrace Group
Forage suitability group: Moderately Well Drained < 15% Slopes
(G002XY004OR)
Map Unit Description: Coburg-Urban land complex---Lane County Area, Oregon Westgate Plaza LLC
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
5/25/2023
Page 1 of 2
Other vegetative classification: Moderately Well Drained < 15%
Slopes (G002XY004OR)
Hydric soil rating: No
Description of Urban Land
Interpretive groups
Land capability classification (irrigated): None specified
Land capability classification (nonirrigated): 8
Hydric soil rating: No
Minor Components
Conser
Percent of map unit:4 percent
Landform:Stream terraces
Hydric soil rating: Yes
Data Source Information
Soil Survey Area: Lane County Area, Oregon
Survey Area Data: Version 21, Mar 13, 2023
Map Unit Description: Coburg-Urban land complex---Lane County Area, Oregon Westgate Plaza LLC
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
5/25/2023
Page 2 of 2
APPENDIX B:
Recommended Earthwork Specifications
GEOTECHNICAL SPECIFICATIONS
General Earthwork
1. All areas where structural fills, fill slopes, structures, or roadways are to be constructed shall be
stripped of organic topsoil and cleared of surface and subsurface deleterious material, including
but limited to vegetation, roots, or other organic material, undocumented fill, construction debris,
soft or unsuitable soils as directed by the Geotechnical Engineer of Record. These materials shall
be removed from the site or stockpiled in a designated location for reuse in landscape areas if
suitable for that purpose. Existing utilities and structures that are not to be used as part of the
project design or by neighboring facilities, shall be removed or properly abandoned, and the
associated debris removed from the site.
2. Upon completion of site stripping and clearing, the exposed soil and/or rock shall be observed by
the Geotechnical Engineer of Record or a designated representative to assess the subgrade
condition for the intended overlying use. Pits, depressions, or holes created by the removal of root
wads, utilities, structures, or deleterious material shall be properly cleared of loose material,
benched and backfilled with fill material approved by the Geotechnical Engineer of Record
compacted to the project specifications.
3. In structural fill areas, the subgrade soil shall be scarified to a depth of 4-inches, if soil fill is used,
moisture conditioned to within 2% of the materials optimum moisture for compaction, and
blended with the first lift of fill material. The fill placement and compaction equipment shall be
appropriate for fill material type, required degree of blending, and uncompacted lift thickness.
Assuming proper equipment selection, the total uncompacted thickness of the scarified subgrade
and first fill lift shall not exceed 8-inches, subsequent lifts of uncompacted fill shall not exceed 8-
inches unless otherwise approved by the Geotechnical Engineer of Record. The uncompacted lift
thickness shall be assessed based on the type of compaction equipment used and the results of
initial compaction testing. Fine-grain soil fill is generally most effectively compacted using a
kneading style compactor, such as a sheeps-foot roller; granular materials are more
effectively compacted using a smooth, vibratory roller or impact style compactor.
4. All structural soil fill shall be well blended, moisture conditioned to within 2% of the material’s
optimum moisture content for compaction and compacted to at least 90% of the material’s
maximum dry density as determined by ASTM Method D-1557, or an equivalent method. Soil fill
shall not contain more than 10% rock material and no solid material over 3-inches in diameter
unless approved by the Geotechnical Engineer of Record. Rocks shall be evenly distributed
throughout each lift of fill that they are contained within and shall not be clumped together in such
a way that voids can occur.
5. All structural granular fill shall be well blended, moisture conditioned at or up to 3% above of the
material’s optimum moisture content for compaction and compacted to at least 90% of the
material’s maximum dry density as determined by ASTM Method D-1557, or an equivalent
method. 95% relative compaction may be required for pavement base rock or in upper lifts of the
granular structural fill where a sufficient thickness of the fill section allows for higher compaction
percentages to be achieved. The granular fill shall not contain solid particles over 2-inches in
diameter unless special density testing methods or proof-rolling is approved by the Geotechnical
Engineer of Record. Granular fill is generally considered to be a crushed aggregate with a fracture
surface of at least 70% and a maximum size not exceeding 1.5-inches in diameter, well-graded
with less than 10%, by weight, passing the No. 200 Sieve.
6. Structural fill shall be field tested for compliance with project specifications for every 2-feet in
vertical rise or 500 cy placed, whichever is less. In-place field density testing shall be performed
by a competent individual, trained in the testing and placement of soil and aggregate fill
placement, using either ASTM Method D-1556/4959/4944 (Sand Cone), D-6938 (Nuclear
Densometer), or D-2937/4959/4944 (Drive Cylinder). Should the fill materials not be suitable for
testing by the above methods, then observation of placement, compaction and proof-rolling with a
loaded 10 cy dump-truck, or equivalent ground pressure equipment, by a trained individual may
be used to assess and document the compliance with structural fill specifications.
Utility Excavations
1. Utility excavations are to be excavated to the design depth for bedding and placement and shall
not be over-excavated. Trench widths shall only be of sufficient width to allow placement and
proper construction of the utility and backfill of the trench.
2. Backfilling of a utility trench will be dependent on its location, use, depth, and utility line material
type. Trenches that are required to meet structural fill specifications, such as those under or near
buildings, or within pavement areas, shall have granular material strategically compacted to at
least the spring-line of the utility conduit to mitigate pipeline movement and deformation. The
initial lift thickness of backfill overlying the pipeline will be dependent on the pipeline material,
type of backfill, and the compaction equipment, so as not to cause deflection or deformation of the
pipeline. Trench backfill shall conform to the General Earthwork specifications for placement,
compaction, and testing of structural fill.
Geotextiles
1. All geotextiles shall be resistant to ultraviolet degradation, and to biological and chemical
environments normally found in soils. Geotextiles shall be stored so that they are not in direct
sunlight or exposed to chemical products. The use of a geotextile shall be specified and shall meet
the following specification for each use.
Subgrade/Aggregate Separation
Woven or nonwoven fabric conforming to the following physical properties:
Minimum grab tensile strength ASTM Method D-4632 180 lb
Minimum puncture strength (CBR) ASTM Method D-6241 371 lb
Elongation ASTM Method D-4632 15%
Maximum apparent opening size ASTM Method D-4751 No. 40
Minimum permittivity ASTM Method D-4491 0.05 s-1
Drainage Filtration
Woven fabric conforming to the following physical properties:
Minimum grab tensile strength ASTM Method D-4632 110 lb
Minimum puncture strength (CBR) ASTM Method D-6241 220 lb
Elongation ASTM Method D-4632 50%
Maximum apparent opening size ASTM Method D-4751 No. 40
Minimum permittivity ASTM Method D-4491 0.5 s-1
Geogrid Base Reinforcement
Extruded biaxially or triaxially oriented polypropylene conforming to the following physical properties:
Peak tensile strength
lb/ft
Tensile strength at 2% strain
ASTM Method D-6637
ASTM Method D-6637
925
300
lb/ft
Tensile strength at 5% strain
ASTM Method D-6637
600
lb/ft Flexural Rigidity ASTM Method D-1388 250,000 mg-cm
Effective Opening Size ASTM Method D-4751 1.5x
rock size