2006 Geotechnical Report.BAN 2 tl X119
DEVELOPMENT SERVICES
COUNTER
Geotechnical Report
Phillip and Sybil Butler
731 Bell Street
Edmonds, Washington
Project 1434-01
November 7, 2006
Prepared for:
Phillip and Sybil Butler
731 Bell Street
Edmonds, WA 98020
Prepared by:
The Galli Group
5034 — 18`h Avenue NE
Seattle, WA 98105
206-525-5097
Table of Contents
SECTION
PAGE
1.0
INTRODUCTION.....................................................................................................1
2.0
PROJECT DESCRIPTION.......................................................................................I
3.0
SITE
FEATURES AND ANALYSES......................................................................2
3.1
SURFACE CONDITIONS AND GEOLOGY..................................................2
3.2
SITE SOIL AND GROUNDWATER CONDITIONS......................................3
3.3
SLOPE STABILITY ANALYSES....................................................................4
4.0
CONCLUSIONS AND RECOMMENDATIONS...................................................4
4.1
SITE GRADING AND TEMPORARY EROSION CONTROL ......................5
4.1.1 Temporary Erosion Control Measures.....................................................5
4.1.2 Temporary Excavations and Shoring.......................................................6
4.1.3 Backfill and Compaction.........................................................................6
4.2
FOUNDATIONS...............................................................................................7
4.2.1 Spread Footings.......................................................................................7
4.2.2 Pier and Grade Beam Foundation System..............................................7
4.2.3 Soldier Piles and Timber Lagging...........................................................8
4.3
SLAB -ON -GRADE FLOORS...........................................................................10
4.4
SLOPE STABILIZATION MEASURES..........................................................10
4.5
DRAINAGE RECOMMENDATIONS.............................................................11
4.6
PERMANENT EROSION CONTROL AND SLOPE PROTECTION ............11
5.0
ADDITIONAL
SERVICES AND LIMITATIONS..................................................12
5.1
ADDITIONAL SERVICES...............................................................................12
5.2
LIMITATIONS..................................................................................................12
LIST OF FIGURES:
Figure 1
Vicinity Map
Figure 2
Site Features
Figure 3
Slope Stability Analyses, Section A -A'
Figure 4
Generalized Cross Section B-B'
Figure 5
Earth Pressure Diagram
Fiugre 6
Soldier Pile Shoring Schematic
APPENDIX
Logs of Borings
Slope Stability Analyses
Geotechnical Report
Phillip and Sybil Butler
731 Bell Street
Edmonds, Washington
November 7, 2006
1.0 INTRODUCTION
The Galli Group performed a geotechnical investigation of the property located at 731 Bell Street
in Edmonds, Washington. The purpose of our investigation was to identify the subsurface soil
conditions on the site and to provide recommendations for foundation support on the site.
This geotechnical report summarizes observations from our research and subsurface exploration
performed for the above referenced property. it also presents our recommendations for the
geotechnical design elements of the project.
2.0 PROJECT DESCRIPTION
The project site is located along a north -south trending ridge north of the downtown area of
Edmonds (see Vicinity Map, Figure 1). The parcel is situated north of Bell Street and above a
topographic flat bench to the west of the parcels. The owner intends to adjust the lot line
common to the existing two parcels and construct a single family dwelling on the lower, westerly
lot. Utilities to the site will be provided from Bell Street and via the unimproved alley to the
north. The parcel is classified as an ESA (Environmentally Sensitive Area) due to steep slopes.
The topography and other site features are shown on Figure 2, Site Features. It should be noted
that the topographic survey shown was conducted prior to construction of the existing residence
at 731 Bell Street.
The existing residence at 731 Bell Street consists of a two-story residence with afull daylight
basement that opens out toward the slope on the west. The existing residence is approximately
64 feet from the far westerly lot line of the two parcels. Proposed improvements call for
adjusting the lot line between the two lots and constructing a new single-family residence on the
lower lot. The proposed residence might consist of a daylight basement that opens out toward
the west, two levels of wood -framed construction above the basement, and a driveway from Bell
Street. At the time of our investigation, the lot line adjustment and proposed footprint of the
residence was not finalized.
Site construction will include excavating approximately 250 to 300 yards of material for the
residence. The anticipated foundation system will be pile and grade beam foundations.
Retaining structures approximately 11 high will be required along the common lot line to support
the hillside above the lot. Access to the site will be from Bell Street to the main level of the
residence. Setbacks are recommended to protect the residences from the influence of shallow
sloughing of the existing slope.
3.0 SITE FEATURES AND ANALYSES
The results of our site investigation and analyses are presented in the sections below. Based
upon our investigation and research, geotechnical elements that must be addressed in moving
forward with the planned improvements include the following:
Preventing settlement of the foundation system constructed on the loose soils
Supporting the proposed residence below the loose fill soil on deep foundations and thus
increasing the stability of the slope system
Constructing a shoring or permanent soldier pile wall system to allow excavation of the
proposed daylight basement while stabilizing upslope properties
Protecting the steep slope from erosion and drainage -related degradation or failures
These issues are discussed and addressed in the sections below.
3.1 SURFACE CONDITIONS AND GEOLOGY
The existing site consists of a slope that descends northwesterly at an overall declination of
approximately 30 percent toward the topographically flat area occupied by the Civic Center
playfield. The slope in the vicinity of the Butler parcels is interrupted by a bench supporting the
existing 731 Bell Street residence and a bench approximately 20 to 30 feet wide on the lower
adjacent lot. The bench on the lower lot is on the order of 14 vertical feet below the likely access
from Bell Street. The slope above the site is terraced by means of small rockeries. The slope
below the parcel declines at approximately 65 percent and has low brush on the slope.
We did not encounter evidence of significant slope failures on the site. Erosion of the surficial
sand unit is evident on steeper portions of the slope resulting in gradual downslope migration of
the material within the upper few feet. This erosion appears to be exacerbated by the burrowing
of small animals. Significant erosion could easily occur if the slope was denuded or left
unprotected by vegetation.
During our site reconnaissance it was evident that the surficial soils on the upper part of the slope
consist primarily of sand. The soil exposed at the base of the slope was also quite sandy. We did
not encounter evidence of springs erupting on the hillside.
1434Butler RPT 2 The Calli Group
Geologic maps of the area indicate that the lot is likely underlain by advance outwash and
transitional beds (Geologic Man of Echnonels East and Pcrri 0j'the F,chnomis Mw Qua(bangles,
James P. Minard, 1983). Advance outwash deposits tend to consist of sand and pebbly gravel
deposited in meltwater streams in front of the advancing glacier. The transitional beds tend to
consist of beds of silt, clay, and fine sand deposited between the most recent glacial advances.
Both deposits were subsequently overridden by the advancing ice and tend to appear compact
and relatively stable except where exposed on steep hillsides. Sometimes the contact between
the two units or the transitional beds can form weak planes that result in slope movement under
extreme conditions.
3.2 SITE SOIL AND GROUNDWATER CONDITIONS
During our subsurface investigation on October 6, 2006, we drilled three exploratory borings at
locations shown on Figure 2, Site Features. A geotechnical engineer from The Galli Group
monitored the drilling. Soil samples were retrieved and classified in the field by a Galli Group
engineer. Generalized cross sections of the project site are provided in Figures 3 and 4. The logs
of our borings are provided in Appendix A.
In all of the borings we encountered a unit of loose to medium dense sand with silt overlying
dense sand. The dense sand was underlain by clayey silt and fine sandy silt at depth shown in the
following table. We interpreted the uppermost loose sandy material as fill or colluvium. The
primary unit of medium dense to dense SAND with silt and gravel, we interpreted as Glacial
Outwash, underlain by very stiff clayey silt or Transitional Beds (see Figure 3).
TABLE 1
Depth of Fill and Depth to Water Table
Boring
B-1
Elev. of Top
of Boring
110,
Thickness
of fill
9'
Elev. Water
Table
88.5'
Depth to Qtb
??
Location of Boring
North end of bench, toe of
upper slope
B-2
126'
9'
97.5 perched
33
South side of lot near R/W
89'
.5'
and proposed drive?
31'
B-3
109,
6.5'
85.5'
South side of bench near
top of lower slope
We encountered water in all three borings at depths on the order of about 21.5 feet to 28.5 feet.
Based upon the underlying soil stratigraphy we anticipate that the water table is perched above
the clayey silt unit (or Transitional Beds). Water might also penetrate the transitional beds by
means of sand seams or beds such as encountered in B-2 at 89' elevation. It seems likely that the
water table could fluctuate with varying seasonal runoff and infiltration. It should be noted that
1434BAIer 14-11 3 The Calli Group
our borings were conducted at a time where regional perched groundwater conditions would be
fairly low.
3.3 SLOPE STABILITY ANALYSES
Using the slope stability program XSTABL, we performed a slope stability analysis of the
hillside in its current condition. We modeled the hillside based upon the soils encountered in our
boring logs (see Figure 3). The core of the slope did not experience failure during the Nisqually
quake, and does not evidence slope movement under static conditions. For existing conditions
the factor of safety (FOS) against slope failure for static conditions was calculated to be 1.2 for
the lower sloe and 1.7 for the upper slope; for dynamic or seismic conditions it was calculated to
be 1.1 for the lower slope and 1.12 for the upper slope. The type of failure represented by these
numbers was a shallow failure within the uppermost loose soils, impacting the soils within about
5 feet of the top of the slope.
The proposed construction removes soil at the toe of the upper slope creating a bench above the
lower slope for the proposed building. A soldier pile retaining wall will support the upper slope
and could possibly provide the foundations wall for the east side of the proposed residence as
well. The proposed residence would be supported on a pier and grade beam system that transfers
the loads to the medium dense to dense sand unit below the fill. We modeled the slope based
upon the final configuration, and calculated the FOS (Factor of Safety) for the static and seismic
conditions to be 2.2 and 1.3 respectively.
In our analyses all of the failures appeared to be shallow colluvial failures or skin slides within
the uppermost fill unit. None of the most critical failure surfaces appeared to intersect the
underlying transitional beds. Based upon our analyses the core of the hillside appeared stable
and the most likely impacts to the steep slope would be shallow skin slides or surficial erosion.
A summary of the slope stability analyses is provided on Figure A-5 in the appendix.
4.0 CONCLUSIONS AND RECOMMENDATIONS
The site appears underlain by medium dense to dense glacial outwash blanketed by a unit of
loose sandy fill or colluvium (slopewash from the last thousand years and recent construction
activity.) The core of the hillside appeared stable. Proposed improvements including excavation
could destabilize the upper slope unless shoring is provided. Foundations supported on the loose
fill soil would likely settle and could be impacted by shallow sloughing of the outboard edges of
the steep slope unless appropriately setback from the top of the slope or supported on piers.
We recommend the following measures to accompany site development and construction of the
proposed residence:
Support the proposed residence on pier and grade beam system
Construct a soldier pile shoring wall to maintain slope stability of the upper slope during
construction.
1434Butler R'T 4 The Gal Ii Group
Provide a minimum of 10 feet setback from the top of the steep slope for structures not
supported on deep foundations and provide edge treatment of the top of the slope to
prevent erosion and shallow sloughing of the slope.
Provide a landscape plan to stabilize the slope faces against surficial erosion.
The sections below address these geotechnical issues and other aspects of site development for
the proposed project. Provided the recommendations provided in this report are followed during
design and construction of the residence, the proposed addition may proceed safely under
appropriate geotechnical supervision.
4.1 SITE GRADING AND TEMPORARY EROSION CONTROL
4.1.1 Temporary Erosion Control Measures
The site contains sandy soils that present severe erosion potential if left unprotected during
construction. Best Management Practices commonly observed should be employed during
construction. We anticipate these will include the following:
A construction entrance should be provided to the site in the vicinity of the proposed
driveway. The entrance should be constructed from 4" — 6" quarry spalls placed over a
woven geotextile fabric such as Mirafi 500X. The entrance can be top dressed with
smaller rock once the excavation and foundation work is completed.
2. It is important to avoid tracking sediment onto the roadway. The contractor should
monitor the tracking of sediment from the site and clean up as necessary. Sand and silt
tracked from the site should be removed or cleaned by the contractor.
3. The existing catch basins in the street should be protected by installing filter fabric in the
grates or silt sacks. During heavy runoff it will be necessary to monitor the fabric in the
drains to avoid clogging or overtopping the grates.
4. Pushing the spoils downslope shall not be permitted. A silt fence or straw wattles should
be installed at the lower reaches of the disturbed area on the slope to prevent migration of
the soil downslope:
5. Spoils should be removed immediately from the site or protected during wet weather by
use of plastic sheeting. Generally stockpiles should not remain uncovered for more than
2 days during the wet season or 5 days during the drier summer months.
6. Once the shoring, piers, foundation system and retaining elements are installed, the areas
disturbed by the construction activity must be restored immediately. We recommend
seeding and mulching the area with a suitable mix for the final use and then covering all
slopes or areas adjacent to the steep slope with an erosion control mat such as SC150 by
North American Green staked to the ground surface.
7. The contractor should monitor the performance of the erosion control measures and
contact the geotechnical engineer if the measures do not provide the intended function.
1434Butler RPT 5 The Calli Group
4.1.2 Temporary Excavations and Shoring
The proposed footprint will require excavations approximately 8 feet deep and possibly more if a
full height shoring wall rather than stepped walls are constructed. The temporary cuts exceeding
four feet must be sloped or shored to prevent unraveling.
Temporary unsupported excavations should be shaped or benched to protect workers below.
Temporary construction cuts should be inclined no greater than 1 H: IV (Horizontal to Vertical)
overall. If the lowermost soil appears dense or cemented then the first 4 feet of the excavation
may be cut near vertical as shown in schematic below. Maintaining safe open excavations for
workers and protecting the exposed cuts shall be the ongoing responsibility of the contractor.
The entire temporary excavation must be contained within the property limits unless permission
is obtained from the adjacent property owners or City of Edmonds in the case of the right-of-way.
The initial excavation of the site should be monitored by the geotechnical engineer to verify that
the lowermost soils are suitable for the recommended cuts.
Shape bad<slope so that
inclination does
not exceed 1.5 H:1 V
Shape benches so that
overall inclination does
not exceed 1 H:1 V
aw,
:: • /1111 K. Pl •
4.1.3 Backfill and Compaction
r
Imported fill soils or site soils approved by the geotechnical engineer used as backfill behind
walls and under slabs should be moisture conditioned to within 3 percent of optimum moisture
content, placed in loose, horizontal lifts less than 6 inches in thickness, and compacted to at least
95 percent of the maximum dry density, as determined using ASTM D1557 (Modified Proctor).
The 95 percent compaction criteria should apply to any material intended to support pavement or
structures. In areas not constructed as fill slopes or not intended to support pavement or
structures, fill material should be placed in loose lifts less than 12 inches in thickness and
1434Butler RPf 6 The Gal li Croup
compacted to at least 90 percent of the maximum dry density. City of Seattle Standard "Type
17" material has been used with great success in a wide variety of weather conditions for
structural fill.
We anticipate that the site material can be used for compacted fill. A sample should be retrieved
and sent to the lab to develop a compaction curve prior to placing the backfill soil so that
compaction may be accurately monitored where needed. The loose soil should be compacted to
form a nonyielding subgrade prior to placing base material for the driveway slab or basement
slabs.
4.2 FOUNDATIONS
4.2.1 Spread Footings
The residence on the site must be supported on drilled piers. However., appurtenant structures
such as landscape walls may be supported on spread footings with the recognition that minor
settlement might occur. Spread footings shall not be utilized unless the geotechnical engineer
can first verify the bearing capacity and confirm that the soil is native undisturbed soil. Provided
the soil is native undisturbed medium dense soil, the following recommendations may be used
for design of the footings:
1. An allowable bearing pressure of 1500 psf may be used for footings bearing on
undisturbed compact sandy soil. This may be increased by 1/3 for temporary loads such
as wind loads or seismic loads.
2. The footing area must be free from loose or wet soil prior to placing reinforcing or
pouring concrete. The geotechnical engineer should verify the bearing.
3. If suitable bearing is not found within the uppermost four feet of excavation we
recommend installing pin piles and grade beams or pile caps instead of spread footings.
4.2.2 Pier and Grade Beam Foundation System
A unit of loose sand blankets the site with silt in the uppermost 7 to 12 feet. This loose soil will
tend to consolidate over time and the settlement could result in loss of support for the
foundations. In order to prevent differential settlement of the foundation system, we recommend
supporting the proposed structure on a pile and grade beam system. This will also improve
stabilization of the lower slope.
Drilled piers are installed by augering holes into soil capable of supporting the proposed
structure. These holes are then filled with concrete and reinforcing steel. The reinforcing
scheme includes grade beams that tie the structure together and translate loads typically carried
by the footings to the piles. Settlement beneath the grade beam is inconsequential since the load
is borne by the piles.
If this approach is utilized we recommend that the following design parameters be incorporated
into the design and construction:
1434Butler RPT 7 The Gail! Croup
• The piles should be a minimum diameter of 18 inches and must penetrate into the
medium dense sand unit a minimum distance of 16 feet from existing grade (to elevation
91 on Figure 4, Generalized Cross Section.
• A licensed structural engineer must design the reinforcing cage or structural members for
the shafts, the pile caps and grade beams, and the connections to other structural
members.
• We anticipate that 18-inch diameter drilled shafts properly reinforced and drilled 16 feet
into the underlying medium dense sand unit will support a working load of 21 kips. This
includes a factor of safety of 3.
• For 24-inch diameter drilled shafts and embedded 16 feet below grade assume a working
capacity of 28 kips with a FOS of 3.
• Concrete should be tremmied into the base of the hole through a tremmie hose after the
hole has been thoroughly "cleaned" of loose material by rotating the auger without down
pressure. The auger should be withdrawn slowly while being rotated in a positive
direction.
• Preparation of work areas for equipment and maintaining safe work conditions and slope
conditions shall be the sole responsibility of the contractor. We recommend creating a
work and staging area for the pile contractor. Tailings from the holes and mud must be
contained and then removed from the site. Appropriate sedimentation measures must be
installed prior to commencing drilling.
4.2.3 Soldier Piles and Timber Lagging
Excavation of the east side of the proposed building footprint will remove support for the upper
slope and could potentially destabilize the hillside. We recommend constructing a soldier pile
shoring wall along the back of the excavation to support the hillside during construction. A
soldier pile wall consists of drilled sh�ii'ts or augered holes advanced to a predetermined depth
and then filled with grout. A steel beam acting as the reinforcing element is lowered into the wet
grout and set into final position. As the excavation proceeds, horizontal timber lagging (typically
4x6 members) are placed between the flanges of the beam after the concrete is chipped away.
This leaves a vertical wall supported steel H-piles embedded in the concrete in the ground. For
deeper excavations horizontal members called tiebacks are used to add lateral resistance.
Tiebacks are often used when walls approach 11 to 13 feet high.
The following preliminary recommendations are supplied for the shoring wall. These
recommendations should be revisited in light of the final design. Terracing the excavation,
removing support below the wall, and final height of the wall are factors that could alter the
recommendations.
We recommend the following for the design of the shoring system:
1) The cantilevered soldier pile shoring system should consist of drilled shafts, grouted and
reinforced with steel beams. The shafts shall consist of structural concrete placed up to at
least the bottom of the proposed excavation and lean mix concrete above that grade. As
143413utler FPT 8 The Gal ll Group
the site is excavated, the lean mix is chipped away and lagging is placed between the
flanges of the H-beams.
2) The drilled piers should be advanced to a depth sufficient to provide support for the
anticipated excavation depth. We anticipate drilling depths on the order of 35 feet from
existing grade for an 11-foot shoring wall to achieve the required embedment and
support. These depths were based upon cantilevered piles spaced 6 feet apart and
correspond to exposed wall heights of 11 feet. The diameter of the hole was assumed to
be 24 inches. The structural engineer should provide detailed calculations for piles after
selecting precise locations, height, spacing, diameter of the hole, reinforcing elements,
and material strength.
3) Based upon the SPT values obtained during drilling, and the consistency of the
underlying soil encountered, and the need to retain the slope above, we have
recommended active earth pressures of 47 pcf (pounds per cubic foot equivalent fluid
weight) for design of the shoring system. This force should be considered to act for the
width of the pile spacing above the excavated depth. Below the final excavation depth it
should be applied only to one pile diameter.
4) Passive resistance may be calculated based upon an equivalent fluid pressure of the sandy
silt and the dense glacial soils of 400 pcf. The passive resistance should be applied to 2
pile diameters in the medium dense soils. If the excavation is temporarily cut below the
base of the shoring wall (for a second tier of basement retaining wall or at outboard edge
of the slope) then the passive resistance should be reduced to 215 pcf to accommodate a
declining slope condition.
5) Surcharge loads within 10 feet of the wall such as traffic loads, material stockpiles,
equipment or structure loads should be included in the design of the wall. It does not
appear that adjacent structures will impact the loading on the wall.
6) A pressure equivalent to 70 percent of the design active pressure may be used to size the
timber lagging, provided the pile spacing does not exceed 8 feet. Pressure treated timber
lagging should be placed as excavation proceeds. Voids behind the lagging should be
filled with free draining material such as pea gravel. Maximum height of the exposed cut
should not exceed 4 feet before placing lagging.
7) To design for temporary equipment loads near the wall, we recommend including a
uniform lateral load equivalent to 20 percent of the area load (in psf) from the equipment
acting along the upper 2/3 of the wall. To avoid having to design for these equipment
loads, all heavy equipment should be kept at least 8 feet from the top of the wall.
The Galli Group should review the design and should monitor the installation of the soldier pile
retaining wall. Please contact us if you need additional clarification regarding the intent of this
section. A schematic showing the lateral earth pressures for design of the soldier pile wall and
drainage features is provided in Figure 5, Lateral Earth Pressures. The soldier pile walls may be
incorporated into the design of the basement retaining walls and/or faced with concrete upon
completion. The design of the wall and facing is up to the structural engineer and architect.
143413utler FPT 9 The Galli Group
The design of the shoring wall and the piles shall be the responsibility of the structural engineer,
utilizing the design parameters provided in this report. Additional requirements related to
concrete strength, grout, reinforcing elements, construction monitoring, and material
specifications should be provided by the structural engineer. A schematic of the soldier pile wall
is provided in Figure 6.
4.3 SLAB -ON -GRADE FLOORS
Reinforced concrete floors that are beneath structures ringed with perimeter footings, grade
beams, or walls can be supported on a 6-inch drain rock layer underlain by structural fill placed
over properly prepared subgrade soils. For slabs on grade, we recommend that granular import
be placed as soon as the subgrade is prepared to protect the subgrade soil. The subgrade must
first be graded level and compacted uniformly to an unyielding condition with a vibratory
compactor prior to placing additional material.
The following recommendations are provided for slabs constructed on the unyielding subgrade
surface:
A six-inch layer of clean crushed rock (1 /2" to 3/4" clean crushed rock works well)
should be placed over the structural fill or native subgrade to provide a positive capillary
moisture break and uniform slab support. The capillary break is especially helpful in
areas with floors that will not "breathe" (such as tile or laminate).
2. An impermeable membrane, such as 6-mil plastic sheeting, should be placed over the
crushed rock layer to further prevent upward migration of moisture vapor into and
through the concrete slab. The membrane is not necessary for exterior slabs.
3. In order to protect the membrane and provide more uniform curing of the slab, it is
advisable to place one to two inches of clean sand on top of the membrane. The sand
should be moistened slightly prior to placing concrete.
We recommend that the contractor use deformed reinforcing steel for slab reinforcement rather
than welded wire fabric. A minimum reinforcement scheme would be #3 or # 4 bars, 18 inches
on center, both ways. Fibermesh may be used to help decrease drying shrinkage cracks, however
it is not a replacement for structural reinforcing.
4.4 SLOPE STABILIZATION MEASURES
Wherever possible a 10-foot building setback should be maintained from the top of the lower
slope. This allows room to add slope stabilization measures at the top of the slope to minimize
sloughing and erosion. Once the final site plan is developed we can provide recommendations
for slope stabilization measures. Some of these measures might include:
Temporary erosion control mats on the slope during construction followed by seeding,
mulching, and mats after construction is completed.
Permanent landscape plan for the slope including groundcover and plants that establish
extensive root systems.
1434Butler FPT 10 The Celli Group
Potentially incorporating geowebs or cells to prevent eroding the loose surficial sandy
soils while plant cover is established.
Short pin pile retaining walls to contain the soils at the top of the slope. The purpose is to
maintain support of site features at the top of the slope and to prevent degradation of the
slope by human traffic along the eastern and western side of the home. If this alternative
is selected, The Galli Group can provide additional recommendations as an addendum to
this report.
4.5 DRAINAGE RECOMMENDATIONS
We recommend capturing all surface water runoff and directing the runoff to a tightlined pipe
toward a suitable collection system or storm drain. We understand that there is a storm drain in
the unimproved alley right-of-way that can be used for the proposed residence. Although the site
is sandy, we do not recommend infiltration or splash blocks on the site since these might increase
risk of erosion or slope movement on the hillside.
4.6 PERMANENT EROSION CONTROL AND SLOPE PROTECTION
The existing slope face is sparsely covered with blackberries. We anticipate that the top of the
slope will be disturbed during construction where the bench is created for the daylight basements.
Retaining walls to handle the grade breaks from the benches will also disturb the top of the slope.
Following construction the slope should be stabilized to prevent erosion. We recommend the
following:
Seed the slope face with rapidly growing and rooting groundcover such as clover and
grass seed. If there is no organic content to the exposed soil, additional mulch should be
added at this time.
2. Cover the seeded area and exposed soil with erosion control mat such as SC150 by North
American Green. Staked according to the manufacturer's recommendations.
3. The owner should consult with a landscape professional to get recommendations for
native plants that can establish root systems and provide additional erosion protection for
the slope face. We can provide a landscaper recommendation if needed. The additional
vegetation can be planted through the erosion control mat once it is installed.
4. Straw wattles staked to the slope can protect areas where the slope is oversteepened or
areas immediately below specific plantings. The location is dependent upon field
conditions and planting, but can be monitored by the geotechnical engineer or landscape
consultant.
5. If the construction is not completed by mid -September, the slope must be seeded and an
erosion control blanket must be staked on the face to protect the slope over the wet
season.
6. Additional recommendations can be provided once the project commences and the timing
of the construction is established.
1434Butler FPT 11 The Gal Ii Group
5.0 ADDITIONAL SERVICES AND LIMITATIONS
5.1 ADDITIONAL SERVICES
Additional services by the geotechnical engineer are important to help insure that report
recommendations are correctly interpreted in final project design and to help verify compliance
with project specifications during the construction process. For this project we anticipate
additional services might include the following:
I . Consult with structural engineer, architect, and contractor regarding the geotechnical
elements of the project and design of the foundation elements..
2. Review final design and construction drawings for conformance with geotechnical
recommendations.
3. Monitor excavation of building footprints and verify soil conditions where foundation
elements are planned
4. Monitor installation of pier and grade beam system.
5. Monitor construction of shoring wall
6. Monitor drainage installation, and erosion control measures.
7. Periodic construction field reports, as requested by the client and required by the building
department.
We would provide these additional services on a time -and -expense basis in accordance with our
Standard Fee Schedule and General Conditions already in place for this project.
5.2 LIMITATIONS
This geotechnical investigation was planned and conducted in accordance with generally
accepted engineering standards practiced presently within this geographic area. Geotechnical
investigations performed by these standards reveal with reasonable regularity soils that are
representative of subsurface conditions throughout the site under consideration.
Recommendations contained in this report are based upon the assumption that soil conditions
encountered in explorations are representative of actual conditions throughout the building site.
However, inconsistent conditions can occur between exploratory borings or test pits and not be
detected by a geotechnical study. If, during construction or subsequent exploration, subsurface or
slope conditions are encountered which differ from those anticipated based upon results of this
investigation, The Galli Group should be notified so that we can review and revise our
recommendations where necessary. If conditions change prior to the proposed construction, we
should be consulted so that we may alter our recommendations if necessary.
This report is prepared for the exclusive use of the owner or the owner's consultants for specific
application on this project at this particular site. Copies of this report should be made available
to the design team, and should be included with the contract drawings issued to the contractor.
Our report, conclusions, and interpretations should not be construed as a warranty of the
subsurface conditions on the site and should not be applied to neighboring sites. No warranty,
expressed or implied is made. We recommend that geotechnical observation and testing be
143413utler RPT 12 The Gal Ii Group
provided during the construction phases to verify that the recommendations provided in this
report are incorporated into the actual construction.
Respectfully submitted,
THE GALLI GROUP
A! V 4/' Mwlw�� 2
Paul L. Stoltenberg, P.E.
Project Geotechnical Engineer
1434BLdier FPT 13 The Galli Group
�� T
Miradrain G100N
Shotcrete Wall
Notes:
1. Active pressure acts on one pile diameter below grade
2. Passive pressure acts on two pile diameters
3. Assume 200 psf uniform load for traffic loading if applicable
4. See Text for pressure variations with backslope or declining slope
Perf Pipe to daylight
Appendix A: Logs of Exploratory Borings and Test Rats
Unified Soil Classification System; from American Society for Testing and Materials, 1985
MAJOR DIVISIONS
GROUP
SYMBOL
GROUP NAME
GRAVEL
MORE THAN 50%OF
CLEAN GRAVEL
GW
WELL -GRADED GRAVEL, FINE TO
COARSE GRAVEL
GP
POORLY -GRADED GRAVEL
COARSE FRACTION
COARSE
RETAINED ON NO.4
GRAVEL WITH
GM
SILTY GRAVEL
GRAINED SOILS
MORE THAN 50%
RETAINED ON
N0.200 SIEVE
SIEVE
FINES
GC
CLAYEY GRAVEL
WELL -GRADED SAND, FINE TO
COARSE SAND
SAND
MORE THAN 50%OF
COARSE FRACTION
PASSES NO.4 SIEVE
CLEAN SAND
SW
SP
POORLY -GRADED SAND
SAND WITH FINES
SM
SILTY SAND
SC
CLAYEY SAND
SILT AND CLAY
LIQUID LIMIT LESS
INORGANIC
ML
SILT
CL
CLAY
FINE GRAINED
SOILS
MORE THAN 50%
PASSES NO.200
SIEVE
THAN 50
ORGANIC
OL
ORGANIC SILT, ORGANIC CLAY
SILT AND CLAY
LIQUID LIMIT 50 OR
MORE
INORGANIC
MH
SILT OF HIGH PLASTICITY, ELASTIC
SILT
CH
CLAY OF HIGH PLASTICITY, FAT
CLAY
ORGANIC
OH
ORGANIC CLAY, ORGANIC SILT
HIGHLY
ORGANIC SOILS
PT
PEAT
FOR SAND AND GRAVELS
FOR SILTS AND CLAYS
DENSITY
STANDARD PENETRATION RESISTANCE
(SPT) BLOWS/FT.
VERY LOOSE
0 4
LOOSE
4 10
MEDIUM DENSE
10 30
DENSE
30 50
VERY DENSE
> 50
CONSISTENCY
STANDARD PENETRATION RESISTANCE
(SPT) BLOWS/FT.
VERY SOFT
0 2
SOFT
2-4
MEDIUM STIFF
4 8
STIFF
8 -16
VERY STIFF
16 32
HARD
> 32
TheGdII Group Figure A-1
0
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