HomeMy WebLinkAboutCT 02-25; NorthPark at La Costa; Final Compaction Report of Grading; 2004-07-30FINAL COMPACTION REPORT OF GRADING
TRADITIONS AT LA COSTA, LOTS 1 THROUGH 14
CARLSBAD, SAN DIEGO COUNTY, CALIFORNIA
HALLMARK COMMUNITIES
SAN DIEGO, CALIFORNIA 92121
W.O. 3975-B-SC JULY 30,2004
10675 SORRENTO VALLEY ROAD, SUITE 200-6
GROUNDWATER
Groundwater was not encountered during grading of this portion of the project and
therefore should not affectthe proposed site development, provided our recommendations
for landscape maintenance and planting are implemented.
As a result of the contrasting nature of the onsite earth materials, the possibility of future,
localized perched water conditions and minor seepage cannot be precluded, and should
be anticipated. Should such conditions become apparent within the project in the future,
additional recommendations for mitigation may be provided upon request.
GEOTECHNICAL ENGINEERING
PreDaration of Existina Ground
1.
2.
Prior to grading, the major surfcia1 vegetation was stripped and hauled offsite.
Removals, consisting of topsoil/colluvium and near-surface weathered artificial fill,
were performed to the minimum depths and lateral extent recommended in the
approved referenced reports by GSI (see Appendix A). The approximate
elevations of the removal bottoms and limits are indicated on Plates 1 and 2.
3. Subsequent to the above removals, the exposed subsoils were scarified to a depth
of about 12 inches, moisture conditioned as necessary to at least optimum
moisture content, then compacted to a minimum relative compaction of 90 percent
of the laboratory standard.
Fills placed on sloping surfaces steeper than 5:l (horizonta1:vertical [h:v]), as
indicated by pre-existing topography, were keyed and benched into competent
soil material or bedrock.
4.
5. All processing of original ground was observed by a representative of GSI.
Fill, consisting of native and import soils, was placed in 6- to 8-inch lifts, watered, and
mixed to achieve at least optimum moisture conditions. The material was then compacted,
using earth moving equipment, to a minimum relative compaction of 90 percent of the
laboratory standard. It should be noted that approximately 3 feet of fill was placed on
Lots 1 through 12, and materials greater than 12 inches in diameter may have been
routinely placed below 10 feet from finish grade during the previous grading
(Benton, 1974). However, oversized materials may not be precluded from occurring,
and/or excavation difficulties may be encountered at depths as shallow as 3 feet, or less,
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below finish grade. Thus, the potential for excavation difficulties and oversized materials
should be disclosed to all homeowners and other interested parties.
Slopes
1.
2.
1.
2.
3.
All slopes are considered grossly and surficially stable and should remain so
under normal conditions of care, maintenance, and rainfall. As a result of the
nature of the onsite materials, slopes may be subject to minor erosion/gullying
under concentrated flow from irrigation and/or misdirected surface drainage.
Landscaping of these slopes should be implemented as soon as possible to
mitigate such conditions. Other recommended mitigation measures are presented
in the “Development Criteria” section of this report.
Compaction on the face of fill slopes was achieved by back-rolling and/or track
walking.
FIELD TESTING
Field density tests were performed using nuclear densometer ASTM Test
Methods D-2922 and D-3017 and sand cone ASTM Test Method ASTM D-1556.
The test results taken during grading are presented in the attached Table 1, and
the locations of the tests taken during grading are presented on Plates 1 and 2.
Field density tests were taken at periodic intervals and random locations to check
the compactive effort provided by the contractor. Where test results indicated less
than optimum moisture content, or less than 90 percent relative compaction in fills,
the contractor was notified and the area was reworked until retesting indicated at
least optimum moisture and a minimum relative compaction of 90 percent were
attained. Based upon the grading operations observed, the test results presented
herein are considered representative of the compacted fill.
Visual classification of the soils in the field was the basis for determining which
maximum density value to use for a given density test.
TRANSITION LOT
Lot 14 contains a plan transition between cut and fill. As requested by the Client, Lot 14
was completed to the grades specified on the grading plans for “Northpark at La Costa”
(Snipes-Dye Associates, 2003). Therefore, the plan transition, which occurs at the
northeast end of Lot 14, was not mitigated during this phase of site grading. If any future
settlement-sensitive structures are planned, GSI should be contacted regarding earthwork
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and foundation recommendations for Lot 14. All other transition lots were overexcavated
in general accordance with the approved geotechnical reports(see Appendix A) for the site.
SOIL TYPE
A - Olive Green, SANDY CLAY
LABORATORY TESTING
MAXIMUM DENSITY MOISTURE CONTENT
(PCF) (PERCENT)
112.0 17.5
Maximum Densitv Testinq
The laboratory maximum dry density and optimum moisture content for the major soil
types within this construction phase were determined according to test method
ASTM D-1557. The following table presents the results:
B - Light Brown, SANDY CLAY 11 6.0 14.0
ExDansion Index
Expansive soil conditions have been evaluated for the site. Representative samples of the
soils exposed at current finish grades were recovered for expansion index testing.
Expansion Index (EL) testing was performed in general accordance with Standard 18-2
of the Uniform Building Code ([UBC], International Conference of Building Officials [ICBO],
1997). Based on the test results obtained of 91 to 1 15, the expansive potentials of the soils
within the subject lots are classified as high (i.e., high expansive potentials 91 to 140). The
test results are included in Table 2 following the text of this report.
SulfatelCorrosion Testinq
Representative samples of the materials exposed at the current grades onsite have been
collected for soluble sulfate testing. The testing included determination of solublesulfates,
pH, and saturated resistivity. Results indicate that site soils are very strongly acidic
(pH=4.9) with respect to acidity and are severely corrosive to ferrous metals. Severely
corrosive soils are considered to be below 1,000 ohm-cm.
Based upon the soluble sulfate results of 0.1 46 percent by weight in soil, the site soils have
a moderate corrosion potential to concrete (UBC range for moderate sulfate exposure is
0.10 to 0.20 percentage by weight soluble [SO4] in soil.
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The use of Type II concrete with an altered water-cementious ratio, per the UBC, is
required; however, corrosion protection for buried metallic structures, including rebar,
piping, etc., has been evaluated by a corrosion engineer. The soil corrosivity study report
is include in this report in Appendix B. Test results are also included in Table 2, following
the text of this report.
Atterberq Limits
Tests were performed on soils exhibiting high expansion potentials (Le., E.I. between
91 and 140), per 1997 UBC requirements, to evaluate the liquid limit, plastic limit, and
plasticity index in general accordance with ASTM D-4318. The test results are presented
below:
CONCLUSIONS AND RECOMMENDATIONS
Unless superceded by recommendations presented herein, the conclusions and
recommendations contained in GSI reports (see Appendix A) remain pertinent and
applicable. All settlement-sensitive improvements should be minimally designed to
accommodate 1 inch of differential settlement in 40 feet (1/480) and the expansive and
corrosive soil conditions outlined herein.
FOUNDATION RECOMMENDATIONS
General
The foundation design and construction recommendations are based on laboratory testing
and engineering analysis of onsite earth materials exposed at current finish grades by GSI.
Recommendations for PT systems are provided in the following sections. The foundation
systems may be used to support the proposed structures, provided they are founded in
competent bearing material. The proposed foundation systems should be designed and
constructed in accordance with the guidelines contained in the UBC (ICBO, 1997).
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Foundation Desian
1.
2.
3.
4.
5.
6.
The foundation systems should be designed and constructed in accordance with
gridlines presented in the latest edition of the UBC.
An allowable bearing value of 1,500 pounds per square foot (ps9 may be used for
design of footings which maintain a minimum width of 12 inches(continuous) and
24 inches square (isolated), and a minimum depth of at least 12 inches into the
properly compacted fill. The bearing value may be increased by one-third for
seismic or other temporary loads. This value may be increased by 20 percent for
each additional 12 inches in depth to a maximum of 2,500 psf. No increase in
bearing value for increased footing width is recommended.
For lateral sliding resistance, a 0.35 coefficient of friction may be utilized for a
concrete to soil contact when multiplied by the dead load.
Passive earth pressure may be computed as an equivalent fluid having a density of
250 pounds per cubic foot (pc9 with a maximum earth pressure of 2,500 psf.
When combining passive pressure and frictional resistance, the passive pressure
component should be reduced by one-third.
All footings should maintain a minimum -/-foot horizontal distance between the base
of the footing and any adjacent descending slope, and minimally comply with the
guidelines depicted on Figure No. 18-1-1 of the UBC (ICBO, 1997).
Construction
The following foundation construction recommendations are presented as a minimum
criteria from a soils engineering viewpoint. The current near finish pad grade soils
expansion potentials are generally in the high expansive potential (E.I. 91to 90).
POST-TENSIONED SLAB SYSTEMS
Recommendations for utilizing PT slabs on the site is based on soil parameters exposed
at current near finish grade on the site. The recommendations presented below should be
followed in addition to those contained in the previous sections, as appropriate. The
information and recommendations presented below in this section are not meant to
supersede design by a registered structural engineer or civil engineer familiar with PT slab
design. PT slabs should be designed using sound engineering practice and be in
accordance with local and/or national code requirements.
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From a soil expansion/shrinkage standpoint, a common contributing factor to distress of
structures using PT slabs is fluctuation of moisture in soils underlying the perimeter of the
slab, compared to the center, causing a "dishing" or "arching" of the slabs. To mitigate this
possibility, a combination of soil presaturation and construction of a perimeter cut-off wall
should be employed.
Perimeter cut-off walls should be a minimum of 18 inches deep for highly expansive soils.
The cut-off walls may be integrated into the slab design or independent of the slab and
should be a minimum of 5 inches thick. The vapor barrier should be covered above and
below with a 2-inch layer of sand (4 inches total), to aid in uniform curing of the concrete;
and it should be adequately sealed to provide a continuous water-proof barrier under the
entire slab.
Specific soil presaturation is not required; however, the moisture content of the subgrade
soils should be equal to or greater than the soils' optimum moisture content to a depth of
18 inches below grade, for highly expansive soils.
Post-Tensionina Institute (PTI) Method
PT slabs should have sufficient stiffness to resist excessive bending due to non-uniform
swell and shrinkage of subgrade soils. The differential movement can occur at the corner,
edge, or center of slab. The potential for differential uplift can be evaluated using the
1997 UBC Section 181 6, based on design specifications of the PTI. The following table
presents suggested minimum coefficients to be used in the PTI design method.
I Thornthwaite Moisture Index -20 inchedyear
Correction Factor for lrriqation I 20 inches/year 11 ~ Depth to Constant Soil Suction 7 feet I
Constant soil Suction (p9
Modulus of Subgrade Reaction (pci)
The coefficients are considered minimums and may not be adequate to represent worst
.case conditions such as adverse drainage and/or improper landscaping and maintenance.
The above parameters are applicable provided structures have positive drainage that is
maintained away from structures. Therefore, it is important that information regarding
drainage, site maintenance, settlements, and effects of expansive soils be passed on to
future owners.
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Based on the above parameters, the following values were obtained from figures or tables
of the 1997 UBC Section 181 6. The values may not be appropriate to account for possible
differential settlement of the slab due to other factors. If a stiffer slab is desired, higher
values of ym may be warranted.
~~~
EXPANSIVE INDEX HIGH OF SOIL SUBGRADE EXPANSION
(per the UBC) (EL= 91 TO 130)
1 e, center lift 5.5 feet
e, edge lift 4.5 feet
y edge liR
II y, center liR I 3.5 inch It
1.2 inch
Deepened footings/edges around the slab perimeter must be used to minimize
non-uniform surface moisture migration (from an outside source) beneath the slab. An
edge depth of 18 inches should be considered a minimum. The bottom of the deepened
footingledge should be designed to resist tension, using cable or reinforcement per the
structural engineer. Other applicable recommendations presented under conventional
foundation and the California Foundation Slab Method should be adhered to during the
design and construction phase of the project.
WALL DESIGN PARAMETERS CONSIDERING EXPANSIVE SOILS
Conventional Retainina Walls
The design parameters provided below assume that very low expansive soils
(Class 2 permeable filter material or Class 3 aggregate base) gr native materials are used
to backfill any retaining walls. The type of backfill (Le., select or native), should be
specified by the wall designer, and clearly shown on the plans. Building walls, below
grade, should be water-proofed or damp-proofed, depending on the degree of moisture
protection desired. The foundation system for the proposed retaining walls should be
designed in accordance with the recommendations presented in this and preceding
sections of this report, as appropriate. Footings should be embedded a minimum of
18 inches below adjacent grade (excluding landscape layer, 6 inches) and should be
24 inches in width. There should be no increase in bearing for footing width.
Recommendationsfor specialty walls (Le., crib, earthstone, geogrid, etc.) can be provided
upon request, and would be based on site specific conditions.
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Restrained Walls
Any retaining walls that will be restrained prior to placing and compacting backfill material
or that have re-entrant or male corners, should be designed for an at-rest equivalent fluid
pressure (EFP) of 65 pcf, plus any applicable surcharge loading. For areas of male or
re-entrant corners, the restrained wall design should extend a minimum distance of twice
the height of the wall (2H) laterally from the corner.
Cantilevered Walls
The recommendations presented below are for cantilevered retaining walls up to 10 feet
high. Design parameters for walls less than 3 feet in height may be superceded by City
and/or County standard design. Active earth pressure may be used for retaining wall
design, provided the top of the wall is not restrained from minor deflections. An equivalent
fluid pressure approach may be used to compute the horizontal pressure against the wall.
Appropriate fluid unit weights are given below for specific slope gradients of the retained
material. These do not include other superimposed loading conditions due to traffic,
structures, seismic events or adverse geologic conditions. When wall configurations are
finalized, the appropriate loading conditionsfor superimposed loads can be provided upon
request.
RETAINED MATERIAL FLUID WEIGHT P.C.F. FLUID WEIGHT P.C.F.
Level' 38
Retaininq Wall Backfill and Drainage
Positive drainage must be provided behind all retaining walls in the form of gravel wrapped
in geofabric and outlets. A backdrain system is considered necessary for retaining walls
that are 2 feet or greater in height. Details 1,2, and 3, present the backdrainage options
discussed below. Backdrains should consist of a 4-inch diameter perforated PVC or ABS
pipe encased in either Class 2 permeable filter material or %inch to3/4-inch gravel wrapped
in approved filter fabric (Mirafi 140 or equivalent). For low expansive backfill, the filter
material should extend a minimum of 1 horizontal foot behind the base of the walls and
upward at least 1 foot. For native backfill that has up to medium expansion potential,
continuous Class 2 permeable drain materials should be used behind the wall. This
material should be continuous (i.e., full height) behind the wall, and it should be
constructed in accordance with the enclosed Detail 1 (Typical Retaining Wall Backfill and
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DETAILS
N.T.S.
Provide Surface Drainage \/ 7 Slope or Level
Native Backfill -
/- @ Filter Fabric
Finished Surface
I I
1 or Flatter P'
I I
0 WATERPROOFING MEMBRANE (optional):
Liquid boot or approved equivalent.
314 to 1-112" (inches) rock.
Mlrafi 140N or approved equivalent; place fabric flap behind core.
4" (inches) diameter perforated PVC. schedule 40 or approved alternative with minimum of
1% gradient to proper outlet point.
Minimum 2" (inches) diameter placed at 20' (feet) on centers along the wall, and 3" (inches)
above finished surface. (No weep holes for basement walls.)
@ ROCK
@ FILTER FABRIC:
@ PIPE:
@WEEP HOLE:
Y Provide Surface Drainage
Membrane (optional)
Finished Sulface
DETAILS
N.T.S.
-. d
.4 Native Backfill
/-- @ Drain P1 1 or Flatter
/- @ /
I I
Q WATERPROOFING MEMBRANE (optional):
@ DRAIN:
Liquid boot or approved equivalent.
Miradrain 6000 or I-drain 200 or equivalent for non-waterproofed walls.
Miradrain 6200 or I-drain 200 or equivalent for waterproofed walls.
Mirafi 140N or approved equivalent; place fabric flap behind care.
4" (inches) diameter perforated PVC. schedule 40 or approved alternative yl of 1% gradient to proper outlet point.
8 FILTER FABRIC:
@ PIPE:
@WEEP HOLE:
mil ium
Minimum 2" (inches) diameter placed at 20' (feet) on centers along the wall, and 3" (inches)
above finished surface. (No weep holes for basement walls.)
RETAINING WALL BACKFILL
AND SUBDRAIN DETAIL
GEOTEXTILE DRAIN
DETAIL 2 0
I Geotechnical 0 Geologic Environmental
DETAILS
N.T.S.
*- Heel Width
RETAINING WALL AND SUBDRAIN DETAll
CLEAN SAND BACKFILL
DETAIL 3
Geotechnical 0 Geologic 0 Environmental
0 WATERPROOFING MEMBRANE (optional):
Liquid boot or approved equivalent.
Must have sand equivalent value of 30 or greater; can be densified by water jetting.
Mirafi 140N or approved equivalent.
1 cubic foot per linear feet of pipe or 314 to 1-112" (inches) rock.
4" (inches) diameter perforated PVC. schedule 40 or approved alternative with minimum of
1% gradient to proper outlet point.
Minimum 2" (inches) diameter placed at 20' (feet) on centers along the wall, and 3" (inches)
above finished surface. (No weep holes for basement walls.)
@ CLEAN SAND BACKFILL:
@ FILTER FABRIC:
@ ROCK:
8 PIPE:
@ WEEP HOLE:
Drainage Detail). For limited access and confined areas, (panel) drainage behind the wall
may be constructed in accordance with Detail 2 (Retaining Wall Backfill and Subdrain
Detail Geotextile Drain). Materials with an E.I. potential of greater than 90 should not be
used as backfill for retaining walls. For more onerous expansive situations, backfill and
drainage behind the retaining wall should conform with Detail 3 (Retaining Wall And
Subdrain Detail Clean Sand Backfill).
Outlets should consist of a 4-inch diameter solid PVC or ABS pipe spaced no greater than
+lo0 feet apart, with a minimum of two outlets, one on each end. The use of weep holes
in walls higher than 2 feet should not be considered. The surface of the backfill should be
sealed by pavement or the top 18 inches compacted with native soil (E.I. ~90). Proper
surface drainage should also be provided. For additional mitigation, consideration should
be given to applying a water-proof membrane to the back of all retaining structures. The
use of a waterstop should be considered for all concrete and masonry joints.
WalVRetainina Wall Footina Transitions
Site walls are anticipated to be founded on footings designed in accordance with the
recommendations in this report. Should wall footings transition from cut to fill, the civil
designer may specify either:
a) A minimum of a %foot overexcavation and recompaction of cut materials for a
distance of 2H, from the point of transition.
Increase of the amount of reinforcing steel and wall detailing (Le., expansion joints
or crack control joints) such that a angular distortion of 1/360 for a distance of 2H on
either side of the transition may be accommodated. Expansion joints should be
placed no greater than 20 feet on-center, in accordance with the structural
engineer's/wall designer's recommendations, regardless of whether or not transition
conditions exist. Expansion joints should be sealed with aflexible, non-shrink grout.
c) Embed the footings entirely into native formational material (Le., deepened footings).
If transitions from cut to fill transect the wall footing alignment at an angle of less than
45 degrees (plan view), then the designer should follow recommendation "a" (above) and
until such transition is between 45 and 90 degrees to the wall alignment.
b)
TOP-OF-SLOPE WALLS/FENCES/IMPROVEMENTS AND EXPANSIVE SOILS
Expansive Soils and Slope Creep
Soils at the site are likely to be expansive and therefore, become desiccated when allowed
to drv. Such soils are susceptible to surficial slope creep, especially with seasonal
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changes in moisture content. Typically in southern California, during the hot and dry
summer period, these soils become desiccated and shrink, thereby developing surface
cracks. The extent and depth of these shrinkage cracks depend on many factors such as
the nature and expansivity of the soils, temperature and humidity, and extraction of
moisture'from surface soils by plants and roots. When seasonal rains occur, water
percolates into the cracks and fissures, causing slope surfaces to expand, with a
corresponding loss in soil density and shear strength near the slope surface. With the
- passage of time and several moisture cycles, the outer 3 to 5 feet of slope materials
experience a very slow, but progressive, outward and downward movement, known as
slope creep. For slope heights greater than 10 feet, this creep related soil movement will
typically impact all rear yard flatwork and other secondary improvements that are located
within about 15 feet from the top of slopes, such as swimming pools, concrete flatwork,
etc., and in particular top of slope fences/walls. This influence is normally in the form of
detrimental settlement, and tilting of the proposed improvements. The dessication/swelling
and creep discussed above continues over the life of the improvements, and generally
becomes progressivelyworse. Accordingly, the developer should provide this information
to any homeowners and homeowners association.
TOD of SloDe WallslFences
Due to the potential for slope creep for slopes higher than about 10 feet, some settlement
and tilting of the walls/fence with the corresponding distresses, should be expected. To
mitigate the tilting of top of slope walls/fences, we recommend that the walls/fences be
constructed on a combination of grade beam and caisson foundations. The grade beam
should be at a minimum of 12 inches by 12 inches in cross section, supported by drilled
caissons, 12 inches minimum in diameter, placed at a maximum spacing of 6 feet on
center, and with a minimum embedment length of 7 feet below the bottom of the grade
beam. The strength of the concrete and grout should be evaluated by the structural
engineer of record. The proper ASTM tests for the concrete and mortar should be
provided along with the slump quantities. The concrete used should be appropriate to
mitigate sulfate corrosion, as warranted. The design of the grade beam and caissons
should be in accordance with the recommendations of the project structural engineer, and
include the utilization of the following geotechnical parameters:
CreeD Zone: 5-foot vertical zone below the slope face and projected upward
parallel to the slope face.
The creep load projected on the area of the grade beam
should be taken as an equivalent fluid approach, having a
density of 60 pcf. For the caisson, it should be taken as a
uniform 900 pounds per linear foot of caisson's depth, located
above the creep zone.
CreeD Load:
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Point of Fixitv: Located a distance of 1.5 times the caisson's diameter, below
the creep zone.
Passive earth pressure of 300 psf per foot of depth per foot of
caisson diameter, to a maximum value of 4,500 psf may be
used to determine caisson depth and spacing, provided that
they meet or exceed the minimum requirements stated above.
To determine the total lateral resistance, the contribution of the
creep prone zone above the point of fixity, to passive
resistance, should be disregarded.
Passive Resistance:
Allowable Axial CaDacity:
Shaft capacity : 350 psf applied below the point of fixity over the surface area
of the shaft.
Tip capacity: 4,500 psf.
EXPANSIVE SOILS. DRIVEWAY, FLATWORK. AND OTHER IMPROVEMENTS
The soil materials on site are likely to be expansive. The effects of expansive soils are
cumulative, and typically occur over the lifetime of any improvements. On relatively level
areas, when the soils are allowed to dry, the dessication and swelling process tends to
cause heaving and distress to flatwork and other improvements. The resulting potential
for distress to improvements may be reduced, but not totally eliminated. To that end, it is
recommended that the developer should notify any homeowners or homeowners
association of this long-term potential for distress. To reduce the likelihood of distress, the
following recommendations are presented for all exterior flatwork:
1. The subgrade area for concrete slabs should be compacted to achieve a minimum
90 percent relative compaction, and then be presoaked to 2 to 3 percentage points
above (or 125 percent of) the soils' optimum moisture content, to a depth of
18 inches below subgrade elevation. The moisture content of the subgrade should
be verified within 72 hours prior to pouring concrete.
Concrete slabs should be cast over a relatively non-yielding surface, consisting of
a4-inch layer of crushed rock, gravel, or clean sand, that should be compacted and
level prior to pouring concrete. The layer should wet-down completely prior to
pouring concrete, to minimize loss of concrete moisture to the surrounding earth
materials.
2.
3. Exterior slabs should be a minimum of 4 inches thick. Driveway slabs and
approaches should additionally have a thickened edge (12 inches) adjacent to all
landscape areas, to help impede infiltration of landscape water under the slab.
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4.
5.
6.
7.
a.
9.
10.
11.
The use of transverse and longitudinal control joints are recommended to help
control slab cracking due to concrete shrinkage or expansion. Two ways to
mitigate such cracking are: a) add a sufficient amount of reinforcing steel,
increasing tensile strength of the slab; and, b) provide an adequate amount of
control and/or expansion joints to accommodate anticipated concrete shrinkage
and expansion.
In order to reduce the potential for unsightly cracks, slabs should be reinforced at
mid-height with a minimum of No. 3 bars placed at 18 inches on center, in each
direction. The exterior slabs should be scored or saw cut, I/z to 3/8 inches deep,
often enough so that no section is greater than 10 feet by 10 feet. For sidewalks or
narrow slabs, control joints should be provided at intervals of every 6 feet. The
slabs should be separated from the foundations and sidewalks with expansion joint
filler material.
No traffic should be allowed upon the newly poured concrete slabs until they have
been properly cured to within 75 percent of design strength. Concrete compression
strength should be a minimum of 2,500 psi.
Driveways, sidewalks, and patio slabs adjacent to the house should be separated
from the house with thick expansion joint filler material. In areas directly adjacent
to a continuous source of moisture (i.e., irrigation, planters, etc.), all joints should
be additionally sealed with flexible mastic.
Planters and walls should not be tied to the house.
Overhang structures should be supported on the slabs, or structurally designed
with continuous footings tied in at least two directions.
Any masonry landscape walls that are to be constructed throughout the property
should be grouted and articulated in segments no more than 20 feet long. These
segments should be keyed or doweled together.
Utilities should be enclosed within a closed utilidor (vault) or designed with flexible
connections to accommodate differential settlement and expansive soil conditions.
Positive site drainage should be maintained at all times. Finish grade on the lots
should provide a minimum of 1 to 2 percent fall to the street, as indicated herein.
It should be kept in mind that drainage reversals could occur, including
post-construction settlement, if relatively flat yard drainage gradients are not
periodically maintained by the homeowner or homeowners association.
12. Due to expansive soils, air conditioning (NC) units should be supported by slabs
that are incorporated into the building foundation or constructed on a rigid slab with
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GeoSoiLs, Inc.
W@He Geotechnical Geologic Environmental
5741 Palmer Way * Carlsbad, California 92008 - (760) 438-3155 FAX (760) 931-0915
July 30,2004
W.O. 3975-B-SC
Hallmark Communities
10675 Sorrento Valley Road, Suite 200-8
San Diego, California 92121
Attention: Mr. Bruce Douthit
Subject: Final Compaction Report c Grading, Traditions at La Costa, “Northpark i
La Costa,” Lots 1 through 14,Carlsbad, San Diego County, California
Dear Mr. Douthit:
This report presents a summary of the geotechnical testing and observation services
provided by GeoSoils, Inc. (GSI) during the rough earthwork phase of development for
Lots 1 through 14, within Traditions at La Costa development. The current phase of
earthwork commenced on, or about, April 21,2004, and was generally completed on July
28,2004. Survey of line and grade was performed by others, and not performed by GSI.
The purpose of grading was to prepare relatively level pads for the construction of single-
family residences and associated infrastructure. Based on the observations and testing
performed by GSI, it is our opinion that the building pads and adjoining areas appear
suitable for their intended residential use.
PREVIOUS WORK
The site has been previously graded under the purview of Benton Engineering, Inc. (see
Appendix A). The reader is referred to the Benton Engineering, Inc. report listed in
Appendix A for prior grading, testing, and observation results. The site was reported to
have been mass graded during the period from September 21, 1972 to February 6, 1974
(Benton, 1974).
ENGINEERING GEOLOGY
The geologic conditions exposed during the process of grading for the current phase of
development were regularly observed by a representative from our firm. The geologic
conditions encountered generally were as anticipated and presented in the preliminary
geotechnical reports (see Appendix A).
flexible couplings for plumbing and electrical lines. A/C waste water lines should
be drained to a suitable non-erosive outlet.
13. Shrinkage cracks could become excessive if proper finishing and curing practices
are not followed. Finishing and curing practices should be performed per the
Portland Cement Association Guidelines. Mix design should incorporate rate of
curing for climate and time of year, sulfate content of soils, corrosion potential of
soils, and fertilizers used on site.
DEVELOPMENT CRITERIA
SloDe Deformation
Compacted fill slopes designed using customary factors of safety for gross or surficial
stability and constructed in general accordance with the design specifications should be
expected to undergo some differential vertical heave or settlement in combination with
differential lateral movement in the out-of-slope direction, after grading. This
post-construction movement occurs in two forms: slope creep, and lateral fill extension
(LFE). Slope creep is caused by alternate wetting and drying of the fill soils which results
in slow downslope movement. This type of movement is expected to occur throughout the
life of the slope, and is anticipated to potentially affect improvements or structures (Le.,
separations and/or cracking), placed near the top-of-slope, up to a maximum distance of
approximately 15 feet from the top-of-slope, depending on the slope height. This
movement generally results in rotation and differential settlement of improvements located
within the creep zone. LFE occurs due to deep wetting from irrigation and rainfall on
slopes comprised of expansive materials. Although some movement should be expected,
long-term movement from this source may be minimized, but not eliminated, by placing
the fill throughout the slope region, wet of the fill's optimum moisture content.
It is generally not practical to attempt to eliminate the effects of either slope creep or LFE.
Suitable mitigative measures to reduce the potential of lateral deformation typically include:
setback of improvements from the slope faces (per the 1997 UBC and/or California
Building Code), positive structural separations (Le., joints) between improvements, and
stiffening and deepening of foundations. Expansion joints in walls should be placed no
greater than 20 feet on-center, in accordance with the structural engineer's
recommendations. All of these measures are recommended for design of structures and
improvements. The ramifications of the above conditions, and recommendations for
mitigation, should be provided to each homeowner and/or any homeowners association.
SloDe Maintenance and Plantinq
Water has been shown to weaken the inherent strength of all earth materials. Slope
stability is significantly reduced by overly wet conditions. Positive surface drainage away
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from slopes should be maintained and only the amount of irrigation necessary to sustain
plant life should be provided for planted slopes. Over-watering should be avoided as it can
adversely affect site improvements, and cause perched groundwater conditions. Graded
slopes constructed utilizing onsite materials would be erosive. Eroded debris may be
minimized and surficial slope stability enhanced by establishing and maintaining a suitable
vegetation cover soon after construction. Compaction to the face of fill slopes would tend
to minimize short-term erosion until vegetation is established. Plants selected for
landscaping should be light weight, deep rooted types that require little water and are
capable of surviving the prevailing climate. Jute-type matting or other fibrous covers may
aid in allowing the establishment of a sparse plant cover. Utilizing plants other than those
recommended above will increase the potential for perched water, staining, mold, etc., to
develop. A rodent control program to prevent burrowing should be implemented.
Irrigation of natural (ungraded) slope areas is generally not recommended. These
recommendations regarding plant type, irrigation practices, and rodent control should be
provided to each homeowner. Over-steepening of slopes should be avoided during
building construction activities and landscaping.
Drainaae
Adequate lot surface drainage is a very important factor in reducing the likelihood of
adverse performance of foundations, hardscape, and slopes. Surface drainage should be
sufficient to prevent ponding of water anywhere on a lot, and especially near structures and
tops of slopes. Lot surface drainage should be carefully taken into consideration during
fine grading, landscaping, and building construction. Therefore, care should be taken that
future landscaping or construction activities do not create adverse drainage conditions.
Positive site drainage within lots and common areas should be provided and maintained
at all times. Drainage should not flow uncontrolled down any descending slope. Water
should be directed away from foundations and not allowed to pond and/or seep into the
ground. In general, the area within 5 feet around a structure should slope away from the
structure. We recommend that unpaved lawn and landscape areas have a minimum
gradient of 1 percent sloping away from structures, and whenever possible, should be
above adjacent paved areas. Consideration should be given to avoiding construction of
planters adjacent to structures (buildings, pools, spas, etc.). Pad drainage should be
directed toward the street or other approved area@). Although not a geotechnical
requirement, roof gutters, down spouts, or other appropriate means may be utilized to
control roof drainage. Down spouts, or drainage devices should outlet a minimum of 5 feet
from structures or into a subsurface drainage system. Areas of seepage may develop due
to irrigation or heavy rainfall, and should be anticipated. Minimizing irrigation will lessen
this potential. If areas of seepage develop, recommendations for minimizing this effect
could be provided upon request.
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Toe of SloDe Drainsnoe Drains
Where significant slopes intersect pad areas, surface drainage down the slope allows for
some seepage into the subsurface materials, sometimes creating conditions causing or
contributing to perched and/or ponded water. Toe of slopehoe drains may be beneficial
in the mitigation of this condition due to surface drainage. The general criteria to be
utilized by the design engineer for evaluating the need for this type of drain is as follows:
Is there a source of irrigation above or on the slope that could contribute to
saturation of soil at the base of the slope?
Are the slopes hard rock and/or impermeable, or relatively permeable, or; do the
slopes already have or are they proposed to have subdrains (i.e., stabilization fills,
etc.)?
Was the lot at the base of the slope overexcavated or is it proposed to be
overexcavated? Overexcavated lots located at the base of a slope could
accumulate subsurface water along the base of the fill cap.
Are the slopes north facing? North facing slopes tend to receive less sunlight (less
evaporation) relative to south facing slopes and are more exposed to the currently
prevailing seasonal storm tracks.
What is the slope height? It has been our experience that slopes with heights in
excess of approximately 10 feet tend to have more problems due to storm runoff
and irrigation than slopes of a lesser height.
Do the slopes “toe out” into a residential lot or a lot where perched or ponded water
may adversely impact its proposed use?
Based on these general criteria, the construction of toe drains may be considered by the
design engineer along the toe of slopes, or at retaining walls in slopes, descending to the
rear of such lots. Following are Detail 4 (Schematic Toe Drain Detail) and Detail 5
(Subdrain Along Retaining Wall Detail). Other drains may be warranted due to unforeseen
conditions, homeowner irrigation, or other circumstances. Where drains are constructed
during grading, including subdrains, the locations/elevations of such drains should be
surveyed, and recorded on the final as-built grading plans by the design engineer. It is
recommended thatthe above be disclosed to all interested parties, including homeowners
and any homeowners association.
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DETAl LS
N.T.S.
SCHEMATIC TOE DRAIN DETAIL
NOTES:
1.1 Soil Cap Compacted to 90 Percent Relative Compaction.
2.) Permeable Material May Be Gravel Wrapped in Filter Fabric (Mirafi INN or Equivalent).
7.) Cleanouts are Recommended at Each Property Line.
3.) 4-Inch Diameter Perforated Pipe (SDR 35 or
4.) Pipe to Maintain a Minimum 1 Percent Fall.
5.1 Concrete Cutoff Wall to be Provided at Transitioi
Equivalent) with Perforations Down.
to Solid Outlet Pipe.
6.) Solid Outlet Plpe to Drain to Approved Area.
I
SCHEMATIC TOE DRAIN DETAIL
DETAIL L
Geotechnical 0 Coastal 0 Geologic 0 Environmental
DETAILS
N.T.S.
a
-?3/
21 SLOPE (TYPICAL)
SUBDRAIN ALONG RETAINING WALL DETAIL
DETAIL 5
Geotechnical Coastal Geologic Environmental
WILL WITH COMPACTED 7 NATIVE SOILS
TOP OF WALL
1.)
RETAINING WALL \ ___-__ ----- Ill2. MIN
NISHED GRADE
-MIRAFI 140
OR EQUAL
FIL .TER FABRIC
3/4" CRUSHED GRAVEL Y-
k4" DRAN
SUBDRAIN ALONG RETAINING WALL DETAIL
NOTTO SCWE
2.)
3.)
NOTES:
Soil Cap Compacted to 90 Percent
Relative Compaction.
Permeable Material May Be Gravel
Wrapped in Filter Fabric (Mirafi 1401
or Equivalent).
4-Inch Diameter Perforated Pipe
(SDR-35 of Equivalent) with
Perforations Down.
4.) Pipe to Maintain a Minimum I
5.) Concrete Cutoff Wail to be Provided
at Transition to Solid Outlet PiDe.
Percent Fall.
6.) Solid Outlet Pipe to Drain to
Approved Area.
7.) Cieanouts are Recommended at
Each Properly Line.
8.) Compacted Effort Should Be
Applied to Drain Rock.
Erosion Control
Cut and fill slopes will be subject to surficial erosion during and after grading. Onsite earth
materials have a moderate to high erosion potential. Consideration should be given to
providing hay bales and silt fences for the temporary control of surface water, from a
geotechnical viewpoint.
Landscape Maintenance
Only the amount of irrigation necessary to sustain plant life should be provided.
Over-watering the landscape areas will adversely affect proposed site improvements. We
would recommend that any proposed open-bottom planters adjacent to proposed
structures be eliminated for a minimum distance of 10 feet. As an alternative,
closed-bottom type planters could be utilized. An outlet placed in the bottom of the
planter, could be installed to direct drainage away from structures or any exterior concrete
flatwork. If planters are constructed adjacent to structures, the sides and bottom of the
planter should be provided with a moisture barrier to prevent penetration of irrigation water
into the subgrade. Provisions should be made to drain the excess irrigation water from the
planters without saturating the subgrade below or adjacent to the planters. Graded slope
areas should be planted with drought resistant vegetation. Consideration should be given
to the type of vegetation chosen and their potential effect upon surface improvements (Le.,
some trees will have an effect on concrete flatwork with their extensive root systems).
From a geotechnical standpoint leaching is not recommended for establishing
landscaping. If the surface soils are processed for the purpose of adding amendments,
they should be recompacted to 90 percent minimum relative compaction.
Gutters and DownsDouts
As previously discussed in the drainage section, the installation of gutters and downspouts
should be considered to collect roof water that may otherwise infiltrate the soils adjacent
to the structures. If utilized, the downspouts should be drained into PVC collector pipes
or non-erosive devices that will carry the water away from the house. Downspouts and
gutters are not a requirement; however, from a geotechnical viewpoint, provided that
positive drainage is incorporated into project design (as discussed previously).
Subsurface and Surface Water
Subsurface and surface water are not anticipated to affect site development, provided that
the recommendations contained in this report are incorporated into final design and
construction and that prudent surface and subsurface drainage practices are incorporated
into the construction plans. Perched groundwater conditions along zones of contrasting
permeabilities may not be precluded from occurring in the future due to site irrigation, poor
drainage conditions, or damaged utilities, and should be anticipated. Should perched
groundwater conditions develop, this office could assess the affected area(s) and provide
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the appropriate recommendations to mitigate the observed groundwater conditions.
Groundwater conditions may change with the introduction of irrigation, rainfall, or other
factors.
Site Improvements
Recommendations for exterior concrete flatwork design and construction can be provided
- upon request. If in the future, any additional improvements (e.g., pools, spas, etc.) are
planned for the site, recommendations concerning the geological or geotechnical aspects
of design and construction of said improvements could be provided upon request. This
office should be notified in advance of any fill placement, grading of the site, or trench
backfilling after rough grading has been completed. This includes any grading, utility
trench, and retaining wall backfills.
Tile Floorinq
Tile flooring can crack, reflecting cracks in the concrete slab below the tile, although small
cracks in a conventional slab may not be significant. Therefore, the designer should
consider additional steel reinforcement for concrete slabs-on-grade where tile will be
placed. The tile installer should consider installation methods that reduce possible
cracking of the tile such as slipsheets. Slipsheets or a vinyl crack isolation membrane
(approved by the Tile Council of America/Ceramic Tile Institute) are recommended
between tile and concrete slabs on grade.
Additional Gradinq
This office should be notified in advance of any fill placement, supplemental regrading of
the site, or trench backfilling after rough grading has been completed. This includes
completion of grading in the street and parking areas and utility trench and retaining wall
backfills.
Footing Trench Excavation
All footing excavations should be observed by a representative of this firm subsequent to
trenching and Drjor to concrete form and reinforcement placement. The purpose of the
observations is to verity that the excavations are made into the recommended bearing
material and to the minimum widths and depths recommended for construction. If loose
or compressible materials are exposed within the footing excavation, a deeper footing or
removal and recompaction of the subgrade materials would be recommended at that time.
Footing trench spoil and any excess soils generated from utility trench excavations should
be compacted to a minimum relative compaction of 90 percent, if not removed from the
site.
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July 30, 2004
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Trenchinq
Considering the nature of the onsite soils, it should be anticipated that caving or sloughing
could be a factor in subsurface excavations and trenching. Shoring or excavating the
trench walls at the angle of repose (typically 25 to 45 degrees) may be necessary and
should be anticipated. All excavations should be observed by one of our representatives
and minimally conform to CAL-OSHA and local safety codes.
Utilitv Trench Backfill
1.
2.
3.
4.
All interior utility trench backfill should be brought to at least 2 percent above
optimum moisture content and then compacted to obtain a minimum relative
compaction of 90 percent of the laboratory standard. As an alternative for shallow
(12-inch to 18-inch) under-slab trenches, sand having a sand equivalent value of
30 or greater may be utilized and jetted or flooded into place. Observation, probing
and testing should be provided to verify the desired results.
Exterior trenches adjacent to, and within areas extending below a 1:l plane
projected from the outside bottom edge of the footing, and all trenches beneath
hardscape features and in slopes, should be compacted to at least 90 percent of
the laboratory standard. Sand backfill, unless excavated from the trench, should
not be used in these backfill areas. Compaction testing and observations, along
with probing, should be accomplished to verify the desired results.
All trench excavations should conform to CAL-OSHA and local safety codes.
Utilities crossing grade beams, perimeter beams, or footings should either pass
below the footing or grade beam utilizing a hardened collar or foam spacer, or pass
through the footing or grade beam in accordance with the recommendations of the
structural engineer.
.
SUMMARY OF RECOMMENDATIONS REGARDING
GEOTECHNICAL OBSERVATION AND TESTING
We recommend that observation and/or testing be performed by GSI at each of the
following construction stages: . During gradinghecertification. . During significant excavation (Le., higher than 4 feet).
During placement of subdrains, toe drains, or other subdrainage devices, prior to .
placing fill and/or backfill.
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After excavation of building footings, retaining wall footings, and free standing walls
footings, prior to the placement of reinforcing steel or concrete.
Prior to pouring any slabs or flatwork, after presoakinglpresaturation of building
pads and other flatwork subgrade, before the placement of concrete, reinforcing
steel, capillary break (i.e., sand, pea-gravel, etc.), or vapor barriers (Le., visqueen,
etc.).
During retaining wall subdrain installation, prior to backfill placement.
During placement of backfill for area drain, interior plumbing, utility line trenches,
and retaining wall backfill.
During slope construction/repair.
When any unusual soil conditions are encountered during any construction
operations, subsequent to the issuance of this report.
When any developer or homeowner improvements, such as flatwork, spas, pools,
walls, etc., are constructed.
A report of geotechnical observation and testing should be provided at the
conclusion of each of the above stages, in order to provide concise and clear
documentation of site work, andlor to comply with code requirements.
GSI should review project sales documents to homeowners/homeowners
associations for geotechnical aspects, including irrigation practices, the conditions
outlined above, etc., prior to any sales. At that stage, GSI will provide homeowners
maintenance guidelines which should be incorporated into such documents.
OTHER DESIGN PROFESSIONALS/CONSULTANTS
The design civil engineer, structural engineer, post-tension designer, architect, landscape
architect, wall designer, etc., should review the recommendations provided herein,
incorporate those recommendations into all their respective plans, and by explicit
reference, make this report part of their project plans. This report presents minimum
design criteriaforthe design of slabs, foundations and other elements possibly applicable
to the project. These criteria should not be considered as substitutes for actual designs
by the structural engineer/designer. The structural engineeddesigner should analyze
actual soil-structure interaction and consider, as needed, bearing, expansive soil influence,
and strength, stiffness and deflections in the various slab, foundation, and other elements
in order to develop appropriate, design-specific details. As conditions dictate, it is possible
that other influences will also have to be considered. The structural engineer/designer
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should consider all applicable codes and authoritative sources where needed. If analyses
by the structural engineer/designer result in less critical details than are provided herein
as minimums, the minimums presented herein should be adopted. It is considered likely
that some, more restrictive details will be required. If the structural engineer/designer has
any questions or requires further assistance, they should not hesitate to call or otherwise
transmit their requests to GSI. In order to mitigate potential distress, the foundation and/or
improvement’s designer should confirm to GSI and the governing agency, in writing, that
the proposed foundations and/or improvements can tolerate the amount of differential
settlement and/or expansion characteristics and design criteria specified herein.
PLAN REVIEW
Final project plans should be reviewed by this office prior to construction, so that
construction is in accordance with the conclusions and recommendations of this report.
Based on our review, supplemental recommendations and/or further geotechnical studies
may be warranted.
LIMITATIONS
The materials encountered on the project site and utilized for our analysis are believed
representative of the area; however, soil and bedrock materials vary in character between
excavations and natural outcrops or conditions exposed during mass grading. Site
conditions may vary due to seasonal changes or other factors.
Inasmuch as our study is based upon our review and engineering analyses and laboratory
data, the conclusions and recommendations are professional opinions. These opinions
have been derived in accordance with current standards of practice, and no warranty is
expressed or implied. Standards of practice are subject to change with time. GSI assumes
no responsibility or liability for work or testing performed by others, or their inaction: or
work performed when GSI is not requested to be onsite, to evaluate if our
recommendations have been properly implemented. Use of this report constitutes an
agreement and consent by the user to all the limitations outlined above, notwithstanding
any other agreements that may be in place. In addition, this report may be subject to
review by the controlling authorities. Thus, this report brings to completion our scope of
services for this portion of the project.
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Gedoils, Inc.
The opportunity to be of service is sincerely appreciated. If you should have any
questions, please do not hesitate to contact
( / Engineering Geologist, CEG 1340
our oftice.
v
BEV/RGC/JPF/DWS/jk
Attachments: Table 1 - Field Density Test Results
Table 2 - Traditions at La Costa Lot Summary - Geotechnical
Conditions
Appendix A - References
Appendix B - Soil Corrosivity Study
Plates 1 and 2 - Field Density Test Location Maps
Distribution: (2) Addressee
(2) Hallmark Communities Site Trailer, Attention: Mr. Jerry Welsh
(1) Snipes-Dyes Associates, Attention: Mr. William Snipes
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Table 1
FIELD DENSITY TEST RESULTS
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July 2004
Page 1
Table 1
FIELD DENSITY TEST RESULTS
LEGEND: * = Indicates Failed Test
A = Indicates Retest
FG = Finish Grade
ND = Nuclear Densometer
SC = Sand Cone
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APPENDIX A
REFERENCES
APPENDIX A
REFERENCES
Benton Engineering, Inc.,l974, Final report on compacted filled ground, La Costa Vale
Unit 1, dated February 28, Project # 72-8-18D.
GeoSoils, Inc., 2004a, Geotechnical foundation plan review, Traditions at La Costa, City
of Carlsbad, San Diego County, W.O. 3975-Ai-SC, dated May 24.
-3 2004b, Geotechnical plan review, Traditions at La Costa, City of Carlsbad,
San Diego County, California, W.O. 3975-A-SC, dated May 11.
-9 2003, Preliminary geotechnical investigation, Proposed Northpark at La Costa,
Tentative Map CT 02-25, Carlsbad, San Diego County, California, W.O. 3975-A-SC,
dated August 5.
International Conference of Building Officials, 1997, Uniform building code, dated April.
Snipes-Dyes and Associates, 2003, Tentative map/conceptual base grading plan,
Northpark at La Costa, dated March 14.
GeoSoils, Inc.
APPENDIX B
SOIL CORROSIVITY STUDY
M.J. SCHIFF 8 ASSOCIATES, INC.
Consulting Corrosion Engineers - Since 1959 Phane: (909) 626-0967 I Fax: (909) 626.3316 431 W. Baseline Road E-mail: rnjsa@rnjschiff.com Clarernont, CA 91711 http:llwww.rnjschiff.corn
June 15.2004
. GEOSOILS, INC.
5741 Palmer Way
Carlsbad, California 92008
Attention: Mr. Brian Voss
Re: Soil Corrosivity Study
Hallmark - Traditions at La Costa
La Costa, California
YOUC #3975-B-SC, MJS&A M4-0738HQ
INTRODUCTION
Laboratory tests have been completed on one soil sample you provided for the referenced project.
The purpose of these tests was to determine if the soils might have deleterious effects on
underground utility piping and concrete structures. We assume that the sample provided is
representative of the most corrosive soil at the site.
The proposed project consists of 12 single-family homes. The site is located at the comer of Levante
Street and La Costa Avenue. Water table depth was not provided; therefore, its effect on site
corrosivity could not be accounted for in this analysis and report.
The scope of this study is limited to a determination of soil corrosivity and general corrosion control
recommendations for materials likely to be used for construction. Our recommendations do not
constitute, and are not meant as a substitute for, design documents for the purpose of construction. If
the architects and/or engineers desire more specific information, designs, specifications, or review
of design, we will be happy to work with them as a separate phase of this project.
TEST PROCEDURES
The electrical resistivity of the sample was measured in a soil box per ASTM G57 in its as-received
condition and again after saturation with distilled water. Resistivities are at about their lowest value
when the soil is saturated. The pH of the saturated sample was measured. A 5:l water:soil extract
from the sample was chemically analyzed for the major soluble salts commonly found in soils and
for ammonium and nitrate. The total acidity was determined on the sample to assess the acidic
buffering of the soil. Test results are shown in Table 1.
CORROSION AND CATHODIC PROTECTION ENGINEERING SERVICES
PLANS &SPECIFICATIONS FAILURE ANALYSIS EXPERT WITNESS CoRRClSlVlN ANn nAMAC= r.CSFCSMEUX
GEOSOILS, INC.
MJS9i.4 #04-073SHQ
June 15. 2004
Page 2
SOIL CORROSIVITY
A major factor in determining soil corrosivity is electrical resistivity. The electrical resistivity of a
soil is a measure of its resistance to the flow of electrical current. Corrosion of buried metal is an
. electrochemical process in which the amount of metal loss due to corrosion is directly proportional
to the flow of electrical current (DC) from the metal into the soil. Corrosion currents, following
Ohm's Law, are inversely proportional to soil resistivity. Lower electrical resistivities result from
higher moisture and soluble salt contents and indicate corrosive soil.
A correlation between electrical resistivity and corrosivity toward ferrous metals is:
Soil Resistivity
in ohm-centimeters Corrosivity Category
over 10,000 mildly corrosive
2,000 to 10,000 moderately corrosive
1,000 to 2,000 corrosive
below 1,000 severely corrosive
Other soil characteristics that may influence corrosivity towards metals are pH, soluble salt content,
soil types, aeration, anaerobic conditions, and site drainage.
The electrical resistivity was in the mildly corrosive category with as-received moisture. When
saturated, the resistivity was in the severely corrosive category. The resistivities dropped
considerably with added moisture because the sample was dry as-received.
Soil pH was 4.9. This value is very strongly acidic. Acidic soils can be corrosive to concrete and
metallic buildkg materials.
Total acidity was 480 mg H'kg. This is high enough to cause significant deterioration of the
concrete as well as heaving if allowed to contact the concrete.
The soluble salt content of the sample was very high.
predominant constituents. Sulfate was in a range where sulfate resistant cement is recommended.
Ammonium and nitrate were detected in low concentrations.
Chloride and sulfate salts were the
Tests were not made for sulfide and negative oxidation-reduction (redox) potential because these
samples did not exhibit characteristics typically associated with anaerobic conditions.
This soil is classified as severely corrosive to ferrous metals, aggressive to copper, and moderate for
sulfate attack on concrete.
GEOSOILS, INC.
MJSStA #04-073SHQ
CORROSION CONTROL RECOhIhIENDATIONS
The life of buried materials depends on thickness, strength, loads, construction details, soil moisture,
etc., in addition to soil corrosivity, and is, therefore, difficult to predict. Of more practical value are
corrosion control methods that will increase the life of materials that would be subject to significant
corrosion.
S tee1 Pipe
Abrasive blast underground steel piping and apply a dielectric coating such as polyurethane,
extruded polyethylene, a tape coating system, hot applied coal tar enamel, or fusion bonded epoxy
intended for underground use.
Bond underground steel pipe with rubber gasketed, mechanical, grooved end, or other
nonconductive type joints for electrical continuity. Electrical continuity is necessary for corrosion
monitoring and cathodic protection.
Electrically insulate each buried steel pipeline from dissimilar metals and metals with dissimilar
coatings (cement-mortar vs. dielectric), and above ground steel pipe to prevent dissimilar metal
corrosion cells and to facilitate the application of cathodic protection.
Apply cathodic protection to steel piping as per NACE International Standard RP-0 169-02.
Iron Pipe
Encase cast and ductile iron piping per AWWA Standard C105 or coat with epoxy or polyurethane
intended for underground use. Note: the thin factory-applied asphaltic coating applied to ductile
iron pipe for transportation and aesthetic purposes does not constitute a corrosion control coating.
Electrically insulate underground iron pipe fiom dissimilar metals and fiom above ground iron pipe
with insulating joints per NACE International Standard RP-0286-02. Bond all nonconductive type
joints for electrical continuity.
Apply cathodic protection to ductile iron water piping as per NACE International Standard RF’-
0169-02.
Copper Tubing
Buried copper tubing shall be protected by:
1. Encasing the copper in two layers of 10-mil thick polyethylene sleeves taking care not to
damage the polyethylene. Protect wrapped copper tubing by applying cathodic protection
per NACE International Standard RP-0169-02. Any damaged polyethylene shall be
repaired by wrapping it in 20-mil thick pipe wrapping tape. The amount of cathodic
protection current needed can be minimized by coating the tubing.
2. Preventing soil contact. Soil contact may be prevented by placing the tubing above ground.
3. Install a factory coated copper pipe with a minimum of 100-mil thickness such as “Aqua
Shield” or similar products. Polyethylene coating protects against elements that corrode
copper and prevents contamination between copper and sleeving. However, it must be
continuous with no cuts or defects if installed underground.
GEOSOILS, INC.
RIIJSkA ii04-073SHQ
June 15,2004
rage 4
Plastic and VitriFicd Clay Pipe
NO special precautions are required for plastic and vitritied clay piping placed undergound kiom a
corrosion viewpoint. Protect all fittings and valves with wax tape per AWWA Standard C2 17-99 or
epoxy.
All Pipe
On all pipes, appurtenances, and fittings not protected by cathodic protection, coat bare metal such
as valves, bolts, flange joints, joint harnesses, and flexible couplings with wax tape per AWWA
Standard C217-99 after assembly.
Where metallic pipelines penetrate concrete structures such as building floors, vault walls, and
thrust blocks use plastic sleeves, rubber seals, or other dielectric material to prevent pipe contact
with the concrete and reinforcing steel.
Concrete
Protect concrete structures and pipe from sulfate attack in soil with a severe sulfate concentration,
0.1 to 0.2 percent. Use Type I1 cement, a maximum waterkement ratio of 0.50, and minimum
strength of 4000 psi per applicable code, such as 1997 Uniform Building Code (UBC) Table 19-A-4
or American Concrete Institute (ACI-3 18) Table 4.3.1.
Standard concrete cover over reinforcing steel may be used for concrete structures and pipe in
contact with these soils.
Concrete structures and pipe should be protected from acid attack due to the low pH and high total
acidity. Concrete can be protected by preventing contact with the moisture in acidic soil. Contact
can be prevented with impermeable, waterproof, acid resistant banier coatings such as Liquid
Boot@. If soiI/concrete contact is prevented, sulfate resistant cement, as specified above, is not
required.
CLOSURE
Our services have been performed with the usual thoroughness and competence of the
engineering profession. No other warranty or representation, either expressed or implied, is
included or intended.
Please call if you have any questions.
Resptfblly Submitted,
*YJ&es T. Keegan
Enc: Table 1
Reviewed by,
$lo7 Jo W. French, P. E.
&I. .J. Schiff& Associ:ites, Inc.
Cc~ti.~Miig Ccrrrcrsiori Orgirieers - Sirrce / 959
431 W'. B(rsclit~e Rood
Cli~reiriiirrl, C.4 91 711
Pllirri~: (9WJ 626-0967 Fii.~: (9119) 626-J3/6
E-iiriiil Iirhk rirj.$cliqJcorir
wch.sitr: rrq.scliq/:corrr
Table 1 - Laboratory Tests on Soil Samples
flu/lrmr!i
Yuirr #3975-BSC, MJS&I #04-073YLA B
26-iWuy-04
Sample ID
Lot 4
FC
Resistivity Units
as-received ohm-cm
saturated ohm-cm
PH
Electrical
Conductivity mS/cm
Chemical Analyses
Cations
calcium Ca" mdkg
magnesium Mg2+ mgikg
sodium Na" mdkg
Anions
carbonate COT mag
bicarbonate HC03'- mgikg
chloride . CI'. mgikg
sulfate SO: mgikg
Other Tests
ammonium NH~'+ mg/kg
nitrate NO," mg/kg
sulfide S2. qual
Redox mV
Total Acidity H' mgikg .. .~ ......... ji .... : .................. ................... ii .......... :... ......
120,000
410
4.9
1.12
289
I12
32 I
ND
ND
255
1,459
1.6
1.8
na
na
480 ... ........................ ................... ... ... ,..,. .......................... ., ...... . :. ............................ ..:
Electrical conductivity in millisiemendcm and chemical analysis were made on a 13 soil-to-water extract.
mgikg = milligrams per kilogram (parts per million) of dly soil.
Redox = oxidation-reduction potential in millivolts
ND = not detected
na = not analyzed
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