HomeMy WebLinkAboutTR 28214 Geotechnical Report PETRA
OFFICES IN THE COUNTIES OF
ORANGE ■ SAN DIEGO ■ RIVERSIDE LOS ANGELES SAN BERNARDINO
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August 30, 2006
J.N. 259-06
Mr. Tom Tomlinson
E ; CASTLE & COOKE ALBERHILL RANCH, INC.
17600 Collier Avenue, Suite C-120
Lake Elsinore, California 92531
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Subject: Updated Geotechnical Recommendations, Proposed Nichols Road
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Realignment (Stations 46+00 through 81+00), City of Lake
Elsinore, Riverside County, California.
.:: Dear Mr. Tomlinson:
In accordance with your request, Petra Geotechnical, Inc. (Petra) is submitting this
updated letter-report presenting geotechnical recommendations for the re-alignment
`f of the proposed Nichols Road from Stations 46+00 through 81+00 south of the
proposed Tentative Tract 30836 (Hoist property) and north of the proposed
Tract 28214, located in Lake Elsinore area of Riverside County, California. This
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report presents the results of our engineering analysis, conclusions and
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1 recommendations pertaining to geotechnical design aspects of the relocation of the
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proposed roadway. It should be noted that grading of the Nicholas Road alignment
is ongoing and recommendations presented herein are being implemented.
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Purpose and Scone of Services
The purpose of this study was to evaluate previous subsurface information and
jbackground data with respect to the site in order to provide geotechnical
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recommendations for the realignment of the proposed roadway. The scope of
services consisted of the following.
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• Review the 40-scale rough-grading plans prepared by KWC Engineers, (KWC,
2006), specifically between Stations 46+00 through 81+00.
t PETRA GE07ECHNlCAL, INC.
41640 Corning Place ■ Suite 107 ■ Murrieta ■ CA 92562 ■ Tel:(909) 600-9271 ■ Fax: (909) 600-9215
August 30, 2006
CASTLE & COKE ALBERHILL RANCH, INC.
Nichols Road/Lake Elsinore J.N. 259-06
' Page 2
® Review of the previous geotechnical reports by Petra (Petra 2005; 2006) for the
project site.
• Meeting on August 2, 2006, with you to discuss options for road construction.
• Construct geologic cross sections depicting site geology and proposed
r• realignment construction grades.
. Prepare this letter-report presenting the geotechnical design considerations for the
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proposed construction.
Slope Stability Recommendations
Based on our analysis, construction of the proposed roadway as shown on the
enclosed Geotechnical Ma p g s and Geolo is Cross Sections A-A', B-B' and E-E'
(Figures I through 5), is considered feasible from a geotechnical point of view. It
is our opinion that the proposed grading and construction will not adversely affect
the geologic stability of adjoining properties provided the grading and construction
are performed in accordance with the recommendations presented herein. The
following mass-grading recommendations pertaining to Nichols Road grading and
construction are referenced by station numbers due to the changes in construction
grades and changes in geologic and soil conditions.
Nichols Road Stations 46+00 Through 60+00
Based on the design cut slopes from Stations 46+00 through 60+00, our previous
stability calculations (Petra, 2005) and the existing subsurface landslide-debris
materials, Petra recommends that the design cut slopes be replaced with
} stabilization fills (Figure 1). The south-facing ascending cut slopes along the north
Li side of the road alignment are anticipated to be permanent.
The stabilization fills should be constructed in accordance with the typical detail
shown on Plate SG-2 (Petra, 2005). The stabilization fill keys should be excavated
CASTLE & COKE ALBERHILL RANCH, INC. August 30, 2006
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Nichols Road/Lake Elsinore J.N. 259-06
Page 3
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M. to a minimum depth of 10 feet (Stations 46+00 to 55+00) and 20 feet
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(Stations 55+00 to 60+00) below design toe of slope and have a minimum bottom
r width of 30 feet. The bottoms of the fill keys should be tilted back at a minimum
U of 2 percent towards the heel of the key. Internal backdrains should also be
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installed in each stabilization fill to mitigate the potential buildup of excessive
L1 hydrostatic pressures. Backdrains should be constructed in accordance with the
details shown on Plates SG-2 and SG-3 presented in Appendix C of our referenced
>- geotechnical investigation report (Petra, 2005). Backdrain locations should be
determined during grading based on local topography and the most feasible exit
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j The stability of temporary backcut slopes associated with stabilization fill and
shear-key construction is dependent on many factors which include slope angle,
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l height, geologic structure of unsupported bedrock, shear strength along planes of
., weakness, groundwater conditions, nuisance water and the length of time
temporary cuts remain unsupported. Consequently, there is a risk of backcut
failures during excavation of basal shear keys for the stabilization fills. In order to
U maintain temporary stability, the backcuts should be laid back no steeper than 1.5:1
;..._ (horizontal:vertical [h:v]). In order to minimize the potential for backcut failures,
Uthe following techniques should also be considered:
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• All shear keys should be excavated, observed by the project geologist and then
LJ filled in the shortest practical period of time. Keyway excavations should never
be allowed to stand open for prolonged periods of time.
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• Provisions should be made for preventing nuisance water and rainwater from
collecting and ponding in keyway excavations.
• Grading equipment and other construction traffic should never be allowed to
traverse along the tops of temporary backcut slopes.
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• The temporary excavations (backcut slopes) for the cut slopes should be
(` ` tentatively planned at a slope ratio of 1.5:1 (h:v). However, flatter slopes may
CASTLE & COKE ALBERHILL RANCH, INC. August 30, 2006
Nichols Road/Lake Elsinore J.N. 259-06
i Page 4
be necessary in local areas due to widely variable subsurface or unforeseen
conditions. Conversely, localized steepening of the backcut slopes may be
suitable, depending on the observed geologic conditions.
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• In addition to the above, OSHA requirements should be followed with respect
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to excavation safety.
Nichols Road Stations 60+00 Through 65+50
E.
As indicated in meetings with Castle and Cooke the proposed stabilization fills and
shear keys to be constructed along Stations 60+00 trough 65+50 cut slopes shall
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take place at a later date to facilitate temporary construction of the proposed
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Tentative Tract 30836 on the Hoist property. Accordingly it is proposed that
temporary 3:1 (h:v) cut slope be constructed along the north side of Nichols Road
(Plate 2). These temporary cut slopes will expose landslide materials that should
.1 be temporarily stable to facilitate the roadway construction at a 3:1 (h:v) grade. It
is our understanding that these temporary cut slopes will be eliminated with future
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g. development of the adjacent Hoist property. Petra recommends at that time a 50-
foot level, non-structural setback be established adjacent to the north side of
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isJ Nicholas Road to allow for future preliminary stabilization which may include a
50-foot wide by 10-foot deep shear key and stabilization fill to remove landslide
materials as part of the remedial grading of Tentative Tract 30836.
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Nichols Road Stations 65+50 Through 90+00
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F Cut and/or fill slopes constructed along the north and sides of Nichols road from
1J Stations 65+50 to 90+00 require remedial removals prior to fill placement.
fills, alluvium and colluvium should be
Existing low-density undocumented
removed to competent bedrock or older alluvium materials. Removals in these
areas are anticipated to be 7 to 10 feet below existing grade along the north side of
Nichols Road and 3 to 4 feet below existing grade on the south side of Nichols
Road. Fill keys should be constructed in accordance with the typical detail shown
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CASTLE & COKE ALBERHILL RANCH, INC. August 30, 2006
Nichols Road/Lake Elsinore J.N. 259-06
Page 5
on Plate 1 reference in our geotechnical investigation report (Petra, 2005). Please
3. note that remedial grading will required beyond Station 90+00 subsequent to
<-0 preparation of a geotechnical investigation for the bridge and abutments.
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LIMITATIONS
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This report is based on the proposed project and Petra's geotechnical data as
ndescribed herein. The materials encountered on the project site described in other
literature are believed representative of the total project area and the conclusions
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and recommendations contained in this report are presented on that basis.
However, soil materials can vary in characteristics between points of sampling,
both laterally and vertically and those variations could effect the conclusions and
recommendations contained herein. As such, observation and testing by a
geotechnical consultant during the grading and construction phases of the project
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are essential to confirming the basis of this report. To provide continuity between
.: the design and construction-phases, consideration should be given to retaining Petra
for geotechnical construction services.
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This report has been prepared consistent with that level of care being provided by
other professionals providing similar services at the same locale and time period.
The contents of this report are professional opinions and as such, are not to be
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considered a guaranty or warranty.
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CASTLE & COKE ALBERHILL RANCH, INC. August 30, 2006
Nichols Road/Lake Elsinore J.N. 259-06
Page 6
We appreciate this opportunity to be of service. If you have questions, please
contact this office.
Respectfully submitted,
POPESS/p
PETRA GEOTECHNICAL, ,Q
O�S10Nq�CFO y�'pN R. Yy�q�Fy
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l J James A. Larwood, CEG (P Nip ray on Walker, G EXP. '5' D
J Senior Associate Geologis A rincipal Engineer
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Attachments:References
DFigures 1 through 4—Geotechnical Maps
Figure 5 —Geologic Cross Sections A-A', B-B' and E-E"
Distribution: (5) Addressee
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REFERENCES
Petra Geotechnical, Inc., 2005, Geotechnical Investigation, Proposed Nichols Road Alignment, Lake Elsinore,
F11 County of Riverside,California,J.N. 160-04,dated September 28.
2006, Geotechnical Investigation, Amended Vesting Tentative Tract No. 30836 (Hoist Property) Lake
Elsinore,County of Riverside,California,J.N.414-03,dated March 31.
KWC Engineers, 2006, Rough Grading Plan, Tract No. 28214, Nichols Road, City of Lake Elsinore, California,
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Sheets 5 through 8,dated July 31.
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J.N. 259-06
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.i 0 100 FEET
SCALE
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GEOTECHNICAL MAP
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REFERENCE: OR � PETRA GEOTECHNICAL, INC.
KWC ENGINEERS,CITY OF LAKE ELSIN E,
TRACT NO. 28214, NICHOLS RD., ROUGH JN 259-06 AUG.,2006
_ GRADING PLAN, SHEET 6 OF 9.
FIGURE 1
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r.' __ / ! '/` 4`l \�'�. .0� ,` ,) ' .>J-r- -c. h'�_ - -�;.1._ ri -y -^r_" - 'T •^ _ �_yam.-_- :-.%.:��.;'=- 1Sy a ��'^- �r _ (Y)
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EXPLANATION
(LOCATIONS ARE APPROXIMATE)
NORTH
APPROXIMATE DEPTH 0 100 FEET
3-4 OF UNSUITABLE
MATERIAL SCALE
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GEOTECHNICAL MAP
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.0": PETRA GEOTECHNICAL, INC.
REFERENCE: ;W
KWC ENGINEERS,CITY OF LAKE ELSINORE,
TRACT NO.28214, NICHOLS RD., ROUGH JN 259-06 AUG.,2006
GRADING PLAN,SHEET 7 OF 9.
FIGURE 2
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A
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I. STATION 57+50 A
1400— 1400
NICHOLS NATURAL
ROAD EXISTING GROUND
rl POWER SURFACE
I ! POLE
w uj 1360—
1360
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z t! Y z
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PROPOSED �P)E
z GRADE z
0 0
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---------------
-000 ////I
1320 1,34V _J
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RECONMENDED
Ts SHEAR KEY Ts
1,J 1280 W=3 ' D=10' 1280
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1420 ST�TION 60+50 1420
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FURS HOIST
PARK SITE
2: CUT PROPERTY
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NICHOLS 50'SETBACK SLDPE FOR DESIGN
u' 1380— ROAD F=POtu EDGE Hdis-r PROFILE — 1380 ul
OF Nl:;HOLS
U- P OPERTY U-
Fy z ROAC EXISTING PROPOSED z
Li z NATURAL POWER 1.5:1 BACKCUT z
0 GROUND TEMPORARY POLE 0
PROPOSED
SURFACE
3:1 CUT SLOE
QIS
1040 GRADE 1340
T
1000o
Qoal QIS ? Ts
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RECOMM�:NDED
Ts 50,wil I, AR KEY 1300 1300
STATION 70+50 Ev
130 1300
w NICHOLS GEOLOGIC
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Lu ROAD ESTIMATED LL CROSS SECTIONS
LL
z REMEDIAL EXISTIND NATURAL z
PROPOSED REMOVAL POWER GROUND A-A'. B-B' AND E-E'
z 1260— 1260 z
L; 0 GRADE BOTTOM POLE SURFACE 0
< 0 40FEET PETRA GEOTECHNICAL, INC.
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Lu SCALE JN259-06 AUG.,2006
QIS (VERTICAL AND HORIZONTAL)
1220 1220 FIGURE 5