HomeMy WebLinkAbout30289 (626)L N G, INEERING
F. Beach Leighton & Associates, Inc.
300 SOUTH BEACH BOULEVARD . LA HABRA, CALIFORNIA 90631 • (213( 694,1826 - (714 526-1337
PRELIMINARY GEOLOGIC INVESTIGATION
017
TRACT 30289, EQUESTRIAN ESTATES
DIAMOND BAR
COUNTY OF LOS ANGELES
June 2, 1971
by
F. Beach Leighton Cf Associates
for Diamond Bar Devc1op11ont Company)
Agowall'hou5and Oaks Laguna Hills
8213) 889-2472 (714) 8'303611
San Binnardino
714) 8041968
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GEMAGMTS F. Beach Leighton & Associates, Inc.
300 SOUTH BEACH BOULEVARD - LA HABRA, CALIFORNIA 90631 - (213) 694-1826 - (714) 526-1337
TO: Diamond Bar Development Company
Attention: Mr. Ben Molina
FRUA: F. Beach Leighton & Associates
SUBJECT: Preliminary Geologic Investigation of Tract 30289, Equestrian Estates,
Diamond Bar, County of Los Angeles
This report summarizes the engineering geologic aspects of Stage 1:
and Stage Il of a geologic -soils study of the subject property. W soils
engineering portion is being provided by Moore & Taber.
The chiet purpose of Stage I was to isolate the lots about which geologic
questions have been raised in previous geologic reports. Stage II consisted
of subsurface e;ploration primarily concentrated in one area where questions
had been raised by previous work.
This report treats these questions concerning daylighted bedding and the
existence of slumps, creep and landslide material. The area probed in Stage 11
lies along Cross -Section AL --AL' (see accompanying Revised index Map of Lots).
Existing graded areas are not within the purview of this investigation,
as rough grading has been approved by the previous consultants and the County
of Los Angeles and no major question marks or problems have come to our atten-
tion.
jES2Eplaying._Illustrations and Supporting Data
Revised Index Map of Lots (attached to back of report)
Revised Cross -Section AL-ALI (40 -scale)
Preliminary Geologic Map (Sheet 4 of 5 and 5 of 5 spliced together)
Boring Logs 1L through SL
FK W MWES: Agoura/fhousarid Oak1.143una IWIS San Ww)M'di*
f21:31 SM1412 0M) OWAM 1 014) 8N4N8
II
1'ransamerica - Equestrian Estates - Phase II June 2, 1971
E
Chief to in Stage I
1. Field reconnaissance
2. Collation and tabulation of all reports received on the subject tract.
3. Transfer of geologic data collected by others to the 40 -scale grading
plans; these data were color keyed.
4. Geologic review of lot by lot reports and other reports received.
5. Preparation of an index map showing those lots with no significant
additional subsurface exploration, lots with additional subsurface
exploration, lots approved by the County of Los Angeles, and lots
previously treated by others that were not included in the scope of
this report.
CliiefSl s fStage _a , e I I
I. Staking of backhoe trench locations and boring locations i
ITransamerica - Equestrian Estates - Phase II June 2, 1971
U
SUMMARY OF FINDINGS, STAGES I AND 11
1. Previous ge6logic reports were reviewed to determine the extent of
the questions asked by others concerning specific lots within the
tract.
2. No major questions have been raised by others on Lots 2-7, 24-26,
38, 40, 41, 48, 50 and 60-61 (16 lots). Based on the information
provided in the previous reports, a geologic review of building
plans or grading plans is all that is geologically anticipated
unless these pl,'ins incorporate re -grading of the pads to the extent
that it will be contrary to previous recommendations, which may
result in an unstable condition.
1. Bedding planes daylight in the natural slope of Lots 20 and 21 below
the graded pad areas and above the Equestrian Easement. Bedding
attitudes in this portion of the slope NIO-450E and dip 7-8'W.
Bedding attitudes at the top of the slope in the vicinity of Lot 20
become flatter with depth (see Cross -Section AL -AL' and Preliminary
Geologic Map).
2. Moore & Taber has prepared a stability analysis of this portion of
the slope and reportedly the analysis indicates a favorable factor
of safety (1.5 or greater) for this portion of the slope.
3. Soil. and weathered bedrock locally exist to a maximum depth of 4 to
5 feet. Caliche stringers paralleling bedding generally exist at
this depth.
4. The bedrock sequence is generally consistent throughout the length
of the slope, which has been reviewed (see Cross -Section AL -AL').
Units of sandstone and siltstone are traceable in the subsurface.
Locally, clay seams exist which are parallel to bedding.
5. No deep-seated slump -creep was exposed in the driA ling program. A
gnarled zone was mapped in the borings but is the result of regional
uplift rather than downslope landsliding.
6. Ground water was exposed in Boring 4 approximately 24 feet below
natural ground. (See Cross -Section AL-ALI). Reportedly, subdrainage
has been provided below the existing fill in this area.
7. Bedding planes do not daylight in the natural. slope below Steeple-
chase Lane in the vicinity of Lots 32 and 33.
3-
F. Beach 1AfflIt011 & Associaics, Inn,I
Transamerica - Equestrian Estates - Phase II
8.
9.
10.
11.
ir„ Rjrjl
Bedding planes did apparently daylight in the natural slope now
buried by controlled fill placed by others in Lots 32 and 33.
A questionable landslide exists at the western margin of Lots 32
and 33. (See Cross -Section AL -AL').
No rock creep was exposed on the periphery of the graded building
pad of of 70.
It is not believed geologically necessary to conmient or to probe
Lots 9-11, 66-68 or the other graded portions of the tract, since no
specific questions have been asked about these areas, and grading has
been approved by former consultants and the County of Los Angeles.
4-
F. Beaelt J.xiglitoti & Associates, 111e. m
4
Transamerica Equestrian Estates - Phase 11 June 2, 1971
CONCLUSION AND 1O.CONSIEN9'>AT IONS
ccan clusi=
Based on the findings of the Stage 11 investigation, major questions raised
by others can be analyzed geologically and soils onginoering-wise by a prudent
s6bsurface exploration program. 'Once the major questions have been answered,
then lot by lot reports required by the County of Los Angeles can incorporate
these findings and be based on the individual building and/or grading plans.
Recommendations
3. The subsurface exploration program for Stage IT should be continued
in the other areas of the tract where major questions have been
raised. These questions should be analyzed and evaluated by the soils
engineer and geologist.
2. The questioned landslide along the western tract boundary should be
evaluated since Moore & Taber has indicated the final stability
analysis of the natural slopes below Steeplechase can not be fully
completed until this slide has been evaluated.
cb c,
Distribution: 2
Diamond Bar Development Co. (1)
Attention: Mr. Ben Molina
Moore A Taber (1)
Attention: Mr. Doug Brown
Respectfully submitted,
2
ncc V Cann 04*fnl
Engineering Geologist (UG 584)
5-
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II
I
Yransainerj,z, - Equestrian Estates - Phase 11 June 2, 1971
CONCLUSION AND RECOMMENDATIONS
Based on the findings of the Stage Il investigation, major questions raised
by others can be analyzed geologically and soils engineering -wise by a prudent
subsurface exploration program. 'Once the major questions have been answered,
then lot by lot reports required by the County of Los Angeles can incorporate
these findings and be based on the individual building and/or grading plans.
Recommendations
1. The subsurface exploration program for Stage II should be continued
in the other areas of the tract where major questions have been
raised. These questions should be analyzed and evaluated by the soils
engineer and geologist.
2. The questioned landslide along the western tract boundary should be
evaluated since Moore & Taber has indicated the final stability
analysis of the natural slopes below Steeplechase can not be fully
completed until this slide has been evaluated.
IMIM
Distribution: 2
Diamond Bar Development Co. (1)
Attention: Mr. Ben Molina
Moore 4 Taber (1)
Attention: Mr. Doug Brown
Respectfully submitted,
Lawrence R. Cann14K
Engineering Geologisp((EG 584)
5-
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REVISED
INDEX NLAP
OF
LOTS
6-1-i1 .
LOTS REQUIRING NO SIGNIFICANT ADDITIONAL SUBSURFACE
EXPLORATION, PROVIDED FUTURE BUILDING PLANS DO
NOT INCLUDE: ADDITIONALIONAL, GRADING
7777, LOTS REQUIRING ADDITIONAL GEOLOGIC AND SOIL
INVESTIGATIONS BASED UPON SUBSURFACE
EXPLORATION (QUESTIONS BY OTHERS)
LOTS PREVIOUSLY TREATED BY OTHERS AND NOT
INCLUDED IN THIS INVESTIGATION
4 L IIT
JE, J LOTS APPROVED BY THE COUNTY OF LOS ANGELES
SYMBOLS
Boxings (Total )
Backhoe "Trenches
Total 8, one old pit Lot 22)
Cross-Section
41- A4
W
PRELIMINARY COPYI
C-1
INDEX MAP
Olk
WIS
LOTS REQUIRING NO SIGNIFICANT ADDITIONAL SUBSURFACE
EXPLORATION, PROVIDED FUTURE BUILDING PLANS DO
NOT INCLUDE ADDITIONAL GRADING
LOTS REQUIRING ADDITIONAL GEOLOGIC AND SOILS
INVESTIGATIONS BASED UPON SUBSURFACE
EXPLORATION
LOTS PREVIOUSLY TREATED BY OTHERS AND NOT
INCLUDED IN THIS INVESTIGATION
LOTS APPROVED BY THE COUNTY OF LOS ANGELES
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DIAMOND BAR EQUESTRIAN ESTATES
TRA CT N0 30289
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TRACT N0. 30289