Prr 5509 DRAFT Landlside Investigation Report Chelton Drive

8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive

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RYAN GEOLOGICAL CONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS

16 Southwood Drive

Orinda, CA 94563

510-520-5592

ENGINEERING GEOLOGY GEOLOGIC HAZARD ASSESSMENT HYDROLOGY GEOTECHNICAL ENGINEERING

LANDSLIDE INVESTIGATION REPORT

CHELTON DRIVE LANDSLIDE

CHELTON DRIVE AND GIRVIN DRIVE

OAKLAND, CALIFORNIA

UNAUTHORIZED USE OR COPYING OF THIS DOCUMENT IS STRICTLY PROHIBITED BY ANYONE OTHER THAN THE

CLIENT AND PROJECT OWNER FOR THIS SPECIFIC PROJECT.

July 25, 2012

Job No. 1082.100


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TABLE OF CONTENTS

INTRODUCTION ............................................................................................................................................ - 1 -

LANDSLIDE HISTORY ................................................................................................................................. - 1 -

PURPOSE AND SCOPE OF SERVICES ......................................................................................................... - 2 -

FIELD INVESTIGATION .............................................................................................................................. - 2 -

SLOPE INCLINOMETER INSTALLATION ..................................................................................................... - 3 -

LABORATORY TESTING ............................................................................................................................. - 3 -

EXISTING GEOTECHNICAL INFORMATION ............................................................................................... - 3 -

Landslide Records at the City of Oakland ............................................................................................ - 3 -

Dames & Moore geotechnical investigation dated October 15, 1969 ................................................ - 4 -

Un-published landslide mapping by the City of Oakland ..................................................................... - 4 -

Geotechnical Investigations of Lot 2344 .............................................................................................. - 5 -

FINDINGS ...................................................................................................................................................... - 5 -

SITE DESCRIPTION .................................................................................................................................... - 5 -

AERIAL PHOTOGRAPH INTERPRETATION ................................................................................................. - 5 -

REGIONAL GEOLOGY ................................................................................................................................ - 6 -

SUBSURFACE CONDITIONS ...................................................................................................................... - 6 -

Landslide Conditions ............................................................................................................................ - 7 -

Bedrock Conditions .............................................................................................................................. - 8 -

Groundwater ........................................................................................................................................ - 8 -

SEISMIC HAZARDS .................................................................................................................................... - 9 -

CONCLUSIONS AND RECOMMENDATIONS ................................................................................................ - 10 -

GENERAL ................................................................................................................................................ - 10 -CHELTON DRIVE LANDSLIDE ACTIVITY ................................................................................................... - 10 -

SLOPE STABILITY ANALYSIS .................................................................................................................... - 11 -

EARTHQUAKE-INDUCED LANDSLIDE POTENTIAL ................................................................................... - 12 -

SEISMIC DESIGN CRITERIA...................................................................................................................... - 12 -


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DRAINAGE GALLERY CONDITIONS ......................................................................................................... - 13 -

SLOPE INCLINOMETER MONITORING .................................................................................................... - 13 -

LIMITATIONS .............................................................................................................................................. - 14 -

REFERENCES ............................................................................................................................................... - 15 -

LIST OF FIGURES

FIGURE 1VICINITY MAP

FIGURE 2SITE PLAN

FIGURE 3CROSS SECTION A-A

FIGURE 4AERIAL PHOTO INTERPRETATION

FIGURE 5REGIONAL GEOLOGIC MAP

FIGURE 6 - REGIONAL LANDSLIDES AND OTHER SURFACE DEPOSITS MAP

FIGURE 7 - OFFICIAL EARTHQUAKE FAULT ZONES MAP

FIGURE 8OFFICIAL SEISMIC HAZARD ZONE MAP, STATE OF CALIFORNIA

FIGURE 911 RESULTS OF SLOPE STABILITY ANALYSES

FIGURE 12SLOPE INCLINOMETER PLOT B-2A

FIGURE 13RING SHEAR TEST RESULTS

FIGURES 14ATTERBERG LIMITS TEST RESULTS

FIGURES 15 AND 16PARTICLE SIZE DISTRIBUTION TEST RESULTS

LIST OF APPENDICES

APPENDIX ACORE LOGS (2013 study)

APPENDIX BBORING LOGS, DAMES AND MOORE (1969)

APPENDIX CDIGITAL PHOTOGRAPHS OF 2013 CORE SAMPLES


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December 1, 2012

Job No. 1082.100

Mr. Edward De MeloC/O BERDING WEIL

2175 N California Blvd, Suite 500

Walnut Creek, California 94596

Attention: Mr. Chad T. Thomas

Subject: DRAFT

Landslide Investigation Report

Chelton Drive Landslide

Chelton Drive and Girvin Drive

Oakland, California

Dear Mr. Thomas:

INTRODUCTION

This report presents the results of our subsurface investigation of the Chelton Drive Landslide located

between Chelton Drive and Girvin Drive in Oakland California. The Chelton Drive Slidewas named

during the late 1960s following failure of the hillside beneath Chelton Drive. Herein we will use the

phrase Chelton Drive Landslide to be clear as to the site conditions. The Chelton Drive Landslidewas

mapped covering an area about 260 feet wide at the head scarp along Chelton Drive and extended

about 320 feet downslope to Girvin Drive at the toe of the landslide mass. The approximate site

location is shown on the Vicinity Map, Figure 1, and the approximate landslide limits are shown onFigure 2.

We previously conducted a preliminary engineering geologic review for Lot 2344 of the Piedmont Pines

development which is located at the base of the Chelton Drive Landslide along Girvin Drive. The review

focused on available geotechnical reports specific to Lot 2344 and landslide records at the City of

Oakland. The results of the review were summarized in our report dated December 1, 2012. The study

revealed that Lot 2344 was located at the base of a historically active deep-seated bedrock landslide

that additional without stabilization would preclude the safe development of Lot 2344 or any of the

surrounding lots.

LANDSLIDE HISTORY

The first reported indications of massive landslide movement occurred in April 1967. Chelton Drive

dropped as much as 10 feet over a period of about 1 week as the landslide slid downslope. Significant

damage resulted from the April 1967 landslide causing closure of Chelton Drive and forcing the

evacuation of 2 homes located within the landslide limits. The City of Oakland restored access through

Chelton Drive by placing fill on the top of the landslide mass and lowering the adjacent street grades.

In January 1969, the landslide mass began to show signs of additional movement along Chelton Drive.

This episode of landslide activity included up to 13 feet of movement over a 1-month period. The two
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homes located on the landslide that were evacuated in 1967 were demolished due to severe structural

damage and the potential for future damage to neighboring properties.

Following the second episode of massive sudden landslide movement in 1969, the City of Oakland

retained Dames & Moore, a reputable geotechnical engineering firm, to provide recommendations for

landslide stabilization. Dames & Moore (report summarized below) characterized the Chelton DriveLandlside as a bedrock landslide with a slip surface as deep as 45 feet below the ground surface. In

order to increase stability of the Chelton Drive Landslide, the City of Oakland installed extensive

drainage galleries to lower groundwater levels. The drainage galleries consisted of a series of vertical

drainage shafts connected at the bottom by corrugated metal pipes. The outlet pipes are visible on the

properties bordering the site and they discharge water below Girvin Drive. We were not able to obtain

the full plan set that shows the bottom elevations or construction details for the drainage galleries or for

any other aspects of the stabilization efforts undertaken by the City of Oakland. The approximate

locations of the drainage galleries are shown on the Site Plan, Figure 2.

The current conditions of Chelton Drive suggest that post-1970 movement of the Chelton Drive

Landslide has occurred. We observed an arcuate pattern of several inches of settlement along thedownslope side of Chelton Drive. The arcuate settlement pattern generally coincides with the landslide

limits reported for the 1967 and 1969 landslide events. Additionally, based on verbal reports, we

understand that lots on the east side of Chelton Drive may have experienced some settlement and

ground deformation. For reference, portions of the 1667 landslide limits were mapped extending into

some lots east of Chelton Drive.

PURPOSE AND SCOPE OF SERVICES

The purpose of this investigation was to evaluate the landslide conditions within and upslope of Lot

2344 of the Piedmont Pines development and to evaluate the feasibility of developing Lot 2344 for

single family residential use. Our scope of services for this project included:

1.

Review of readily available published geologic maps and reports covering the site vicinity.

2.

Reviewing readily available files from the City of Oakland Planning Department.

3.

Site reconnaissance by a State of California licensed Certified Engineering Geologist.

4.

Drilling and logging of 4 exploratory borings to depths between about 30 and 80 feet.

5.

Installation and monitoring of a slope inclinometer in one boring drilled on Lot 2344.

6.

Lab testing on selected slide plane materials.

7.

Evaluation and analysis of the information obtained during the course of this study.

8.

Preparation of this report.

FIELD INVESTIGATION

Our field investigation for this project was conducted in May, 2013. The main aspect of the investigationincluded the drilling and logging of 4 exploratory borings designated as Borings B-1, B-2, B-2A and B-3.

Borings were drilled by Gregg Drilling and Testing, Inc. out of Martinez, California using a six inch

diameter core barrel equipped with HQ coring systems. Borings B-1, B-2 and B-2A were drilled to depths

up to 80 feet below the ground surface using a small limited access Fraste Mito 4000 track-mounted drill

rig and B-3 was drilled using a truck-mounted CME 850 drill rig. Core samples recovered from B-2 were

disrupted by drill rig malfunctions. Therefore, the boring was terminated at a depth of 25 feet, the drill

rig moved about 10 feet south and re-drilled as B-2A. Borings were continuously sampled and logged


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by a certified engineering geologist as samples were recovered. The borings were backfilled with

cement grout in accordance with drilling permit requirements, except for B-2A in which a slope

inclinometer was installed. The boring locations were surveyed in the field by Moran Engineering out of

Berkeley, California. Boring locations are shown on the Site Plan, Figure 2. Core Logs are provided in

Appendix A.

During the field investigation, we also conducted a reconnaissance of the hillside and adjacent streets.The reconnaissance was conducted in attempt to locate the piezometers noted on the 1969 Dames &

Moore map and to identify any other landslide related features at the site. We located man-holes (MH-

1 and MH-2) with PVC pipes above the mapped location of the drainage galleries and one piezometer

along the western shoulder of Chelton Drive. The man-hole locations were surveyed by Moran

Engineering at the locations shown on the Site Plan. The piezometer located along Chelton Drive

appears to coincide with the location of observation well Afrom the 1969 Dames & Moore report and

the approximate location is shown on the Site Plan.

SLOPE INCLINOMETER INSTALLATION

We installed 2.75-inch (70mm) slope inclinometer casing into the borehole at the B-2A location. The

inclinometer was positioned based on surface indications of landslide deformation and site access. Theinclinometer was installed to readable depth of 76 feet below the top of casing. The top of casing was

surveyed by Moran engineering to be at Elevation 1067.4 feet Mean Sea Level, about 1.5 feet above the

ground surface. The A+ groves within the casing were aligned downslope, an azimuth direction of about

270 degrees.

Baseline readings of the slope inclinometer were taken on April 2, 2013 and one set of subsequent

readings were taken on July 17, 2013. The current plots are inconclusive with respect to subsurface

landslide movement but do show minor blip at about 44 feet, about the same elevation as the slide

plane identified in the core samples. Plots of the slope inclinometer readings are provided on Figure 13.

LABORATORY TESTING

Representative samples of the slide plane materials encountered in B-2A were transmitted to Cooper

Testing Labs, Inc., in Palo Alto, California for laboratory analysis. Testing included performing residual

torsion ring shear tests (ASTM D 6467) to get residual strength values for the gouge zone in B-2A at a

depth of 42 feet. The sample was prepared over a -200 sieve and sheared at 2000, 4000 and 8000 ksf.

Atterberg limits and particle size distribution tests were run on slide plane materials in B-2A at 15 and 42

feet. Lab test reports label the samples as being from a depth of 40 feet which represents the middle of

the shear zone noted on the sample, however we provided the lab with the actual clay gouge material at

42 feet for testing. Lab tests indicate that the gouge materials at the base of the landslide have a

residual strength (phi angle) of 15 degrees and a plasticity index (PI) between about 15 and 17. Lab test

results are provided on Figures 16 through 20.

EXISTING GEOTECHNICAL INFORMATIONLandslide Records at the City of Oakland

The City of Oakland Planning Department has record files regarding a large bedrock landslide named the

Chelton Drive Slide that occurred in the Late 1960s. The subject files have the City file designation L

275-1 which is stamped on documents in the file. Movement of the landslide is reported to have

occurred in 1967 and again in 1969. The approximate historic limits of the Chelton Drive Landslide are

shown on the Site plan, Figure 2. The record documents in the City files that were reviewed as part of

this project include the following:


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Proposal to conduct a landslide investigation by Dames & Moore dated June 11, 1969

Landslide investigation report by Dames and Moore dated October 15, 1969. Several enlarged

prints of the figures from this report are also in the City files.

Undated (circa 1969?) topographic map of the subject landslide area by the City of Oakland.

One sheet of a plan set titled Plans for the construction of drainage galleries in the vicinity of

Chelton Drive and Chelsea Drive. The sheet shows the limits of landslide movement prior to

1970, limits of repair grading at the top of the landslide and the location of drainage galleries.

The documents suggest that the first episode of landslide activity extended down to Girvin Drive based

on the map provided in the Dames & Moore proposal and the slide limits shown on the single plan

sheet. The 1969 Dames & Moore report shows the toe of the landslide as much as 50 feet upslope of

Girvin Drive, generally in the middle of Lot 2344. Both of the reported landslide limits are shown on the

Site Plan, Figure 2.

Dames & Moore geotechnical investigation dated October 15, 1969

The City of Oakland retained Dames & Moore to evaluate the Chelton Drive Landslide and provide

recommendations for stabilization. The results of the Dames & Moore study are provided in their reportdated October 15, 1969 which can be found on file at the City of Oakland. In summary, Dames & Moore

drilled 5 exploratory borings through the landslide mass. The earth materials encountered in the

borings were interpreted to indicate a bedrock landslide with a depth of sliding between about 30 and

45 feet deep. The landslide materials were described as highly weathered and fractured shale with

abundant clay seams. Additionally, a 4 to 10 foot thick zone of highly sheared and fractured bedrock

was encountered at the base of the landslide. Bedrock underlying the landslide was described as gray to

black fractured siltstone with little weathering. Groundwater levels were reported to include significant

seasonal fluctuations up to 30 feet which appeared to have been a significant contributing factor in the

landslide activity. The highest groundwater levels noted on the borings logs were up to 15 feet above

the interpreted basal slip plane except for in Boring B-4 which was noted about 11 feet below the

interpreted basal slip plane at that location. The toe of the landslide was described as poorly defined in

the field at that time and the mapping at the toe was inferred based on the occurrence of seepage on

the slope just above Girvin Drive. Additionally, Dames & Moore made some assumptions regarding the

depth of sliding coinciding with the depth at which wells were sheared-off during the 1969 movement.

It is not known if the wells sheared at the deepest portion of movement or if the wells sheared deeper,

possibly at multiple intervals. The approximate locations of borings drilled at the site by Dames and

Moore (1969) are shown on the Site Plan, Figure 2, copies of their boring logs are provided in Appendix

B.

Un-published landslide mapping by the City of Oakland

Historic landslides in the Oakland Hills were previously noted by the City engineer, Mr. Earl Buckingham.

Mr. Buckingham kept detailed unofficial notes of landslides and landslide features as they occurred in

the area between the early 1950s up to about 1970. Portions ofMr. Buckinghams maps and notes are

archived at the offices of Alan Kropp and Associates in Berkeley, California who allowed us to review the

Buckingham information located in their archives. We were able to locate pertinent maps for the

Piedmont Pines development but not the notes that would accompany each landslide feature. The

unpublished Buckingham maps show the subject Chelton Drive Landslide with the same general slide

limits as the 1969 Dames & Moore report. Buckingham noted the landslide as 11 A 34. Additionally,

Buckingham shows another separate landslide on the downhill side of Girvin Drive with the note 11 A

28.


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Geotechnical Investigations of Lot 2344

Previous geotechnical investigations at Lot 2344 were summarized in our December 2012 report. At the

site geotechnical consultant Mohan Shrinivas and Purcell, Rhoades & Associates conducted a

geotechnical studies of Lot 2344 who presented their results in reports dated June 15, 2011 and

December 30, 2010, respectively. The investigation test pits and borings from those studies are shown

on the Site Plan, Figure 2. Since these studies did not detect, mention or evaluate the presence of the

Chelton Drive Landslide, they provide no pertinent data regarding site conditions.

FINDINGS

SITE DESCRIPTION

The site is defined as Lot 2344 of the Piedmont Pines development and the portion of the hillside

located directly above that is underlain by the Chelton Drive Landslide. The site is located between

Chelton Drive at the top of the hill and to Girvin Drive at the bottom. The area was developed well over

75 years ago; however, several lots in the site vicinity are vacant. Lot 2344 is a vacant lot located on the

east side of Girvin Drive in steep hillside terrain typical of the Oakland Hills. Lot 2344 is surrounded byundeveloped vacant lots on all sides, including downslope of Girvin Drive. We understand that these

lots are vacant largely due to the presence of the Chelton Drive Landslide that caused damage,

demolition and removal of 2 homes that were located along Chelton Drive. The approximate locations

on the demolished and removed homes are shown on the Site Plan, Figure 2. Large concrete blocks,

remnants from the former house foundations, were observed on the hillside.

Geomorphically, the site is situated near the head of a tributary drainage basin to Shepherd Canyon

Creek which is located downslope to the northwest. The ground surface at the site is steep with

topography ranging from about Elevation 1160 at the top along Chelton Drive to about Elevation 965 at

the bottom along Girvin Dive. Site topography slopes as steep as about 1 horizontal to 1 vertical (1H:1V)

along Girvin Drive and much flatter and irregular within the landslide mass. There is a subtle yet visiblebulge on the hillside within Lot 2344 that has the appearance of the leading edge of a landslide deposit.

A relatively horizontal (un-natural looking) bench traverses the hillside at the location of the lower tier

of drainage galleries installed in response to the Chelton Drive Landslide. Two man-hole covers (MH-1

and MH-2) were observed at the northern end of the bench at the locations shown on the Site Plan,

Figure 2. Several larger trees at the site are either severely leaning downslope or have fallen.

Chelton Drive currently has an arcuate-shaped cracking and settlement pattern that appears to coincide

with the late-1960s landslide limits. Corrugated metal drainage pipes traverse the slopes north and

south of Lot 2344 and discharge water to the slope below Girvin Drive. The pipes appear to be the

outfall pipes for the drainage galleries installed upslope. The pipes are separated slightly on the north

side of Lot 2344 at the approximate location shown on Figure 2. An erosion gully has formed along the

alignment of the southern pipe below Girvin Drive. We understand that these pipes are the outlet pipesfor the drainage galley installed above Lot 2344 to stabilize the Chelton Drive Landslide. Directly

downslope of the site, the outer edge of Girvin Drive is settling into the ravine.

AERIAL PHOTOGRAPH INTERPRETATION

We reviewed stereo-paired aerial photographs focusing on the years of reported landsliding including

review of aerial photographs from 1967, 1969 and 1970. Aerial photographs were obtained and viewed

at the archive library at Pacific Aerial Surveys office in Oakland, California.


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The 1969 photography showed that Chelton Drive and Chelsea Drive had been recently paved where the

roadway was reported to be damaged and repaired following the 1967 event. The slope between

Chelton Drive and Girvin Drive was covered with trees and not readily viewable. The 1969 photography

provided the best viewing of landslide conditions and show several landslide related features as noted

below. We observed several subparallel cracks in the asphalt along Chelton Drive in the location of the

recent repaving noted in 1967. The slope between Chelton Drive and Girvin Drive appeared to bedisturbed based on tonal contrasts suggesting bare ground rather than vegetation. The area that

appeared disturbed extended down to Girvin Drive. In the 1970 photography, Chelton Drive appeared

repaved as the cracks were no longer visible. A portion of the 1969 photograph annotated with our

interpretations of landside-related features noted is provided on Figure 4.

REGIONAL GEOLOGY

The site is located within the Coast Ranges Geomorphic Province of California. The Coast Ranges are

characterized by northwest-southeast trending series of folded and faulted mountain ranges and valleys.

Folding, faulting and tectonic uplift of the region is the result of rightlateral and oblique relative

motions between the Pacific and North American tectonic plates which has deformed the region for the

past several million years. The San Andreas fault is the generally accepted boundary between theseplates, although in the San Francisco Bay Area, stresses and deformation are distributed across a broad

network of subparallel right-lateral strike slip faults.

The site is situated on the west flank of the Oakland-Berkeley hills which is a northwest-trending band of

uplifted bedrock units forming steep hillsides along the east side of the San Francisco Bay plain.

According to regional geologic maps prepared by the U.S. Geological Survey (Graymer, 2000; Graymer et

al, 1996; Radbruch, 1969; Radbruch and Case, 1967) several bedrock units have been tectonically

juxtaposed against each other in the area. In general, in the site vicinity, sedimentary bedrock units of

the Franciscan Complex are located on the west side of the Hayward fault, while several slivers of

volcanic, metamorphic and sedimentary rocks are located to the east of the fault.

Bedrock underlying the site includes siltstone and shale of the Shepherd Creek formation. The ShepherdCreek formation is a series of sea floor sedimentary layers that were deposited during the Late

Cretaceous Period of geologic time, roughly 65 to 144 million years before present. Outcrops along

Girvin Drive indicate the bedrock is steeply inclined and aligned with a northwest northwest-trending

structure. Regional geologic maps depict a northwest trend and variable dip of the bedrock layers that

is distorted by folding. Locally, based on our observation of several bedrock outcrops along Girvin Drive,

this portion of the Shepherd Creek formation consists of thinly bedded layers of sandstone and shale

that strike to the northwest and dip at inclinations between about 75 to 90 degrees, generally consistent

with the regional geologic maps. A portion of Graymers map is provided on Figure 5.

The site is located in an area of known landslides and relatively high landslide hazards. Regional

landslide maps prepared by the U.S. Geological Survey (Nilsen, 1975) shows a landslide featuredownslope of Girvin Drive but do not show a landslide deposit in the location of the Chelton Drive

Landslide. However, regional maps are generally created without site-specific investigation and are

considered guidelines for planning only. A portion of Nilsens landslide map is provided on Figure 6.

SUBSURFACE CONDITIONS

The site is underlain by the Chelton Drive Landslide which is a deep-seated bedrock landslide extending

to depths of about 45 to 50 feet below the ground surface. Artificial fill was placed along the top of the


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landslide to re-establish the roadway along Chelton Drive following the 1967 and 1969 landslide events.

We did not investigate the fill. The landslide mass is composed of a displaced block of bedrock overlying

the Shepherd Creek formation. Descriptions of the landslide mass, basal shear zone and the underlying

bedrock are provided below.

Landslide ConditionsBased on the findings of this investigation and review of the 1969 Dames & Moore report, the Chelton

Drive Landslide is composed of a displaced mass of disrupted Shepherd Creek Formation with abundant

clay infilling. Many portions of the rock mass recovered in our borings have a block-in-matrix texture

with clay infilling between dilated fractures in the rock. The majority of clay infilling was interpreted to

be washed away during the drilling processes based on the recovery of rubble only at several intervals.

The landslide mass was found brown to orange brown, highly weathered, highly fractured to crushed

and weak.

Our borings were drilled in the northern half of the landslide, where we generally encountered deeper

landslide debris than encountered in Dames & Moores nearby borings. For example, we encountered

up to 42 feet of landslide debris in Boring B-2A, whereas Dames & Moore encountered only about 27feet of landslide debris in their nearby B-4 which was drilled more in the center of the landslide mass

(see Figure 2). This can be attributed to the underlying bedrock structure. While the landslide cuts

across dip, thereby shearing across beds, we believe that the northern edge of the landslide is, at least

in part, along one of the more resistant steep south-dipping sandstone or siltstone beds. Therefore, the

Chelton Drive Landslide is likely wedge-shaped across its width, resulting in deeper landslide deposits to

the north and a steep northern margin along bedrock structure.

The basal landslide slip plane was identified in Borings B-1 and B-2A. In Boring B-1, the slide plane

identified at 32 feet included a 2 foot thick shear zone consisting of angular rock fragments in a

sheared soil matrix demonstrating block-in-matrix textures. At the top of the shear zone, we identified a

1 inch thick layer of olive brown clay gouge with well-developed dip slip striations. The gouge layer was

measured dipping 17 degrees. Internal shearing within the landslide mass was also interpreted betweenabout 20 to 23 feet below the ground surface in Boring B-1.

In Boring B-2A, we encountered sheared zones at depths of about 15 and 42 feet below the ground

surface. The shear zone at 15 feet includes 8 inches of sheared clay gouge with a sub-horizontal foliated

shear fabric. We interpreted this zone to represent a higher slide plane within the landslide mass.

Samples of the sheared zone at 15 feet were submitted to the laboratory for Atterberg limits and

gradation tests. The lab tests indicate the slide plane clay gouge is moderately expansive with a

Plasticity Index (PI) of 27. Digital photographs of the slide plane recovered from the core samples at 15

feet are provided in Appendix C.

The basal shear zone was identified in Boring B-2A between about 38 and 42 feet below the ground

surface. Within this interval we identified a 12 to 18 inch zone of blue gray sheared clay with angular

rock fragments and a foliated shear fabric dipping 10 to 15 degrees. About 12 inches of rubble were

encountered that may be slough from the borehole above, however the driller insists they did not raise

the core barrel through this interval, therefore, the rubble may represent a block of fractured rock

within the shear zone. At the base of the shear zone, we identified the slide plane at a depth of about

42 feet. At this depth we identified a 6-inch thick layer of sheared black clay with a inch thick layer

of foliated clay gouge at the base. The clay gouge was measured dipping 10 degrees. The slide plane at


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42 feet was submitted to the laboratory for torsional ring shear, Atterberg limits and gradation tests.

The lab tests indicate the slide plane gouge is relatively granular with a Plasticity Index (PI) of 15 and a

residual phi angle of 15 degrees. Digital photographs of the shear zone and slide plane recovered

between 37 and 42 feet are provided in Appendix C.

Bedrock Conditions

Bedrock underlying and surrounding the Chelton Drive Landslide belongs to the Shepherd Creek

formation. The Shepherd Creek formation was deposited as a series of sea floor sediments during the

Cretaceous Period of geologic time (65 to 144 million years before present). The Shepherd Creek

formation consists of thinly laminated clay rich shale, siltstone and occasional beds of sandstone. At the

site the in-place bedrock was found gray to dark gray, weak to moderately strong and thinly laminated.

Bedrock structure measured in outcrops along Girvin Drive shown a northwest strike of the beds that

dip steeply to the northeast and southwest between 75 to 90 degrees. This structure is typical of the

steeply bedded, occasionally overturned structures shown on the regional geologic maps.

We observed outcrops or relatively strong sandstone beds up to a few feet thick along the slope above

Girvin Drive, just north of the site. The beds were striking northwest and dipping south (towards thelandslide mass). The strike of the bedrock structure is about the same or at least similar to the direction

of movement of the Chelton Drive Landslide. Therefore, the steeply dipping stronger beds observed

near the northern margin of the landslide mass likely influences the subsurface geometry of the

landslide as noted above.

Groundwater

Groundwater conditions at the site are influenced by the presence of the drainage galleries installed by

the City of Oakland as their stabilization efforts of the Chelton Drive Landslide. The drainage galleries

include vertical drains connected at the base by horizontal shafts. We were not able to locate any

records of the drainage gallery construction other than the plan view locations that are shown on the

Site Plan, Figure 2. We made several inquiries to the City of Oaklands planning, engineering and

drainage departments. None of these departments had any knowledge or records regarding the

subsurface drainage system installed at the site.

Groundwater conditions were generally obscured during drilling of our borings due to the addition of

water as part of the HQ coring methods. We were able to obtain some groundwater information from

B-1, where water continually rose from the core barrels after the drilling system was shut off suggesting

some artesian conditions at about 50 feet below the ground surface. Groundwater information was not

obtained from Borings B-2, B-2A or B-3.

We located an 8-inch diameter Christy box along the western shoulder of Chelton Drive covering a near-

vertical, 1 inch diameter PVC pipe that appears to correspond to the location of observation well A

from the 1969 Dames & Moore report. We inserted a water level meter into the 1 inch diameter PVCpipe and found that the meter has trouble passing a blockage or kink at a depth of about 34 feet.

Groundwater was detected at a depth of 44 feet and the bottom of the PVC pipe appeared to be about

49 feet below the ground surface. The approximate location of observation well A is shown on the Site

Plan, Figure 2.

We located 2 man-holes along the northern limits of the Chelton Drive Landslide, located roughly mid

slope. The locations of the man-holes, MH-1 and MH-2, were surveyed in the field by Moran


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Oakland, California

Job No. 1082.100

- 9 -

July 25, 2013


Engineering at the locations shown on the Site Plan, Figure 2. Note that the surveyed man-hole

locations correspond to the north end of the middle row of the drainage galleries installed by the City of

Oakland. Therefore, we believe these are observation wells to check the drainage gallery conditions.

Manhole MH-1 covers an 8-inch diameter PVC pipe. We inserted the water level reader into the 8-inch

PVC pipe on the uphill side of the pipe. The water level meter hit the downhill side of the pipe at a

depth of about 20 feet demonstrating that the PVC pipe is severely out of plumb. The water level meterencountered a muddy bottom of the pipe at about 54 feet below the ground surface. Man-hole MH-2

covers a 2-inch diameter PVC pipe that is leaning over about 20 degrees at the ground surface. Similar

to MH-1, the water level reader encountered a muddy bottom of the pipe at about 49 feet below the

ground surface. Groundwater was not detected in the PVC pipes.

Our interpretations of the groundwater conditions underlying the site are shown on the Cross Section,

Figure 3. The following table summarizes the groundwater conditions described above.

LOCATION

GROUND SURFACE

ELEVATION

(Ft MSL)

DEPTH TO

GROUNDWATER

(Ft)

GROUNDWATER

ELEVATION

(Ft MSL)

B-1 1133.3* 50 feet 1083.3

Well A Estimated 1058 44 feet 1014

MH-1 1101.9* >54 feet 49 feet


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Oakland, California

Job No. 1082.100

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July 25, 2013


Given the relatively high seismicity in the region, the site is expected to experience at least one

moderate to large magnitude earthquake in the future. The Working Group on Earthquake Probabilities

(1999) estimates there is a roughly 65% chance that the San Francisco Bay Area will experience a

magnitude 6.7 (or greater) earthquake within in the next 30 years. Interactive probabilistic seismic

analysis tools available at the U.S. Geological Survey and California Geological Survey websites suggest

the site is expected to experience peak ground accelerations (pga) with a 10% chance of being exceededin the next 50 years of 0.71g and 0.77g; respectively.

The site is located within a State of California designated Seismic Hazard Zone for earthquake-induced

landslide displacement (CGS, 2003). In contrast, seismic hazards maps covering the cities of Oakland

and Piedmont prepared by the U.S. Geological Survey (Miles and Keefer, 2001) shows the seismic

landslide hazard at the site to be low to very low. The official State of California seismic hazard map is

provided on Figure 8, the U.S. Geological Survey map is not provided to avoid confusion.

CONCLUSIONS AND RECOMMENDATIONS

GENERAL

Based on the results of this study, experience with similar large bedrock landslides, and professional

judgment, in our opinion none of the vacant lots between Chelton Drive and Girvin Drive or the vacant

lots below Girvin Drive are developable in the current conditions due to the high potential for the hazard

of damage resulting from movement of the Chelton Drive Landslide. The primary geologic hazards

impacting the site are the presence of the Chelton Drive Landslide and the potential for sudden mass

landslide displacement during a seismic event. Extensive movement of the existing landslide mass could

burry, knock over or destroy future improvements located within the landslide mass.

The current landslide conditions are considered marginally stable at best. The 1969 stability analysis

provided in the Dames & Moore report indicates that the landslide repair was designed to be marginally

stable in the static conditions, however, their analysis and parameters do not indicate the landslide is

stable in the pseudo-static (seismic) conditions. Based on our analysis, the Chelton Drive Landslide is

expected to undergo on the order of 5 to 10 feet of seismically induced deformation during a moderate

to large earthquake.

Based on the results of this study, we recommend the Chelton Drive Landslide be treated as an active

landslide feature for planning purposes.

CHELTON DRIVE LANDSLIDE ACTIVITY

Bedrock landslides in the region often creep along the basal slip surface at very slow rates for several

years, sometimes decades, without showing indications of activity such as cracks or bulges at the ground

surface. We believe there is physical evidence at the site that suggests the Chelton Drive Landslide hasexperienced episodic creep or movement since the historic landslide movement in 1969. The surface

indications of landslide activity include:

1)

There are several semi-arcuate cracks in the pavement along Chelton Drive, at about the

locations of the head scarp of the Chelton Drive Landslide.

2)

The leaning PVC pipes located at man-holes MH-1 and MH-2 suggest downslope movement

after installation.


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Oakland, California

Job No. 1082.100

- 11 -

July 25, 2013


3)

The bend or block in the PVC pipe at a depth of about 34 feet at observation well A which

corresponds to the approximate depth of the landslide at that location.

SLOPE STABILITY ANALYSIS

The stability analysis conducted by Dames & Moore in 1969 (for the shallowest condition) indicated that

the drainage galleries would only marginally stabilize the Chelton Drive Landslide. The analysis

calculated factor of safety of 1.2 for the non-seismic condition. With this relatively low calculated static

factor of safety, the existing landslide was expected to experience significant displacement during a

moderate to large earthquake event, specifically on the Hayward fault, which is located just mile west

of the site. It should be noted that the Dames and Moore analysis is well over 43 years old.

In order to model the static and seismic stability of the existing slope, we conducted a series of limit-

equilibrium slope stability analyses using the computer program SLOPE-W. Our slope stability analyses

were based on the interpreted slip surface geometry shown on the Cross Section (Figure 3).

Groundwater was modeled predominantly below the landslide mass due to the presence of the

drainage galleries and the results of our field investigation. The results of our various slope stability runs

are discussed in more detail below. . Plots of the slope stability analysis are provided on Figures 9though 11

In our initial static stability run, we modeled the slide plane gouge zone using a drained residual friction

angle of 15 degrees, which is consistent with the results of the laboratory ring shear test (Figure 13).

The analysis resulted in a factor of safety well below 1.0. These results are not supported by field data

or the initial inclinometer readings, which indicate the 15-degree drained friction angle measured in the

lab is not representative of the entire slide plane and likely represents the lower bound strength. In

addition, the slope stability analyses were performed using a two-dimensional model, which neglects

the three-dimensional effects of the potentially wedge-shaped landslide, which tend to increase the

actual factor of safety in the field. The results of the initial analysis using the 15-degree drained friction

angle are presented on Figure 11.

During our second slope stability run, we estimated the shear strength along the existing slide plane

through back-calculation, based on the assumption that the slope is currently at a static factor of safety

of about 1.0. The back-calculation using the two-dimensional slope stability model resulted in a drained

friction angle of about 24 degrees, as presented on Figure 11. The 24-degree strength is, in theory,

inflated due to the fact that it is influenced by the three-dimensional effects of the landslide present in

the field, which are not captured in the two-dimensional model. We conclude the assumed

approximate factor of safety of 1.0 is reasonable due to the observations of the arcuate cracking and

settlement pattern along Chelton Drive, roughly at the location of the 1967 and 1969 head scarp.

However, we believe the 24-degree strength likely represents an upper-bound for the strength of the

gouge zone, and therefore, our subsequent analyses utilize strength values between the 15- and 24-

degree values discussed above. The results of the back-calculation analysis are presented on Figure 11.

For our third run, we used a drained friction angle of about 20 degrees, which we believe is a realistic

strength approximation for long-term static conditions, given the available data and field observations.

As presented on Figure 12 this analysis resulted in a factor of safety of less than 1.0, which indicates

active failure, however, considering the shortcomings of two-dimensional modeling discussed above, we

believe 20 degrees represents a realistic average strength for the slide plane under static conditions. The

results of the analysis for the long-term static condition are presented on Figure 12.


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Oakland, California

Job No. 1082.100

- 12 -

July 25, 2013


Given that the slope is marginally stable under static conditions, we conclude the slope is subject to

significant deformations during moderate to large seismic events. As discussed in more detail in the

following section, we performed a deformation analysis to estimate the magnitude of potential

displacements during future earthquakes. We performed a fourth slope stability run in SLOPE-W toestimate the yield acceleration of the slide mass. The fourth run utilized a horizontal pseudo-static

coefficient to represent seismic loading. We also assigned an estimated undrained strength of 1,500 psf,

which is based on previous TxUU testing on the slide mass by Dames & Moore (1969) with consideration

of potential strength reduction due to the cyclic nature of seismic loading. We performed a series of

runs, increasing the horizontal pseudo-static coefficient until a factor of safety of 1.0 was achieved.

EARTHQUAKE-INDUCED LANDSLIDE POTENTIAL

The site is located within a State of California designated Seismic Hazard Zone for earthquake-induced

landslide displacement. The probabilistic seismic analysis web tools from the CGS and USGS indicate the

site is expected to experience relatively high peak ground accelerations. The stability of all slopes is

lowest during ground shaking from a large magnitude earthquake. Areas underlain by existinglandslides are generally considered to have the highest probability of coseismic displacement. Based on

our analysis, the potential for severe damage resulting from seismically-induced movement of the

Chelton Drive Landslide is the primary geologic hazard precluding development at the site. In our

opinion, the risk of earthquake-induced landslide damage at the site is very high.

As discussed in the previous section, to model the earthquake loading, we assigned an equivalent static

(pseudo-static) horizontal force equal to the soil weight multiplied by a seismic coefficient, k. Limit

equilibrium slope stability analyses were then performed to determine the critical (yield) seismic

coefficient (ky) that will reduce the static factor of safety against sliding of the potential slide mass to

unity. The analysis indicates ky for the slip surface defined in the geologic cross section (Figure 3) is

about 0.07g.

To estimate the amount of lateral movement the critical slide mass may experience during a seismic

event, we used the methodology developed by Bray and Travasarou (2007), which is presented in the

paper titled Simplified Procedure for Estimating Earthquake Induced Deviatoric Slope Displacements.

The method indicates the median displacement for the critical slip surface shown in Figure 3 is

approximately 5 to 10 feet, for a Mw7.33 earthquake occurring approximately 1.2 kilometers from the

site on the Hayward Fault.

SEISMIC DESIGN CRITERIA

Due to the relatively high seismicity of the San Francisco Bay region, the project should be expected to

undergo at least 1 moderate to strong earthquake during the lifespan of the project. Ground shaking

from a strong earthquake is a hazard that cannot be eliminated but can be partially mitigated throughproper attention to seismic structural design and observance of good construction practices. Based on

the an approximate center of the landslide located coordinates of 37.8264 degrees latitude and -

122.1953 degrees longitude, we recommend the structural engineer use the following design

parameters for seismic design in accordance with the ASCE 7-10 Standard, which is based on the 2008

USGS seismic hazard data.

SITE CLASS B - PERIOD (sec) 0.2 1.0


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Oakland, California

Job No. 1082.100

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July 25, 2013


SPECTRAL RESPONSE Ss, S1 2.371g 0.986g

SITE COEFFICIENT Fa, Fv 1.0 1.0

MAXIMUM SPECTRAL RESPONSE

Sms, Sm1

2.371g 0.986g

DESIGN SPECTRAL RESPONSE

SDs, SD11.581g 0.657g

The above mentioned values are empirically generated and the actual ground response at the site can

vary.

DRAINAGE GALLERY CONDITIONS

The drainage galleries installed to lower groundwater levels from within the landslide area are over 40

years old and we could not find record of any maintenance activities by the City of Oakland. The

drainage galleries include vertical shafts connected at the base by metal pipes at the approximatelocations shown on the Site Plan, Figure 2. If the drainage galleries continually maintain groundwater

levels below the base of the landslide, they can be effective in lowering the potential for sudden massive

landslide movement.

Two man-hole covers (MH-1 and MH-2) were located along the alignment of the drainage galleries as

shown on the Site Plan, Figure 2. As previously discussed, both man-holes cover PVC pipes, both of

which were observed to have a significant downslope lean. Additionally, muddy sediments were

encountered at the bottom of each pipe. Based on our observations at the site, we have the following

concerns regarding the drainage galleries:

1)

We could not find any records of the as-built depths of the drainage galleries nor could we

locate any records of maintenance or knowledge of the system at the City of Oakland offices.

2)

Post-1970 movement of the Chelton Drive Landslide that has likely damaged some of the

vertical shafts allowing sediment to enter the pipes and the movement has deformed the

vertical PVC pipes.

3)

Some of the vertical shafts may not have penetrated through the deeper portions of the wedge

shaped landslide along the northern margin, above Lot 2344.

Properly functioning drainage galleries are essential to the stability of the Chelton Drive Landslide. As

previously mentioned there is a high risk of seismically-induced ground displacement of the Chelton

Drive Landslide which could severely damage the drainage gallery system. This can allow groundwater

to back up in the system and saturate the landslide mass which would increase the potential for

movement. The drainage galleries should be maintained in a functioning capacity for the lifespan of theneighboring developments.

SLOPE INCLINOMETER MONITORING

The slope inclinometer was installed in boring B-2A for the purpose of monitoring subsurface movement

of the Chelton Drive Landslide. Baseline readings of the slope inclinometer were taken on April 2, 2013

and one set readings were taken on July 17, 2013. The current plots are inconclusive with respect to

subsurface landslide movement but do show a very minor blip in the data plot at about 44 feet (below


17/63


Oakland, California

Job No. 1082.100

- 14 -

July 25, 2013


the top of casing), corresponding to about the same elevation as the slide plane identified in the core

samples. At this time the readings are considered inconclusive with respect to landslide movement due

to the relatively short time period it has been installed. Slow landslide creep can take several months to

fully engage the inclinometer casing. We recommend the current quarterly monitoring period be

revised to take readings at 6 month intervals rather than every 3 months. Additionally, we recommend

the inclinometer be read as soon as possible following any small to large earthquake that causes groundshaking at the site. The post-earthquake readings should be performed to cross check the seismic

deformation analysis provided above, and to demonstrate activity of the Chelton Drive Landslide and

the magnitude of earthquake-induced movement of the landslide mass.

LIMITATIONS

The conclusions and recommendations contained in this report are based on the information provided

to us regarding the proposed improvements, the results of this investigation, our experience in the area

and professional judgment. This study has been conducted in accordance with currently accepted

standards of professional engineering geology; no other warranty is expressed or implied. The locations

of features discussed in the text above are those that existed at the time of our last site visit in July 2013and are not necessarily representative of other locations or times. If the subsurface conditions

encountered during any repair work or any future investigations of the Chelton Drive Landslide differ

from those interpreted in this report, our firm should be afforded the opportunity to review the changes

and respond accordingly.

Respectfully submitted,

RYAN GEOLOGICAL CONSULTING, INC.

Kevin James Ryan, P.G., C.E.G.

Principal Engineering Geologist

Copies: Addressee (1 pdf via email)

Attention: Mr. Chad Thomas

Mr. Ed De Melo (1 pdf via email, 2 hard copies via hand-delivery)

RGC_Landlside investigation report/Chelton Drive Landlside/1082.100.doc


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Oakland, California

Job No. 1082.100

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July 25, 2013


REFERENCES

California Division of Mines and Geology, January 1, 1982, State of California special studies zones,

Oakland East, Revised official map.

California Geological Survey, February 14, 2003, State of California Seismic Hazard Zones, Oakland East

and part of the Las Trampas Ridge quadrangles, Official map.

California Geological Survey, 2003, Seismic hazard zone report for the Oakland East 7.5-minute

quadrangle, Alameda County, California: Seismic Hazard Zone Report 080.

Dames & Moore, October 15, 1969, Geological and soil engineering studies, Chelton Drive Slide, Chelton

Drive near Chelsea Drive, Oakland, California. Job No. 1363-005. Consulting report for the City of

Oakland.

Herd, D.H., 1978, Map of quaternary faulting along the northern Hayward fault zone: Mare Island,Richmond, Briones Valley, Oakland West, Oakland East, San Leandro, Hayward, and Newark 7

quadrangles, California: U.S. Geological Survey Open-File Report 78-308. Sheet 5 of 8.

Graymer, R.W.; 2000; Geologic map and database of the Oakland Metropolitan Area, Alameda, Contra

Costa, and San Francisco Counties, California: U.S. Geological Survey Miscellaneous Field Studies MF

2342, Online Version 1.0.

Graymer, R.W., Jones, D.L. and Brabb, E.E., 1996, Preliminary geologic map emphasizing bedrock

formations in Alameda County, California: A digital database: U.S. Geological survey Open File Report

96-252.

Leinkaemper, J.J.; 2008 (revised); Digital database of recently active traces of the Hayward fault: U.S.Geological Survey Data Series 177, Version 1.1.

Leinkaemper, J.J.; 1992; Map of recently active traces of the Hayward fault, Alameda and Contra Costa

Counties, California: U.S. Geological Survey Miscellaneous Field Studies Map MF-2196.

Miles, S.B. and Keefer, D.K., 2001, Seismic landslide hazard for the Cities of Oakland and Piedmont,

California: U.S. Geological Survey Miscellaneous Field Studies Map MF-2379.

Nilsen, T.W., 1975, Preliminary photointerpretation map of landslide and other surficial deposits of the

Oakland East quadrangle, Contra Costa and Alameda Counties, California: U.S. Geological Survey

Open File Map 75-277-41.

Purcell, Rhoades & Associates, December 30, 2012, Geotechnical Study, proposed single family home,

Lot 2344, Girvin Drive, Piedmont Pines, Oakland, California. Project No. 04-232/7500-01. Consulting

report for Mr. Edward De Melo.

Radbruch-Hall, D.H.; 1974; Map showing recently active breaks along the Hayward fault zone and the

southern Calaveras fault zone, California: U.S. Geological Survey Miscellaneous Investigations Series

Map I-813.


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Oakland, California

Job No. 1082.100

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July 25, 2013


Radbruch, D.H.; 1969; Aerial and engineering geology of the Oakland East quadrangle, California: U.S.

Geological Survey Geologic Quadrangle Maps GQ-769.

Radbruch, D. and Case, J.E., 1967, Preliminary geologic map and engineering geologic information,

Oakland and vicinity, California: U.S. Geological Survey Open-File Report 67-183.

Radbruch, D.H., 1967, Approximate location of fault traces and historic surface ruptures within the

Hayward Fault Zone between San Pablo and Warm Springs, California: U.S. Geological Survey

Miscellaneous Geologic Investigations Map I-522.

Roberts, S., Roberts, M.A., and Brennan, E.M., 1999, Landslides in Alameda County, California. A digital

database extracted from preliminary photointerpretation maps of landslides and other surficial

deposits by T.H. Nilsen in U.S.G.S. Open-File Report 75-277, U.S. Geological Survey Open-File Report

99-504.

Ryan Geological consulting, Inc., December 1, 2012, Preliminary engineering geologic review, Lot 2344

Piedmont Pines, Girvin Drive, Oakland, California. Consulting report for Mr. Ed De Melo, Job No.

1082.000.

Shrinivas, M., June 15, 2011, Geotechnical engineering investigation and design recommendations, new

residenceAPN 048D-7281-052Girvin Drive, Oakland, California. Consulting report for Mr. Edward

De Melo.


20/63

APPROXIMATESITE LOCATION

BASE: PORTIONS OF U.S.G.S. 7.5 MINUTE TOPOGRAPHIC QUADRANGLE, OAKLAND

EAST, CALIFORNIA AT A SCALE OF 1:24,000.

0 1000

1"=1000'



OAKLAND , CA

DATE: 7-22-13 Figure 1Project No. 1082.100

RYAN GEOLOGICALCONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS


21/63

0 50

1"=50'

BASE: DRAFT TOPOGRAPHIC SURVEY, PREPARED BY MORAN ENGINEERING, INC., DATED APRIL 20 13, AND CITY OF OAKLAND TOPO OF LANDSLIDE SURVEYED PRIOR TO 1970 LANDSLIDE MOVEMENT


22/63

0 50

1"=50'


23/63

?

?

TENSION CRACKS

ALONG CHELTON

DRIVE

APPROXIMATE LANDSLIDE

LIMITS BASED ON

APPARENT GROUND

DISTURBANCES

CHELTON

DRIVE

GIRVINDRIVE

CHELSEA DRIVE

BASE: PORTION OF AERIAL PHOTOGRAPH AV-902-09-26 FLOWN ON 5-16-1969

ACQUIRED FROM PACIFIC AERIAL SURVEYS IN OAKLAND CALIFORNIA

0 200

1"=200'


NOTE: LANDSLIDE FEATURES NOTED ABOVE ARE INTERPRETED

FROM STEREO-PAIRED AERIAL PHOTOGRAPHS DESIGNATED AS

FLIGHT AV-902, LINE 09, FRAMES 25 AND 26 FLOWN ON 5-16-1969

(APPROXIMATE)




OAKLAND , CA


24/63

APPROXIMATE

SITE LOCATION

Ko

Kjm

Kfn

Qpaf

jb

0 1000

1"=1000'





OAKLAND , CA

BASE: PORTION OF R.W. GRAYMER, 2000, GEOLOGIC MAP AND MAP DATABASE OF THE

OAKLAND METROPOLITAN AREA, ALAMEDA, CONTRA COSTA, AND SAN FRANCISCO

COUNTIES, CALIFORNIA: U.S. GEOLOGICAL SURVEY MISCELLANEOUS FIELD STUDIES

sp

EXPLANATION

CONTACT - DEPOSITIONAL OR

INTRUSIVE CONTACT, DASHED

WHERE APPROXIMATELY LOCATED,

DOTTED WHERE CONCEALED

REVERSE OR THRUST FAULT -

DASHED WHERE APPROXIMATELY

LOCATED, DOTTED WHERE

ONCEALED

STRIKE AND DIP OVERTURNED

BEDDING

STRIKE AND DIP OF BEDDING

ALLUVIAL FAN AND FLUVIAL

DEPOSITS (PLEISTOCENE)

FRANCISCAN COMPLEX

Qpaf

Ksc

Kr

CHERT BLOCKS

SHEPARD CREEK FORMATION

REDWOOD CANYON FORMATION

OAKLAND CONGLOMERATE

JOAQUIN MILLER FORMATION

SANDSTONE

fs

Ko

Kjm

Kfn


25/63


BASE: PORTION OF NILSEN, T.H. 1975 PRELIMINARY PHOTOINTERPRETATION MAP OF

LANDSLIDE AND OTHER SURFICIAL DEPOSITS OF THE OAKLAND EAST 7-1/2 QUADRANGLE

CONTRA COSTA AND ALAMEDA COUNTIES, CALIFORNIA, BY TOR H. NILSEN US

GEOLOGICAL SURVEY OPEN-FILE REPORT 75-277-41

0 1000

1"=1000'



REGIONAL LANDSLIDES AND OTHER

SURFICIAL DEPOSITS MAPCHELTON DRIVE LANDSLIDE


OAKLAND , CA


26/63


HAYWARD FAULT

NORTHERN SECTION

BASE: PORTIONS OF STATE OF CALIFORNIA SPECIAL STUDIES ZONES , OAKLAND

EAST, CALIFORNIA AT A SCALE OF 1:24,000.

0 1000

1"=1000'


OFFICIAL EARTHQUAKE FAULT ZONES MAP




OAKLAND , CA


27/63

APPROXIMATE

SITE LOCATION

BASE: PORTIONS OF SEISMIC HAZARD ZONES , OAKLAND EAST AND PART

OF LAS TRAMPAS RIDGE, CALIFORNIA AT A SCALE OF 1:24,000.

0 1000

1"=1000'


OFFICIAL SEISMIC HAZARD ZONES MAP

STATE OF CALIFORNIA




OAKLAND , CA


28/63

DATE: 7-31-13 Figure XProject No. 1082.100




OAKLAND , CA

STATIC ANALYSIS - NO SESMIC LOAD

LANDSLIDE MASS

Wt: 130 pcf

C: 0 psf

Phi: 15 degrees

BEDROCK

Impenetrable


GEOLOGIC SECTION A-A' - FULLY SPECIFIED FAILURE SURFACE


Residual Strength conditionsFactor of Safety = 0.6

9


29/63





OAKLAND , CA


LANDSLIDE MASS

Wt: 130 pcf

C: 0 psf

Phi: 24 degrees

BEDROCK

Impenetrable


Back-CalculationFactor of Safety = 1.2

10




30/63





OAKLAND , CA


LANDSLIDE MASS

Wt: 130 pcf

C: 0 psf

Phi: 20 degrees

BEDROCK

Impenetrable


Long-Term Static ConditionFactor of Safety = 0.8




31/63

RSTInstrumentsLtd.

Inclinalsis

.2.44.3

CUM

ULATIVEDISPLACEMENT

Borehole:B

2GIRVIN

Project:RYAN

Location:

Northing:

Easting:

Collar:

SpiralCorrection:NA

CollarEle

ation:0.0feet

Bore

holeTotalDepth:76.0feet

AG

roo

eA

imuth:270degrees

BaseReading:2013Apr0214:48

AppliedA

imuth:0.0degrees

A

is-A

CumulatieDisplacement(inches)

-1.00

-0.80

-0.60

-0.40

-0.20

-0.00

0.20

0.40

0.60

0.80

1.00

Depth(feet)

2.00.0

-2.0

-4.0

-6.0

-8.0

-10.0

-12.0

-14.0

-16.0

-18.0

-20.0

-22.0

-24.0

-26.0

-28.0

-30.0

-32.0

-34.0

-36.0

-38.0

-40.0

-42.0

-44.0

-46.0

-48.0

-50.0

-52.0

-54.0

-56.0

-58.0

-60.0

-62.0

-64.0

-66.0

-68.0

-70.0

-72.0

-74.0

-76.0

-78.0

-80.0

-82.0

B

2GIRVIN(3)

17-Jul-13

B

2GIRVIN(2)

02-Apr-13

A

is-B

CumulatieDisplacement(inch

es)

-1.00

-0.80

-0.60

-0.40

-0.20

-0.00

0.20

0.40

0.60

0.80

1.00

Depth(feet)

2.00.0

-2.0

-4.0

-6.0

-8.0

-10.0

-12.0

-14.0

-16.0

-18.0

-20.0

-22.0

-24.0

-26.0

-28.0

-30.0

-32.0

-34.0

-36.0

-38.0

-40.0

-42.0

-44.0

-46.0

-48.0

-50.0

-52.0

-54.0

-56.0

-58.0

-60.0

-62.0

-64.0

-66.0

-68.0

-70.0

-72.0

-74.0

-76.0

-78.0

-80.0

-82.0

B

2GIRVIN(3)17-Jul-13

B

2GIRVIN(2)02-Apr-13


32/63

Job No.: Boring: Date: 05/03/2013

Client: Sample: By: PJ

Project: Depth: Checked: DC

Soil Type: Clay, %: 13 X

Remarks:

LL: 30

2000 4000 8000 PL: 15 Residual: X

16 15 15

804-001 Undisturbed:

Peak:

Residual:

B-2A

40'

Ryan Geological

Chelton Drive Slide - 1082.100

Normal Stress, psf

Secant Phi, deg.

Fully Softened:

Peak:

Bluish Black Lean Clayey SAND w/ GravelThe sample was processed over the #200 sieve per

clients instructions. A small friction correction was

applied to each point.

564

1068

2140

0

2000

4000

6000

8000

0 2000 4000 6000 8000

ShearStress,psf

Normal Stress, psf

Secant Residual Friction Angles

0

500

1000

1500

2000

2500

0 10 20 30 40

She

arStress,psf

Degrees

Deformation Curves2000 psf

4000 psf

8000 psf

To convert degrees to inches of

Drained, Residual Torsional Ring ShearTest ASTM D 6467

0

2000

4000

6000

8000

0 2000 4000 6000 8000

ShearStress,psf

Normal Stress, psf

Strength Envelope

-0.001

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

0.010 0.2 0.4 0.6 0.8 1

Chan

gein

Height,inches

Deformation, inches

Vertical Deformation

2000 psf4000 psf

8000 psf

FIGURE 13


33/63

Project:Remarks:Client:Project No.

%


34/63

Project No.:

Project:

Client:

Cu

Cc

COEFFICIENTSD10

D30

D60

REMARKS:GRAIN SIZE

SOIL DESCRIPTIONPERCENT FINERSIEVEPERCENT FINERSIEVE

LLPLAASHTOUSCS% CLAY% SILT% SAND% GRAVEL

sizesizenumber

Particle Size Distribution Report

10

20

30

40

50

60

70

80

90

0

100

PERCENTFINER

100 10 1 0.1 0.01 0.00200

GRAIN SIZE - mm

6in.

3in.

2in.

1-1/2in.

1in.

3/4in.

1/2in.

3/8in.

#4

#10

#20#30#40

#60

#100

#140

#200

Figure

% COBBLES

804-001


Ryan Geological

Source: B-2A Elev./Depth: 15'

0.0112

43.216.3CL37.839.223.0

inches Olive Lean CLAY w/ Sand

COOPER TESTING LABORATORY

100.089.286.684.080.077.075.6

#10#30#40#50

#100#200#270

FIGURE


35/63

Project No.:

Project:

Client:

Cu

Cc

COEFFICIENTSD10

D30

D60

REMARKS:GRAIN SIZE

SOIL DESCRIPTIONPERCENT FINERSIEVEPERCENT FINERSIEVE

LLPLAASHTOUSCS% CLAY% SILT% SAND% GRAVEL

sizesizenumber

Particle Size Distribution Report

10

20

30

40

50

60

70

80

90

0

100

PERCENTFINER

100 10 1 0.1 0.01 0.00200

GRAIN SIZE - mm

6in.

3in.

2in.

1-1/2in.

1in.

3/4in.

1/2in.

3/8in.

#4

#10

#20#30#40

#60

#100

#140

#200

Figure

% COBBLES

804-001


Ryan Geological

Source: B-2A Elev./Depth: 40-42'

0.0115

0.861

30.014.7SM13.133.132.920.9

inches Bluish Black Lean Clayey SAND w/ Gravel

COOPER TESTING LABORATORY

79.170.256.153.150.748.046.245.4

#4#10#30#40#50

#100#200#270

100.087.0

3/4"3/8"

FIGUR


36/63


Oakland, California

Job No. 1082.100


RYAN GEOLOGICAL CONSULTING, INC.

PROVIDING LOGICAL GEOLOGICAL SOLUTIONS

APPENDIX A

CORE LOGS

BORINGS B-1 THROUGH B-3


37/63

CORE LOG

PROJECT:DRILLING COMPANY:

NUMBER OF CORE BOXES:

DRILLING METHOD:

LOGGED BY:

BORING NO.:DATE INITIATED:DATE COMPLETED:TOTAL DEPTH OF HOLE:BOREHOLE ELEVATION:

JOB NO.:Gregg DrillingMud Rotary

4K. Ryan

B-13-5-13

3-6-1355 Feet1133 Feet MSL

1082.100

RUNNO.

DRILLING

PRESSURE(ps

i)

CUT

RECOVERED

%R

ECOVERY

%D

RILLING

FLUIDLOSS

RQD(%)

DEPTH

LOG

DESCRIPTION

2

4

6

8

10

12

14


DRILLRATE

(MIN/FT)

DRILL RIG: Fraste MITO 4000

CASING TYPE: Steel (During Drilling Only)GROUNDWATER ELEVATION:CASING ELEVATION: n/a

Not encountered

A-1

1

1

1

1

1

1/2

1/2

1

1

1

5

5

2.8

2.5

56

50

70

70

n/a

0

1

drilled to 5 feet without sampling

GRAVELLY CLAY, tan-brown, moist, stiff, angularfragments of sandstone and shale

SILTY CLAY, dark gray-brown, moist

SANDSTONE interbedded with SHALE mixed with CLAY,dark yellowish orange to yellow-brown, weak, highlydisrupted with abundant clay, block-in-matrix texture

2

RYAN GEOLOGICALCONSULTING, INC.



38/63

CORE LOG

A-2

RUN

NO.

DRIL

LING

PRESSU

RE(psi)

CU

T

RECOV

ERED

%R

ECOVERY

%D

RI

LLING

FLUID

LOSS

RQD

(%)

DEP

TH

LO

G

DESCRIPTION

16

18

20

22

24

26

28

DRILL

RATE

(MIN

/FT)

1

1

1

1

1

1

1

1

0

1.5

1.5

3

2

3

0

2

2

4

1

2.5

2.5

2.5

2.5

3.3

1/2

2.5

2.2

1.5

2.5

50

100

88

72

100

70

70

70

30

30

30

0

0

0

0

0

0

3

4

5

6

7

8

SANDSTONE interbedded with SHALE mixed with CLAY,dark yellowish orange to moderate yellow-brown, friable,highly disrupted with abundant clay, block-in-matrix texture

clayey crushed zone

planar J 40 dip SHEAR ZONEbetween 20.3 to 23 feet with

multiple clay-lined shear planes 50-70 dip

*set casing to 20 feet to control water loss

SANDY SILTSTONE and SANDSTONE, severelyfractured into gravel-size pieces bound with clay

brecciated rock fragments in clay

remnant bedding 70 dip interbedded shale and sandstone predominately silty sandstone (less fractured than

above)

J 40 dipJ 30 dip

PROJECT:



Chelton Drive Landslide BORING NO.:TOTAL DEPTH OF HOLE:CORE LOG PAGE:

JOB NO.:B-155 Feet2 of 4

1082.100BORE HOLE ELEVATION: 1133 Feet MSLLOGGED BY: K. Ryan


39/63

A-3

RUN

NO.

DRIL

LING

PRESSU

RE(psi)

CU

T

RECOV

ERED

%R

ECOVERY

%D

RI

LLING

FLUID

LOSS

RQD

(%)

DEP

TH

LO

G

DESCRIPTION

31

33

35

37

39

41

43

DRILL

RATE

(MIN

/FT)

2

2

2

2

2

3

3

3

5

2

2

5

5

2

2

2

2.5

2.5

2.5

1.5

2

1.5

2.5

1.8

2.5

0

0

0.5

1.5

1.25

72

100

0

0

25

100

50

30

30

30

30

30

30

30

0

0

0

0

0

0

0

9 SANDY SILTSTONE and hard SANDSTONE, severelyfractured into gravel-size pieces

SLIDE PLANEat 32.5 feet, 1 inch clay gouge with welldeveloped dip-slip striations, 17 dip at top ofshear zone containing angular rock fragments in clay

matrix, block-in-matrix texture

samples being washed out during drilling.Water in mud tub is black, suggesting black shale

driller reports much harder drilling, below 40 feet

rubble

1/2 inch clay seam 70 dip

10

11

12

13

14

15

CORE LOG

BORING NO.:TOTAL DEPTH OF HOLE:CORE LOG PAGE:


1082.100



PROJECT: Chelton Drive LandslideBORE HOLE ELEVATION: 1133 Feet MSLLOGGED BY: K. Ryan

LANDSLIDE DEBRIS

SHEPHERD CREEK FORMATION


40/63

A-4

RUN

NO.

DRIL

LING

PRESSU

RE(psi)

CU

T

RECOV

ERED

%R

ECOVERY

%D

RI

LLING

FLUID

LOSS

RQD

(%)

DEP

TH

LO

G

DESCRIPTION

46

48

50

52

54

56

58

DRILL

RATE

(MIN

/FT)

2

2

2

5

5

5

13

8

8

8

2

1

2

1

3

0

1

1.5

0.9

0

0

100

75

90

0

75

80

80

0

0

0

0

0

SANDY SILTSTONE and hard SANDSTONE, severelyfractured into gravel-size pieces

rubble

J 30 and 70 dip

ground up clay zone

water rising out of borehole after drilling stoppedsuggesting groundwater at about 50 to 51 feet

rubble ground up clay zone with rock chards

Boring terminated at 55 feetBorehole backfilled with cement groutfluid loss estimated by driller

B - BeddingJ - Joint

S - Shear

area of no recovery

16

18

19

20

17

CORE LOG



1082.100





41/63

CORE LOG



DRILLING METHOD:

LOGGED BY:



1K. Ryan

B-23-7-13

3-7-1325 Feet1063 Feet MSL

1082.100

RUNNO.

DRILLING

PRESSURE(ps

i)

CUT

RECOVERED

%R

ECOVERY

%D

RILLING

FLUIDLOSS

RQD(%)

DEPTH

LOG

DESCRIPTION

2

4

6

8

10

12

14


DRILLRATE

(MIN/FT)

DRILL RIG:

CASING TYPE:GROUNDWATER ELEVATION:CASING ELEVATION: n/a

Not encountered

A-5

1

1

1

1

1

1

1

1

1

1

1

1

1

5

4

3.5

2.5

2

1

2.4

2

1.4

2.5

48

50

100

50

50

50

50

n/a

n/a

0

0

2

SILTY SANDY CLAY, brown to tan-brown, moist, stiff

(FILL FOR DRILLING PAD)

GRAVELLY CLAY, tan-brown, moist, stiff, angularfragments of shale up to 1 inch

driller reports very hard drilling, below 9 feet

3 SILTSTONE, highly weathered, weak to moderatelystrong, crushed, thinly bedded

*set casing to 10 feet

remnant bedding laminations 30 dip

crushed clay zone 30 dip

1

4

Fraste MITO 4000

Steel (During Drilling Only)




42/63

A-6

RUN

NO.

DRIL

LING

PRESSU

RE(psi)

CU

T

RECOV

ERED

%R

ECOVERY

%D

RI

LLING

FLUID

LOSS

RQD

(%)

DEP

TH

LO

G

DESCRIPTION

16

18

20

22

24

26

28

DRILL

RATE

(MIN

/FT)

1

1

1

2

1

2

1

1

1

1

1

2.5

2.5

2.5

1

0.5

0.5

0.5

5

5

20

20

20

50

50

50

50

50

0

0

0

0

0

5

7

6

SILTSTONE, highly weathered, weak to moderately strong rubble

rubble

rubble

rubble

LANDSLIDE DEBRIS

8

9

Boring terminated at 55 feetBorehole backfilled with cement groutfluid loss estimated by driller

B - BeddingJ - Joint

S - Shear

area of no recovery

*Core barrel not properlyengaging, runs #8 and #9 bothrecovered 5 feet of sloughfrom previous runs. Boringterminated due to drilling

malfunctions and drill rig. Holemoved 10 feet south to re-drill.See log for boring B-2A

CORE LOG



1082.100





43/63

CORE LOG



DRILLING METHOD:

LOGGED BY:



5K. Ryan

B-2A3-7-13

3-9-1380 Feet

1065.9 Feet MSL

1082.100

RUNNO.

DRILLING

PRESSURE(ps

i)

CUT

RECOVERED

%R

ECOVERY

%D

RILLING

FLUIDLOSS

RQD(%)

DEPTH

LOG

DESCRIPTION

2

4

6

8

10

12

14


DRILLRATE

(MIN/FT)

DRILL RIG: FRASTE MITO 4000

CASING TYPE: 2.75-Inch Slope InclinometerGROUNDWATER ELEVATION:CASING ELEVATION: 1067.4 Feet MSL

Not encountered

A-7

1

1

1

1

2

2

2

3

2

4

5

5

2

3

40

Prr 5509 DRAFT Landlside Investigation Report Chelton Drive

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