WHITE POINT LANDSLIDE - Los Angeles · landslide area for groundwater elevations and possible subsurface movement. Site observations for landslide movement during the weeks of 12/12/11,

Gary Lee Moore, P.E., City Engineer Vince Jones, P.E., Deputy City Engineer

WHITE POINT LANDSLIDE GEOTECHNICAL INVESTIGATION

January 2012 Status Report

White Point Landslide Geotechnical Investigation January 2012 Status Report Page 2 January 17, 2012

City of Los Angeles, Bureau of Engineering

TABLE OF CONTENTS

1.0 Background 2.0 Site Observations and Activities for the Period December 21,

2011 to January 12, 2012

3.0 Landslide Monitoring for the Period December 21, 2011 to January 12, 2012

4.0 Geotechnical Investigation

5.0 Survey Monitoring

Attachment 1– Status Report Prepared by Shannon & Wilson, Inc. for 12/17/11 through 1/12/12 White Point Landslide Investigation

Attachment 2– Summary of Survey Monitoring Points at Weymouth Avenue and Paseo Del Mar, prepared by the Bureau of Engineering January 12, 2012

Attachment 3– DRAFT Preliminary Geotechnical Report by Shannon & Wilson January 6, 2012



1.0 Background This January 2012 Status Report provides a progress summary of the Geotechnical Investigation and monitoring of the White Point Landslide for the period if December 21, 2011 to January 12, 2012. The Bureau of Engineering (BOE) continues to oversee and support the geotechnical investigation of the landslide being conducted by Shannon and Wilson, Inc., a private consulting firm. Attached to this report are the January 2012 Status Report by Shannon & Wilson, Inc. (Attachment 1), the Summary of Survey Monitoring Points by the Bureau of Engineering (Attachment 2), and the DRAFT Preliminary Geotechnical, January 6, 2012 by Shannon & Wilson (Attachment 3). 2.0 Site Observations and Activities for the Period December 21, 2011 to

January 12, 2012 During this last month Shannon & Wilson completed exploratory drilling of the landslide. This effort included the drilling of nine (9) borings around the margin and headward area of the landslide, collection of soils samples, construction of groundwater monitoring wells and installation of earth movement monitoring instruments. The Bureau authorized Shannon & Wilson to engage the services of a private survey firm to prepare a detailed topographic survey map of the landslide and surrounding area. The Bureau directed that the survey be very detailed so as to document ground surface variations of as little as six inches. This map was completed on January 6, 2012, and is used as the base for Figure 1 of Attachment 1 and will be used by Shannon & Wilson in the future phases of the landslide investigation. Geologists from both BOE and Shannon &Wilson continue to conduct site observation of the landslide and surrounding area. Observation of existing ground cracks around the immediate edge of the landslide suggests that the ground within a few feet of the head of the landslide is tilting and crumbling and may fall toward the landslide. Future activities will include opening of the abandoned "The Launcher Area at White Point, Los Angeles Defense Missile Site LA-43." facility within the nature park for the purpose of observing its condition.

3.0 Landslide Monitoring for the Period December 21, 2011 to January 12, 2012 As described in Attachment 1, Shannon & Wilson continues with the measurement of earth monitoring instruments (inclinometers) that were placed in some borings to detect ground movement (see Table 1). A Draft Preliminary Geotechnical Report by Shannon &Wilson (Attachment 3) indicates that ground measuring instruments show no significant movement. Shannon & Wilson indicate that this suggests that over the time of instrument readings, properties adjacent to the landslide and the newly constructed storm drain improvements have not been subject to movement related to the current landslide limits.



BOE is currently working to install a series of ground surface monitoring stations to help detect potential ground movement. These survey stations will be installed on the sides and landward perimeter of the landslide and will be periodically monitored for evidence of ground movement. 4.0 Geotechnical Investigation A status report prepared by Shannon and Wilson and dated January 13, 2011 is presented in Attachment 1. This report summarizes the progress of the Geotechnical investigation through January 12, 2012. As indicated in the report, drilling at the site was completed on December 21, 2011. Completion of the field exploration by Shannon & Wilson is a significant milestone in the investigation of the White Point Landslide. At BOE direction Shannon & Wilson has prepared a 300 page Draft Preliminary Report (Attachment 3) which provides a description of their site observations and initial findings. This report was submitted to BOE and is currently under review. Based on their studies completed to date, Shannon & Wilson preliminarily conclude that the risk of landslide movement beyond the chain link fence placed along the White Point Nature Preserve trail is low. This early phase reporting allows the Bureau to confirm that the perimeter fencing erected around the landslide is appropriate and continues to provide a safe setback of the public from the landslide area. 5.0 Survey Monitoring The BOE continues survey monitoring of points set on the street, curb and ground around the landslide to check for evidence of ground movement which might indicate landslide movement or enlargement. A summary of the survey monitoring is provided in Attachment 2. Survey measurements continued during this period on the three monitoring points reported in the previous status report. Two additional survey monitor points were measured during this period and the data has been included on Figures 1 and 2, Attachment 2. Figure 1 in Attachment 2 shows the location of the monitoring points. As indicated previously, the first three monitor points were established on November 3, 2011. Points #4 and #5, shown on Figure 1, were established on November 21, 2011, subsequent to the landslide event on November 20, 2011. Survey measurements are reported in hundredths of a foot. Therefore, a reading of 0.02 represents approximately ¼ of an inch. Figure 2 indicates the horizontal and vertical movement of each of the points. The expected limits of precision for the monitoring measurements is + 0.02’. The survey monitoring data therefore indicates that no movement has occurred at these points. Survey data shows no indication of ground movement at this time which might signal landslide enlargement.

Attachment 1

Status Report Prepared By Shannon & Wilson, Inc.

ALASKA CALIFORNIA

COLORADO FLORIDA

MISSOURI OREGON

WASHINGTON

664 WEST BROADWAY GLENDALE, CALIFORNIA 91204-1008 www.shannonwilson.com 51-1-10052-012

January 13, 2012 Bureau of Engineering 1149 South Broadway Street, Suite 120 Los Angeles, California 90015 Attn: Mr. Mark Oborne

RE: STATUS REPORT FOR 12/17/11 THROUGH 1/12/12 WHITE POINT LANDSLIDE INVESTIGATION CITY OF LOS ANGELES W.O. E1907483, TOS 11-087 SHANNON & WILSON PROJECT NO. 51-1-10052-012

We are providing this letter outlining the subtask status for the period ending January 12, 2012. Shannon & Wilson is performing a subsurface investigation of the White Point Landslide following significant movement of the landslide on November 20, 2011. During the course of our services, we have not observed new surface cracks outside of the fenced perimeter of the landslide. We recorded groundwater depths in the inclinometer borings and wells that were installed (Table 1) along the landslide perimeter at depths ranging from approximately 50 to 98 feet below ground surface. Groundwater levels measured within the recently completed borings appear to be relatively stable with only minor fluctuations (Table 2). We believe the projected landslide failure plane is about 100 feet deep in the area of the active landslide.

As previously reported, ground cracks immediately adjacent to the landslide widened a few inches after the initial landslide movement. Visual observation of the existing cracks adjacent to the main head scarp suggests that the material immediately adjacent to the scarp is moving or rotating into the graben area. We expect to see periodic calving of this material throughout the upcoming winter months. It is also likely that the main landslide mass will continue to move ocean-ward and likely accelerate during periods of heavy precipitation. No new significant ground cracks have been observed in the area between the fence and main landslide mass. These conclusions are preliminary and are subject to change as our studies develop.

Mr. Mark Oborne City of Los Angeles January 13, 2012 Page 2 of 3

51-1-10052-012-L02rev3.docx/wp/DGF 51-1-10052-012

SUBTASK STATUS

The status of each subtask is listed below:

Subtask Status 1. Health and Safety Plan Complete 2. Geologic Mapping Ongoing - 95% Complete 3. Preliminary Report Submitted for Review 4. Subsurface Exploration Complete 5. Waste Handling and Management Ongoing - 30% Complete 6. Geophysical Downhole Logging Complete 7. Laboratory Testing of Samples Ongoing - 5% Complete 8. Geologic Cross Sections Ongoing - 20% Complete 9. Stability Analysis Pending 10. Meetings Ongoing – 33% Complete 11. Geotechnical Report Ongoing - 5% Complete

TASKS COMPLETED FOR THIS PERIOD

For this work period, tasks completed include:

Completion of the subsurface exploration program on December 21, 2011.

The Draft Preliminary Report was submitted to the City on January 6, 2012. The report included a preliminary geologic map, preliminary boring logs, inclinometer baseline readings, and preliminary observations regarding the landslide and immediate areas adjacent to the landslide. The base map includes the Navigate LA 2006 topographic contours.

Completion of the aerial survey flown on December 13, 2011 and submittal of the updated topographic base map to the City on January 6, 2012

Instrumentation installation and reading dates shown in Tables 1 and 2. Instrumentation will be read on weekly basis for the first month following installation to monitor the landslide area for groundwater elevations and possible subsurface movement.

Site observations for landslide movement during the weeks of 12/12/11, 12/19/11, 12/26/11, 1/2/12 and 1/9/12. Based on visual observations, no ground fractures have appeared at the fenced perimeter of the landslide area.

White Point LandslideCity of Los Angeles

TABLE 1Summary of Explorationsand Instrumentation

Shannon & Wilson, Inc.

Boring

Nam

e

Drill Type

Status

Dep

th (feet)

Completion

Type

(2)

Well/VW

P Install D

ate

Date

Installed

Baseline

Reading

12/28/11

Reading

1/4/12

Reading

1/11

/12

B‐1 Rotary Core (1) Complete 130 11/29/11 VWP/ Incl. 11/29/11 11/29/11 (4) 0.0 <0.1 in. <0.1 in.B‐2 Bucket Auger Complete 120 12/2/11 None ‐B‐3 Bucket Auger Complete 120 12/6/11 Well (3) 12/22/11B‐4 Bucket Auger Complete 100 12/8/11 None ‐B‐5 Bucket Auger (1) Complete 121 12/15/11 VWP/ Incl. 12/16/11 12/16/11 0.0 <0.1 in. <0.1 in.B‐6 Sonic Core Complete 110 12/16/11 Well 12/16/11B‐7 Rotary Core (1) Complete 118 12/14/11 VWP/ Incl. 12/16/11 12/16/11 0.0 <0.1 in. <0.1 in.B‐8 Sonic Core Complete 110 12/18/11 Well 12/18/11B‐9 Rotary Core (1) Complete 120 12/20/11 VWP/ Incl. 12/21/11 12/21/11 0.0 <0.1 in. <0.1 in.

Notes:(1) Inclinometer installed in boring (Total of 4)(2) VWP = Vibrating Wire Piezometer(3) 8‐inch diameter well installed(4) Baseline re‐established 12/28/11

InstrumentationExploration Information Inclinometer Cumulative Displacement

1/20/2012, Copy of Exploration Summary Status No. 2a Rev2.xlsx, RTD Page 1 of 1 51‐1‐10052‐012

White Point LandslideCity of Los Angeles

Table 2Groundwater Data

Shannon & Wilson, Inc.

Reading Date

Water Elevation

(ft.)

Water Elevation

(ft.)

Water Elevation

(ft.)

Water Elevation

(ft.)

Water Elevation

(ft.)

Water

Depth2

(ft.)

Water Elevation

(ft.)

Water

Depth1

(ft.)

Water Elevation

(ft.)

Water

Depth2

(ft.)

Water Elevation

(ft.)

Water Elevation

(ft.)

11/29/2011 60 * 63

12/2/2011 88 * 36.5

12/8/2011 98 * 26.5 55 * 75

12/16/2011 68 * 56

12/30/2011 25.4 50.2 86.5 75.5 52.0

1/4/2012 59.4 60.2 95.4 27.1 86.5 (4) 42.5

1/11/2012 59.2 25.6 60.0 50.0 86.7 95.5 27.0 75.6 51.9 36.6

Notes:

1. Measured using vibrating wire piezometer.

2. Measured using electronic well sounder from the top of the casing.

Top of casing below ground surface:

B-3 ~ 6 inches

B-6 ~ 4 inches

B-8 ~ 5.5 inches

3. (*) Measured during drilling.

4. Suspected Insturment Error

63.8 98.4 64.0 92.4

98.6

63.6 63.8

Elev. ~122.5 ft. Elev. ~128 ft. Elev. ~129 ft.

Water

Depth1 (ft.)

Water

Depth3 (ft.)

Water

Depth2 (ft.)

Water

Depth3 (ft.)

Water

Depth1 (ft.)

Water

Depth1 (ft.)

B-6 B-7 B-8 B-9

Elev. ~123 ft. Elev. ~ ft. Elev. ~124.5 ft. Elev. ~ ft. Elev. ~124 ft. Elev. ~137 ft.Well/ VWP

B-1 B-2 B-3 B-4 B-5

1/20/2012, 51‐1‐10052‐003‐T01.xlsx, JXM Page 1 of 1 51‐1‐10052‐011

148.675 AT4

122.400 AT5

123.5

40.3

41.0

CONC

GNV

ASPH

ASPH

CONC

GNV

GNV

GNV

GNV

PIPE

PIPE

PIPE

PIPE

PIPE

DIRT

DIRT

DIRT

ASPH

ASPH

ASPH

ASPH

ASPH

PACIFIC OCEAN

PASEO DEL MAR

CONC

CONC

CONC

ROCKS

ROCKS

PIPE

DI

DI

ASPH

ASPH

144.6

137.1 136.4 136.5

137.1 136.6

139.1

137.5

132.8132.3

132.1 131.6

131.9 131.1

131.1

143.1

130.6

128.6

129.3128.9

128.3

127.9

129.8130.3

127.2

126.7126.4 125.7

125.2124.7

126.2

128.3

124.4

123.7123.2

122.7122.4

122.5

124.9125.2

123.4

131.9

132.3

133.5 134.6

132.5131.8

131.9

128.3

129.3

144.8

142.5138.5

138.1138.1

138.9

137.9

138.3138.1138.1

138.3138.4

138.5

138.4

138.5

138.5

138.3

138.3

138.1

137.1

132.8

133.1133.8

137.8

135.4

135.3

137.1

138.8139.6

135.9

134.8

BRUSH

BRUSH

BRUSH

CONC CONC

CONC

CONC

TREES

CONC

CONC

TREES

CONC

CONC

CONC

CONC

CONC

CONC

BRUSH

BRUSH

BRUSH

BRUSH

BRUSH

BRUSH

BRUSH

CONC

CONC

DIRT

DIRT BRUSH

BRUSH BRUSH

BRUSH

TREES

BRUSH

BRUSH

BRUSH BRUSH

CONCASPH

ASPH ASPH

CONC

81.6

82.7

87.2

88.5

74.5

64.7

67.4 76.2 98.9

112.1

107.8

116.0

GNV

GNV

VC

VC

VC VC

UB

VC VCVC

VC

VC

VC

ROCKS

R

R

R

ROCKS

ROCKS

PIPE

S

PIPES

PIPES

PIPES PIPES

PIPE

DI

PACIFIC OCEAN

PACIFIC OCEAN

PASEO DEL MAR

ASPH

ASPH

ASPH

ASPH

ASPH

DIRT

DIRT

DIRT

DIRT

138.1137.4

136.5

136.6

137.1

138.1

138.3

137.9

136.9

137.4

127.9

128.1128.8128.5

128.5

137.8

131.1

131.9130.9

138.4

127.2

127.2

126.9

126.7

124.2

122.5

123.9 123.9

125.2

126.2

122.2121.9

122.7 122.7

123.0 122.7

121.5

123.5

127.2

126.2

126.2125.7

126.2

122.7

122.0

122.2 122.7

122.7

122.2

123.2

123.7123.4

125.2

148.4

240.9

239.3

132.5

91.2

101.0

124.2123.7

124.4

120.2

137.8

133.9

132.3132.6

133.1

132.3

136.4

135.6

138.1

140.9

138.6139.8

141.8

140.5

142.5

WEY

MOUT

H AV

E.

37TH ST.

HAMI

LTON

AVE.

prepared by

Advanced Digital Maps, Inc

626-33 7-997 1

Map Scale: 1" - 40'

ADM 2371

Photo Date: 12-14-11

Con tour In terval= .5 Ft.

PASEO DEL MAR LANDSLIDE

0'120'80'40'

SCALE 1"=40'

CONCCONC

CONC

CONC

GNV

E 6,467,200

N 1,718,400

N 1,718,800

145

130

127.5

125

122.5

130

132.5

122.5

120115

110105100

9590

8580

22.5

52.5

7.5

3545

5565

75

125

2.557.5

12.515

20253035404550

110

105

70

107.5

67.570

72.5

95

122.5

85 82.590

82.580

2.55

7.5

3040

50

60

7080

90

100

122.5

122.5

120

120

122.5

125

145

142.5

140

137.5

135

132.5

130

147.5

150

152.5

155

257.5

265

260

137.5

135

130

132.5

127.5

140

142.5

137.5

142.5

132.5

142.5

140.6

137.8137.1

128.6

137.8

147.1

150.5

142.9

137.6

141.9

ROCKS

ROCKS

61.2

68.5

7.2

22.8

20.6

6.7

8.8

85.774.9

80.0

92.2

70.7

94.2

75.7 119.2

70.9 71.060.8

6.7 5.56.2 6.4

8.4

125.7

126.9

126.7

122.7

127.9128.1

136.3

128.8

124.2

138.3

138.3

137.9

138.4

138.5

133.3

139.5

!>!(

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!(

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!.

!>

!>Paseo Del Mar

Qsf

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B-7

B-1

B-3

B-8B-9

B-4

B-6

B-2 B-5

Filen

ame:

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White Point LandslideSan Pedro District

Los Angeles, California

SITE AND EXPLORATION PLAN

FIG. 1January 2012 51-1-10052-012

³

1 inch = 100 feet0 100 20050 Feet

LEGEND!( Boring!. Groundwater Well!> Inclinometer

Head ScarpApproximate Access Routes


Attachment 2

Summary of Survey Monitoring Points

FIGURE 2

PT #1 N= 1718635.94 E= 6467068.78 EL= 121.92

DATE HORIZ CHANGE VERT CHANGE11/3/2011 0.00 0.0011/7/2011 0.01 0.00

11/14/2011 0.01 0.0111/21/2011 0.00 0.0011/25/2011 0.04 0.0111/26/2011 0.04 0.0012/21/2011 0.02 0.0012/28/2011 0.01 0.00

1/5/2012 0.02 0.001/12/2012 0.01 0.01

Standard Deviation 0.015 0.004

PT #2 N= 1718655.69 E= 6467008.02 EL= 121.53


11/14/2011 0.01 0.0111/21/2011 0.00 0.0011/25/2011 0.01 0.0111/26/2011 0.01 0.0112/21/2011 0.00 0.0012/28/2011 0.01 0.01

1/5/2012 0.02 0.021/12/2012 0.00 0.02


PT #3 N= 1718667.49 E= 6466973.29 EL= 121.50


11/14/2011 0.02 0.0011/21/2011 0.00 0.0011/25/2011 0.01 0.0111/26/2011 0.01 0.0112/21/2011 0.01 0.0112/28/2011 0.00 0.01

1/5/2012 0.03 0.021/12/2012 0.02 0.02


White Point Landslide

Page 1

FIGURE 2White Point Landslide

PT #4 N= 1718768.94 E= 6466747.41 EL= 121.97

DATE HORIZ CHANGE VERT CHANGE11/21/2011 0.00 0.0011/25/2011 0.03 0.0011/26/2011 0.01 0.00

1/5/2012 0.01 0.011/12/2012 0.01 0.00


PT #5 N= 1718777.57 E= 6466719.69 EL= 121.74

DATE HORIZ CHANGE VERT CHANGE11/21/2011 0.00 0.0011/25/2011 0.01 -0.0211/26/2011 0.03 0.00

1/5/2012 0.03 0.001/12/2012 0.03 0.01


The standard deviation for the measurements listed above are within the expected errors generated by the instrumentation and techniques employed to obtain the

values.

These results indicate that there is no observable ground movement.

Page 2

Documents

WHITE POINT LANDSLIDE - Los Angeles · landslide area for groundwater elevations and possible subsurface movement. Site observations for landslide movement during the weeks of 12/12/11,