01-16-2001 - Geotechnical Evaluation Report for the 2400 Block of Belinda Streeti
City of West Covina
10 Memorandum
TO: Daniel G. Hobbs, City Manager
and City Council
FROM: Thomas M. Mayer
Public Works Director/City Engineer
AGENDA
ITEM NO: C-6d
DATE January 16, 2001
SUBJECT: GEOTECHNICAL EVALUATION REPORT FOR THE 2400 BLOCK OF
BELINDA STREET
SUMMARY: Converse Consultants of Redlands has provided a geotechnical review of the site
conditions on twelve properties located in the 2400 block of Belinda Street.
BACKGROUND:
During the City Council meeting on July 18, 2000, residents of four properties on the southerly
side of the 2400 block of Belinda Street presented a package of information that included a cover
letter, location map, letter from the City, and four soils engineering reports from three soils
engineering companies. The properties are located to the northeast of Shadow Oak Park with
2416 Belinda Street adjoining the park and with 2424, 2428, and 2436 Belinda Street adjoining a
paseo (open space) between Shadow Oak Park and Adrienne Drive. There is a slope within the
public areas adjacent to the rear of these properties. The slope is approximately 20 feet high and
descends away from the properties in a southerly direction. The properties are experiencing
damages (cracking and movement) to both the houses and rear yard improvements.
In order to have a professional third party evaluation, the City in September 2000 contracted with
Converse Consultants of Redlands to provide a geotechnical review of the submitted package
and the site conditions. The contract provided for a review of ten properties (later expanded to
twelve properties) along the southerly side of the 2400 block of Belinda Street. Converse
Consultants has submitted their, report dated December 15, 2000.
DISCUSSION:
Converse Consultants reviewed the soils reports submitted by the property owners and on
November 4 and 5, 2000, visited each of the twelve properties on the southerly side of the 2400
block of Belinda Street and made visual investigation of the structures and the site. A
comprehensive report by Converse Consultants dated December 15, 2000 is on file.
Copies of the last four pages from the report by Converse Consultants are attached. These pages
encompass the conclusions, possible further investigations and suggested remedial repairs. In
summary, the report concludes that the situ structures have been affected by differential fill
settlement and expansive soil movement, but there is no indication that the distress in the
structures is related to any slope creep. In' the consultant's opinion, slope creep could have
influenced the distress in the walls at the top of the slope, but the main contribution to the
distress in these walls is inadequacy in the design and construction. If the walls were properly
constructed, the anticipated creep would not have affected the wall.
The soils reports_ submitted by the property owners and the findings of Converse Consultants
agree that inadequate drainage -is a major contributor to the distresses in the structures. In many
cases over the years, site drainage has been altered considerably by property owners, which
diverts the drainage pattern towards the building foundation rather than away from it.
Converse Consultants' report indicates that there is no liability on behalf of the City. Therefore,
the property owners should pursue their own remedies. Four copies of the report were provided
to Mrs. Arciniega Marisela who lives on Belinda Street in order to share it with her neighbors.
Also, staff has attempted to notify all affected property owners that the report would be presented
to the City Council at this meeting.
\\JUPITER\BLDE'S FILES\AGENDA - 2001\GEOTECHNICAL EVALUATION REPORT 2400 block of Belinda.doc:200 1 -101 (ct)
Daniel G. Hobbs, City Manager
and City Council
Page 2 — January 16, 2001
OPTIONS:
The City Council has the option of considering further investigation. Converse Consultants'
report does not indicate any responsibility on behalf of the City to pursue further investigation.
FISCAL IMPACT:
There is no fiscal impact unless there is any further investigation.
RECOMMENDATION:
It is recommended that the City Council receive and file this report.
Prepared by:
7
Oscar Caplin
Civil Engineering Assistant
Reviewed and approved by:
::;� Ce� / / /'-
y
Thomas M. Mayer
Public Works Director/City Engineer
Attachment
\\IUPITER\BLDE'S FILES\AGENDA - 2001\GEOTECHNICAL EVALUATION REPORT 2400 block of Belinda.doe
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0
5.0 CONCLUSIONS
Conclusions presented here are based o
observation of nearby topographic features,
subsurface exploration, laboratory testing or
been performed.
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December 15, 2000
Page 13
n
our visual observation of site conditions,
experiences and professional judgement. No
other invasive and non-invasive testing has
It is our opinion that site structures have been affected primarily due to (i) differential fill
settlement and (ii) expansive soil movement. These conditions have been exacerbated due
to adverse drainage conditions in the lots. Observation in the vicinity indicate that prior to
development, the entire site topography was sloping downward from north to south and
west to east. In order to create level pads, conditions were created whereby fill depth in the
lots increased from north to south and west to east. It is also possible that lots have natural
material in their northwest portion and deepening fill towards southeast portion. Such
conditions (i.e. either differential fill or fill -natural transition) provide environment for
differential settlement. It appears that the lots have rotated towards deepening fill.
Slope creep may have influenced the masonry block -walls on top of the slope. However,
creep is a common phenomena in all slopes, especially fill slopes in an expansive soil
environment. Slope top walls should have incorporated this into design and construction.
Generally creep influence is minimized by deepening foundations. At this site, it does not
appear that the walls have adequate foundation. Even in lots where there was no slope
immediately behind the wall (2408 and 2412 Belinda Street), significant tilting of wall was
observed. There is no observable evidence to relate distress of structures away from the
slope and slope creep, especially the main residential structure. The residential structure is
at a significant distance away from the slope. Observation of the condition indicates that
structures are moving towards deepening fill, i.e. towards east, south, or southeast
direction. The block -masonry walls between residences are also tilting towards east, the
direction of possible increasing fill thickness. Expansive soil influence was observed at a
number of locations. Both settlement and expansive soil influence have been exacerbated
due to adverse drainage conditions in the lots.
Discussion of site history with the homeowners indicates that distress has been on going for
many years. However, many homeowners indicate that distress conditions have
accelerated in recent years. Wood framed residential structures are flexible enough to
withstand earth movement for many years without showing significant distress. However, a
threshold condition comes when any slight increase in stress can accelerate distress
conditions. Another possible scenario is that in an expansive soil environment, due to
repeated cycle of.expansion and contraction, the structures undergo cyclic stresses which
causes worsening conditions with a passage of time.
In, conclusion, the structures at the site are experiencing distress caused by differential
earth settlement and expansive soil movement exacerbated by inadequate drainage
conditions. There is no reasonable factor to relate slope creep with the distress of the
residential structures and other appurtenant away from the slope. Slope creep may have
influenced the slope -top masonry wall. However, inadequacy in design and construction of
these walls appears to have contributed to wall distress.
CONVERSE CONSULTANTS
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6.0 FURTHER INVESTIGATION
As mentioned before, it is our opinion that based on site conditions, slope conditions, slope
height and distance of the main structure from the slope top, it is reasonable to conclude
that the slope has not influenced the residential structures. As such, we do not feel it is
necessary to do any further investigation to establish this. However, if the City wants to
find the cause(s) for distress to residential structures, the geotechnical investigation Option
No. 1 can be undertaken. If the City wants to investigate the cause(s) of distress of slope -
top structures (such as masonry block wall and other nearby flatwork), investigation Option
No. 2 should be performed.
6.1 Investigation — Option No. 1
Our recommended scope of work and cost estimate for this option is presented below.
6.1.1 Manometer Survey
A manometer can be used to perform floor -level survey of the residences. Contoured
manometer data can provide very important information regarding magnitude and
deformation pattern of the slab -foundation system. It is possible to identify plausible
causative factors based on deformation pattern. It is proposed to perform
manometer survey in all the residences.
Estimated Fee $650 per residence which includes manometer survey, data
processing and preparation of a brief summary report. This fee is based upon
assumption that floor plans of the residences will be available. If Converse needs to
prepare the floor plans, an additional $200 per residence should be included in the
cost.
6.1.2 Borings
The purpose of the borings is to identify subsurface conditions, determine if
differential fill and/or fill natural material transition exists within the lots. Data from
field exploration and laboratory testing can be then used to evaluate cause(s) of
earth movement and associated distress to the structures.
A limited access rig will be used to drill 8-inch-diameter, hollow -stem auger borings
to depths up to 40 feet below existing ground surface. Borings will be located both
on the front and rear side of the lots. A total of eight (8) borings are proposed.
Estimated Fee: $3,000/boring _(includes - fees for subcontractor, field engineer,
and laboratory testing).
6.1.3 Test Pits
The purpose of the test pits is to determine the adequacy of the foundation system of
the residential structures for existing site conditions. It is proposed to excavate 8 test
pits adjacent to the foundation.
Estimated Fee: $550/test pit. (includes fees for subcontractor, field engineer,
and laboratory testing)
CONVERSE CONSULTANTS
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6.1.4 Summary of Estimated Cost for Investigation - Option No. 1
Manometer Survey @ $650-$850/residence,
12 residences................................................................................$7,800 — 10,200
Borings @ $3,000/boring, 8 borings..........................................................$ 24,000
Test Pits @ $550/Test Pit, 8 test pits ........................................................ $ 4,400
Engineering analyses .............................................. ............................... $ 1,500
Report Preparation....................................................................................$ 2,000
OfficeServices.......................................................................................... 750
Estimated Total............................................................... $ 40,450 — 42,850
6.2 Investigation — Option No. 2
As mentioned before, slope creep may have some influence. in causing distress to the
slope top walls. Option No. 2 is proposed to determine the cause(s) for distress to the
top -of -slope walls. The scope of work and cost for this option is presented below.
6.2.1 Test Pits
It is proposed to excavate a test pit adjacent to the slope -top wall at each
residence. Test pit data will.provide information regarding adequacy of footings,
soil conditions, and other important data.
Estimated Fee: $550/Test Pit (includes subcontractor fee, field engineer, and
laboratorytesting).
6.2.2 Estimated Cost for Investigation — Option No. 2
Test Pits @ $550/Test Pit, 12 Test.Pits.....................................................$ 6,600
Engineering analyses............................................................................:...$ 1,500
ReportPreparation....................................................................................$ 2,000
OfficeServices.......................................................................................... 1 000
Estimated Total .................................................. ........................$ 11,000
CONVERSE CONSULTANTS
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7.0 CONCEPTUAL REMEDIAL REPAIR
This section provides conceptual remedial repair options to mitigate distress conditions.
For the residential structures, options include deepening existing footings. Extent of
deepening will depend on conditions in each lot, especially depth to natural material within
the footprint of the building. In conjunction with deepening foundation, the house can be
re -leveled using mudjacking. Depending on condition of the slab, partial or complete slab
removal may be required in a few residences. However, repair options and extent of repair
can be decided upon completion of investigation Option No. 1, as discussed above.
For the appurtenant flatwork, depending upon the conditions, repair options include from
patching cracks to complete removal and replacement. Any new flatwork should be
designed for site soil conditions including soil expansivity. For appurtenant property line
walls, properly engineered wall will include deepened footing as an option.
For the slope top walls, design and construction should consider isolating these from creep
influence. This would need deepened foundation such as short piles, which should be
designed to withstand active lateral creep forces in the upper 5 to 10 feet.
Recommendations in this case can be provided upon completion of investigation Option
No. 2 as discussed above.
A very important aspect of the overall investigation measures would be to improve
drainage conditions. A suitable roof -gutter and downspout system should be connected to
a well designed surface drainage system in each lot.
8.0 CLOSURE
This report has been prepared for the sole benefit and exclusive use of the City of West
Covina in accordance with the terms and conditions attached to our proposal under which
these services have been provided. Any reliance on this report by third parties shall be at
third party's sole risk. Our services have been performed in accordance with applicable
state and local ordinances, and generally accepted practices within our profession. No
other warranty, either expressed or implied, is made.
Converse Consultants is not responsible or liable for any claims or damages associated
with interpretation of available information provided by others. Opinions provided in this
report are based on visual review of site conditions, review of reports and plans by others
and professional judgement. No subsurface exploration or laboratory tests have been
performed.
CONVERSE CONSULTANTS
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