HomeMy WebLinkAbout1982-3451
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RESOLUTION NO. 82--34 5
RESOLUTION OF THE CITY OF SAN BERNARDINO ADOPTING PROCEDUPFS
AND GUIDELINES FOR EVALUATING THE HAZARD OF LInUFFACTT+)N OF SOILS
AND SUBJACENT FORMATIONS FOR NEW CONSTRUCTION THF.T ARE DETF7'11TNJFn
TO BE WITHIN THE LIQUEFACTION POTEI`ITIA.L AREA.
BE IT RESOLVED BY THE MAYOR AND COMMON COUNCIL OF THE CITY
OF SAN BERNARDINO AS FOLLOWS:
SECTION 1. Introduction
Liquefaction is defined. as the transformation of a -ranular
material from a solid state into a licruefied. state a� a conse-
quence of increased ?-)ore-water pressures (You( -I, 1973). Soils an(,,.
clastic sediment with particle size in the medium sand to silt
range are particularly susceptible to liquefaction when they are
saturated with water and. shaken by an earthc,ua]Le. burin- lique-
action at or near the surface, foundations of buildings or other_
structures may rail, with loss of property and lives.
SECTION 2. Purpose
The purpose of this guideline is:
(a) To assist the developer/engineer who is developing, or
will develop, a project located within an area identified. as
having a nigh water table (see Exhibit "A") in orenarinn a needed
report evaluating the liquefaction hazard, and
(b) To provide a written format for the mini -mum information
to be included in such a report.
SECTION 3. Map
A map indicating{ an artesian pressure zone boundary and
approximate water table depths shall be on display in the Planning
Department. Said map may be modified as required trom th.e
information provided by the San Bernardino City i17ater Deoar.tment
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or as directed by the Mayor and Common Council. This map shall b
used to determine the need for a liquefaction rePor.t. The map
shall display three (3) zones within the artesian. pressure zone
boundary. These zones shall be described as:
Zone "A" extreme liquefaction Potential
Zone "B" - high 1i.guefaction potential
Zone "C" - liauefaction potential
Properties which are situated within zones "7\." and "R" shall have
a liquefaction report prepared. properties which are situated
within zone "C" would require certification from a soils engineer
that potentiality of liquefaction occurring on that site is
extremely unlik..ely. Tn the event said soils enai:neer certi-Fica-
tion is not received a liquefaction report shall he required.
SECTION 4. Excentions
All commercial., industrial and residential developments shall
comply with the .requirement of providing a liquefaction report
with the followina exceptions:
(a) a single-family wood frame detached. residential
structure, or,
(b) a two -unit wood frame single -store attached. _r.es _d_enti.al_
structure, or,
(c) additions of up to 2.50 of the area of the ori.ninal.
structure.
No critical structures (i.e. schools, hospitals, police anC 17ire
stations and public asserlbly buileings over 300 occurants) �7i_11
be excepted from the requirement of a liquefaction report.
SECTION 5. The Investigation
(a) Purpose. The investigation shall. he designed and
A carried out to determine the Dotential for liquefaction. For
2 modest structures the investigation may be relatively simple, but
3 for complex, critical structures, the investigation should he as
4 thorough as the "state-of-the-art" will nermi.t. Many i_nvest.i'xa-
5 tions will require the expertise of the geologist and the soils
6 engineer, since both geologic/seismic elements and. quantitative
7 materials testing will be involved.
8 (b) Site investigation.
9 1. Seismic factors. The history o-F earthquake activity
and recurrence intervals of damaging earthquakes should be
,l discussed. A design earthquake shall be rostulated, with a hest
12 estimate of the _following characteristics as they will be
B experienced at the site:
34 (a) Richter magnitu(.e,
15 (b)_ maximum repeatable accelerations,
16 (c) time (duration) of strong shaking,
17 (d) dominant frequencies of seismic spectra.
18 2. Hydrologic condi tions. The historic-0- reco r �
d �
19 depths to the ground water table (or_ saturated conditions) shouirll
20 be determined for the site. The depth to around. water used in thf
21 analysis should be stated.
22 3. Surface geology. The axe of the soil nrorile and
23 the age of the near-surface sedimentary formation are imnortant
24 since decree of compaction and resistance to liquefaction can
25 commonly be correlated with age. If there is more than one
26 geological formation exposed at the surface, lines of contact anO_
27 formational names should be identified.
28 4. Subsurface investigation. Borinqs shall I-e- used to
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determine the necessary subsurface information. They should
extend to a minimum depth of 30 feet and be spaced across the site
so that significant variations in subsurface conditions will be
defined. Examples of significant subsurface data would be:
(a) drilling rate,
(b) standard penetration test at every five feet
from surface ASTM No. D 1586-67,
(c) classification, definition, and depth of soils
(d) general stratigraphy,
(e) quantitative grain size determination,
(f) samples, coherent or granular, for quantita-
tive testing: grain size distribution and density.
For critical projects, more subsurface information utilizing
pits, trenches and geophysical investigations may be necessary.
They allow direct observation of the undisturbed vertical section
so that evidence of liquefaction such as sand boils, sand dikes,
or chaotic disturbance of the soil or sediment can be viewed.
Also, horizontal and vertical permeability can be better estimates
from a view of the undisturbed layering. Furthermore, the
ancient sedimentary environment of the site can be interpreted
from the trench or pit walls.
5. Geophysical investigation. Refraction seismic
techniques may be useful to define the ground water table, but
this indirect method should be used to confirm or extend downhole
or trench data.
SECTION 6. The Report
The report may be simple or comprehensive, depending upon
the vulnerability of the site to liquefaction and the kinds of
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buildings or other structures to be built. The following topics
should be considered and included if pertinent.
(a) Text.
1. Site location relative to established property
boundaries.
2. Purpose and scope of investigation.
3. Design earthquake parameters (discussed above).
4. Description of kind and location of proposed
construction.
5. Procedures and techniques used in the investigation.
6. Detailed description of subsurface conditions and
results of quantitative testing.
(b) Conclusions and recommendations.
1. Identify the location and distribution of areas
vulnerable to liquefaction and estimate the size and depth of
zones of possible failure due to liquefaction.
2. Identify critical parameters of the design
earthquake: magnitude, accelerations, duration, frequency, etc.
3. Identify procedures for reducing hazard of
liquefaction.
(a) geotechnical
(b) structural
(c) Documentation of report.
1. Include index map showing location of site.
2. Include site plan which shall display:
(a) topography (if available),
(b) proposed building location,
(c) locations of borings (if known), wells,
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trenches,
(d) surface geological features.
3. Include logs of borings (with blow counts), wells,
trenches.
4. Include sample descriptions and locations.
5. Include sample analyses and tests.
6. Include computations, graphs and charts.
7. Include description of analytical techniques used.
8. Include signatures and license numbers of geologists
and engineers responsible for the report.
9. Include a list of references utilized in report.
I, HEREBY, CERTIFY that the foregoing resolution was duly
adopted by the Mayor and Common Council of the City of San
Bernardino at a regular meeting thereof, held on the
16th day of August 1982, by the following
vote, to wit:
AYES: Council Members Castaneda, Reilly, Hernandez,
Ouiel, Strickler
NAYS:
ABSENT:
None
Council Member Hobbs
City Clerk
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The foregoing resolution is hereby approved this �'�day
Auqust , 1982.
Approved as to form:
Ci y Atto ney
CITY %jF oAN BERNARMNO
(� LIQUEFACTION ZONE BOUNDARIES
- EARTHQUAKE FAULT ZONES
-e--NORTON AIR FORCE BASE