Page 25 - Building Regulation and Design Guidelines - Structural (Grey Code)

SECTION: 1 GEOTECHNICAL GUIDELINES & REGULATIONS SECTION: 1 GEOTECHNICAL GUIDELINES & REGULATIONS
1.4.4
Fig. (1.32): Cone Penetration Test Readings
1.4.3 CALCULATION THEORY:
Cyclic stress ratio (CSR) induced in the soil due to earthquake shall be
estimated as per clause 1.2.32. Cyclic resistance ratio (CRR) induced in
the soil shall be estimated as per clause 1.2.33.
Liquefaction potential shall be evaluated by calculating the factor
of safety against liquefaction for specific earthquake load and soil
strength. (F.S. = CRR / [(1.2-1.5) CSR). The accepted factor of safety
against liquefaction shall be more than unity.
Recommended Procedures for Implementation of DMG Special
Publication – 117 Guidelines for Analyzing and Mitigating Liquefaction
Hazards in California. Implementation Committee, March 1999-
“Preliminary screening of Liquefaction”
The ground water table adopted by the designer for liquefaction analysis
shall consider the surrounding site conditions.
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For CPT-Based liquefaction analysis, soil profiling according to Robertson
1996, or similar method shall be performed to highlight localities of high
fines content.
Level survey (before & after improvement) shall be submitted along with
soil improvement tests result report for CED approval.
EVALUATION OF LIKELY LIQUEFACTION INDUCED HAZARDS
“Special Publication 117, GUIDELINES FOR EVALUATING AND MITIGATING
SEISMIC HAZARDS IN CALIFORNIA”, adopted on March 1997 by the State
Mining and Geology Board.
The evaluation of likely liquefaction hazard shall be carried out by
competent and qualified geotechnical Engineer. The evaluation shall be
based on the results of adequate number of filed tests (preferably CPTU).
Wherever, the analysis indicates significant liquefiable zones, and then
the site or part of it shall be recommended for further deep compaction.
Wherever, minor, localized liquefiable zones within limited depth were
indicated, and then it is important to assess the likely induced effects
such as:
a) Liquefaction induced settlement of surface foun dations,
b) Surface Manifestation,
c) Loss of bearing strength of surface foundations,
d) Loss of lateral stiffness of piles,
e) Effects on life lines,
f) Any other influences…
1.4.4.a Settlement:
If shallow footings exist and no improvement has done,
differential settlement more than the maximum liquefaction
induced settlement should be expected and considered.
1.4.4.b Surface manifestation:
Surface manifestation such as sand boils or ground fissure
may be occurred during earthquake shaking emphasising that
ground settlement have already takes place noting that the
settlement may be occurred even with the absence of surface
manifestation. The evaluation of the potential for ground
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