W912HV-16-B-0001_Misawa_HS_Geotech_Report_and_Memo-030613.pdf

MASA FUJIOKA & ASSOCIATES

Environmental Geotechnical Hydrogeological Consultants

98-‐021 Kamehameha Highway, Suite Aiea, Hawaii

96701-‐4914

Telephone:

(808) 484-‐5366 Facsimile:

(808) 484-‐0007

MEMO REGARDING SOIL LIQUEFACTION April 10, 2014

Edgren HS, Misawa AFB, Japan

Background:

Three existing buildings are being renovated.

Building 746 is founded on deep piles to below liquefaction zones. The slabs are on grade.

Building 747, a GOJ project, is supported on shallow piling to a dense sand layer, mostly to 5 meters. Liquefiable sands underlie the dense sand layer. The slabs are on grade.

Building 742, a GOJ project, is supported by deep piles below liquefaction zones on the west side, and shallow piles (mostly 6m) on a dense sand layer on the east side. Liquefiable sands underlie the dense sand layer. The slabs are on grade.

References:

U.S. Army references provide procedures on analysis of liquefaction but do not provide guidance on building performance during liquefaction.

The IBC similarly provides procedures on analysis of liquefaction potential but does not provide guidance on building performance during liquefaction.

To my knowledge, the NAVFAC Port Hueneme manual, TR077SHR, is the only one that provides guidance on allowable building performance during liquefaction.

In the absence of other guidance, we recommend use of the NAVFAC manual. We would recommend classification of the high school structures as ordinary construction under this manual, however the Corps should make this determination. The requirements for ordinary construction are:

Ordinary Construction - Liquefaction associated with construction categorized as “ordinary” shall be evaluated to insure the level of performance is maintained. In general ordinary construction is expected to:

1. Resist a minor level of ground motion without damage;

2. Resist a moderate level of ground motion (100 year recurrence) without structural damage, but possibly experience some nonstructural damage;

3. Resist a major level of earthquake (500 year recurrence) ground motion without collapse, but with structural as well as nonstructural damage.

Structures classified as Essential Construction are expected to:

1. Resist the maximum probable earthquake likely to occur one or more times during the life of the structure (100 year recurrence) with minor damage without loss of function and the structural system to remain essentially linear.

2. Resist the maximum theoretical earthquake with a low probability of being exceeded during the life of the structure (1000 year recurrence) without catastrophic failure and a repairable level of damage.

Discussion:

Most of the ground improvement methods in the Army references are only applicable to open sites, and cannot be applied where there are existing structures.

The existing piling provides protection against near surface liquefaction, which is the most likely to occur and instances of near surface liquefaction are common.

The IBC requires protection against liquefaction occurring within the first 50 feet. Deeper liquefaction between approximately 25 to 50 feet is theoretically possible but is not historically common.

I believe the level of protection we would be providing with the recommended micropiles to be appropriate for structures determined to be ordinary construction.