geotechnical engineering report
Earth Systems__________________________________________________________________________________ Southern California
September 11, 2015
2114 East Walnut Street Pasadena, California 91411 (626) 356-0955 Fax (626) 356-0956 www.earthsystems.com
LA-01617-01
Pasadena Unified School District (PUSD) 740 W. Woodbury Road Pasadena, CA 91103 Attention:
Mr. George Kwiter
Subject:
Fault Rupture Hazard Investigation Project Status #2 San Rafael Elementary School 1090 Nithsdale Road Pasadena, California
Earth Systems has recently completed “Phase 2” of a Fault Rupture Hazard Evaluation, which included the evaluation of two, approximately 15-foot deep trenches that spanned the subject property in an east-west trend, see Site Map attached. The northerly trench, ST1, located in the front yard portion of the school, was approximately 80 feet long; the second trench, ST2, was approximately 500 feet long in the playground area, located in the middle of the school property. These trenches extended through the area of the previously identified anomalies identified by Hydrologue and GeoVision in 2012. The trenching allowed for the physical observation of the underlying soil to determine if a recent fault displacement has occurred under the site. Mr. William LaChapelle, P.G., C.E.G. (Earth Systems), Mr. Christopher Allen, P.G. (Earth Systems), and Dr. Thomas Rockwell, P.G. (third party soil stratigrapher and professor at San Diego State University) observed and logged the trench; periodic observations were completed by Mr. Brian Olsen, P.G., C.E.G., Jerry Treiman, E.G., and Brian Swanson, E.G. of the California Geological Survey (CGS). This portion of the study was completed for the purpose of identifying possible faulting in stratigraphy exposed in the recently excavated trenches. It was determined that Pleistocene or older (greater than 11,000 years) soils were exposed in the trenches. However, the stratigraphy observed in the westerly 100 feet of ST2 was massive and in close proximity to the water table. The massive (near structureless) nature of the soil exposed in that area, coupled with the saturated condition which prohibits soil structure development, provided inconclusive evidence with respect to age and fault activity.
June 15, 2015
2
LA-01617-01
Based on the results of our investigation described above, it is Earth Systems opinion that there is no evidence of active faults present at the site. Earth Systems has identified undisrupted, laterally continuous pre-Holocene age geologic strata across the site that indicates active faulting is not present within the depth and location explored. Therefore, the potential for surface fault rupture at the subject site during the design life of the existing structures is considered to be very low. However due to inconclusive evidence in the westerly 100 feet of ST2 a restricted use area has been proposed. It is our opinion that no restrictions on future development at the site, outside the proposed restricted use area, are necessary with respect to the hazard of surface fault rupture. The site is located in southern California, which is within an active seismic area. Large numbers of earthquakes are recorded each year in southern California. Provided the close proximity to a number of faults, the site could be subject to strong ground shaking in the event of a large earthquake on a nearby fault. The effects of ground shaking can be mitigated by proper engineering design and construction in conformance with current building codes and engineering practices. Respectfully submitted, Earth Systems
Christopher F. Allen, P.G. Project Geologist Attachment: Site Map Distribution: Mr. George Kwiter [email protected]
EARTH SYSTEMS
C1 ST1
LEGEND C3
APPROXIMATE CONTINUOUS CORE BORING LOCATION
ST2
APPROXIMATE TREND EXPLORATION TRENCH (Actual location subject to field conditions) APPROXIMATE LOCATION OF GEOPHYSICAL ANOMALIES (Hydrologue, 2011 and 1012)
RESTRICTED USE AREA
ST2 C2
C3
RESTRICTED USE AREA
SITE MAP SAN RAFAEL ELEMENTARY SCHOOL 1090 NITHSDALE ROAD PASADENA, CALIFORNIA
APPROXIMATE SCALE 1 inch = 40 feet (1:480) 20 BASE MAP: Carmichael-Kemp Architects, 4/11/11
0
20
40
80
Earth Systems Southern California 9/11/2015
LA-01617-01
September 11, 2015
2114 East Walnut Street Pasadena, California 91411 (626) 356-0955 Fax (626) 356-0956 www.earthsystems.com
LA-01617-01
Pasadena Unified School District (PUSD) 740 W. Woodbury Road Pasadena, CA 91103 Attention:
Mr. George Kwiter
Subject:
Fault Rupture Hazard Investigation Project Status #2 San Rafael Elementary School 1090 Nithsdale Road Pasadena, California
Earth Systems has recently completed “Phase 2” of a Fault Rupture Hazard Evaluation, which included the evaluation of two, approximately 15-foot deep trenches that spanned the subject property in an east-west trend, see Site Map attached. The northerly trench, ST1, located in the front yard portion of the school, was approximately 80 feet long; the second trench, ST2, was approximately 500 feet long in the playground area, located in the middle of the school property. These trenches extended through the area of the previously identified anomalies identified by Hydrologue and GeoVision in 2012. The trenching allowed for the physical observation of the underlying soil to determine if a recent fault displacement has occurred under the site. Mr. William LaChapelle, P.G., C.E.G. (Earth Systems), Mr. Christopher Allen, P.G. (Earth Systems), and Dr. Thomas Rockwell, P.G. (third party soil stratigrapher and professor at San Diego State University) observed and logged the trench; periodic observations were completed by Mr. Brian Olsen, P.G., C.E.G., Jerry Treiman, E.G., and Brian Swanson, E.G. of the California Geological Survey (CGS). This portion of the study was completed for the purpose of identifying possible faulting in stratigraphy exposed in the recently excavated trenches. It was determined that Pleistocene or older (greater than 11,000 years) soils were exposed in the trenches. However, the stratigraphy observed in the westerly 100 feet of ST2 was massive and in close proximity to the water table. The massive (near structureless) nature of the soil exposed in that area, coupled with the saturated condition which prohibits soil structure development, provided inconclusive evidence with respect to age and fault activity.
June 15, 2015
2
LA-01617-01
Based on the results of our investigation described above, it is Earth Systems opinion that there is no evidence of active faults present at the site. Earth Systems has identified undisrupted, laterally continuous pre-Holocene age geologic strata across the site that indicates active faulting is not present within the depth and location explored. Therefore, the potential for surface fault rupture at the subject site during the design life of the existing structures is considered to be very low. However due to inconclusive evidence in the westerly 100 feet of ST2 a restricted use area has been proposed. It is our opinion that no restrictions on future development at the site, outside the proposed restricted use area, are necessary with respect to the hazard of surface fault rupture. The site is located in southern California, which is within an active seismic area. Large numbers of earthquakes are recorded each year in southern California. Provided the close proximity to a number of faults, the site could be subject to strong ground shaking in the event of a large earthquake on a nearby fault. The effects of ground shaking can be mitigated by proper engineering design and construction in conformance with current building codes and engineering practices. Respectfully submitted, Earth Systems
Christopher F. Allen, P.G. Project Geologist Attachment: Site Map Distribution: Mr. George Kwiter [email protected]
EARTH SYSTEMS
C1 ST1
LEGEND C3
APPROXIMATE CONTINUOUS CORE BORING LOCATION
ST2
APPROXIMATE TREND EXPLORATION TRENCH (Actual location subject to field conditions) APPROXIMATE LOCATION OF GEOPHYSICAL ANOMALIES (Hydrologue, 2011 and 1012)
RESTRICTED USE AREA
ST2 C2
C3
RESTRICTED USE AREA
SITE MAP SAN RAFAEL ELEMENTARY SCHOOL 1090 NITHSDALE ROAD PASADENA, CALIFORNIA
APPROXIMATE SCALE 1 inch = 40 feet (1:480) 20 BASE MAP: Carmichael-Kemp Architects, 4/11/11
0
20
40
80
Earth Systems Southern California 9/11/2015
LA-01617-01
