Airport Liquefaction Susceptibility Analysis Report - ABAG ...

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Fugro Consultants, Inc. Project No. 04.79221200 Table 3. Calculated Liquefaction Settlement Summary Calculated Liquefaction Induced Settlements Range (inches) Airport Location San Francisco International Airport Oakland International Airport 1906 San Francisco Earthquake Scenario 1 Hayward- Rodgers Creek Scenario 1 Concord- Green Valley Scenario 1 10% Probability of Exceedance in 50-Years Scenario 2 2% Probability of Exceedance in 50-Years Scenario 2 1 to 4 1 to 3 0 to 2 1 to 4 1 to 4 2 to 9 2 to 9 2 to 8 2 to 9 2 to 9 Buchanan Field Airport 1 1 to 4 1 to 4 1 to 4 1 to 4 1 to 4 Livermore Municipal Airport 2 N/A N/A N/A N/A N/A Moffett Federal Airfield 3 1 to 3 1 to 3 below 1 2 to 3 2 to 3 Notes: 1 Based on limited number of data points. No data points available along the runways. 2 Available borings to shallow to evaluate liquefaction induced settlements. 3 Based on seven CPTs along the runway (USC-01 to USC-07). Seven CPTs located adjacent to the airport and analyzed using partial data not considered for this summary. 6.1 Liquefaction Hazards 6.1.1 San Francisco International Airport The liquefaction analyses performed for San Francisco used data available from 86 CPT locations, representing the largest number of data locations used for analysis at any of the five airport locations. The CPT data used are well-distributed across the property and mostly exceed 30 feet in depth. The CPT data indicate that the surficial deposits at the airport are primarily composed of artificial fill and are underlain by Young and Old Bay Mud. The analyses performed for each of the five scenarios results in a calculated settlement of between 0 and 4 inches (Table 3), and suggest that both coarse grained artificial fill and Holocene alluvium have the highest susceptibility to liquefaction. The range of settlement values calculated for the assessment are significantly lower than the range of settlement values of 12 inches to 30 inches calculated during the study performed by WLA in 1999. A number of factors could be responsible for the different settlement values, including: 23 May 31, 2013
Fugro Consultants, Inc. Project No. 04.79221200 • Data distribution: the data locations used in the WLA study were concentrated in the main terminal area and the northern end of the property. The data used in this study are more equally distributed across the site, and may be more representative of the site conditions. • Data extent: of the approximately 230 boreholes evaluated as part of the WLA study, approximately 130 of the boreholes were shallower than 30 feet, with approximately 80 of those boreholes shallower than 10 feet. • Sampling intervals: the number and spacing of sampling intervals using borehole data can be limited, where as CPT data locations contain more sampling intervals for better resolution of liquefiable materials thicknesses. • Updated liquefaction procedures: the updated ground motion data of Petersen and others (2008) and procedures outlined by Youd and others (2001) applied during this study are different than those applied during the WLA (1999) study. 6.1.2 Oakland International Airport The liquefaction analyses performed for Oakland used data available from 48 borehole locations. The borings analyzed were concentrated within the southwestern and northeastern edges of the property. Additional data is available, but it was either 1) in a format that was difficult to analyze, or 2) not provided before the analysis was completed. As a result of the data limitations, no subsurface data was analyzed in the main terminal area located in the center of the property. The borehole data indicates that the surficial deposits at the airport are primarily composed of artificial fill and are underlain by Young and Old Bay Mud and Merritt Sand. The analyses performed for each of the five scenarios results in a calculated settlement of between 2 and 9 inches (Table 3). This settlement range is lower than the settlement range of 4 to 12 inches calculated during the initial study performed by WLA in 1999. A number of factors could be responsible for the different settlement values, including: • Data distribution: The data locations used in the WLA study are located throughout the property, but are located in smaller clusters and widely spaced. The data used in this study are clustered along the western and northeastern portions of the property. No subsurface data was available or analyzed for the main terminal area for this study. • Data extent: Of the approximately 180 boreholes evaluated as part of the WLA study, approximately 70 of the boreholes were shallower than 30 feet, with approximately 4 of those boreholes shallower than 10 feet. Liquefiable material may be present below the maximum depth achieved by the borings. • Updated liquefaction procedures: the updated ground motion data of Petersen and others (2008) and procedures outlined by Youd and others (2001) during this study are different than those applied during the WLA (1999) study. 24 May 31, 2013
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