Shear Wave Velocity- and Geology-BasedShear Wave Velocity and Geology Based Seismic Site Classification of Port-au-Prince

Brady R. Cox, Ph.D., P.E.Brady R. Cox, Ph.D., P.E.The University of Arkansas

Department of Civil Engineering

Geotechnical Earthquake Engineering for Seismic Design Workshop,

Department of Civil Engineering

Port-au-Prince, Haiti, November 18-19, 2010

Seismic Site ClassificationRequired by Seismic Provisions in Building CodesRequired by Seismic Provisions in Building Codes

IBC (2009) ASCE 7-05

IBC & ASCE Codes – Seismic Site Classification

Vs N SuSite Class: A - F> 1 500 m/s> 1,500 m/s760 – 1,500 m/s360 – 760 m/s180 360 /180 – 360 m/s< 180 m/s

V i f d b it i di tl l t d t th

ASCE 7-05

Vs is preferred because it is directly related to the shear stiffness of the soil deposit (G = Vs

2)

Vs Measurement Locations in Port-au-Prince

MASW used to determine Vs profiles at 36 locations across Port-au-Prince in April, 2010

Vs (Vs30) values calculated from the Vs profiles at each test location

Show testing pictures

Show site locations in Google Earth with Vs values and associated Seismic Site Classification

Sit Cl BSite Class BSite Class CSite Class D/ESite Class D/E

MASW Surveys in Port-au-Prince

For Seismic Site Classification A - E

Demo Locations, Vs Profiles, Vs ValuesShear Wave Velocity (m/s)

0 04003002001000

Shear Wave Velocity (m/s)

20

10

5

60

40

Dep

th (f

t) 15

Depth (m

)

80 25

20

100 30Vs = Vs30 = 250 m/s

160012008004000

Shear Wave Velocity (ft/sec)

Site Class D

Locations Relative to Geology

Vs – Geology CorrelationsShear Wave Velocity (m/s)Shear Wave Velocity (m/s)

150010005000

Shear Wave Velocity (m/s)

Median profile with +/- 1 sigma

0150010005000

Shear Wave Velocity (m/s)

TL# 8 TL# 9TL#10

20

TL#10 TL# 11 TL# 13 TL# 15 TL# 17 TL# 32

40

epth

(ft)

Vs profile comparison for geologic unit Qpf

80

60De

100

80

6000400020000

Shear Wave Velocity (ft/sec)

6000400020000

Shear Wave Velocity (ft/sec)

Median Vs Profiles for all Geologic Units

Geology – Site Classification Correlations

Geology Number of Profiles

Median Vs,30m

(m/s)NEHRP Site

Class( )Af 3 278 D

Qham 3 335 DQh 2 1 346 DQht2 1 346 DQphf 2 480 CQpf 8 499 CQpPpf 1 504 CPf 7 564 C

b 3 CMpb 3 513 CLmst 1 1014 B

Seismic Site Classification Map of Port-au-Prince

Some Potential Refinements?Shear Wave Velocity (m/s)

0 04003002001000

Shear Wave Velocity (m/s)

20

10

5

S ft

60

40

Dep

th (f

t) 15

Depth (m

)

Soft Clay???

80 25

20

Site

100 30Vs = Vs30 = 250 m/s

Class D

Site Class D or E? 160012008004000

Shear Wave Velocity (ft/sec)

IBC & ASCE Codes – Seismic Site Classification

Vs N SuSite Class: A - F> 1 500 m/s> 1,500 m/s760 – 1,500 m/s360 – 760 m/s180 360 /180 – 360 m/s< 180 m/s

ASCE 7-05

Questions?Questions?