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Khan et al. /Int.J.Econ.Environ.Geol.Vol. 8(2) 63-68, 2017

Assessment of Soil Liquefaction Potential in Defence Housing Authority,

Karachi, Pakistan

Sumaira Asif Khan1*

, Zubaid Saeed1, Adnan Khan

1, Gulraiz Hamid

1, Syed Waseem Haider

2

1Department of Geology, University of Karachi, Pakistan 2National Institute of Oceanography, Karachi, Pakistan

*Email: thesaksrk@yahoo.com

Received: 30 December, 2016 Accepted: 22 February, 2017

Abstract: The occurrence of liquefaction phenomenon may be induced in the event of a large magnitude earthquake

but sometimes loose, saturated and poorly graded sand may be subjected to liquefaction due to the vibration produced

by other sources. Liquefaction could cause damage to building and infrastructure due to sudden increase of pore

pressure in the loose layers of saturated sand causing the loss of bearing capacity and shear strength. Defence Housing

Authority (DHA) is the well planned residential scheme established by Pakistan Army along the coastal belt of

Karachi. The soil occurring in DHA is fine grained, poorly graded and mainly comprises of sandy silt and silty sand of

Recent age, where water table is encountered at very shallow depth. Hence, it is important to assess the geotechnical

behavior of the soil in DHA area, where most of the high rise buildings and mega civil structures are being constructed.

In present study, seismic soil liquefaction was evaluated at 15 sites (30 bore holes) in DHA by using simplified

empirical method in terms of Factor of Safety (FS). The Relative Density (RD) was determined with the help of

Standard Penetration Test (SPT) data. Grain size analysis was also carried out on each borehole samples. The results

revealed that the DHA area is vulnerable to liquefaction during severe seismic event of magnitude between 6.5 and 7.5

in Karachi.

Keywords: Silty-sand, liquefaction, factor of safety, DHA, Karachi.

Introduction

Soil liquefaction mainly occurs in sand, silty-sand,

sandy-silt and sensitive clays. Liquefaction is generally

ground shaking caused by strong earthquake, where

saturated, cohesionless granular soil is transformed

from a solid to nearly liquid state. The liquefaction

potential depends on the earthquake intensity,

magnitude, duration of ground motion, distance from

the source of earthquake, site specific conditions,

ground acceleration, type and thickness of soil

deposits, relative density, grain size distribution, fine

contents, plasticity of fines, degree of saturation,

confining pressure, permeability of soil layer, position

and fluctuation of ground water table, reduction of

effective stress and shear modulus degradation (Youd

and Perkins, 1978; Tuttle et al., 1999; Youd et al.,

2001). This study is based on consideration of factor

of safety (FS), relative density (RD) and grain size

analysis. The soil occurring in the study area is non-

plastic in nature.

Karachi is the largest city of Pakistan with population

of about 18 millions (CDGK, 2007). It is the economic

hub of country having a sea-port. As a result,

construction activities are exponentially increasing in

Karachi. Along the coast, Defense Housing Authority

(DHA) is the most fascinating and luxurious residential

scheme in Karachi. All the residential and commercial

settlements of DHA are founded on sediments

comprises of fine grained, saturated and poorly graded

sand of Holocene age (Hamid et al., 2015).The Factor

of Safety (FS), which is the resistance of soil against liquefaction can be determined by taking the ratio of

seismic demand and capacity of soil to resist

liquefaction (Seed and Idriss, 1971). Ability of soil to

resist against is calculated as Cyclic Resistance Ratio

(CRR), while seismic demand is determined by

computing Cyclic Stress Ratio (CSR). There are

numerous tests including Standard Penetration Test

(SPT), Cone Penetration Test (CPT), Beaker

penetration test and shear wave velocity (Vs) test could

be used to find out the FS of given soil layer (Youd et

al., 2001). Most commonly applied procedure for

assessing the liquefaction resistance of soil is SPT. Other FS is generally assessed by peak ground

acceleration (PGA), earthquake magnitude, SPT blow

counts, overburden pressure (σ), fine content (FC),

Atterberg limit and grain size distribution along the

depth of soil profile (Seed and Idriss,1971; Seed et al.,

1985; Youd et al., 2001). Liquefiable layer possesses

FS<1 and the soil layer with FS>1 falls in the category

of nonliquefiable soil (Seed and Idriss, 1971).

Geology of Study Area

Coastal part of Sindh lies in the seismically active zone

(Tatheer and Yasmeen, 2012). The coastal margin of

Karachi appears to depict regional conformity with the

folding pattern of the region in general and with the

Int. J. Econ. Environ. Geol. Vol. 8 (2) 63-68, 2017

Journal home page: www.econ-environ-geol.org

Open Access

ISSN: 2223-957X

Copyright © SEGMITE

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Khan et al. /Int.J.Econ.Environ.Geol.Vol. 8(2) 63-68, 2017

faulting pattern in particular. There is a major

geological fault, which runs from Ahmadabad and

Bhuj to Ormara along Makran coast. Besides, some

minor faults are also reported in Karachi. One of the

minor faults is Allah Bund fault, which passes through

coastal town of Shah Bundar and runs through eastern

parts of the city ending near Cape Monze. Another

fault lies in the Rann of Kutch near southeastern border

of Sindh with India. The third one is Pub fault, which

lies near the Makran coast (West of the city) while

fourth fault is located in Dadu district on the northern

boundary of Karachi (PMD, 2007). South eastern part

of Karachi city is mainly resting on the Quaternary

deposits such as beach sand, coastal sand dunes and

tidal mud flat underlain by Tertiary rocks including

Nari, Gaj and Manchar formations (Mohsin et al.,

1995). The coastal belt has significantly thick

Quaternary deposits, which need to be assessed in

order to understand geotechnical behavior. Drainage

conditions are poor and the problem of salinity and

water logging are also common in the coastal areas as

the ground water occurs at very shallow depth (< 3 m).

The soil occurring in DHA area is found to be poorly

graded, which is mainly comprised of sand, silty sand

and sandy silt of Recent age with negligible clay

fraction, most probably due to coastal geographic

control and dominance of aeolian deposits from the

beach (Mohsin et al., 1995).

Materials and Methods

Assessment of liquefaction potential was evaluated in

terms of Factor of Safety (FS) using SPT based

simplified empirical procedure originally proposed by

Seed and Idriss (1971).

Estimation of Factor of Safety

The Factor of Safety (FS) against liquefaction can be

determined by using following equation:

F.S=

Values of CRR (Cyclic Resistance Ratio) and CSR

(Cyclic Stress Ratio) vary with depth, so the FS was

calculated at different depths within the soil profile.

Estimation of Cyclic Stress Ratio

Seed and Idriss (1971) proposed a simplified equation

for computing the horizontal shear. This equation is

expressed in term of Cyclic Stress Ratio (Seed et al.,

1983, 1985).

Fig.1 Location map of the study area.

Fig. 2 Geological map of Karachi area, Sindh, Geological Survey of Pakistan (after Qureshi et al., 2001).

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CSR = 0.65*(amax/g) * (σt/σˊ)*rd

Where:

amax=Peak horizontal acceleration

g = Acceleration due to gravity

σt= Total vertical over-burden stress

σˊ = Effective vertical overburden stress at the depth

of interest.

rd=Stress reduction factor

Average value of Stress reduction factor (rd) is given

as:

rd=1.0- 0.00765z; for z ≤ 9.15 m

rd= 1.174 - 0.0267z; for 9.15 m < z ≤ 23 m

rd= 0.744 - 0.008 z; for 23 m < z ≤ 30 m

rd= 0.50; for z > 30 m

The mean value of rd calculated from above equation

is shown in Fig 3.

Estimation of Cyclic Resistance Ratio from SPT Blow

counts

Evaluation of cyclic resistance ratio (CRR) requires

value of fine content (FC, particles <0.007 diameter)

and corrected values of (N1)60 (from the measured

blow counts). This equation is suggested by Idriss and

Boulanger (2006) for estimation of CRR for cohesion

less soil with fine content.

CRR=exp

(N1)60cs is an equivalent clean sand standard

penetration resistance value.

(N1)60cs= (N1)60 + ∆ (N1)60

The measured SPT blow counts (NSPT) is normalized

for the overburden stress at the depth of the test and

corrected to a standardized value of (N1)60. Using the

recommended correction factors given by Robertson

and Fear (1996). The corrected SPT blow count is

calculated with:

(N1)60=NSPT.CN.CE.CB.CS.CR

The correction factors CN, CE, CB, CS and CR are

described below.

The first correction factor (CN) normalizes the

measured blow counts to an equivalent value under

one atmosphere of effective overburden stress.

CN=

Where:

σ =Vertical effective stress

Pa=1atm of pressure (0.000101325 KN/m²)

The factor CE is used to correct the measured SPT

blow counts for the level of energy delivered by the

SPT hammer. Using 60% of the theoretical maximum

energy as a standard.

CE=ER/60

By assuming ER=60, CE = 1

CB is another correction factor for borehole diameters

(Table 1, Robertson and Fear, 1996).

Another correction factor CS is for SPT samplers used

without a sample liner, CS=1 is used for a standard

sampler.

Table 3. Correlation among SPT-N value, angle of friction

and relative density (Meyerhoff, 1956).

SPT-N

(Blows/0.3m

or 1ft )

Soil

Packing

Relative

Density

(%)

Angle of

Friction

<4 Very loose <20 <30

4-10 Loose 20-40 30-35

10-30 Compact 40-60 35-40

30-50 Dense 60-80 40-45

>50 Very Dense >80 >45

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CR correction factor is used for rod length correction

with respect to depth (Table 2).

The correction factor ∆ (N1)60 is computed with the

linear function.

1. For FC ≤ 5% ; ∆(N1)60 =0

2. For 5<FC<35 % ; ∆(N1)60=7*(FC-5)/30

3. For FC ≥ 35 % ; ∆(N1)60=7

Where: FC= Fine Contents.

Grain Size Analysis

American Society for Testing and Material (ASTM, D-

422) is used for grain size analysis. This procedure

reveals the size, shape and sorting of sand. Soil having

uniformity coefficient less than five is more susceptible

to liquefaction (Ross, et al., 1969; Lee and Fitton, 1969).

Atterberg Limit

Atterberg limit test was performed to determine the

nature of soil (plastic or non plastic) and Plasticity

Index (PI). Soil with substantial plastic fine should be

appraised on the Atterberg limits for the liquefaction

potential (Seed and Idriss 1981, 1982, Seed et al.,

1983).

Relative Density

Liquefaction occurs principally in loose saturated clean

sands and silty sands having a relative density less than

50%. Relative density was determined by using the

SPT-N values because the number of blow counts has

a direct relation with relative density.

Results and Discussion

This study attempts to evaluate liquefaction potential

of the soil occurring in DHA area, for which different

parameters were used including Grain Size Analysis,

Factor of Safety (FS) and Relative Density. Factor of

Safety (FS) was calculated against the liquefaction

potential in DHA using SPT based semi empirical

procedure. Soil liquefaction potential was determined

at 15 sites (30 bore holes) across the DHA area for the

earthquakes of magnitude Mw=6.5, Mw=7 and

Mw=7.5 with peak ground acceleration of 0.2g. The

soil deposited at these sites comprises layers with filling material composed of silty sand, medium to stiff

clayey silt, sand and soft to medium stiff silty clay of

Holocene age (Hassan et al., 2015). It is widely

accepted that only recent sediments or fills of

saturated, cohesionless soils at shallow depths will

liquefy in a large magnitude earthquake. Soil gradation

curve depicts that the soil of all sites may be

categorized as sand (medium to fine) and there is

negligible amount of clay with the plasticity range of

30 to 35%. Loose sand with less amount of clay

(particles <0.005) is more prone to liquefy, if it

encounters with 0.9 times water content (Seed and

Idriss, 1982).

Fig. 4 Boundaries of liquefiable and non-liquefiable layers.

Loose uniformly graded materials are more susceptible

to liquefaction than well-graded materials (Ross, et al.,

1969; Lee and Fitton, 1969). While, Tsuchida (1970)

proposed ranges of grain size curves separating

liquefiable and nonliquefiable soils (Fig. 4). Factor of

safety (FS) against the earthquake of magnitude

Mw=6.5, Mw = 7 and Mw=7.5 reveals that all the 15

sites have FS < 1 which are liable to liquefy because

liquefiable layers possess FS < 1. A few layers depict

FS=1 which indicates the critical point and FS >1

indicates the safe zone. However, these layers are

relatively very thin. Calculations for FS (Mw=6.5, 7,

7.5) are given in Table 4.

Table 1. Correction factor for borehole diameter.

Diameter of Borehole CB

65 mm to115 mm (2.5 to 4.5 inch) 1

150 mm (6 inch) 1.05

200 mm (8 inch) 1.15

Table 2. Rod length correction with respect to depth.

Depth (m) Correction for Rod length (CR)

3 0.75

3-4 0.8

4-6 0.85

6-10 0.95

10-30 1.0

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Conclusion

Based on computation of FS from 15 sites of DHA, it

is concluded that study area is highly vulnerable to

liquefaction. Factor of Safety (FS) was computed

against earthquake magnitudes of 6.5, 7 and 7.5.

Moreover, the detailed textural analysis and relative

densities of borehole sediment samples also supported

the liquefaction potential favoring the earthquake

magnitude of 6.5, 7 and 7.5. Presence of groundwater

table along with the presence of non-cohesive soil (silt

and sand) further supported the likelihood of

liquefaction phenomena to occur in DHA during any

noticeable seismic event. Therefore, high rise buildings

should be designed under the provision 2B (Uniform

Building Code) for moderate seismic zone in Karachi.

Acknowledgement

We gratefully acknowledge Managing Director of Soil

Mat. Lab., Mr. Kazim Mansoor and Engr. Noor

Ahmed for their valuable suggestions and technical

support. We are also thankful to Mr. Khalid Alvi,

Museum Curator Department of Geology, University

of Karachi for his constant support.

References

Fig. 5 Textural analysis of 15 sampling sites.

Table 4. Calculation for FS of a representative site.

Site Borehole Layer Thickness

(ft) CSR NSPT CRR

FS

Mw=6.5 Mw=7 Mw=7.5

1

1

6 0.19 9.00 0.10 0.81 0.63 0.53

10 0.19 13.00 0.10

0.78 0.60 0.51 14.00 0.06

GWT

(m)

2.286

5 0.21 14.00 0.10 0.73 0.56 0.47

17 0.20 22.00 0.06

0.75 0.58 0.49 24.00 0.06

2

6 0.20 5.00 0.10 0.75 0.58 0.49

4 0.20 7.00 0.10 0.74 0.57 0.48

5 0.21 8.00 0.10 0.72 0.56 0.47

10 0.21 19.00 0.10

0.71 0.55 0.46 21.00 0.06

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Akhtar, J. M., Shah, A. A. S., Pasha, A. M., Tariq, A.

M. Khan, A. I., Khan, S. M., Khanzada, I. M.,

Ahsan, N. S. (2001). Geological map of Karachi,

Sindh. Geological Survey of Pakistan, Karachi.

Andrus, R. D., Stokoe, K. H., Roesset, J. M. (1991).

Liquefaction of gravelly soil at Pence Ranch

during 1983 Borah Peak, Idaho Earthquake. In:

First International Conference on Soil Dynamics

and Earthquake Engineering, Karlsruhe, Germany.

Hassan, K., Bilal, M., Siddiqui, S. N., Hamid, G.,

Mallick, K. A. (2015). Soil classification as a tool

for evaluating soil behavior as foundation

materials. Int. J. Econ.and Environ.Geol, 5, 41-46.

Ishihara, K. (1985). Stability of natural deposits during

earthquakes. In: Proceedings of 11th International

Conference on Soil Mechanics and Foundation

Engineering, CA, San Francisco, 1, 321–376.

Jospeh, E. Bowles (1984). Physical and geotechnical

properties of soil. Second edition, Mc Graw Hill,

Singapore.

Lee, K. L., Fitton, J. A. (1969). Factors affecting the

cyclic loading strength of soil, vibration effects of

earthquakes on soils and foundation. American

Society for Testing and Materials, ASTM STP

450.

Luna, R., Frost, J. D. (1998). Spatial liquefaction

analysis system. J. Comput. Civil Eng., 12, 48–56.

Meyerhof, G. (1956). Penetration tests and bearing

capacity of cohesionless soils. J. Soils Mechanics

and Foundation Division, 82, 1-19.

Ministry of Housing and Works (2007). Building code

of Pakistan (seismic provisions). Government of

Islamic Republic of Pakistan, 303 pages.

Mohsin, S. I., Hamid, G., Siddiqui, E., Zubair, A.

(1995). Engineering properties of soil layers of

Karachi. Pak. Journal of Science and Industrial

Research, 38, 384-390.

NORSAR, (2007). A report on seismic hazards

analysis and zonation for Pakistan, Azad Jammu

and Kashmir by Pakistan Meteorological

Department and Norway.

Robertson, P. K., Wride, C. E. (1997). Cyclic

liquefaction and its evaluation based on the SPT

and CPT. Proceedings of the NCEER Workshop

on Evaluation of Liquefaction Resistance of Soils,

Technical Report, NCEER-97-0022, 41-87.

Ross, G. A., Seed, H. B., Ralph. R. (1969). Bridge

Foundations in Alaska Earthquake. Journal of the

Soil Mechanics and Foundation Division, 95,

1007-1036.

Seed, H. B and Idriss, I. M. (1983). Ground motions

and soil liquefaction during earthquakes.

Earthquake Engineering Research Institute,

Berkeley, Calif, 134.

Seed, H. B. (1968). Landslides during earthquakes.

Journal of the Soil Mechanics and Foundation

Division, 94, 1055-1122.

Seed, H. B., Idriss, I. M. (1971). Simplified procedure

for evaluating soil liquefaction potential. Journal

of the Soil Mechanics and Foundations Division,

97, 1249-1273.

Seed, H. B., Idriss, I. M. (1982). Ground motions and

soil liquefaction during earthquakes. Earthquake

Engineering Research Institute. Engineering

Monograph, 5, 127-134.

Seed, H. B., Idriss, I. M., Arango, I. (1983). Evaluation

of liquefaction potential using field performance

data. American Society of Civil Engineers.

Journal of Geotechnical Engineering, 109, 458-

482.

Seed, H. B., Tokimatsu, K., Harder, L. F., Chung, R.

M. (1985). Influence of SPT procedures in soil

liquefaction resistance evaluations. Journal of

Geotechnical Engineering, 12, 1425-1445.

Tsuchida, H. (1970). Prediction and counter measure

against the liquefaction in sand deposits. Seminar,

Port and Harbor Research Institute, Japan, 3, 1-3.

Tuttle, M., Chester, J., Lafferty, R., Dyer-Williams, K.,

Cande, R. (1999). Nuclear Regulatory

Commission Publication, 96, NUREG.CR-5730.

Youd, T. L, Perkin, M. (1978). Mapping liquefaction

induced general failure potential. Journal of the

Geotechnical Engineering Division, 104, 433-446.

Youd, T. L. (2001). Liquefaction resistance of soils:

Summary 1996. NCEER and 1998. NCEER/NSF

workshops on evaluation of liquefaction resistance

of soils. Journal of Geotechnical and

Geoenvironmental Engineering, 10, 817-833.

Zehra, T., Zehra, Y. (2012). Effects of rising seismic

risks in Karachi. Int. J. of Civil and Environmental

Engineering, 2, 42-45.