Liquefaction Potential of Nusajaya City Aminaton Marto Professor Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Malaysia e-mail:
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Choy Soon Tan PhD Candidate Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Malaysia e-mail:
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Nur Naemah Esa Student Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Malaysia e-mail:
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Faizal Pakir PhD Candidate Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Malaysia e-mail:
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Siti Norafida Jusoh Lecturer Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Malaysia e-mail:
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ABSTRACT Nusajaya city, as part of the Iskandar Malaysia region had experienced a precedence growth in population since the year 2006. This reflexes a direct increase of necessity in urban seismic hazard evaluation. This paper presents a preliminary evaluation of liquefaction potential of the soils in Nusajaya City using both deterministic and probabilistic analysis methods. The general soil profile of the study area is sand, which vulnerable to soil liquefaction risk. The results of both approaches are quantitatively in good agreement, but varied qualitatively. New assessment chart incorporating the boundary limit of factor of safety and Liquefaction Probability Density Function was proposed. Based on the chart, it can be concluded that Nusajaya City is quite safe against liquefaction due to earthquake originating from Indonesia.
KEYWORDS:
Simplified procedure, liquefaction probability density function.
INTRODUCTION The occurrence of the earthquake has been continually threatened millions of people throughout the world. Peninsular Malaysia is expected to be seismically free since it is located on - 17231 -
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tectonically stable crust on a Sunda Plate while the nearest potential seismic features are located at least 350 km away. In normal case, affected region caused by high intensity earthquake is up to 700 km (Megawati et al., 2005). In contraction, both empirically evidences and the outcomes of some seismic hazard assessments proven that this common presumption is misleading. In addition, the initiation of local originating earthquakes in Peninsular Malaysia as shown in Figure 1 since 20th Century is threatening (Marto et al., 2013). Geologist stated that this is a symptom of inactive ancient faults’ reactivation caused by 2004 Indiana Ocean earthquakes. There is still lacking of reliable scientific investigation on regional seismic assessment, in particular, the Geotechnical Earthquake Engineering. Seismic hazard analyses are prudent to be conducted to assist the engineering community in producing seismically resistant structures, in particular the new development region such as the Iskandar Malaysia Region. A series of reclamation works in this region have reshaped a big portion of coastal shoreline. The reclamation works using sand make these areas highly susceptible toward soil liquefaction behaviour. The seismic waves originated from a far field earthquake could travel through bedrock for a longer distance. Along the transmission, the resonance effect could cause amplification behaviour during upward propagation. The amplified waves make possible the soil liquefaction to be occurring within the region. With the expected increase of population density in the near future; it reflexes a direct increase of necessity in urban seismic hazard evaluation. Concerning the matter, the objective of this study is to perform preliminary evaluation of liquefaction potential of soils in Nusajaya City using both deterministic and probabilistic analysis methods.
Figure 1: Seismotectonic map of Malaysia (Mineral and Geosciences Department, 2008)
LIQUEFACTION POTENTIAL Soil liquefaction is defined as a phenomenon wherein a mass of soil loses its large percentage of shear resistance due to subjected loading in either monotonic or cyclic forms (Terzaghi et al. 1996). The assessment of liquefaction potential could be done either in probabilistic or deterministic manner. The Simplified Procedure (Seed and Idriss, 1971) has become a standard of
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practice throughout the world after several times of update. There are two main variables in this semi-empirical procedure, cyclic shear ratio (CSR) and cyclic resistance ratio (CRR). The liquefaction potential could be identified based on the concept of factor safety. By comparing the CRR to CSR values, the factor of safety (FS) could be estimated to indicate liquefaction potential of the study site. The higher the factor of safety, the more resistant the soil is toward liquefaction. Sonmez and Gokceoglu (2005) had noticed that the factor of safety at 1.2 is marginally distinguished between liquefiable to non-liquefiable zone. The equations for CSR, CRR and FS are as follows: τcyc
CSR = �
𝐶𝐶𝐶𝐶𝐶𝐶 = 𝑒𝑒 [
σ’
σ
amax
σ’
g
� = 0.65rd � � �
�
(𝑁𝑁1 )60𝑐𝑐𝑐𝑐 (𝑁𝑁 )60𝑐𝑐𝑐𝑐 2 (𝑁𝑁 )60𝑐𝑐𝑐𝑐 3 (𝑁𝑁 )60𝑐𝑐𝑐𝑐 4 +� 1126 � − � 123.6 � + � 125.4 � − 2.8] 14.1
𝐹𝐹𝐹𝐹 =
𝐶𝐶𝐶𝐶𝐶𝐶 𝐶𝐶𝐶𝐶𝐶𝐶
(1) (2) (3)
However, more and more researchers had pointed out that the concept of safety factor computation in Simplified Procedure at a given depth could not give tangible information on severity of possible ground instability (Kanth and Dash, 2009) The reason is that the relation between liquefaction potential and probability is linear whereas liquefaction potential and FS is non linear (Lee et al., 2011). Some researchers proposed formulation of probabilistic based procedure to replace Simplified Procedure, which is a deterministic based procedure. For example, the Liquefaction Potential Index (Iwasaki et al, 1982) was used to predict the liquefaction hazard of the entire soil column at a specific location rather than the concept of FS which only represent a particular soil element. Instead of that, this paper utilised the fully probabilistic method in evaluating liquefaction hazards as shown in Figure 2. The Nusajaya is one of the five key flagships in Iskandar Malaysia Region. This region covers a total area of 24,000 acres, with estimated 500,000 populations by 2025. It is also one of the largest privately-owned land bank in Southeast Asia (Iskandar Region Development, 2010). As a preliminary assessment, this study only covers five major masterpiece projects in Nusajaya City which are (a) Ledang Height; (b) Medini Iskandar Malaysia; (c) Pinewood Iskandar Malaysia Studio; (d) Puteri Harbour Waterfront and (e) Mall of Medini; as labelled in Figure 3. The total area of considered project sites which had been included in this preliminary study covers an area of about 94.13 km2. Seven Site Investigation reports from five projects with a total number of 78 boreholes data had been collected in this study.
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Figure 2: Probabilistic liquefaction hazard evaluation (Hwang et al, 2005)
Figure 3: Location of the project site
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Due to the fact that liquefaction behaviour is prone to shallow saturated soil deposited in loose state, the boundary limit of this study was on susceptible soil deposits up to 20 m depths from ground surface. . The general soil profile of the study area is sand and silt, which vulnerable to soil liquefaction risk. The ground response analyses were carried out by performing a computer program for Nonlinear Earthquake Response Analysis. As in the preliminary stage, analysis had been focusing on 500 years return period, which corresponds to serviceability failure only. The range of peak ground accelerations value is ranging from 0.057-0.091 g.
RESULTS AND DISCUSSION Liquefaction susceptibility analysis is the first step in the soil liquefaction engineering assessment. Although Modified Chinese Criteria is the most recognized criteria since 1979, the usability is in doubt as it is inadequate to define the vulnerability of fine grained soil towards liquefaction. Therefore, two different analysis methods were performed. This is not only to ensure the assessment’s accuracy, but also to assess for comparison purposes. The general soil composition of Nusajaya city is sand and silt. The results of the first assessment of liquefaction susceptibility analysis based on the method proposed by Andrew and Martin (2000) is presented in Figure 4. Most of the soil profile is laid within the region of “Non-liquefaction”. However, there are still some boreholes is either liquefiable or need further investigation. The Heritage District potentially liquefiable sites while Iskandar Financial District and Creative Park need further study. Since the main soils’ component of the project sites is silty sand, and the susceptibility of silts toward liquefaction is unclear; the further assessment for all project sites is essential at this stage. In fact, the NCEER Workshop in year 2001 stated that researchers had started to question and debate on the use of the clay fraction as a means to indicate the susceptibility of soil liquefaction hazard. More and more consensus studies are underway to improve the current assessment criteria. Instead of clay fraction, researchers believed that plasticity index is more relevance in representing the basic characteristic of fines in altering soil liquefaction behaviour, especially plastic fines such as clay. Liquefaction potential analyses were carried out with both deterministic (Simplified Procedure) and probabilistic (Probability Density Function) methods for comparison purposes. Both deterministic and probabilistic based liquefaction potential analyses are based on standardised corrected earthquake magnitude of 7.5. Figure 5 shows the results of the deterministic liquefaction potential analysis while Figure 6 presents the results of probabilistic liquefaction potential analysis. Quantitatively, the total number of liquefiable sites is in good agreement for both deterministic and probabilistic methods. Out of five project sites, only Pinewood Studio Iskandar Malaysia, Puteri Harbour and Mall of Medini show the eligibility of liquefaction potential while the other two projects remain safe against liquefaction potential. Qualitatively, the severity of liquefaction potential at the same site is varying. For example, the results of probabilistic based analysis show that the Mall of Medini is very like to be liquefying, but it is safe in term of safety factor against liquefaction potential. Therefore, it becomes a good effort to incorporate both the results of both deterministic and probabilistic findings as one assessment criteria in order to serve as better assessment criteria. By correlating the boundary limit, factor of safety (FS) of 1.2 and occurrence probability (Pf ) of 65%; an assessment chart was proposed as shown in Figure 7. These two boundary limit were
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chosen based on the assumption given by Sonmez and Gokceoglu (2005) and Hwang et al (2005). For the area that Pf > 0.65 and FS < 1.2, there are great potential that liquefaction could occur. On the other hand, the area that Pf < 0.65 and FS > 1.2, no liquefaction will occur. However, further study is required for the area that does not belong to these two conditions.
Figure 4: Liquefaction susceptibility of Nusajaya City
Figure 5: Results of deterministic based liquefaction potential analysis
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Figure 6: Results of probabilistic based liquefaction potential analysis
Figure 7: Proposed liquefaction potential criteria
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CONCLUSION Preliminary assessment of liquefaction potential of the Iskandar Malaysia region, in particular Nusajaya City has been carried out. A new assessment chart was proposed by incorporating the boundary limit of deterministic and probabilistic methods. Based on the chart, it can be concluded that Nusajaya City is quite safe against liquefaction due to far field earthquake originating from Indonesia. However, further verification is needed in order to characterize the usability of the proposed assessment chart
ACKNOWLEDGEMENT The authors gratefully acknowledged the financial supports by the Ministry of Education (MOE) under the Fundamental Research Grant Scheme (Vot 4F316) and also the Universiti Teknologi Malaysia (UTM) through Zamalah program in undertaking the research to publish the results. The support of the Construction Research Centre and Construction Research Alliance, UTM is also acknowledged.
REFERENCES 1. Andrews, D.C.A. and Martin. G.R (2000) “Criteria for Liquefaction of Silty Soils”, Proceedings of 12th World Conferences on Earthquake Engineering, Auckland, New Zealand 2. Hwang, J-H., Chen C-H. and Juang C.H. (2005) “Liquefaction Hazard analysis: A fully probabilistic method”, Proceedings of the Sessions of the Geo-Frantiers 2005 Congress, GSP 133 Earthquake Engineering and Soil Dynamics. 3. Iskandar Regional Development Authority (2010) Touching Lives Instilling Values. 4. Iwasaki, T., Arakawa T. and Tokoda, K. (1982) “Simplified Procedures for Assessing Soil Liquefaction during Earthquake”, Proceeding of Soil Dynamics & Earthquake Engineering Conference, Southampton, 925-939 5. Kanth, G.R. and Dash., S.K. (2009) “Evaluation of Seismic Soil Liquefaction at Guwahati City”, Environmental Earth Science, 61(2), 355-368 6. Lee, D.H., Juang C.H. and Ku. C.S. (2011) “Liquefaction Performance of Soils at the Site of a Partially Completed Ground Improvement Project during the 1999 Chi-Chi Earthquake in Taiwan”, Canadian Geotechnical Journal, 38, 1241-1253 7. Marto, A., Tan, C.S., Kasim, F. and Mohd Yunus, N.Z. (2013) “Seismic Impact in Peninsular Malaysia”, Proceedings of the 5th International Geotechnical SymposiumIncheon, Seoul, Korea. 8. Megawati, K., Pan, T-C. and Koketsu K. (2005) “Response Spectral Attenuation Relationships for Sumatra Subduction Earthquakes and the Seismic Hazard Implications to Singapore and Kuala Lumpur”, Soil Dynamics and Earthquakes Engineering, 25, 1125. 9. Mineral and Geosciences Department (2008) “Assessment of the Seismic Threats to Malaysia from Major Earthquakes in the Southeast Asian Region”, 1-97.
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10. Seed, H.B. and Idriss, I.M. (1971) “Simplified Procedure for Evaluating Soil Liquefaction Potential”, Journal of Geotechnical Engineering, 97 (9), 929–936. 11. Sonmez, H. and Gokceoglu C. (2005). “A Liquefaction Severity Index Suggested for Engineering Practice”, Environmental Geology, 48, 81-91 12. Terzaghi, K., Peck, R.B. and Mesri. G. (1996) “Soil Mechanics in Engineering Practise”, Wiley-Interscience.
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