Literature Review of Liquefaction Research with a Case Study of Christchurch, NZ

Transcription

1 Literature Review of Liquefaction Research with a Case Study of Christchurch, NZ Brianna Svoboda CEEN514 4/23/14

2 Introduction Natural disasters, such as earthquakes that trigger liquefaction, landslides, and rock fall, have impacted societies for generations. The more the human population spreads into rural areas and chooses to live where these events may occur, the greater the impact these phenomena have had on human life and infrastructure. Due to the sporadic occurrence of earthquakes and subsequent events that specifically impact cities and towns, research on liquefaction in general began, only recently, in the late 1960 s and 1970 s. In an effort to better understand liquefaction and its impact on human societies, a literature review was completed, which focused on past, present, and future research on liquefaction. The initial focus of past research looked to understand why liquefaction occurred and if it could be predicted. Later, beginning in the 21 st century, with the accessibility to a greater wealth of data and information, the performance of various types of infrastructure with respect to liquefaction could be evaluated and analyzed. Using a case study of a series of earthquakes that struck Christchurch, New Zealand, in 2010 and 2011, the impacts of liquefaction are uniquely analyzed on the performance of infrastructure. Following the case study of current research, a brief discussion looks at where research may be heading in the field of liquefaction. Overview of Liquefaction Liquefaction is the loss of soil strength due to cyclical loading or earthquake movement (de Vallejo and Ferrer, 2011). In general, liquefaction occurs in loose saturated soils that are mostly composed of silty sands (de Vallejo and Ferrer, 2011). If the pore pressures in the soil increase due to either cyclical loading or earthquake shaking, the pore pressures can reach the total normal stress of the soil. If the total normal stress is reached, then effective stress is approximately zero (Holzer et al., 1987). When effective stress is approximately zero, there is no longer any friction between soil particles and shear strength disappears, allowing the soil to behave like a liquid (de Vallejo and Ferrer, 2011). When the soil material is in this state, horizontal and vertical ground movements or settlement may result. Past Research on Liquefaction Beginning in the late 1960 s and early 1970 s, liquefaction research focused primarily in two areas: 1. When does liquefaction occur? 2. Can liquefaction be predicted? In the 1960 s, damage to structures not directly related to earthquake movement was acknowledged and attributed to liquefaction that was triggered by the ground shaking (Ambraseys and Sarma, 1969). Damage to buildings that met seismic design codes in various areas was re-evaluated. The building damage was found to be due to foundation failures, ground settlement, and tilting related to liquefaction conditions in the area.

3 From the 1970 s into the 1980 s, evaluation of ground displacement and settlement due to liquefaction dominated the research field. Studies measured permanent ground displacement due to liquefaction first using aerial photo imagery (Hamada, 1987). Once measured data was obtained, empirical equations were developed to calculate a magnitude of displacement in the area. Finite element techniques were also used to predict the magnitude and direction of ground displacement (Hamada, 1987). In addition to empirical equations and finite element analysis to predict magnitude of ground displacement, the Seed and Idriss method for estimating liquefaction potential was also developed in 1971 (Seed and Idriss, 1971). Primary controls on settlement due to liquefaction involved the cyclic shear stress ratio (CSR) and max shear strain induced in saturated soils (Tokimatsu and Seed, 1987): CSR = τ!" σ! where: τ!" = average cyclic shear stress σ! = effective stress Specifically, if the CSR produced by an earthquake is greater than the shear strength of the soil, [then the soil will liquefy] (de Vallejo and Ferrer, 2011). The Seed and Idriss method became one of the most widely used methods for evaluating and predicting liquefaction potential (Tuttle, et. al, 1990). To further predict magnitude of liquefaction induced settlements, soil density and factors of safety against liquefaction of each soil layer were used to calculate volumetric strain in an area (Kenji and Mitsutoshi, 1992). By integrating the change in volume throughout the soil depth, an estimate of ground settlement could be calculated (Kenji and Mitsutoshi, 1992). Therefore, since the 1960 s, research began to answer the complex and variable questions of when and where liquefaction may occur. In general, liquefaction occurs or is associated with the following (de Vallejo and Ferrer, 2011): - Earthquakes of magnitude 5.5 or greater with ground accelerations greater than or equal to 0.2 g. - Above depths of 15 meters - Water depths of less than 3m (If water table is below 5m, low liquefaction potential) - Loose, unconsolidated soils composed predominately of fines (silts and sands) Current Research: Case Study, Christchurch, New Zealand based primarily on Cubrinovski s Research Beginning in the 21 st century, data collection of earthquake and liquefaction events became more accessible with an increased understanding of liquefaction and where it might occur with relation to the epicenter of an earthquake (Papadopoulus and Lefkopoulos, 1993 and

4 Galli, 2000). Looking at a case study of Christchurch, New Zealand, the current research emphasizes a move toward understanding and evaluating infrastructure performance and lifeline performances during liquefaction events. Christchurch is the second largest city in New Zealand and is located on the South Island (refer to Figure 1). A series of seismic events occurred near the City of Christchurch between 2010 and The events were well documented with multiple seismograph stations located in the area. High resolution light detection and ranging (LiDAR) surveys of the ground surface before and after the events and detailed surveys of damage to structures that are well documented with building plans and pre-earthquake site investigation were captured (Bray, et al., 2013). With the amount of documentation and information available, the City of Christchurch became an excellent case study for comparing and evaluating building and lifeline infrastructure performance with regard to liquefaction under multiple earthquake events with differing magnitudes and distances from the epicenter. Regional Tectonics New Zealand is located on the boundary of the Pacific and Australian Plates (refer to Figure 1). A brief summary of the active tectonics in the area is provided in Table 1. Table 1. Active tectonics in New Zealand (Cubrinovski, et al., Dec 2011) Type of Movement Location Oblique Subduction along Hikurangi Trough North Island Oblique Subduction along Puysegur Trench SW of South Island Oblique Lateral Slip Movement Within Axial Tectonic Belt Unrecognized Fault (SE dipping blind fault) Located SE of Christchurch City Center (refer to Figure 2) Note: Refer to Figures 1 and 2 for locations of movements Over the past 150 years, many significant earthquakes have impacted both the North and South Islands of New Zealand. Case Study Specific Earthquakes The four earthquakes that impacted the City of Christchurch between 2010 and 2011 include the following (Cubrinovski et al. 2011): Table 2. Earthquake Events in Christchurch, NZ from 2010 to 2011 (refer to Figure 3) Date Moment Magnitude of the Earthquakes (M w ) September 4, 2010 M w = km December 26, 2010 M w = February 22, 2011 M w = 6.2 2km June 13, 2011 M w = Epicenter Distance from Central Business District of Christchurch

5 The most devastating of the four earthquakes to the Central Business District (CBD) of Christchurch was the February 22, 2011 event. The earthquake caused massive damage to city buildings, underground water and waste services, roads, parks and facilities (Christchurch City Council, 2011). The epicenter of the earthquake was 2km west of Lyttelton, located within the CBD (refer to Figure 2). Given that the epicenter of the earthquake is located in close proximity to the CBD, it was expected for liquefaction to occur in this region (Papadopoulus and Lefkopoulos, 1993). Overall, the ground movement and building failures claimed 181 lives in Christchurch (Christchurch City Council, 2011). Regional Geology Christchurch is generally located in sedimentary units composed of loose, un-compacted materials, which are environments in which liquefaction frequently occurs during periods of seismic activity. Refer to Table 3 for the composition and type of deposit based on specified locations around the Christchurch area. Table 3. Geology of Christchurch (refer Figure 3.1) (Brown and Weeber, 1992 and Forsyth et. al, 2008) Location Deposit Name Deposit Type Composition of Deposit General Christchurch Area East Christchurch Area South-east Edge of Christchurch Canterbury Plains Fan Deposit Sequence of gravels inter-bedded with silt, clay, peat, and shelly sands Christchurch Formation Estuary, Lagoon, Dune and Swamp Gravel, sand, silt, clay, shells, and peat (approximately 40 meters thick) Banks Peninsula Volcanic Complex Christchurch Earthquakes: Triggering Liquefaction The Christchurch earthquake series all triggered liquefaction events. However, the February 22, 2011 event triggered the most severe of the liquefaction events (refer to Figures 4 and 5). The horizontal ground motions in and around the CBD of Christchurch were generally 0.2 g or greater (refer to Figure 4). These significant horizontal ground motions resulted in a band of severe to moderate liquefaction occurring through the CBD (refer to Figure 5). Note that in Figure 5, the soil descriptions are variable which suggests that the severity of liquefaction throughout the CBD is also variable. Variability may also result due to the differences in the dissipation of seismic energy, which is proportional to the increase in pore water pressure in an area (Ishac and Heidebrecht, 2006). Areas in closer proximity to the Avon River, in clean and deep sands, are locations of the most severe liquefaction (Cubrinovski et al., Dec 2011).

6 The CBD provided an opportunity to assess and evaluate the performance of infrastructure throughout the variable zones of liquefaction during the February 22, 2011 event. It is also important to note that during the September 4, 2010 event, liquefaction damage in the CBD was limited in comparison to the February 22, 2011 event (refer to Figure 4) (Cubrinovski et al., Dec 2011). The performance evaluation of the following types of infrastructures was completed following the February 22, 2011 event: Shallow Foundation Performance Adjacent Structure and Shallow Foundation Performance Pile-Supported Performance Residential Homes Performance Bridge Performance Lifeline Performance Performance of Improved Ground to Resist Liquefaction Shallow Foundation Building Performance Several types of shallow foundation buildings were evaluated in zones of liquefaction. One apartment building that was in a zone of severe liquefaction experienced 40 cm of differential settlement and three degrees of tilt towards the SW (refer to Figure 7) (Cubrinovski et al., Dec 2011). The building was built on a shallow foundation; however, nearly identical structures located next to the damaged building did not experience any damage. Therefore, the damage to the apartment building was a direct result of liquefaction on the southern edge of the building. Other shallow foundations were observed to have experienced punching settlement and differential settlement in the Madras-Salisbury-Peterborough area (refer to Figure 5 for location of the area within the CBD). A two story industrial building experienced punching settlement, indicated by the 25 cm of water and ejected soils surrounding the building due to severe liquefaction (refer to Figure 7) (Cubrinovski et al., Dec 2011). Other indications of liquefaction included large ground distortion and sinkholes resulting from excessive pore water pressures (Cubrinovski et al., 2011). Further characterization of shallow foundation performance was marked by differential settlement and lateral sliding. Shallow foundations that experienced this type of deformation were located in the Armagh-Madras area (refer to Figure 5 for location of the area within the CBD). Liquefaction in this area surfaced with a narrow zone of surface cracks, fissures, and depression of the ground surface about 50 m wide, as well as water and sand ejecta (Cubrinovski et al., Dec 2011). Shallow foundations in this area experienced lateral displacement, differential settlement, and tilting. On the other hand, in the Victoria Square area that had a greater presence of shallow gravelly soils, shallow foundations performed well since they were not located in liquefiable soils (Cubrinovski et al., Dec 2011). In general, if shallow foundations were located in weak soils (loosely compacted soils composed of clean and fine sands and silt) and experienced strong ground shaking, buildings suffered moderate to severe damage. Damage to structures ranged from punching settlement to differential settlement, lateral displacement, and tilting.

7 Adjacent Structure Performance The Christchurch Town Hall located in the CBD was connected to several structures, including a kitchen facility add-on and air bridges connecting the Town Hall to the Crowne Plaza and to the Christchurch Convention Center (Cubrinovski et al., Dec 2011). These structures all experienced damage. The Town Hall was initially damaged due to differential settlement and punching settlement beneath the main building s internal columns, which carried the largest loads (Cubrinovski et al., 2011). The failure of the internal columns resulted in the distortion of the Town Hall building. The distortion of the Town Hall then resulted in the detachment of an air bridge connecting the Town Hall to the Convention Center. Further lateral movement and settlement of the Town Hall caused damage to adjoined structures (Cubrinovski et al., Dec 2011). However, in close proximity to the Town Hall (just across the street), another seven story building on shallow foundations did not experience significant differential or punching settlement (refer to Figure 7) (Cubrinovski et al., Dec 2011). This variation in damages to shallow foundation buildings and adjacent structures further supports the spatial variation in the soils throughout the CBD and the varying levels of liquefaction associated with different soil compositions throughout the zone. Pile Supported Building Performance In comparison with shallow foundation performance, pile supported buildings in severe liquefaction areas tended to suffer less damage than shallow foundations (Cubrinovski et al., 2011). Pile-supported buildings in the Kilmore area still experienced damage, though, particularly near the Avon River (refer to Figure 5 for location of the area within the CBD). Near the Avon River, pile-supported structures experienced lateral spreading and settlement. Also, following the February 22, 2011 event, the June 13, 2011 earthquake resulted in re-liquefaction in the Kilmore area and further settlement of the ground (Cubrinovski et al., Dec 2011). As another point of comparison, a seven story reinforced concrete building on shallow spread footing foundations, across from pile supported structures that were not severely damaged, suffered damage due to liquefaction (Cubrinovski et al., Dec 2011). The shallow spread footing foundations experienced both tilting and differential settlement like many other shallow foundation buildings in the CBD. Overall, it was found that both the ground and foundation conditions were key to the performance of infrastructure in the CBD. Shallow foundations typically experienced more severe damage due to liquefaction and pile supported structures tend to experience less severe damage due to liquefaction. Additionally, liquefiable areas can undergo re-liquefaction in different earthquake events. Re-liquefaction has tended to be more severe in subsequent events in the CBD area near Avon River.

8 Residential Homes Performance near the CBD In the September 4, 2010 and February 22, 2011 earthquakes, nearly 15,000 residential properties were damaged due to liquefaction and lateral spreading (Cubrinovski et al., 2011). Residential areas that were most significantly impacted by liquefaction and lateral spreading were located near the Avon River (refer to Figure 8). This location of severe damage further supports that both soil resistance to liquefaction and the magnitude of ground shaking are key to predicting severity of damages on structures. Site characterization of the suburbs near the Avon River (refer to Figure 6), determined that cone penetration test (CPT) values for the loose fluvial deposits in the area were around 2-4 MPa (Cubrinovski et al., 2011). Cone penetration tests have become a reliable way to measure and evaluate liquefaction soils (Robertson and Wride, 1998 and de Vallejo and Ferrer, 2011). The CPT values were specifically used to evaluate liquefaction triggering and its effects on buildings in the CBD (Bray et al., 2013). Moreover, the proximity of these suburbs to the epicenter of the February 22, 2011 earthquake was much closer than the September 4, 2010 earthquake and greatly contributed to the liquefaction in the area (Cubrinovski et al., 2011). In general, the intensity thresholds for liquefaction according to the Minimum Magnitude (MM) Intensity scale in New Zealand, were around MM 7 and MM 8 in some of the liquefaction zones in the CBD and close to the river where sand boils and lateral spreading were resulting (Hancox et al. 2002). Another contributing factor to the severe zone of liquefaction near the Avon River was the high water table that was located only about one meter below the surface (Bray et. al, 2013). Damages in residential areas were similar to those in the CBD, consisting of differential settlements and lateral movement. Other damages near the river were due to flooding resulting from liquefaction and lateral spreading (Cubrinovski et al., Dec 2011). Bridge Performance in the CBD Most of the bridges in the City of Christchurch are constructed from reinforced concrete and are symmetric, spanning small to moderate areas (Cubrinovski et al., 2011). General bridge damage in the Christchurch area was due to kinematic loads imposed by lateral spreading of the Avon and Heathcote River banks (Cubrinovski et al., 2011). The most significant bridge damage occurred outside the CBD, near the Avon River. Damages tended to consist of settlement and lateral spreading of approaches, back rotation and cracking of abutments, and pier damage (Wotherspoon et al., 2011). Lifelines Performance The lifelines of the city included pipe networks for potable water and waste-water systems along with electrical infrastructure. The potable water system was composed of a shallow pipe network that did suffer some damage consisting of breaks in areas affected by liquefaction (Cubrinovski et al., Dec 2011). However, the damage to the waste-water system was particularly severe compared to the potable water system. This was due to liquefaction and lateral spreading that resulted in loss of grade, joint failures, and cracks in pipes (Cubrinovski

9 et al., 2011). The lateral ground strain was calculated using the large amount of LiDAR data obtained (O Rourke et al., 2012). Further damage resulted from aftershocks that triggered additional liquefaction events that damaged pipelines (O Rourke et al., 2012). Other damage to the waste-water systems were due to the loss of pump stations (Cubrinovski et al., Dec 2011). The electrical infrastructure also suffered severe damage in the CBD. Underground cables were damaged due to liquefaction, disrupting electrical flows throughout the city (Cubrinovski et al., Dec 2011). However, the excellent performance of the gas distribution network [was] the result of highly ductile polyethylene pipelines (Bray, et al. 2013). Thus, lifeline systems were impacted by varying degrees of liquefaction and lateral ground movement resulting in variable damages and repairs. Performance of Improved Ground to Resist Liquefaction In Christchurch, the Waterside apartment building, a six story structure supported on shallow foundations was assessed for its performance due to the improved ground efforts prior to construction (Cubrinovski et al., 2011). Improved ground generally consists of compaction of soils and or removal of weak material and backfilled with engineered fill. The building suffered minor cracks and settlement, but was evaluated to have suffered less damage than the surrounding area. Therefore, the improved ground to resist liquefaction was effective at this site. Summary of Infrastructure and Lifeline Performance from the Christchurch Case Study The case studies of the series of Christchurch earthquakes provides a unique opportunity to evaluate the effects of liquefaction on infrastructure and lifeline systems performance with respect to varying degrees of liquefaction with each respective earthquake that impacted the city. Typical damages resulting to infrastructure included differential settlements, punching settlements (particularly associated with shallow foundations), tilting, and lateral ground strain. The most severe liquefaction was located just outside the CBD, along the Avon River where both stronger ground shaking and weaker soils resided. Also, the high water table made the area along the river more susceptible to severe liquefaction. Research for the Future Based on current research, there are still unanswered questions regarding the variability in infrastructure performance and predictability of variable zones of liquefaction. One area of research that requires more attention in the future is calculating ground settlement. Current ground settlement calculations do not capture important shear-induced deformation mechanisms and the effects of ground loss due to sediment ejecta (Bray et al., 2013). Thus, improved techniques for predicting the variable levels of infrastructure performance, such as that observed in Christchurch, are still needed (Bray et al., 2013).

10 Figure 1. Location Map of Christchurch, New Zealand (Forsyth et. al, 2008) Note: Location map displays where Christchurch is located on the South Island along with the regional tectonic setting of New Zealand. The red arrows show the rate and direction of plate movement of the Pacific Plate relative to the Australian Plate (Forsyth et. al, 2008).

11 Figure 2. Christchurch Central Business District location with respect to previously Unrecognized fault Note: Location map also shows ground motion recordings located within and near the Central Business District. Ground motion is typical greater than 0.2g, a condition required for liquefaction to occur.

12 Figure 3. Principal Earthquake Locations for Christchurch Earthquake Series (O Rourke et al., 2012)

13 Figure 3.1. Geology of Christchurch, New Zealand (Forsyth et. al, 2008) Note: The shaded topographic relief was derived from a 20 meter contour data set supplied by Land Information, New Zealand (Forsyth et. al, 2008)

14 Figure 4. Horizontal Ground Acceleration History and Recording Station Locations (Cubrinovski, et al., Dec 2011) *Note: R rup = source to site distance of the causative fault, PGA = Peak Ground Acceleration, PGA v = Peak Vertical Ground Acceleration **Note: Non-linear soil response, particularly at stations LPOC and LPCC, where there is a distinct difference in response between soil and rock sites (Cubrinovski, et al., Dec 2011).

15 Figure 5. CBD Liquefaction Map from February 22, 2011 Earthquake *Note: Sources referred to by [10] and [12] respectively are (Cubrinovski and Taylor, 2011) and (Cubrinovski and McCahon, 2011). **Note: The numbered areas correlate with images taken from these liquefaction zones discussed throughout the evaluation of infrastructure performance. ***Note: Red: Indicates areas of severe to moderate liquefaction Yellow: Indicates areas of moderate to low liquefaction General Soil description listed in yellow with approximate thickness of units.

16 Figure 6. Comparison of Repeated Liquefaction Areas between the September 4, 2010, February 22, 2011, and June 13, 2011 Earthquakes (Cubrinovski, et al., Dec 2011) Note: The suburbs to the east of the CBD along the Avon River were severly impacted by liquefaction (Avonside, Dallington, Avondale, Burwood, and Bexley) (Cubrinovski, et al., Dec 2011).

17 Figure 7. Shallow Foundation Building Damages within CBD Area Apartment Complex: Tilted 3 degrees and approximately 40 cm differential settlement (Cubrinovski et al., 2011) Two Story Industrial Building- Punching Settlement (Cubrinovski et al., 2011)

18 7 Story Building- Did NOT Experience differential or punching settlement (Cubrinovski et al., 2011)

19 Figure 8. Typical Liquefaction Damage to Residential Properties (Cubrinovski et al., 2011)

20 References 1. Ambraseys, N. and Sarma, S. (1969) Liquefaction of Soils Induced by Earthquakes. Bulleting of Seismological Society of America, Vol. 59, No. 2, p Accessed online at on March 29, Bray, J., O Rourke,T., Cubrinovski, M., Zupan, J., Jeon, S., Taylor, M., Toprak, S., Hughes, M., van Ballegooy, S., Bouziou, D. (2013) Liquefaction Impact on Critical Infrastructure in Christchurch United States Geological Survey Research Report. Accessed online at on March 21, Brown, L. and Weeber, J. (1992) Geology of the Christchurch Urban Area. Geological and Nuclear Sciences Cetin, K., Seed, R., Der Kiureghian, A., Tokimatsu, K., Harder, L., Jr., Kayen, R., and Moss, R. (2004). Standard Penetration Test-Based Probabilistic and Deterministic Assessment of Seismic Soil Liquefaction Potential. Journal of Geotechnical and Geoenvironmental Engineering, Vol.130, Issue 12, p Christchurch City Council (2011) Stronger Christchurch Infrastructure Rebuild Plan- How we plan to fix our earthquake damaged roads and underground services. Accessed online at on February 27, Cubrinovski, M., Bradley, B., Wotherspoon, L., Green, R., Bray, J., Wood, C., Pender, M., Allen, J., Bradshaw, A., Rix, G., Talyor, M., Rob, K., H, D., Giorgini, S., Ma, K., Winkley, A., Zupan, J., O Rourke, T., DePascale, G., Wells, D. (2011) Geotechnical Aspects of the 22 February 2011 Christchurch Earthquake. Bulletin of the New Zealand Society for Earthquake Engineering, Vol. 44, No. 4, Dec Accessed online at AspectsFeb22Eq_BNZSEE_11.pdf on March 22, Cubrinovski, M., Bray, J., Taylor, M., Giorgini, S., Bradley, B., Wotherspoon, L., and Zupan, J. (2011) Soil Liquefaction Effects in the Central Business District during the February 2011 Christchurch Earthquake. Seismological Society of America. Seismological Research Letters, Vol. 82, No. 6, Nov/Dec Accessed online at on March 21, Cubrinovski, M. and McCahon, I. (2011) Foundations of deep alluvial soils. University of Canterbury, Christchurch Cubrinovski, M. and Taylor, M. (2011) Liquefaction map of Christchurch based on drivethrough reconnaissance after the 22 February 2011 earthquake. University of Canterbury. 10. Das, S., Bradley, B., and Cubrinovski, M. (2013) Soil-foundation-structure-interaction: A unified approach and applicability of constitutive relations for sandy soils NZSEE

21 Conference. Accessed online at on March 22, De Vallejo, L. and Ferrer, M. (2011) Geological Engineering. CRC Press. Taylor and Francis Group, London, UK 12. Forsyth, P., Barnell, D., Jongens, R. (2008) Geology of the Christchurch Area, Scale 1: Institute of Geological and Nuclear Sciences, Geological Map GEER Association Staff (2011) Liquefaction and Lateral Spreading. Accessed online at %20-%20Liquefaction%20rev1.pdf on March 22, Hamada, M. (1987) Study on Permanent Ground Displacement induced by Seismic Liquefaction. Computers and Geotechnics. Vol. 4, Issue 4, p Accessed online at on March 28, Hancox, T., Perrin, D., Dellow, D. (2002) Recent Studies of Historical Earthquake- Induced Landsliding, Ground Damage, and MM Intensity in New Zealand. Bulletin of the New Zealand Society for Earthquake Engineering, Vol. 35, No. 2, p Accessed online at on March 29, Holzer, T., Hanks, T., and Youd, T. (1989) Dynamics of Liquefaction during the 1987 Superstition Hills, CA, Earthqauke. Science, Vol. 244, No. 4900, p Accessed online at on March 29, Ishac, M. and Heidebrecht, A. (2006) Energy Dissipation and Seismic Liquefaction in Sands. Earthquake Engineering and Structural Dynamics. Vol. 10, Issue 1, p Accessed online at on March 27, Kenji, I. and Mitsutoshi, Y. (1992) Evaluation of Settlements in Sand Deposits Following Liquefaction during Earthquakes. Society of Soil Mechanics and Foundation Engineering. Soils and Foundations, Vol. 32, No.1, p Accessed online at on March 29, Massie, A. and Watson, N. (2011) Impact of the Christchurch Earthquakes on the Electrical Power System Infrastructure. Bulletin of the New Zealand Society for Earthquake Engineering, Vol. 44, No. 4, Dec Accessed online at on February 27, O Rourke, T., Jeon, S., Toprak, S., Cubrinovski, M., and Jung, J. (2012) Underground Lifeline System Performance during the Canterbury Earthquake Sequence Fifteenth World Conference on Earthquake Engeering. Accessed online at on March 27, 2014.

22 21. Papadopoulous, G. and Lefkopoulos, G. (1993) Magnitude-distance relations for liquefaction in soil from earthquakes. Bulletin of the Seismological Society of America, Vol. 83, No. 3, p Accessed online at on March 28, Robertson, P. and Wride, C. (1998) Evaluating Cyclic Liquefaction Potential Using Cone Penetration Test. Canadian Geotechnical Journal, Vol. 35, No. 3, p Accessed online at on March 29, Seed, H. and Idriss, I. (1971) "Simplified Procedure for Evaluating Soil Liquefaction Potential," Journal of the Soil Mechanics and Foundations Division, ASCE, Vol. 97, No. SM9, p Tokimatsu, K. and Seed, H. (1987). Evaluation of Settlements in Sands Due to Earthquake Shaking. Journal of Geotechnical Engineering, Vol. 113, Issue8, p Accessed online at on March 27, Tuttle, M., Law, K., Seeber, L., and Jacob, K. (1990) Liquefaction and ground failure induced by the 1988 Saguenay, Quebec, Earthquake. Canadian Geotechnical Journal, Vol. 27, Issue 5, p Accessed online at on March 27, Wotherspoon, L., Bradshaw, A., Green, A.G., Wood, C., Palmero, A., Cubrinovski, M., and Bradley, B.A. (2011) Bridge Performance during the 2011 Christchurch earthquake. Seismological Research Letters, Focused Issue on the 2011 Christchurch New Zealand Earthquake. Vol. 82, No. 6, p , Nov/Dec Youd, T. and Idriss, I. (2001) Liquefaction resistance of soils: summary report from the 1996 NCEER and 1988 NCEER/NSF Workshops on Evaluation of Liquefaction Resistance of Soils. ASCE, Vol. 127, No. 4, p Accessed online at on March 28, 2014.