Estimation of Liquefaction-Induced Building

8th Regional Symposium on Infrastructure Development in Civil Engineering (RSID8) University of the Philippines Diliman, Quezon City, Philippines, 25-26 October, 2018 ISSN 2465-3942, Paper ID: 2C-4

Estimation of Liquefaction-Induced Building Settlement due to 6.3 Mw Chiang Rai Earthquake 2014 Yayat Kusumahadi Department of Civil Engineering, Faculty of Engineering Kasetsart University Bangkok, 10900 THAILAND

Suttisak Soralump Department of Civil Engineering, Faculty of Engineering Kasetsart University Bangkok, 10900 THAILAND

Suriyon Prempramote Department of Civil Engineering, Faculty of Engineering Kasetsart University Bangkok, 10900 THAILAND

ABSTRACT On May 5th 2014 the northern part of Thailand has been beaten by an earthquake called Chiang Rai earthquake with the focal depth of epicenter which is approximately 10 km below the ground surface. This event is one of the most significant effects to the social community and human lives in the hazard area which causes several damages such as liquefaction and associated ground failures. The effect of liquefaction subjected to the seismic compaction (lateral deformation) has performed in order to predict the performance of the ground in the free-field condition. Seismic hazard of the study area located in 6.45 km away from the nearest active fault. It makes the site as classified as 2B (moderate to high level) of Seismic hazard. Therefore, one of the critical effects due to the ground shaking is the vertical displacement in the hazard area that is expected to occur. Based on the field observation and post-prediction analysis, the vertical displacement was found to be 6 cm at one station and 4 cm of average value for most of the borehole locations, respectively. This is large enough to cause a structural damage due to the differential settlement of shallow foundations. Keywords: Liquefaction, differential settlement, earthquake, seismic hazard, amplification.

I. Introduction On 5th May 2014 the norther part of Thailand has been beaten by an earthquake of magnitude 6.3 called Chiang Rai earthquake with the focal depth of epicenter which is approximately 10 km below the ground surface. This event is one of the most significant effects to the social community

and human lives in the hazard area which caused several damages such as liquefaction, landslides, and associated ground failures. Other than that, the geological and geotechnical conditions of the study area which were investigated previously indicated the evidence of the liquefiable material that was based on the soil type and properties.

The previous study with regard to the assessment of the liquefaction potential in this area was done by several researchers to assess the probability of liquefaction potential by employing several approaches in order to acquire the liquefaction hazard maps of a defined surrounding area. Hence, in this study, the effect of liquefaction on a building (liquefaction-induced building movements) needs to be further investigated in order to predict the behaviors of both ground and structure.

Based on the liquefaction event after Chiang Rai earthquake in 2014, there were several researchers studying the liquefaction assessment using various methods of spectral analysis of surface wave (SASW) observation field [2], numerical approaches and ground response analysis by DEEPSOIL program in order to assess the ground amplification of site [13].

(a)

(b)

Figure 1. (a) Liquefaction evidence, (b) liquefaction-induced soil boiling

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II. Geological and geotechnical conditions Mae Lao district, Chiang Rai Province, Thailand, is located in the northern part of Thailand close to the Myanmar border. The study area (White Temple) is found to lay on the deposit sediment area, which is considerably composed of course and fine sands, and also gravels. 2.1 Deposit soil layer

As shown in Figure 2, Mae Lao district has several types of geological profiles. In the study area it is found to be Quaternary deposit, including alluvium sand, silt and clay of floodplain deposits (Qa) [13]. Generally, Qa deposit is considered as the liquefiable soil (potentially high) to be liquefaction. In the research of assessing liquefaction potential of Mae Lao district for Earthquake Mw 6.3 2014, there are 15 boring log observations and 15 spectral analyses of surface wave (SASW). The study area of White Temple is represented three borehole explorations, including BH1, BH2 and BH3. Based on the site investigations and the test of basic properties in a laboratory, the ground profile consists of the 2-m-thick silty sand at the depth of 5-7 m that is covered by 3 m silty clay as illustrated in Figure 4.

Figure 2. Geological map (observation point) of Mae Lao District, Chiang Rai, Thailand

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BH2

BH1

BH3

Figure 3. Top view of White Temple and locations of three boreholes

Depth of Borehole (m.)

BH-2 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0 17.0 18.0

Very stiff Sandy CLAY. (CL) Medium to stiff Silty CLAY. (CL) Loose Silty SAND trace gravel. (SM)

Medium dense to very dense Silty SAND trace, trace to some, some, and gravel. (SM)

End of Boring 17.45 m.

Figure 4. Soil profile of BH2 2.2 Shear wave velocity profile One of the key parameters that must be defined is the shear wave velocity (Vs). This parameter is a valuable indicator of dynamic properties of soil in its relationship with the maximum shear modulus (Gmax). Tangjittham et al. (2017) performed the spectral analysis of surface wave (SASW) in 15 locations, including BH1 and BH2 representing the shear wave velocity of the study area.

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However, there were some limitations of investigation and the maximum depth that could be reached is 30 m.

Figure 5. Shear wave velocity profiles of BH1 (left) and BH2 (right) III. Seismological condition Department of Mineral Resource associated with The Meteorological Department and National Earthquake Information Center created a seismic hazard zoning map of Thailand to present the earthquake intensity in every zona as a reference for the design code. Mae Lao Chiang Rai is located in zone 2B with the earthquake intensity VII-VII Mercalli scale and the severity is slight to moderate damage for well-built ordinary structure.

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Thailand has about 27 active faults located in and near the country area [20] which mainly are obtained from recent paleo-seismic investigations discovered by Woodward-Clyde Federal Services in Northern Thailand (DMR, 1996), Western Thailand (EGAT, 1998), and Southern Thailand (RID, 2005) (Figure 6). Seismicity surrounding the site is considered by several significant faults which are Mae Chan, Mae Ing and Phayao faults as shown in Figure 7 within the focal mechanism of past significant events. Pennung (2010) presented the characteristic earthquake parameters of these faults, which all are left-lateral strike-slip except southern segments of Phayao fault as s normal fault. Mae Chan fault with the length of 118 km, and the slip rate of 0.3 to 3 mm/yr has maximum credible earthquake (MCE) Mw of 7.5. Mae Ing fault with the length of 38 km, slip rate of 0.3 to 1.2 mm/yr has (MCE) Mw 7.4, and Phayao fault with the length of 100 km, slip rate of 0.1 mm/yr can create Mw of 6.8, respectively.

In order to analyze the seismic hazard, the closest active Phayao fault is considered as the cause of Chiang Rai earthquake in 2014 and as the fault that gives a high effect to the seismic hazard of the study area (White Temple). Finally, as shown in Figure 2, all 15 boring logs were observed surrounding Phayao fault and have a very close distance to the sites especially for Borehole BH1, BH2, and BH3. Source-to-site distance (Rrup) for Mw of 6.3 Chiang Rai earthquake is 11.21 km, for Mw of 5.67 of building standard code for the period of 475 years and Mw of 6.8 MCE are 6.45 km, respectively.

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(a) (b) Figure 6. (a) Seismicity in the study region Mw>3 within 100 years from 1917 to 2017 (Clustered from USGS and TMD catalogs), (b) A Seismic hazard zoning map of Thailand by Department of Mineral Resources, The Meteorological Department, and National Earthquake Information Center (USA) (2005)

Figure 7. Position of study area to the focal mechanism of several recent earthquakes and active faults. 3.1 Ground Motion Prediction Equations (GMPEs) Target response spectrums for three considered magnitudes were done by NGA-West2 which consist of five equations, developed by five models. In this case, the Vs30 of the site is 242.28

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m/s2 which could not be used for Idriss (2014) model (Vs30 = 450 m/s2). Therefore, the weighting value for every models are 0.25, averaged by geometric of the natural logarithm of the spectral values. The damping ratio is 5% with the damping scaling factor (DSF) of 1. Figure 8 shows the result of the target response spectrum of three considered Magnitudes, with the PGA of 0.26g, 0.23g, and 0.36g for Magnitudes of Mw 5.67 (Rjb = 6.45 km), Mw 6.3 (Rjb = 11.21 km), and MCE Mw 6.8 (Rjb = 6.45 km), respectively.

(a)

(b)

(c) Figure 8. Target response spectrum of three considered magnitudes with Median 5% damping (red lines), Median + 1.σ 5% damping (short dash lines), Median - 1.σ 5% damping (long dash lines) (a) Magnitude Mw 5.67 (b) Magnitude of Chiang Rai EQ Mw 6.3 (c) MCE 6.8 8

3.2 Acceleration time history The target response spectrum design, is applied to create an acceleration time history from PEER database that afterward passes through the scaling and matching steps. Finally, N. Palm Springs motion (Figure 9) is selected for these PGAs. Three analyses have done for 3 considered PGAs of 0.23g, 0.26g and 0.36g, respectively. Each of acceleration time history files then is cut in order to pick the significant motion of the record. 20 sec

Acceleration (g)

0.2 0.1 0

0

20

40

60

-0.1 -0.2

-0.3

Time (sec)

(a) 0.4

Acceleration (g)

0.3 0.2 0.1 0 -0.1 0

2

4

6

8

10

12

14

16

18

20

-0.2 -0.3 -0.4

Time (Sec)

(b) Figure 9. Input acceleration time history from PEER database (a) before cut and (b) after cut

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IV. Dynamic Vertical Deformation Prediction In order to establish the vertical deformation due to the dynamic behavior from earthquake shaking, there are two types of analysis. Firstly, the vertical deformation of free-field condition must be defined by an approach. The approach only considers the densification of volumetric strain from the loose sand only due to the earthquake shaking. Secondly, the vertical deformation of soil layer will be analyzed by numerical program of both Sigma/W and Quake/W in GeoStudio. The Sigma/W calculates the stress conditions of the initial ground without any structure and with foundation above. Furthermore, the results from the stress analysis are linked to the Quake/W to apply the motions. Finally, the results from shaking connect to the dynamic deformation by Sigma/W to obtain the permanent deformation of ground with the shallow foundation due to the ground shaking. 4.1

Vertical deformation of free-field condition

In this research, the vertical deformation prediction that caused by loose sand has been done for two conditions, analysis for the free field settlement (without surcharge loads) by using and comparing three approaches, Ishihara and Yoshimine (1992), Tokimatsu and Seed (1984, 1987), and calibration method by Cetin (2009) (Figure 10).

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(a)

(b)

(c) Figure 10. Charts for estimating post-liquefaction volumetric strain for free field condition by (a) Tokimatsu and Seed (1984, 1987), (b) Ishihara and Yoshimine (1992), and (c) calibration method by Cetin (2009)

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4.1.1

Method of Tokimatsu and Seed (1984, 1987)

Based on the charts that created by Tokimatsu and Seed (1984, 1987), the prediction of settlement due to the volumetric strains of liquefied soil layer, Table 1 shows the result of layer 5 to 7 m with the CSRfield was obtained from the ground response analysis of DEEPSOIL program. As shown in Figure 10, volumetric strain value can be obtained from cross plotting between (N1)60 and CSRfield. Table 1 Volumetric strain analysis by Tokimatsu and Seed (1984, 1987) Layer

depth

5-5.5 5.5-6 6-6.5 6.5-7

5.25 5.75 6.25 6.75

0.23g 0.25 0.24 0.24 0.23

CSR 0.26g 0.25 0.24 0.24 0.23

0.36g 0.28 0.27 0.26 0.25

(N1)60 12.97 12.31 15.65 14.97

0.23g 2.10 2.20 1.80 1.90

Vol strain 0.26g 0.36g 2.10 2.10 2.20 2.20 1.80 1.85 1.90 1.90 m ∑SL cm

0.23g 0.0105 0.011 0.009 0.0095 0.04 4.0

delta H 0.26g 0.36g 0.0105 0.0105 0.011 0.011 0.009 0.00925 0.0095 0.0095 0.04 0.04 4.0 4.0

4.1.2 Method of Ishihara and Yoshimine (1992) Using the chart of Ishihara and Yoshimine (1992), the settlement is predicted by plotting FSL value and converted N-SPT blow number (N1 ≈ 0.833 (N1)60) [14]. So that, the settlement of each layer of loose silty sand is given by the product of the volumetric strain and layer thickness. The total settlement is calculated as 5.1 cm for PGA 0.23g and 0.26g, and 5.9 cm for 0.36, respectively. Table 2 Volumetric strain analysis by Tokimatsu and Seed (1984, 1987) Layer Depth (m) 5-5.5 5.5-6 6-6.5 6.5-7

5.25 5.75 6.25 6.75

0.23g 0.81 0.74 1.02 0.94

FS(L) 0.26g 0.81 0.74 1.02 0.94

0.36g 0.72 0.67 0.93 0.88

N1 10.81 10.26 13.04 12.47

0.23g 3.35 3.45 1.80 1.90

Vol strain 0.26g 0.36g 3.35 3.35 3.45 3.45 1.80 2.00 1.90 2.90 m ∑SL cm

0.23g 0.01675 0.01725 0.00625 0.01025 0.0505 5.1

delta H 0.26g 0.36g 0.01675 0.01675 0.01725 0.01725 0.00625 0.01 0.01025 0.0145 0.0505 0.06 5.1 5.9

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4.1.3 Method of Cetin (2009) By Method of Cetin (2009) for the loose sand of 2 m, resulting the total vertical deformations of 3.25 cm for PGA 0.23g and 0.26g, and 3.5 cm for 0.36, respectively. By numerical calculation for 𝜏𝑐𝑦𝑐

CSRfield = ( 𝜎′𝑣𝑜 ) have done by DEEPSOIL analysis, the certain values are picked from 5 to 7 m to concentrate only for the liquefiable layer. These values then converted to CSRSS,20,1D,1 atm which is equivalent to unidirectional, 20 loading cycle simple shear test performed under confining stress of 100 kPa. Plotted on the volumetric strain curves as demand term, together with normalized SPT N value as the capacity term. The result of volumetric strain analysis by Cetin (2009) is presented in Table 15 These values are categorized as a small amount of settlement or light to no damage. However, this should be taken in consideration for the ground profile with the thicker layer of loose sandy soils. Table 3 Volumetric strain analysis by Cetin (2009) Layer

depth

5-5.5 5.5-6 6-6.5 6.5-7

5.25 5.75 6.25 6.75

CSR (SS,20,1D,1atm) 0.23g 0.26g 0.36g 0.17 0.19 0.20 0.17 0.18 0.19 0.17 0.18 0.18 0.17 0.17 0.18

(N1)60 12.97 12.31 15.65 14.97

Vol strain 0.23g 0.26g 0.36g 1.65 1.70 1.90 1.70 1.80 1.90 1.30 1.50 1.50 1.40 1.40 1.50 m ∑SL cm

delta H 0.23g 0.26g 0.00825 0.009 0.0085 0.009 0.0065 0.0075 0.007 0.007 0.03025 0.0325 3.025 3.25

0.36g 0.0095 0.0095 0.0075 0.0075 0.034 3.4

4.2 Vertical deformation by numerical analysis As mentioned in the previous section, that the vertical deformation by numerical analysis is assessed by using SIGMA/W and QUAKE/W. The engineering properties of the soils are presented in Table 4 and each of the analysis is discussed below.

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Table 4 Engineering properties of the soils in the study area Thickness γT SPT-N (m) (kN/m3) blows/ft Stiff silty clay 3 18.4 10 medium silty clay 2 18.4 5 Loose silty sand 2 19 10 Medium dense silty sand 11 19 73 Soil Description

4.2.1

φ (°) 20 18 25 32

c (kPa) Es (kPa) 5 5 0 25

8000 5000 7000 30000

Poisson Q (kPa) ratio 0.4 0.4 0.2 0.335

26.36

Finite element method

Quake/W formulated the two-dimensional plane strain problems using small displacement and small strain theory. The governed motion equation for the seismic response of a system in finite element is expressed as: [𝑀]{𝑎̈ } + [𝐷]{𝑎̇ } + [𝐾]{𝑎} = {𝑎̈ 𝑔 }

(1)

where, [M], [D], [K] are the mass, damping, and stiffness matrixes, respectively. {𝑎̈ 𝑔 } is the vector ground accelerations; 𝑎̈ , 𝑎̇ , 𝛼 are the nodal acceleration, velocity, displacement vectors, respectively 4.2.2

Permanent deformations

After the static and dynamic stresses were defined, the information can be used in SIGMA/W to estimate the plastic permanent deformations. This is done with the analysis type of Dynamic deformation in SIGMA/W. This analysis is fundamentally an elastic-plastic stress redistribution analysis. The dynamic stresses are redistributed for each time step that QUAKE/W results are saved to a file.

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SIGMA/W computed an incremental load vector based on the stress difference between two steps. The increment load {∆𝐹} vector is computed for each element from the equation below: (2)

{∆𝐹} = ∫ [𝐵]𝑇 {∆𝜎} 𝑑𝑣 𝑣

where {∆𝝈} = {𝝈𝒏 } − {𝝈𝒏−𝟏 }, [𝑩] is the strain-displacement matrix and n is the time station. The incremental load vector is the algebraic difference in the stress states between two successive time steps. Each load step that has been computed may produce some elastic and plastic strains. The permanent deformation is the accumulation of those plastic strains and deformations that were measured. Figure 11 shows the mesh deformation of the foundation soil at the end of the 20 seconds of shaking.

Figure 11. Mesh deformation resulting from the PGA 0.36g of 20 seconds time step

Vertical displacement (m)

0.01 PGA 0.23g

PGA 0.26g

PGA 0.36g

0 0

5

10

15

20

-0.01 -0.02 -0.03 -0.04 -0.05

Time (Sec)

Figure 12. Vertical permanent settlement at the base of White Temple

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According to the analysis using finite element method, Figure 12 shows the results of permanent settlement at the base of White Temple for 3 considered PGAs. With one acceleration time history and 3 different PGAs, resulting similar mode of displacement, but different amount of settlement. PGA of 0.23g and 0.26 have close value of settlement which is 0.0085 m. In another hand, PGA of 0.36g resulting permanent settlement of 0.03 m. These settlements occurred, affected by the volumetric strain of the Liquefied (loose sandy) soil under the cyclic loading of the earthquake. However, after the field is shaken at the first to third second, there was a bulge or lateral spreading which caused a positive value of displacement. By the time, while the field was being shaken, the soil layers are self-densified, causing the volume change and resulting in the settlement. V. Conclusions According to the location site, it is located on Hazard area that earthquake have to be considered as a dynamic factor in damaging houses or other infrastructures. In this case, there are at least three considered PGAs. PGA 0.23g with the magnitude of 6.3 Chiang Rai earthquake, 0.26g with the magnitude of 5.67 Standard Building Code with a return period of 475 years, and 0.36g with the magnitude of 6.8 Maximum credible earthquake of Phayao fault.

Base on the results of settlement predictions of free field and surcharge load, there are several differences of value depending on the condition that was applied. In free field condition, amount of settlement from three methods varies from 3 cm to 6 cm. For the surcharge load condition by finite element method, the settlement that occurred at the base of White Temple are 1 cm for 0.23g and 0.26g, and 3 cm of 0.36 PGA. The free field condition has a higher value of settlement in comparison with the load condition. This could be mentioned that the confining condition by an

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additional load is reducing the volumetric strain (reconsolidation) of the liquefied soil. However, since the settlement is less than 10 cm, it is classified as light to no damage to a structure. VI. Acknowledgements The authors would like to thank Civil Engineering Department, Faculty of Engineering, Kasetsart University, and grateful thanks to Geotechnical Engineering Research (GERD) Center and the Thailand Research Fund (TRF). VII. References [1]

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