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Top1. Introduction
Liquefaction is the phenomena related to the earthquake shaking, as causes of increasing of pore water pressure and induced loss of shear resistance in granular soils. The susceptibility of liquefaction is controlled several of factors including grain size distribution (texture), soil density, depth to groundwater and the liquefaction triggering threshold with concerning the level of ground shaking that might be anticipated for the study area (Pyke, 2003). The texture and soil density are strongly influenced by the depositional system and deposit age, which allow the correlation between the characteristic of a Quaternary deposit with soil gradation, soil properties, and the level of ground shaking. The Northern part of Thailand was hit by an earthquake of magnitude 6.2 Mw Chiang Rai earthquake on May 5, 2014. This event has one of the most significant effects on the social community and human lives in the hazard area causing several damages such as liquefaction, landslides, and other associated ground failures. The epicenter was located in the Phayao fault zone ranging from northeast to southeast of Mae Lao District, Chiang Rai Province, at Latitude 19.750ºN and Longitude 99.690ºE with the focal depth of epicenter is approximately 10 km (TMD, 2014). Some zones were affected by liquefaction within a radius of 20 km from the epicenter shown in Figure 1. From the soil investigation, it was determined that the soil layers of some boreholes consist of a poorly graded loose saturated sand layer in the shallow depth from the ground surface. Hence, some settlements of shallow foundation and structural damage were observed induced by the liquefaction although it is not serious damage. Moreover, the geological and geotechnical considerations of the study area which were investigated previously indicated the evidence of the liquefiable material are susceptible to liquefaction.
Figure 1.
(a) Liquefaction at the edge of the road, (b) liquefaction-induced soil boiling (c) liquefaction on the paddy field
The depositional mechanism controls the texture, sorting, and packing of sediments (Youd & Perkins, 1978). Investigation of the study area including borehole log measurement, spectral analysis of surface wave, observation well, and examination of the geological surface have been established to assess the liquefaction susceptibility of the study area. The investigation focuses on the Mae Lao area where the high seismic and ground failure hazards occurred after the 2014 earthquake. All those measurements were conducted in both locations where the liquefaction was experienced (eyewitness evidence) and the area without evidence of liquefaction. Furthermore, the site class of particular locations has been defined in this study. In general, the results brought an understanding of the effect of geotechnical and geological conditions on the liquefaction susceptibility and the soil behavior under the event of 6.2 Mw Chiang Rai Earthquake 2014.
Top2. Study Area
Figure 2 shows the exact location of the study area which is located in Mae Lao district, Chiang Rai Province, Northern part of Thailand close to the Myanmar and Laos borders. The area was found to lay on a complex geological formation, the middle part is composed of deposited sediment of Quaternary deposit alluvium (Qa), Terrace (Qt), Floodplain (Qff) which is known to have a medium-to-high potential of liquefaction. Additionally, some of the mountainous areas were dominated by Sandstone (CP) at stations BH8 and BH13, and volcanic basic rocks (SD) at station 9 along the northern-western part (Figure 3). These types of sediment deposition affect varying liquefaction behavior. Therefore, to describe the character of each type, further investigations were carried out by performing such as Standard Penetration Test (SPT) to define the liquefaction behavior due to the compositional criteria and solve the liquefaction potential prediction. Moreover, observation well was performed to monitor the influence of groundwater level and overburden pressure.
Figure 2. Location of the study area (Source: GERD, 2020)