Datasets for liquefaction case studies of gravelly soils during the 2008 Wenchuan earthquake

This Data in Brief article provides summarized information of the liquefaction case histories from the 12 May 2008 Mw7.9 Wenchuan earthquake. According to the data processing procedures recommended in the related research article, all eighty-one case histories investigated by the present authors and seven other case histories from the literature are carefully compiled. All necessary information and the mean and standard deviation for some key parameters are given for these liquefaction case histories (i.e., site name, site location, site inclination angle, liquefaction manifestations, critical layer, soil sampling information, ground motion, total and effective stresses, shear-mass participation parameter, cyclic stress ratio (CSR) for Mw=7.5, normalized shear wave velocity (Vs1), data class and field testing time). These data may be used by colleagues to study the effect of gravel content on liquefaction behaviour of gravelly soils and develop the corresponding deterministic or probabilistic methods for liquefaction triggering evaluation.


Value of the Data
• These data are useful to enrich the global database of field liquefaction case histories with emphasis on gravelly soils and high seismic intensity. • These data could be of benefit to other researchers to develop new liquefaction triggering boundary curves and the corresponding liquefaction evaluation method for gravelly soils. • These data give an insight into the gravel content effect on soil stiffness and liquefaction resistance of sand-gravel mixtures, which urges more detailed element tests to understand the liquefaction behaviors of gravelly soils.
• These data encourage researchers to carry out further physical modelling and numerical analysis to reveal the dynamic response and liquefaction hazard of gravelly soil deposits.

Data Description
All 81 case histories compiled by the authors and 7 case histories re-compiled from Cao (2010) [2] are summarized in Table 1 , which is given at the end of this article. The investigated sites spread throughout an area of 200 km × 180 km and are mainly distributed in three regions, as shown in Fig. 1 (a). Detailed locations of these investigated sites in the three regions are marked in Fig. 1 (b)-(d), and most of these cases spread in Chengdu plain area and a few others are in mountain valleys. Note that the case number of each site shown in Fig. 1 (b)-(d) are consistent with the spreadsheet file of raw data provided in the above Specifications Table. In this compiled database, some basic information including the site name, location coordinates, site inclination angle, liquefaction information, ground water table, soil classification, permeability and gravel content (GC) are obtained by field investigation and testing, borehole sampling and laboratory tests. The other parameters like the depth of critical layer, peak ground acceleration, total and effective overburden stresses, shear-mass participation parameter, cyclic stress ratio, overburden stress-corrected shear wave velocity are determined or calculated according to the data processing procedures introduced in the related research article [1] .

Experimental Design, Materials and Methods
The procedure of V s -based liquefaction case study is illustrated in Fig. 2 . The first task in field liquefaction case study is to select sites within the earthquake affected area, wherein the liquefied and the non-liquefied sites should be equally treated instead of just focusing on the liquefied sites. This can avoid a data bias between the liquefied case histories and the nonliquefied case histories, which is vital to obtain the liquefaction triggering boundary curve for engineering application. The site with features of soil boils or blows, lateral spreading, building tilting or settlement, ground loss and broken lifelines was identified as liquefied, and the liquefaction manifestations were identified by field investigations right after the occurrence of the 12 May 2008 M w 7.9 Wenchuan earthquake. The in-situ soil samples were obtained by core drilling according to Chinese Code for Investigation of Geotechnical Engineering (GB50 021-20 01, 2009 [4] ), and the borehole samples of different depths were taken back to the laboratories to do sieve analysis tests and density tests. By these field investigation and laboratory tests, key parameters including ground water table, soil classification, gravel content, soil density and the soil strata profile could be obtained. At some sites, the in-situ pumping tests were conducted to obtain the permeability coefficient according to reference [4] . The surface inclination angle of each site was determined by dividing the elevation difference by lateral distance (measured by digital laser range finder) of two points at a site. The shear wave velocities of each site were obtained by down-hole testing or spectral analysis of surface wave (SASW) testing after the 2008 Wenchuan earthquake, and at some well-defined sites (e.g., Mianzhu Banqiao School site, Case No.3-5 in Table 1 ), both SASW and down-hole testings were conducted in parallel to check the reliability of the SASW method by treating the result of down-hole testing as the reference. Typical field work, soil strata and the corresponding profile of shear wave velocity at a site are illustrated in Fig. 3 .
The criterion for the identification of the critical layer is to find the soil stratum that is the most likely to trigger and manifest liquefaction at the ground surface for a given site [5] . To specify, the identification of the critical layer should meet the following requirements: (i) the stratum is liquefiable and below the ground water table, this feature could be judged from soil boring and soil classifications via laboratory tests; (ii) the stratum has the lowest normalized shear wave velocity ( V s1 ), meanwhile the chosen stratum should be as shallow as possible; (iii) ( continued on next page )    one auxiliary identification comes from the surface ejecta which helps to indicate the liquefaction of a specific stratum, but caution should be exercised with gravelly soils as it consists of both sand and gravel particles. As shown in Fig. 3 , the critical layer in the soil profile at Santai construction site is identified as the fine sand layer, which has the lowest shear wave velocity and is most likely to trigger and manifest liquefaction at the ground surface. Key parameters of the critical layer at a given site were determined according to the borehole sampling record, field testing of shear wave velocity and laboratory tests for the fine contents, gravel contents and particle size distributions. The mean and variance of the normalized shear wave velocity given in Table 1 could be calculated based on the V s1 profile within the critical layer as the average thickness-weighted value. The earthquake-induced cyclic stress ratio (CSR) is calculated from PGA estimation in a linear interpolation manner based on the USGS ShakeMap (see Fig. 1 (b)-(d)) for the 2008 Wenchuan earthquake. Some key parameters like the normalized shear wave velocity and the CSR could be calculated by using the following equations [6] : where P a is the atmosphere pressure; n is the exponent in Hardin equation [7] ; V s is the shear wave velocity; a max is the peak horizontal ground surface acceleration (PGA) in unit of gravity; g is the acceleration of gravity; σ v is the total overburden stress at the depth in question; σ ' v is the effective overburden stress at the depth in question; and r d is the shear-mass participation parameter to adjust for the flexibility of the soil profile [8] . The calculation of other parameters such as the standard deviations of these parameters could be found in the related research article [1] or other literatures [ 9 , 10 ]. Based on this procedure, the authors drove through the whole earthquake-impacted areas including the Chengdu plain and the mountain area along the fault rupture, to do reconnaissance work and identify the liquefied and non-liquefied sites from May to early June in 2008, and then carried out field drilling and testing work from July to November for most of the selected sites. Some other sites were investigated later when the site condition allowed doing so. For a few sites where field testing could not be conducted directly, the necessary geotechnical information from the adjacent construction projects are adopted. Finally a total number of 81 well-identified cases are compiled with all detailed information given in the spreadsheet file of raw data, and some key parameters of these cases are summarized in Table 1 .

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships which have, or could be perceived to have, influenced the work reported in this article.