Papers by Author: Long Wei Chen

Abstract: The analysis of ground motion on seasonal frozen soil mainly focused on the conventional soil, neglecting the impact of the permafrost which causes the obvious defeats in the existed calculation procedure. In this paper, the author proposed that we should apply the field test of shear wave velocity to the soil layer response calculation, improve the test method of dynamic shear modulus, and adopt the regular analysis method of soil layer response to the calculation of frozen soil site.

Abstract: Based on survey of the Bachu-Jiashi earthquake liquefaction sites, much new basic liquefaction information were obtained and China’s liquefaction database was enriched. A detailed investigation of the Bachu earthquake liquefaction site was conducted, in which three kinds of in situ test measures were used to obtain the site information, and given China mainland SPT data of liquefaction site increase by 40%. By site investigation, international standard liquefaction site CPT data were obtained, and also, the first measurement of liquefaction site data by SPT and CPT index was conducted. With the new data, the feasibility of liquefaction discrimination methods of China was inspected.

Abstract: The serious soil liquefaction phenomenon in Bachu-Jiashi earthquake on 24th February, 2003, which is the most prominent phenomena of sand liquefaction since the Tangshan Great Earthquake in 1976. Based on the earthquake liquefied investigation, inspect SPT and CPT applicability in situ tests. The results show that our country SPT specification and CPT specification of non-liquefied sites evaluation rate is higher than liquefied sites evaluation success rate, the liquefied sites evaluation rate are 88% and 88% respectively, but for liquefied sites evaluation rate are 38% and 55%. The result is tends to danger and the reason need further investigation, so establish a suitable liquefied prediction method should be to the future work in the local area.

Abstract: Flexible fiber Bragg grating (FBG) sensing beams are used to measure dynamic shear response of liquefied soil to ground motions in a shaking table test. Measurement systems typically consisting of bulky arrays of sensor bundles can be instead. But the different frequency response characteristics between the soil and beam generate testing errors. In this work, the sensing beam method is introduced, and the frequency response of the sensing beams will be obtained in an experiment on a shake table.

Abstract: To mitigate liquefaction hazard, real-time liquefaction monitoring technique is investigated. And the reverse liquefaction detection method from seismic records is the key point. The existing methods are limited and the reliability requires test. In 2011, an earthquake of magnitude 6.3 struck in New Zealand's South Island. Serious liquefaction phenomena were reported, which provides an opportunity to verify the existing liquefaction detection methods. Twenty-seven acceleration records within 50km to the epicenter are selected to perform a blind detection for existing two methods, including Suzuki and Sun-Yuan method. The blind detection results indicate that Sun-Yuan method obtains correct results for three known liquefied sites, and both method are correct for a reported non-liquefied site. The number of identically detected results is 22 by two methods. The identified results will be verified by actual observation for the 23 sites excluding 4 confirmed sites.

Abstract: In Wenchuan earthquake, liquefaction and relevant damage in Mianyang region were significant and of the three major regions, but the liquefaction phenomena were clearly different from Chengdu and Deyang regions. Through field investigation and engineering geological data analysis, this paper studies the liquefaction features and distribution in Mianyang area. Analysis shows that: (1) Liquefaction zones (belts) mainly were located in Youxian area of Mianyang city, Jiangyou city and Weicheng-Dongxuan town area; (2) Liquefaction has been observed in regions of intensities VII and VIII, but mainly concentrated in intensity VII; (3) Heights of water-jet were about one meter with the highest 3-4m; (4) The ejected materials in liquefied sites basically covered kinds of soil types, i.e., nearly 80% of fine sand followed by 11% of gravel; (5) Liquefied zones were associated with cracks, resulting in farmland, houses, a railway station, schools and factories damage in different extents. Jiangyou railway station is the most typical example of gravelly soil liquefaction. (6) The liquefied soil in Mianyang region is mixed, e.g., liquefied layers were gravel layers in Jiangyou city; sandy layer liquefied in Youxian area of Miangyang city; and the liquefied soil was probable gravel or sand in Weicheng-Dongxuan town area but the gravel liquefaction possibility was high

Abstract: The frequency of ground records on liquefied and non-liquefied sites is different. The calculation method of frequency decreasing rate is given here and the division line between liquefied and non-liquefied sites is proposed. To analyze the time-frequency curves of acceleration, the zero-crossing method is employed. The soft sites and ordinary non-liquefied sites are included in non-liquefied sites. The results show: (1) The concept and calculation method of frequency decreasing ratio, which is proposed in this paper, can describe the characteristics and regulations of time-frequency on liquefied and non-liquefied sites; (2) Before peak ground acceleration (PGA), the difference of the average frequencies of acceleration on liquefied and non-liquefied sites is not obvious and the average frequency of acceleration on soft sites is smaller than that either on liquefied or non-liquefied sites; (3) After PGA, the average frequency of acceleration on ordinary non-liquefied sites is the highest in the three types of sites, that of soft sites is the middle and that of liquefied sites is the smallest; (4) If the absolute change of the time-frequency is used as the criteria, it will be confused between soft sites and liquefied sites; (5) The threshold value of frequency decreasing ratio is 0.5 between liquefied and non-liquefied sites, which can judge the liquefied sites, non-liquefied sites and soft sites correctly.

Abstract: Using a double-layer horizontal strata model, a simplified time-history analytical method which considers liquefiable layer existence is proposed for calculating ground motion acceleration and displacement. Solutions in frequency and time domains under arbitrary loading are given. By the cycle-by-cycle method, the calculating results of ground acceleration and displacement time histories under arbitrary loading are presented. Adopting a proper pore-water pressure ratio incremental model, shear modulus of the liquefiable layer is modified cycle by cycle that the nonlinearity of the liquefiable layer induced by soil liquefying is proximately simulated. Through numerical analysis, ground displacement on liquefied sites is much larger than that on non-liquefied sites during liquefaction process. Before initial liquefaction, ground displacement and acceleration on liquefied sites are obviously higher than those on non-liquefied sites. After initial liquefaction, ground acceleration remarkably decreased but displacement remains much larger than that on non-liquefied sites. Normalized acceleration response spectra are calculated. It shows that the low period components on liquefied sites are lower than those on non-liquefied sites, but long period components are higher than those on non-liquefied sites.