Papers by Author: Lan Min Wang

Abstract: Loess with large thickness is widely distributed mainly in Gansu provinces of China. The kind of loess has special microstructure to induce lower dynamic strength and larger seismic deformation. It brings to difficult loess processing challenges for engineering building foundations or high way and railway constructions. The large deformation dangers could induce to serious seismic subsidence, watering deformation or loess landslip. There have been series problems of how to change its natural microstructure for engineering demanded which is major concerned in this paper. We put forward Phosphoric modified methods to treat loess problems. By changing different proportions of adding filling materials, such as Calcium carbonate, barite, talcum powder, and others auxiliaries including phosphoric acid and barium metaborate, found it get to be better effect. It’s dynamic deformation coefficients dropped lower than 2‰. After loading test, the methods prove to be greatly enhanced loading strength and changed its unreasonable microstructure. Because of no toxicity materials be adopted and produced during course, the method can be popularized and applied.

Abstract: On the basis of the dynamic triaxial liquefaction test of the loess samples which were taken from the Shibei tableland, Guyuan city, and evaluating the liquefaction potential of the loess through laboratory experiment and response analysis. Then the liquefaction characteristics of saturated undisturbed loess under different level of liquefaction are analyzed based on the evaluation results. The results are shown that: when the saturated undisturbed loess liquefaction is light, dynamic stress is decayed barely, weak dynamic residual deformation is generated, pore water pressure begins to grow, the dynamic stress dynamic strain stagnant curves have not marked change, and the deformation of the soil is at viscoelastic stage. When the loess liquefaction is middling, attenuation of dynamic stress is not obviously, dynamic strain is increasing, amount of pore water pressure much higher than stage one, the long axis slope of hysteresis curves is reduced significantly, the sizes and shapes difference of adjacent hysteresis loop is obvious, and the deformation of the soil is at viscoelastic-plastic stage. When the loess is liquefied completely, dynamic stress is decayed evidently, dynamic strain increased dramatically, and its crest value could exceed 10%, the peak value of pore water pressure is sustainable increasing, and emerge the apparent fluctuation under the action of a drastic dynamic strain, the form of the stagnant curves tend to be irregular, the loess is in elastic-plastic stage.

Abstract: In the light of heavy seismic landslide disasters in the valley city of loess area, 104 typical loess landslides caused by the 1654 Tianshui(Ms 8.0), 1718 Tongwei(Ms 7.5) and 1920 Haiyuan(Ms 8.5) earthquakes were studied, main landslide type and basic characteristics of seismic landslide in the valley city were analyzed. The landslides in the valley city of loess area are divided into three types: homogeneous loess landslide, loess interface landslide and loess-mudstone cutting layer landslide. Through the investigation and analysis of earthquake risk, the suggestion about the 22 dangerous landslides in Tianshui is given. The study is expected to supply scientific basis for seismic landslide disaster prevention and reduction in valley city of loess area.

Abstract: Use of Seed’s simplified liquefaction evaluation method, combined with the dynamic triaxial test results, and the wave velocity of site liquefaction, to evaluate liquefaction potential of the three typical loess sites under the action of different seismic magnitudes, and calculate the boundary depth of the liquefaction site. Moreover, give the corresponding relationship between the typical loess site liquefaction boundary depth and shear wave velocity, and get the critical shear wave velocity of typical loess liquefaction site. The results of the study show that, (1) saturated loess site could be liquefied under the action of a certain intensity earthquake. (2) saturated soil layers which do not produce liquefied under the action of 6.5 degree earthquake，its critical shear wave velocity is about 200 m/s, and under the action of 7 degree earthquake its critical shear wave velocity is about 303 m/s, under the action of 8 degree earthquake its critical shear wave velocity is about 368 m/s. This conclusion enriches and develops the basis of liquefaction potential evaluation in the loess region.

Abstract: To reveal development law of seismic subsidence of loess, through in-situ explosion test at one loess site, ground settlement and layered underground settlement were monitored, by which the time-space-domain development of seismic subsidence of loess are gained. Furthermore, the time-domain development law of seismic subsidence in different directions is analyzed, so as the variation characteristics of layer-settlement and its contribution rate, and the development law of seismic subsidence distribution in the horizontal direction. The time-domain development of seismic subsidence of loess consists of rapidly growing stage and slowly growing stage. The former is under blasting ground motion, and its seismic subsidence ratio approaches to 46.5% invariably. While in the later stage, development of seismic subsidence ratio can be described by power function with index of 0-1. And, seismic subsidence distribution and contribution rate of layer-settlement are varying with time, which are consistent to the time-domain development law of seismic subsidence.

Abstract: By using the DSD-160 dynamic triaxial apparatus, liquefaction experiments under random seismic loading of the saturation original samples from a passenger rail line which located in the loess tableland in china was tested. Based on the test results, connected with the forecasting method of the liquefaction test under random seismic loading and the results of seismic hazard analysis, the liquefaction potential of the saturation loess from different regions in the passenger rail line is distinguished. Moreover, the predictions include 50 years probability of exceedance 10% and 2%of the loess liquefaction potential of the sites mentioned above is obtained.

Abstract: In this paper, the effects of the main property indexes on the saturation original loess liquefaction is analyzed through the dynamic triaxial test by using the WF-12440 testing system, combined with the experimental results, the influence of density-grain degree coupling on saturated loess liquefaction is comprehensively analyzed. The result shows that the influence of density-grain degree coupling on saturation loess liquefaction has a feature of segmentation, plastic index plays the main role for loose loess, whereas density is the main control factor to dense loess; Moreover, the influence of density-grain degree coupling on saturated loess liquefaction controlled by cyclic numbers of the vibration, plastic index plays the leading role while the vibration times is small, while the more vibration times, the bigger density and higher strength of liquefaction.

Abstract: Based on mobile strong motion array observation, borehole exploration and site seismic response analysis, the site effects of mountainous topography in southeastern Gansu and the topography of loess tableland on ground motion were investigated in details. The analysis on acceleration records of aftershocks showed that the peak ground acceleration at top of the mountain is nearly 2 times of that at the foot of it. The seismic response analysis of sites shows that the loess tableland may amplify PGA by 1.44-2.0 times. Therefore, site effects of mountains and loess topography on ground motion should been taken account into seismic design.

Abstract: Loess is widely distributed in China and the Loess Plateau is one of the major areas where strong earthquakes often take place. From the field investigation on earthquake damages caused by Wenchuan Ms 8.0 of 12 May. 2008, the seismic amplification effects were observed. In order to analyze the mechanism of the seismic amplification effects, microtremor surveys were carried out to detect the ground condition and the predominant frequency of the different sites of the same mountain was obtained. Moreover, the typical mesa of loess plateau is studied applying the dynamic finite element analysis method of two dimensions linearly equivalent for dynamic response numerical calculation, with different loess thickness and different slope grades. The magnifications of peak acceleration at the mountaintop and mountainside are obtained under different conditions. It is found that the magnification is related to the loess thickness and slope grades, which is in accordance with the earthquake damages, and the results show that the loess thickness and slope grade are important factors influencing earthquake damage.

Abstract: Seismic subsidence of loess is a kind of disaster induced by strong ground motion in loess area, while seldom example of this subsidence was found in long time study, usually instead of laboratory test. An explosion ground motion in a typical loess field was designed to verify seismic subsidence of loess with natural condition and laboratory test of loess seismic subsidence was conducted in China. The result proved seismic subsidence of loess could be induced by explosion ground motion, while the maxmuim settlement of 3.3cm in the case of experiment is much less than 53cm with a moderate or strong dynamic stress in laboratory due to an incomplete seismic subsidence of loess in this field. The seismic subsidence of toper loess layers is less than the below in the field test although it is opposite to in laboratory test due to closer distance between the below layers and explosion shots.