Incompressible or nearly incompressible soil dynamic behaviour—a new staggered algorithm to circumvent restrictions of mixed formulation

The restriction of the Babuska–Brezzi stability criteria for the mixed formulation requires non-uniform interpolation of displacement and pore-pressure variables, which complicates the coding in the finite element analysis. This will certainly preclude the use of many otherwise useful elements. A possible solution to overcome this problem introduced earlier by the authors requires a semi-explicit form. However, the effectiveness of the semi-explicit procedure is dependent on the time step length used, which presents difficulties for transient analysis. In this paper, an unconditionally stable staggered implicit-implicit algorithm is developed, which is generalised from the semi-explicit form. For non-uniform mesh configurations, the results indicate a significant improvement compared with those obtained by using the semi-explicit procedure.     

应用Mehlich3浸提剂提取风沙土中速效磷,速效钾的条件实验

应用正交实验法研究了Ｍｅｈｌｉｃｈ３试剂测定风沙土中速效磷、速效钾的适宜条件，并以Ｏｌｓｏｎ法（测磷）、ＮＨ＿４ＯＡＣ法（测钾）为标准对所确定的条件进行了检验，结果表明：浸提剂：沙样为１０：１，浸提温度为常温，震荡时间为５ｍｉｎ适宜于待测容液的提取。用钼锑法测定待测溶液中的磷，适宜的显色酸度为０．５５ｍｏｌ／Ｌ１／２Ｈ＿２ＳＯ＿４条件下测定结果与参比法测定结果显著相关；且精密度高、提取量多，是一种适宜风沙土测定的通用浸提剂。     

晚更新世末期南海北部陆架的古地理探讨

根据地球物理综合调查,沉积物的粒度、矿物成分、石英砂粒扫描电镜分析,14T测年,以及微体古生物等成果,表明南海北部外陆架地区在更新世末期,冬半年气候干寒,东北风强劲,风沙活动强烈,砂丘广布,为干寒多风沙的自然环境。     

Observations of several characteristics of aeolian sand movement in the Taklimakan Desert

With both sides of the Taklimakan Desert highway line as the study area, three typical aeolian sand landforms, i.e. complex dune ridge, barchan dune and flat sand land, were selected as sand beds for the observation, analysis and research of the characteristics of aeolian sand movement such as aeolian sand stream structure, sand transport intensity, etc. in the Taklimakan Desert. The results show that there is a linear relation between the height and the log of sand transport rate over transverse dune chain, longitudinal dune ridge and flat sand land, i.e. the sand transport percentage decreases exponentially with increasing height. Sand transport rate within the 10 cm height above the bed surface accounts for 80%-95% of the total sand transport rate of the observed height (40 cm), while the sand transport rate in 20 cm occupies 98% of the total amount. Sand transport rate (g·cm-1·min-1) differs greatly with respect to different landform types and different topographic positions. Based on the investig     

生态经济型防风治沙体系优化配置技术规程研究

通过对景电灌区农林业生产状况、自然环境条件、以及风沙危害程度的实地调查，应用系统工程学和生态经济学原理，研究提出：景电灌区防风治沙工作应该走系统工程和生态经济相结合的道路，以封沙育林草为主导措施发展沙区自然植被系统，进一步建立和健全工程治沙系统，并营造和发展人工生态经济型林草植被系统。通过这三大子系统的合理搭配和联合交互作用，使新灌区形成新型的生态经济型防风治沙体系。文章就该体系的合理配置问题及建设技术规程进行了论述     

Climatology of yellow sand (Asian sand, Asian dust or Kosa)in East Asia

In order to study climatology of yellow sand (Asian sand, Asian dust or Kosa) in EastAsia, secular fluctuation in China, Korea and Japan in the recent 30 years was presented. Thenumber of days with sand-dust storm at five stations in China-Hotan, Zhangye, Minqin, Jurhand Beijing, decreases a lot at the former three stations, but changed little at the latter two stations.Suggesting that the recent global warming is more evident in Xinjiang and Gansu, where the fre-quency of cold air invasions from the higher latitudes is decreasing. But, the eastern parts ofMongolia, inner Mongolia, and North China encounter stronger cyclones in early spring as a resultof global warming. These cyclones bring cold air from higher latitudes, causing severe duststorms. Secular variation in the annual days with sand-dust storms in China and Kosa days in Ko-rea and Japan show a parallel change with higher frequency from 1975 to 1985. This may be re-lated to the higher frequency of La Nina years. However, different tendency was shown in theperiod from 1986 to 1996. Since 1996 or 1997, a sharp increase is clear, which may be caused bythe developed cyclones in East Asia as well as human activities, and stronger land degradationunder La Nina conditions. Anomalies of the total number of stations with Kosa days were dis-cussed in accordance with some synoptic meteorological conditions such as the differences be-tween Siberian anticyclone and Aleutian cyclone center at 500 hPa level during the previous winter.     

A THERMO-VISCOPLASTIC CONSTITUTIVE MODEL FOR CLAYS

The effect of heat on clay behaviour is characterized by non-linearity and irreversibility. Due to the complex influence of temperature, thermomechanical factors have to be taken into account for the numerical simulation of the behaviour of such materials. A cyclic thermo-viscoplastic model is developed for this purpose. It includes thermal hardening and the evolution of yield surfaces with temperature. From the physical point of view, it is built on the basis of available experimental results for a temperature range in which no phase change occurs. Conceptually, it is the generalization of an isothermal multimechanism cyclic model. A thermoplastic formulation of the model is also derived. The results obtained from numerical simulations compare well with experiments. © 1997 by John Wiley & Sons, Ltd.     

北疆铁路沿线风沙危害的研究

北疆铁路沿线存在着严重的风沙危害。在三个典型路段风沙危害有不同的表现形式, 北疆铁路沿线风沙危害发生与当地干旱多风的气候条件、铁路沿线下伏含沙地层、铁路施工对地表的破坏以及艾比湖周围沙漠化的发展有关。作者通过实验计算空气动力学粗糙度, 比较了三种典型的机械防沙措施的效果, 指出了其中存在的不足。并根据研究结果, 提出了一个优化的防沙体系方案。     

Yielding seismic response of code-designed single-storey asymmetric structures

A study on the seismic performance of asymmetric structures with non-linear behaviour and random properties is presented. The structural response of single-storey models, designed using different code criteria is studied using both a deterministic and a probabilistic approach. The worst structural behaviour, in terms of ductility demands, is obtained for symmetric models considering uncertain properties. It is shown that an arbitrary increase of the total lateral strength of the structures does not lead to an increment of the structural safety proportional to the total lateral strength increase, implying that an expensive structure is not always the safest. © 1998 John Wiley & Sons, Ltd.     

Fundamental yet simplified model for liquefaction instability

A fundamental procedure is proposed for the identification of liquefaction in saturated soils based on the instability in the material's microstructure. The disturbed state concept (DSC) provides a unified constitutive model for the characterization of entire stress–strain behaviour under cyclic loading, and the values of disturbance at threshold states in the deforming microstructure provides the basis for the identification of liquefaction. The procedure is verified with respect to laboratory behaviour of two sands, saturated Ottawa and Reid Bedford. A mathematical analysis of the DSC constitutive matrix is also performed. Procedures for the application of the DSC for simplified analysis and design, and in finite element procedures are presented. It is believed that the proposed model can provide a fundamental yet simplified procedure for liquefaction analysis, and as a result, it is considered to be an improvement over the available empirical and energy-based procedures. © 1998 John Wiley & Sons, Ltd.