正循环机械回转钻孔灌注桩在卵石层中的应用

在粒径、密实度较大的卵石层采用正循环机械回转钻进行灌注桩施工,存在钻具类型、合理的泥浆比例和钻探工艺等问题。以西安绕城高速公路谢王立交桥桥桩基工程实践为例,探讨正循环机械回转钻孔灌注桩在卵石层施工工艺等问题。     

东亚地区夏季大气环流季节循环进程及其在区域持续性降水异常形成中的作用

利用32年(1968～1999年)月平均NCAR/NCEP再分析资料,分析了东亚地区夏季大气环流的季节循环进程, 并以1991/1994年为例,探讨了东亚地区夏季7～8月对流层上层环流的季节循环提前和延迟与气候平均的季节循环的差异,以及在江淮流域持续性降水异常过程中的作用,证实东亚地区季节循环的变异对形成我国东部地区持续性降水异常,特别是7月旱涝起着重要作用,江淮流域旱涝一般是和东亚地区大气环流季节循环的提早或推迟一个月左右相对应.通过波作用量的动力学诊断分析,研究了欧亚大陆沿副热带西风急流传播的异常准静止波的传播特征,并从以副热带西风急流为波导的准静止波(或者遥相关)角度对东亚地区夏季7～8月环流季节循环进程提前和延迟的可能机制作了分析.     

藏北改则--班戈地区下白垩统多巴组的高频旋回沉积特征与盆地性质

西藏北部改则——班戈地区的下白垩统多巴组中所发育的Ⅴ级旋回表现出3种垂向沉积序列:潮坪相碎屑岩沉积序列(Ⅰ)、浅海相碳酸盐岩沉积序列(Ⅲ)和碳酸盐岩、陆源碎屑岩混合沉积序列(Ⅱ)。其中序列Ⅰ-1和Ⅲ是正常的沉积水体向上变浅的沉积序列,而序列Ⅱ具有明显的陆源碎屑先进积后退积的特征,可进一步分成3个亚类:Ⅱ-1、Ⅱ-2和Ⅱ-3。横向上从南部物源区向北呈Ⅰ→Ⅱ-1→Ⅱ-2→Ⅱ-3→Ⅲ的变化过程。结合盆地构造背景和沉积特征,本文提出多巴组高频旋回的形成与弧背盆地南部冲断带的冲断作用相对应。冲断作用期,物源区粗碎屑物质大量进积,大于盆地基底沉降速率,沉积水体逐渐变浅;冲断间歇期,物源区碎屑物质的供应迅速减少,基底沉降速率逐渐大于碎屑物质的进积速率,沉积水体又有所加深。     

A Note on Tsunami Bore Front

A note is presented on tsunami bore front. This tsunami bore front is an old dynamical problem but also a new problem to be understood. The tsunami event on 2004 December 26 has raised this is an urgent problem. The author introduces here a model in order to see a hydrodynamical specific property of the tsunami bore front. This modeling gives us a new understanding about what mechanics is for the interested tsunami bore front, especially, around a coastal zone. This work adds a new understanding about mechanics of water motions as the tsunamis generated by the earthquake undersea at a distant area from the coast. The model in this work points out a specific transitional pattern as a function of time and space of tsunami bore front. This modeling gives what is essential at considering tsunami bore front.     

Laboratory Study on the Hydraulic Conductivity and Pore Pressure of Sand-Silt Mixtures

The hydraulic conductivity plays a major role on the excess pore pressure generation during monotonic and cyclic loading of granular soils with fines. This paper aims to determine how much the hydraulic conductivity and pore pressure response of the sand-silt mixtures are affected by the percentage of fines and void ratio of the soil. The results of flexible wall permeameter and undrained monotonic triaxial tests performed on samples reconstituted from Chlef River sand with 0, 10, 20, 30, 40, and 50% nonplastic silt at an effective confining stress of 100 kPa and two relative densities (D_r = 20, and 91%) are presented and discussed. It was found that the pore pressure increases linearly with the increase of the fines content and logarithmically with the increase of the intergranular void ratio. The results obtained from this study reveal that the saturated hydraulic conductivity (k) of the sand mixed with 50% low plastic fines can be, on average, four orders of magnitude smaller than that of the clean sand. The results show also that the hydraulic conductivity decreases hyperbolically with the increase of the fines content and the intergranular void ratio.     

Settlement Prediction Under Linearly Loading Condition

The relationship between time and settlement is a key problem in geotechnical engineering. Current methods used to predict the time-dependant settlement are based mainly on instantaneous loading condition. In this paper, the settlement curve under linearly loading condition, which is suitable for building and embankment projects, is mathematically proved to be “S” shaped. Subsequently, a new model, the Poison model, is raised to predict the settlement, and the method of parameter solution is also introduced. Finally, several problems about the Poisson prediction model are discussed.     

Analytical Theory for One-Dimensional Consolidation of Soil Induced by Time-Dependent Pumping and Loading

Analytical solutions are derived for one-dimensional consolidation induced by time-dependent pumping and loading, in which both the effects of different pumping types and loading conditions are considered, i.e., step pumping, cyclic pumping, constant loading, and step loading. Based on the solutions obtained, some diagrams are prepared and the relevant consolidation behavior of soil is discussed in detail. It has been shown that the consolidation behavior is greatly influenced by pumping velocity, loading pressure, pumping and loading type.     

Cyclic behavior of natural organic clay under variable confining pressure that match traffic loading conditions

ABSTRACT

One-way cyclic loading is more typical for traffic loading and cyclic triaxial test has been recognized as a useful method for solving many engineering problems. Under traffic loading, the influence of variable confining pressure on cyclic behavior of natural organic clay subjected to cyclic traffic loading is rarely reported in the literature. In this study, a laboratory investigation on undrained cyclic behavior of natural organic clay is presented and conducted by cyclic triaxial apparatus. Tests are conducted by both constant confining pressure and variable confining pressure, to simulate the loading conditions induced by passing vehicles in actual engineering. Different stress levels are also considered in this study. By comparing between the results of constant confining pressure tests and variable confining pressure tests, it shows that the one-way cyclic behavior of organic clay is influenced significantly by variation of confining pressure, in terms of pore water pressure, permanent axial strain and stress–strain hysteretic loops.     

Breeding in the freshwater crayfish paranephrops planifrons white

The breeding cycle of female Paranephrops planifrons is described. The incubation of eggs and young takes place between April and December and covers about 25–26 weeks. The winter population contains some apparently adult females which do not breed. The number of eggs laid increases with the size of the parent, and in the population studied varied from some 20 to 30 eggs at 17 mm carapace length to 150 eggs at 30 mm carapace length. After hatching the young pass through two moults while still attached to the parent.     

Sexual reproduction in Sarcotragus spinosulus from two different shallow environments

The reproductive cycle of the demosponge Sarcotragus spinosulus from two different shallow environments (La Pierta and La Strea) of the Ionian coasts of Apulia (SE Italy) was studied from February 2006 to February 2007 in 20 tagged specimens. The sponge is viviparous. All the monitored specimens showed sexual reproduction, even if the process usually involved small portions of the sponge tissue. Most of the specimens showed hermaphroditism, with contemporaneous production of oocytes and spermatic cysts in the same reproductive season. Young oocytes occurred from June to September in specimens from La Pierta and from June to October in those from La Strea. Large mature eggs, measuring up to 200 μm, showed a peak in August to September, concomitant with the appearance of spermatic cysts, whose density values were about 100 times higher than those estimated for female elements. At La Pierta, embryos were present for 11 months, whereas at La Strea they were very scarce during the first 4 months of observation, with the results that there was a significant difference in the production of embryos between the two groups of sponges. Embryo development occurred in patches inside the choanosomal region. Cleavage started in September and led in June to a solid stereoblastula, which, only at La Pierta, produced parenchymella larva (371.3 + 31.3 μm on average) from June to July. In the specimens from La Strea, larvae were never observed. The slight differences in the reproductive cycle between the two groups of sponges may be explained in the light of the major variability of the environmental parameters which could have affected the specimens from La Strea negatively.