Quadruple LVDT local rotational displacement measurement in torsional shear tests     

《Geomechanics and Geoengineering》2013,8(2):109-115

Experience has shown that to obtain pre-failure deformability of geomaterials in laboratory element tests, it is imperative to make local strain measurements. For torsional shear tests, the local measurement is complicated by coupling of the axial, radial, and rotational movement experienced by the soil specimen during shear. The rotational displacement must be isolated from other modes of movement for the interpretation of test results. Existing techniques designed for torsional shear tests under general stress conditions can be complicated and difficult to use. A simplified scheme using two pairs of linear variable displacement transducers (LVDTs) is proposed for local rotational deformation measurement, specifically for cyclic torsional shear tests under constant normal stress conditions. The subtraction of readings within an LVDT pair nullifies displacements at the measurement point caused by axial and radial movement or bulging of the specimen. The same subtraction accumulates and thus isolates LVDT readings caused by rotational movement. The error associated with the simplified set-up is expected to be <0.125%. A series of hollow cylinder torsional shear tests have been performed to verify the effectiveness of the new measurement scheme. The results are repeatable and consistent with well-documented test data.  相似文献   

http://www.sciencedirect.com/science/article/pii/S167498711100137X     

Amir Hossein Alavi  Amir Hossein Gandomi 《地学前缘(英文版)》2012,3(4):541-555

This study presents promising variants of genetic programming (GP),namely linear genetic programming (LGP) and multi expression programming (MEP) to evaluate the liquefaction resistance of sandy soils....  相似文献   

淮安地震台沙层应力仪器观测数据变化的特征分析   总被引：1，自引：0，他引：1  

仇中阳  毛华峰  王富才 《地震工程学报》2013,35(2):372-377

用小波变换和傅里叶变换的分析方法对2009年5月至2012年6月淮安沙层应力数据进行频谱分析.发现:淮安台沙层仪器所记录数据中含有多个频率成份,其中低频信号频率以1.157 4×10-5 Hz附近信号最强,在2.314 8×10-5 Hz附近次之,高频信号频率在0.25～0.45 Hz之间.低频信号反映在日、月等引潮力的作用下固体地球产生的周期性潮汐变化的地壳形变特征;高频信号更多的反映地壳应力变化特征.淮安沙层应力观测数值变化不仅与其他沙层应力台站有相同变化形态和一致的年变规律,还与地震活动有较好的对应关系.沙层应力数据变化能反映大地震从孕育到发生的完整过程,一般具有上升、平稳、下降、回升发震等几个阶段.  相似文献   

Adsorption of copper(II) from aqueous solution by Beidellite     

M. S. Öncel 《Environmental Geology》2008,53(8):1767-1775

Dry lakes, degraded sandy grasslands, abandoned farmland and mobile dunes which are widely distributed throughout the arid areas of northern China have been investigated in this work. Gain-size distribution of the surface sediments of Manas lake in Junggar basin, Juyan lake in the Alxa plateau, Zhuye lake in Minqin basin and most deserts (such as Mu Us desert, Otindag desert, Horqin desert and Hulun Buir desert) in China have been analyzed. The results show clay with particle sized <10 μm on the surface sediments of dry lakebed and sandy grassland developed from dry lakebed, respectively, account for >60% and ∼50% of the total mass. Since the tiny particles on the surface of abandoned farmland are blown away easily and rapidly, the content of clay particles in Minqin basin is <14%. The grain-size distribution of mobile dunes in northern China mainly consists of particles >63 μm and few particles <10 μm. Consequently, although sand/dust storms originate primarily in the western deserts, the gobi areas of the Alxa plateau, the north and east of Hexi Corridor and in central Mongolia, the widely distributed dry lakebeds, sandy grasslands and abandoned farmland adjacent to the deserts also contribute to aeolian dusts. Hence, the material sources for sand dust storm in East Asia include inland deserts, but also dry lakes, sandy grasslands and abandoned farmland, which are widely distributed throughout the arid inlands of northern China.  相似文献   

Efficacy of Cement-stabilized Fly Ash Cushion in Arresting Heave of Expansive Soils     

M. Rama Rao  A. Sreerama Rao  R. Dayakara Babu 《Geotechnical and Geological Engineering》2008,26(2):189-197

Expansive clays swell and shrink seasonally when subjected to changes in the moisture regime causing substantial distress to the structures built in them. Techniques like sand cushion and cohesive non-swelling soil (CNS) layer have been tried to arrest heave and consequent damages to structures. Sand cushion has been proved to be counter-productive. Studies have indicated that even though CNS layer was effective initially, it became less effective after the first cycle of swelling and shrinkage. Research carried out by the authors, using cement-stabilized fly ash as a cushioning material, has shown that it was quite effective in arresting heave. Fly ash cushion, stabilized with 10% cement with thickness equal to that of the expansive soil bed reduces heave by about 75% in the first instance. With subsequent swell-shrink cycles, the performance further improves, unlike in the case of a black cotton soil provided with a CNS cushion. At the end of fourth cycle of swelling, the reduction in the amount of heave is as high as 99.1%.  相似文献   

长江口北支兴隆沙XL2孔沉积物的磁性特征   总被引：3，自引：0，他引：3  

周开胜  孟翊  刘苍字  张卫国  洪雪晴 《沉积学报》2008,26(2):300-307

通过对兴隆沙XL2孔沉积物磁性特征研究,发现该地区沉积物的磁性矿物以低矫顽力的亚铁磁性矿物为主。按磁化率χ等磁参数曲线的变化特征将XL2孔划分出4个磁性层,同时对比沉积物的粒度特征和微古分析结果,探讨了长江口北支兴隆沙沉积环境的演化过程,以及沉积物磁性特征与沉积环境的关系。  相似文献   

Dynamic compaction properties of bentonite-based materials     

Hiroshi Ito  Hideo Komine 《Engineering Geology》2008,98(3-4):133-143

Dynamic compaction tests of bentonite-based materials (BBMs) with 100, 70 and 50% bentonite contents have been performed using five powdery bentonites with different physicochemical properties to establish the simplified evaluation method for dynamic compaction properties of BBMs. For a given bentonite content and a total compaction energy condition, the maximum dry density, ρ_dmax, and the optimum water content, w_opt, which are well-known indexes of compaction properties, for BBMs were determined according to the type of bentonite used for BBMs. For evaluation of those values of BBMs derived in this study, the plastic limit of BBM, w_pbbm, was defined as the plastic limit that was measured using the sample pulverized to a maximum grain size of less than 425 μm in the case of BBM with sand having a maximum grain size of more than 425 μm and was measured using the powdery bentonite itself in the case of BBM without sand. This study proposed equations for evaluating ρ_dmax and w_opt of BBMs with more than 50% bentonite content under the total compaction energy conditions of 551–2755 kN-m/m³ using w_pbbm. Finally, we related the equations derived in this study to the equation for evaluating hydraulic properties of compacted BBMs proposed in previous work and proposed the preparation method of BBMs with more than 50% bentonite content for constructing BBM buffer by in-situ compaction method.  相似文献   

Sand dunes as a major proximal dust source for late Pleistocene loess in the Negev Desert, Israel   总被引：3，自引：0，他引：3  

Onn Crouvi  Rivka Amit  Naomi Porat 《Quaternary Research》2008,70(2):275-282

Grain size analyses of three hilltop, primary eolian loess sequences in the Negev desert, southern Israel, show a bimodal grain-size distribution at 50-60 μm and 3-8 μm. Using analyses of mineralogy and OSL ages we demonstrate that the coarse mode is composed mostly of quartz grains and its relative magnitude increases regionally with time, suggesting an enhancement of a time-transgressive proximal dust source compared to a distal, Saharan fine-grain dust. The only proximal dust source for large amount of coarse silt quartz grains is the sands that advanced into Sinai and the Negev concurrently with the loess accretion during the late Pleistocene as a result of the exposure of the Mediterranean shelf. We therefore propose that the coarse silt quartz grains were formed through eolian abrasion within the margins of an advancing sand sea. This relationship between desert sand seas as a source for proximal coarse dust and desert margin loess deposits can be applicable to other worldwide deserts such as Northern Africa, China and Australia.  相似文献   

剪胀性砂土边界面模型的研究     

迟明杰  赵成刚  李小军 《工程地质学报》2008,16(3):415-421

剪胀性对于砂土,尤其是中密以及密实砂土,是一个非常显著的特性。相变线是剪胀性砂土的特征曲线,能够反映砂土的围压以及初时孔隙比对变形特性的影响。本文在边界面塑性理论的框架内,把相变状态参量引入到剪胀方程以及塑性硬化模量中,建立了一个能够描述砂土剪胀性以及循环特性的本构模型。本模型采用一套参量可以模拟不同初时孔隙比、不同围压、排水(或不排水)条件下单调(或循环)加载的应力-应变特性。验证表明本模型数值计算与试验结果相吻合。  相似文献   

华南老红砂沉积年代学及其环境意义：以福建青峰老红砂为例   总被引：1，自引：0，他引：1  

靳建辉  李志忠  雷国良  凌智永  姜锋  申健玲  刘秀铭 《地理科学》2017,37(2):301-310

对福建海坛岛青峰老红砂进行了系统的光释光测年研究,结合已发表的相关测年数据,在统一的时间标尺上探讨了老红砂发育过程及其与海平面变化和东亚季风变化之间的关系。结果表明：① QFS剖面沉积年龄为110~33 ka,起始发育年龄延伸到了末次间冰期。主要涵盖了MIS5c~MIS3阶段,其中存在4个快速堆积期。结合已发表的年代学数据进行综合分析,认为前人得出的老红砂发育在末次冰期以来的结论需要得到修正。② 华南老红砂发育过程与区域海平面变化密切相关。在末次间冰期和末次冰期均有发育,高海面（>-50 m）或较高海面（-50~-70 m）时期是老红砂普遍发育期。区域地壳运动叠加海平面变化造成闽南和闽东北老红砂的沉积差异：海退过程中的较高海面时期北部先发生快速堆积;海侵过程中的较高海面时期南部先发生快速堆积。LGM（海平面<-70 m）期,老红砂不发育。③ 老红砂在冰期-间冰期尺度上的沉积速率体现了源区气候和海平面变化对老红砂物源输送的双重制约。  相似文献