Evaluation of Engineering and Cement–Stabilization Parameters of Clayey–Sand Mixtures under Soaked Conditions     

Evangelos?I.?StavridakisEmail author 《Geotechnical and Geological Engineering》2005,23(6):635-655

Clay soils, especially clay soils of high or very high swelling potential often present difficulties in construction operations. However, the engineering properties of these clay soils can be enhanced by the addition of cement, thereby producing an improved construction material. Higher strength loss of cement stabilized clay soils after soaking in water is attributed to water absorbing capacity of the clay fraction (e.g. montmorillonite). Kaolinite and illitic soils are largely inert and resist to water penetration. These clays generally develop satisfactory strengths resulting to low strength reduction [Croft, 1967]. The swelling clays such as bentonite soaked in water, due to environmental conditions, result to volume increase causing macro and micro-fracturing in engineering structures. These fractures accelerate water penetration and consequently cause greater strength loss [Sällfors and Öberg-Högsta, 2002]. The water intrusion during soaking creates swelling and disrupts the cement bonds. The development of internal and external force systems in soil mass, due to soaking conditions, establish the initiation of slaking. Internal force system of a stabilized clayey soil consists of the resultant stresses established by the bonding potential of a cementing agent and the swelling potential of a clay fraction. In an effort to study this influence of soaking conditions and final absorbed water content on the stabilization parameters (cement, compaction, curing time), both unconfined compressive strength and slaking (durability) tests were carried out on two different cement stabilized clayey mixtures consisted of active bentonite, kaolin and sand.  相似文献   

Structuring factors and recent changes in subtidal macrozoobenthic communities of a coastal lagoon, Arcachon Bay (France)     

Hugues Blanchet  Xavier de Montaudouin  Pierre Chardy  Guy Bachelet 《Estuarine, Coastal and Shelf Science》2005,64(4):561-576

Sediment stability in the shallow Venice Lagoon was investigated by means of numerical modelling. Results from a hydrodynamic model allowed for the determination of the wave climate and bottom effective parameters so that simulations with a Lagrangian model for suspended particulate matter could be performed. A spring–neap cycle in summer 1998 was chosen as integration period since data for calibration and verification were collected within the European project F-ECTS between summer 1998 and spring 1999. Deposition on shallow mud flats as well as short term erosion during a strong wind event were reproduced and mass balances for two areas computed. A relation of patterns of SPM in the water and in the sediment was found and can be ascribed to the displacement of material during storm events from shallow areas to the bottom of very small channels. Assuming about 10 to 14 storm events during the year comparable to the Bora event during the integration time, estimates for long-term trends of sediment loss on shallow flats by Day et al. [Day, J.W., Rybczyk, J., Scarton, F., Rismondo, A., Are, D., Cecconi, G., 1999. Soil accretionary dynamics, sea-level rise and the survival of wetlands in Venice Lagoon: a field and modelling approach. Estuarine, Coastal and Shelf Science 49, 607–628] are met by the simulation results. Evidently, long-term sediment evolution of the lagoon is therefore not dominated by the average (residual) processes that occur in the lagoon, but by the few peak events that happen randomly over the year.  相似文献   

多组多滞后区间中立型非线性时变控制系统的鲁棒镇定     

王殿坤  高存臣 《中国海洋大学学报(自然科学版)》2005,35(4):591-596

采用无滞后控制系统与滞后控制系统的等价性方法，研究了多组多滞后区间系数中立型非线性时变控制系统的鲁棒镇定问题，给出了区间长度及时滞的估计范围，进而得到了系统渐近稳定的判定条件。此判据包涵了有关文献的结果，结论更具有一般性。  相似文献   

基于积分不等式的时滞Markovian跳变系统的稳定性分析和镇定     

夏卫锋  徐胜元 《南京气象学院学报》2017,9(4):417-422

文章研究了时滞 Markovian 跳变系统的稳定性和镇定问题.首先,运用一个新的积分不等式,得到了保守性更小的稳定性判据;其次,基于此判据,获得了一个状态反馈控制器存在的充分条件,使得闭环系统具有随机稳定性并满足扩展耗散性;最后,两个实际例子说明了设计方法的可行性和有效性.  相似文献   

混杂随机微分方程理论概述     

毛学荣 《南京气象学院学报》2017,9(3):246-261

本文对混杂随机时滞微分方程的当前发展及最新的研究成果进行了概述.主要回顾了混杂随机微分方程解的存在唯一性定理、稳定性、鲁棒有界性以及离散时间反馈镇定性等部分对混杂随机微分方程的研究起到关键推动作用的成果.  相似文献   

线性时变大系统的分散最优控制与镇定     

唐功友 《中国海洋大学学报(自然科学版)》1994,(Z2)

本文提出一种关于线性时变大系统最优控制的二次型性能指标分解方法。据此研究线性时变大系统局部分散最优控制的逆问题．得到大系统关于某二次型性能指标存在最优状态反馈控制律的条件，同时它也是大系统局部分散镇定的一个新的充分条件．  相似文献   

Active fin control for yacht using virtual instrumentation     

V. Anantha Subramanian  G. Asokumar  V. Jagadeesh Kumar 《Ocean Engineering》2007,34(3-4):390-402

Virtual instrumentation represents a PC based control system which incorporates manipulation of data acquired from physical transducers in specific ways using a very high level graphical environment. The deployment of this non-traditional approach is demonstrated in this paper by application to design of a fin control system for a yacht. One of the disadvantages of the traditional stabilizer system is the enormous hardware involved in the controllers and instrumentation panels, which make maintenance and troubleshooting difficult. With the help of virtual instrumentation, design of the stabilization controller and instrumentation panels can be carried out much more effectively, in comparison with the traditional hardware approach. A multi-disciplinary approach is adopted here and it consists of the assessment of the hydrodynamic coefficients of the yacht using a numerical package, representation of the hydrodynamic coefficients by suitable polynomial functions, identification of the time dependent fundamental frequency in the roll disturbance signal sample, generation of control signal for an appropriate fin angle based on the fin lift characteristics of the chosen fin and employment of feedback control to maintain the fin at the appropriate angle for maximum control. Once the ship based hydrodynamic coefficients are generated, the entire control algorithm is developed in the virtual instrumentation mode using LabVIEW environment. The effectiveness of the system is verified through laboratory tests on a yacht hull form. The control algorithm permits choice of frequency dependent hydrodynamic coefficients by use of a harmonic distortion analyzer in the virtual instrumentation environment.  相似文献   

Biological soil crust development and its topsoil properties in the process of dune stabilization, Inner Mongolia, China   总被引：4，自引：0，他引：4  

Yirui Guo  Halin Zhao  Xiaoan Zuo  Sam Drake  Xueyong Zhao 《Environmental Geology》2008,54(3):653-662

This study was undertaken at Horqin Sand Land, Inner Mongolia, Northern China. Field samples of biological soil crusts (BSCs) and underlying topsoil (0–5 cm under BSC) were taken in areas of different dune stabilization stages, and their physicochemical properties were analyzed, including particle size distribution, bulk density, organic matter, nitrogen, phosphorus, electrical conductivity (EC), pH, and CaCO₃ content. The results revealed that semi-mobile dunes, semi-fixed dunes and fixed dunes had developed a physical crust, algae crust and moss crust, respectively. The thickness, hardness, water content, fine fraction and nutrient contents of BSCs were gradually increasing along the dune stabilization gradient. Meanwhile, BSC establishment and development enhanced the bulk density, silt and clay content, and nutrients of the topsoil under it, in an increasing tend from semi-mobile dune to fixed dune. Organic matter concentrations and other nutrients in the 0–5 cm topsoil layer under BSCs were significantly higher compared to unconsolidated soil (control). Moreover, there were strong significant positive correlations between topsoil and BSCs’ organic matter, total nitrogen, available nitrogen, available phosphorus, CaCO₃, and <0.05 mm particle content, suggesting that BSCs have an influence on some of the properties of the underlying topsoil.  相似文献   

基于传递系数法的滑坡滑带土强度参数反分析研究   总被引：4，自引：0，他引：4  

易朋莹  王凯  任佳  何涛 《中国地质灾害与防治学报》2008,19(4)

基于对滑坡强度参数反分析基本原理的分析,利用工程实践应用最为广泛的传递系数法建立了滑坡反分析计算模型,进而得出反分析理论基础,从数学意义上揭示了滑坡反分析本质为求解由滑坡状态条件确定了的系数项和常数项的二元多次方程。通过滑坡反分析状态分析,根据滑坡变形特征确定了稳定性评估指标。利用至少两个反分析剖面,采用试算法和插值法求解了一系列当Fsi′=Fs时的c、φ组合,然后用图解法求解滑坡滑带土强度参数。该方法在某滑坡中得到成功的应用,其计算精度基本满足工程要求,为反分析在滑坡稳定性分析及预测中的应用进行了有益的探讨。  相似文献   

黄土填方高边坡变形破坏机制分析   总被引：1，自引：1，他引：0  

宋焱勋  彭建兵  张骏 《工程地质学报》2008,16(5):620-624

本文依据西北某油田倒班基地黄土填方高陡边坡工程勘察, 研究了该边坡的变形破坏机制, 通过对边坡工程地质条件及变形破坏分析, 建立FLAC3D地质模型, 采用数值模拟方法研究了边坡变形破坏机制。研究结果表明, 主要变形区或破坏区为陡坎周围至其沿坡面向下20～25m 的范围之间, 其破坏深度底界为全新世填土层Q4与原状黄土Q3接触面, 但要重点控制沿坡面向下20～25m 的范围之间的变形。数值模拟结果表明, 该边坡目前整体稳定性较好, 不会发生整体变形破坏。  相似文献