Laboratory Investigation on the Effects of Overconsolidation and Saturation on Undrained Monotonic Shear Behavior of Granular Material

In order to study pore water response and static liquefaction characteristics of silty sand, which has previously experienced liquefaction, two series of monotonic triaxial tests were run on medium dense sand specimens (RD = 50%) at confining pressure of 100 kPa. In the first test series, the influence of the soil saturation under undrained static loading has been studied. It summarizes results of monotonic tests performed on Chlef sand at various values of the Skempton's pore pressure coefficient. Analysis of experimental results gives valuable insights on the effect of soil saturation on sand response to undrained monotonic paths. In the second series of tests, the overconsolidation influence on the resistance to the sands liquefaction has been realized on samples at various values of overconsolidation ratios (OCR). It was found that the increase of overconsolidation ratio (OCR) increases the resistance of sands to liquefaction.     

Evaluation of Liquefaction Potential Index Along Western Coast of South Korea Using SPT and CPT

For South Korea, liquefaction potential along the western coast has not been widely assessed because South Korea is considered to be a low seismic hazard. However, recent earthquake events and historical records indicate that the seismic hazard of South Korea should not be ignored. Moreover, as artificial fills are extensively used along the western coast for development, liquefaction evaluation of the soils in this area is necessary. In this paper, we present: (1) the seismic characteristics of the study area; (2) procedures for evaluating liquefaction potential, focusing on the liquefaction potential index (LPI) approach; and (3) LPI distributions at several representative locations along the western coast of South Korea under various seismic scenarios. The liquefaction potential index represents the liquefaction potential over the upper 20 m of a boring or sounding. Using cone penetration test (CPT) and standard penetration test (SPT) data from two coastal sites, we compare and discuss CPT-based and SPT-based LPI values, particularly values computed in nonplastic, silt-rich soils. In these soils, it appears that the CPT yields lower liquefaction resistance, resulting in large LPI values. Finally, discussion and suggestions are provided for CPT- and SPT-based liquefaction assessment of low plasticity and high fines content soils.     

高压气藏不动管柱分层压裂工艺研究与应用

川西低渗高压气藏具有多层系的特点,层间距离一般在十至百米左右。为了提高气井产量与开采经济效益,鉴于气井加砂压裂后压井会严重伤害储层,影响压裂效果,采用压裂管柱直接作为生产管柱,研究形成了以FCY211及Y241封隔器不同组合的两层不动管柱分层压裂工艺。同时,在成熟的两层分压工艺基础上,结合投球选压工艺,研究形成了以“工具分层＋投球选压”不动管柱三层分层的压裂工艺。现场应用实践表明,分层压裂极大地增加了单井的产能,取得了明显经济效益,对类似气藏的多层压裂与开采提供了有益参考。     

辐射沙洲南翼“水道-沙洲”系统与西太阳沙的稳定

通过对江苏岸外辐射沙洲动态和西太阳沙海域动力泥沙环境的分析,论述了西太阳沙演变的宏观背景;由实测固定断面资料、地形资料的对比得出近40年来西太阳沙表面形态和水下地形的变化;结合西太阳沙表面泥沙在波浪和波流共同作用下运动特性的水槽试验研究,分析了西太阳沙冲淤变化的动力机制。从“烂沙洋水道-西太阳沙-西太阳沙南水道”系统的角度研究了西太阳沙演变的控制因素和演变规律。     

A finite element approach for predicting the full resistance profile of a spudcan deeply penetrating in dense sand overlying clay

This paper presents a finite element approach to calculate the full resistance profile of a spudcan deeply penetrating in dense sand overlying clay, in which a potential for an installing spudcan to experience a sudden uncontrolled punch-through failure exists. A modified Mohr-Coulomb model characterized by incorporating a four-phase variation of the mobilized strength and dilation parameters with an equivalent accumulated plastic strain is developed and tested for the overlying dense silica sand. An extended Tresca model is used for the strain softening of the underlying clay. A series of large deformation finite-element (LDFE) analyses are carried out, varying the strength and dilation parameters as well as the spudcan geometries. A fairly good performance of the present approach is verified by validating against groups of centrifuge tests data, allowing the numerical study to be extended parametrically. The four-phase variation of the mobilized strength and dilation parameters involved in the progressive failure of the upper dense sand is parametrically studied and extended to cover the range of sand relative densities that are of practical interest. Additionally, comparisons with the typical existing LDFE analyses using both simple and sophisticated constitutive models are carried out. It shows that the present approach performs fairly well to calculate the full resistance profile of a spudcan deeply penetration in both thin and thick dense sand overlying clay, especially the peak and post-peak resistance, within around 5% of the corresponding centrifuge tests results.     

辐射沙脊主要水道的演变特征及其水动力机制研究

近四十年来的水下地形资料对比显示：南黄海辐射沙洲区水道普遍存在逐渐向南偏移的趋势（西洋主槽冲深、南延,南翼烂沙洋水道、小庙洪水道向南逼进）。有关辐射沙洲整体南移的原因及机理虽有诸多猜想,但至今没有统一可靠的认识,这种趋势性过程的驱动力成为辐射沙洲区海岸冲淤动态研究及港口建设过程中亟待解决的问题。在恢复黄河北归以来苏北黄河三角洲海岸不同发育阶段的岸线位置和水下地形的基础之上,通过所建立的潮波数学模型,研究了在苏北黄河三角洲不同演变阶段南黄海潮波系统的特征及水动力变化。研究表明,随着岸线后退和水下三角洲的夷平,辐射沙洲地区潮差不断增大;水动力不断加强,而且加强的区域逐渐向南偏移,这种大范围区域性水动力主轴的向南偏移就有可能是导致辐射沙洲整体南移的主导因素之一。     

扬子浅滩东南海域海底潮流沙脊、沙波特征

利用seabat8101多波束系统对扬子浅滩东南海底地形进行了高精度探测。发现海底呈明显近乎平行排列的条带状起伏,脊谷相间,沙脊大部分呈NW-SE向排列,发育在45~50 m水深范围之内,沙脊横剖面不对称,大部分沙脊西南侧坡度大、东北坡缓。沙脊规模略有差异,沙脊宽度约0.6~9.8 km,沙脊之间间距可达8.9~22.4 km,高度约1.8~13.3 m,研究区内最长可达53 km。部分脊槽过渡区域发育成片链状海底沙波,沙波大致呈NE-SW走向,波高约0.3~1 m,波长1 km左右。研究区中西部有海底礁石孤立地突兀于相对平坦的海底之上,暂定名为扬礁,最浅水深35.9 m,位于30°59'7.4'~31°N,124°36'48.7'~124°37'40'E。扬子浅滩东南海域沙脊是介于活动沙脊和衰亡沙脊之间的准活动沙脊。该研究将为我国海洋开发和海洋经济发展、海洋行政管理以及海洋安全保障提供服务。     

Explicit stress–strain equations for modeling frictional materials

In this paper, a comprehensive study on simulating the shearing behavior of frictional materials is performed. A set of two explicit equations, describing the relationship among the shear stress ratio and the distortional strain and the volumetric strain, are formulated independently. The equations contain three stress parameters and three strain parameters and another parameter representing the nonuniformity of stress and strain during softening. All the parameters have clear physical significance and can be determined experimentally. It is demonstrated that the proposed equations have the capacity of simulating the complicated shearing behavior of many types of frictional materials including geomaterials. The proposed equations are used to simulate the stress–strain behavior for 27 frictional materials with 98 tests. These materials include soft and stiff clays in both reconstituted and structured states, silicon sands and calcareous sands, silts, compacted fill materials, volcanic soils, decomposed granite soils, cemented soils (both artificially and naturally cemented), partially saturated soils, ballast, rocks, reinforced soils, tire chips, sugar, wheat, and rapeseed. It has been demonstrated that the proposed explicit constitutive equations have the capacity to capture accurately the shearing behavior of frictional materials both qualitatively and quantitatively. A study on model parameters has been performed.     

Numerical study of sand scour with a modified Eulerian model based on incipient motion theory

Application of the standard Eulerian model to simulations of sand scour results in unrealistic phenomena. Therefore, the present work develops a modified Eulerian model based on sand incipient motion theory. The modified model is applied for simulating a two-dimensional single vertical jet and a moving planar jet. The simulation results generally demonstrate fairly good agreement with published results of scour profiles and the velocity contours of the water and sand phases. In addition, equations to describe self-similar scour profiles for the moving planar jet cases are given. The results demonstrate that the modified model efficiently and accurately simulates the two-dimensional sand scour produced by jets, particularly for the moving jet cases.     

南黄海辐射沙脊群西洋水道污水输移扩散研究

采用沿深平均二维数值模型对南黄海辐射沙脊群西洋海域的潮流场和物质扩散场进行了模拟,计算和分析了大潮情况下海域5 m、7 m和10 m 3种水深(理论基准面下)排放位置处达标污水输移扩散的范围及分布规律。结果表明,污水排入海后,会很快被稀释,各排放位置200和500稀释度等值线包络面积均较小,且包络面积随水深增加有明显变小的规律。拟合了不同污水排放量对应的200和500稀释倍数包络面积,发现两者呈良好的幂级数关系。