南海东北部两种软珊瑚

金黄编笠软珊瑚Morchellana boleliformis(Ridley)和黎明编笠软珊瑚Morchellana auroro(Ridley)隶属于棘软珊瑚科Nephtheidae编笠软珊瑚属Morchellana,于1979—1983年采自南海东北部水域。     

病害路基地基加固处理工程实例

针对胶济客运专线某段路基沉降加大的状况,提出以潜孔钻机开孔、以高压旋喷注浆加固地基的方案。在施工过程中,对高压旋喷注浆的工序进行合理打破常规的优化,既保证了既有铁路的运营安全,也保证了处理线路的质量,有效解决了本工程的难题。优化后的方案经过实践的检验,有进一步研究分析和推广的价值。     

基于离心模型试验的水泥土搅拌法加固斜坡软弱土地基变形特性分析

为充分掌握斜坡软弱土地基在路堤荷载作用下的变形特性,寻求合理的地基加固措施,以新建达成铁路扩能改建工程某工点为原型,设计了5组基于水泥土搅拌法地基处理方案的室内土工离心模型试验。通过对试验数据的整理分析,结果表明：（1）针对斜坡软弱土地基的上、下坡侧分别采取不同的桩间距布设,可减小斜坡软弱土地基沿横向的差异沉降变形,提高地基加固的均匀性;（2）在斜坡软弱土地基的下坡一侧布设斜桩,具有较好的水平变形约束效果,但在竖向沉降控制方面表现略差;（3）斜坡软弱土地基下坡一侧产生的变形将引起上坡一侧产生相同方向的变形,并以水平变形的表现较明显,地基加固应以控制下坡一侧的变形为重点;（4）地基水平变形沿深度的变化规律因地基布桩疏密的不同而表现出先增大后减小的单峰型曲线和单调衰减的双曲线型两种形态。     

Response of the soft coral Heteroxenia fuscescens to ultraviolet radiation regimes as reflected by mycosporine-like amino acid biosynthesis

The variation in mycosporine‐like amino acid (MAA) concentration in the soft coral Heteroxenia fuscescens in relation to changes in ultraviolet radiation (UVR) regimes was investigated at the Gulf of Eilat, northern Red Sea. Solar radiation (300–700 nm) was measured for different depths and seasons. The UVR irradiance was measured to a depth of 25 m on the reef. The mean attenuation coefficient for UV‐B measured in winter was twofold that of the summer value. Separation of H. fuscescens extracts by reverse‐phase isocratic high‐performance liquid chromatography revealed a single MAA compound, palythine (λ_max = 320 nm). Possible seasonal changes in MAAs in colonies of H. fuscescens along a depth gradient were examined on different dates. Palythine concentrations in the colonies were significantly higher in summer than in the other seasons particularly in shallow water. Possible changes in MAA content in colonies of H. fuscescens as a result of UVR protection, were determined by experiments conducted for periods of 1 week, 1 month and 3 months, at a depth of 5 m. In these experiments colonies were removed from the natural substrate and placed underwater, protected from UVR by a PVC filter. Significant differences between UV‐exposed and protected colonies of H. fuscescens were found only in the 3‐month experiment conducted during the summer. These findings demonstrate that UVR is an important environmental factor regulating MAA biosynthesis in the soft coral H. fuscescens.     

Numerical Analyses of Caisson Breakwaters on Soft Foundations Under Wave Cyclic Loading

A caisson breakwater is built on soft foundations after replacing the upper soft layer with sand. This paper presents a dynamic finite element method to investigate the strength degradation and associated pore pressure development of the intercalated soft layer under wave cyclic loading. By combining the undrained shear strength with the empirical formula of overconsolidation clay produced by unloading and the development model of pore pressure, the dynamic degradation law that describes the undrained shear strength as a function of cycle number and stress level is derived. Based on the proposed dynamic degradation law and M-C yield criterion, a dynamic finite element method is numerically implemented to predict changes in undrained shear strength of the intercalated soft layer by using the general-purpose FEM software ABAQUS, and the accuracy of the method is verified. The effects of cycle number and amplitude of the wave force on the degradation of the undrained shear strength of the intercalated soft layer and the associated excess pore pressure response are investigated by analyzing an overall distribution and three typical sections underneath the breakwater. By comparing the undrained shear strength distributions obtained by the static method and the quasi-static method with the undrained shear strength distributions obtained by the dynamic finite element method in the three typical sections, the superiority of the dynamic finite element method in predicting changes in undrained shear strength is demonstrated.     

Assessment of Compressibility Behavior of Naturally Cemented Soft Clays

It Naturally cemented soft clays have components of strength and stiffness, which cannot be accounted for by classical soil mechanics (Leroueil and Vaughan 1990). This stems from the influence of structure caused by cementation due to environmental factors. It is necessary to evaluate the cementation bond strength at preyield and postyield stress levels of loading, to understand comprehensively the observed response from micromechanic considerations. This helps to better understand and evolve approaches to model the constitutive behavior in a consistent manner, according to the physical phenomenon of formation of cementation as an additional component to what is otherwise normally regarded as frictional behavior arising only from particulate nature of clays. Comparing the behavior of deep deposits of Pusan soft clays under stress with corresponding response of the same clay in its remolded state, it has been possible to take into account particulate and nonparticulate responses. The evolution of cementation bonding is modeled for different Pusan clays with the yield stress in oedometer compression as a normalizing parameter for obtaining the generalized relationship of cementation bonding with increase in stress. The already established model for determining the remolded behavior is appropriately modified to assess the behavior influenced by cementation. The model proposed consists of parameters, which are determined in routine investigations.     

Behavior of a shallow plate anchor in clay under sustained loading

Laboratory model test results for the uplift of a shallow circular plate anchor embedded in a soft saturated clay are presented. For all tests the bottom of the anchor plate was vented to eliminate the mud suction force. The tests were divided into two categories: (1) short‐term tests to determine the variation of the net ultimate uplift capacity and hence the breakout factor with embedment ratio, and (2) creep tests with sustained uplift loads at varying embedment ratios. Based on the model test results, the variation with time, has been determined for the rate of strain of the soil located above the plate anchor. Empirical relationships for obtaining the rate of anchor uplift have been proposed.     

Evaluation of the Strength Increase of Marine Clay under Staged Embankment Loading: A Case Study

This article presents a case history of the performance of a full-scale test embankment constructed on a marine soft clay deposit improved by prefabricated vertical drains (PVDs) in the east of China. For analyzing the subsoil behavior, a 2D FEM model is established, in which the PVD-improved effect is considered by a simplified method of equivalent vertical hydraulic conductivity. The calculated results can predict the settlement behavior well; however, the FEM gives an underestimate for the value of excess pore pressures and it predicts similar values for the dissipation rate of excess pore pressures. The measured undrained shear strength of subsoil, C_u, is compared with the predicted value based on Ladd’s empirical equation and the Modified Cam-Clay model (MCC). The shear strength predicted by Ladd’s equation agrees well with the measured value, whereas the MCC overestimates the ability to improve subsoil shear strength during consolidation. The undrained shear strength of subsoil, C_u, increased as the construction progressed, and the shear strength incremental ratio, ΔC_u/Δp′, decreased slightly with the degree of consolidation, U.     

Rheological characteristics and one-dimensional isotache modelling of marine soft clays

Abstract

This paper presents a novel elasto-viscoplastic constitutive formulation based on the isotache concepts and the Nishihara model. Incorporating a novel viscoelastic body to include the delay elastic deformation of marine soft clays under the external load, the proposed model is used to evaluate the theories of consolidation-creep coupling, strain rate dependency and stress relaxation of saturated marine soft clays, and hence, the methodology used to determine the parameters of the model is discussed. Ningbo marine soft clay is selected as an example to interpret the determination of the model parameters on a field scale. A series of conventional oedometer tests are conducted as well. Eventually, we utilize the model to simulate several kinds of rheological tests, including one-dimensional (1-D) long-term compression tests on Ningbo marine soft clays, 1-D constant rate of strain (CRS) tests on Batiscan clays and 1-D stress relaxation tests on Hong Kong marine deposits. These findings indicate good agreement between the computational and experimental results, suggesting the given model can provide reliable forecasts for the rheological characteristics of marine soft clays.