Mechanical properties of calcareous silts in a hydraulic fill island-reef

Abstract

The mechanical characteristics of calcareous silt interlayers play an important role in the stability of island-reef foundations. Direct shear and consolidation tests were performed to study the relationship between the mechanical properties and the physical parameters of calcareous silt. Based on the consolidation test results and analysis of the settling examples, different calculation methods for soil settling were compared. The results show the following. (1) The relationship between the cohesion and water content of calcareous silt can be represented by an M-shaped curve. The water contents corresponding to the two peaks of the M-type curve increase with increasing dry density. (2) When the dry density is less than 1.33?g/cm³, increasing the density significantly improves the internal friction angle of calcareous silts. When the dry density of the calcareous silt is greater than 1.33?g/cm³, the internal friction angle is affected by both the dry density and the water content. (3) The shear strength decreases when the water content exceeds the optimum level. (4) The compressive modulus of calcareous silt is larger than that of terrigenous silt. Specifically, it decreases with decreasing dry density and increasing water content. (5) The stepwise loading method should be used to estimate the soil settling before fill engineering construction.     

南海东部次海盆地震背景噪声分析

背景噪声的强弱是影响地震台站观测的一个重要因素。获取背景噪声的分布特征对评估海底地震仪记录数据质量及对数据的降噪处理均具有重要的指示意义。利用概率密度函数方法获取台站数据的功率谱密度的概率分布特征并与全球背景噪声高值模型和低值模型进行对比是研究台站周围环境背景噪声水平的有利手段。本研究基于南海大规模的被动源海底地震仪台阵长期观测实验的部分数据,利用概率密度函数方法研究了南海的背景噪声。首先,在全频段上对背景噪声进行了分析,并与其他台站做了对比,发现海洋的背景噪声在微震段和低频段大于高值模型且在全频带上远大于陆基台站的背景噪声,这表明海底地震仪数据质量并不高;其次,对观测过程中出现的地震事件以及其他典型信号的概率密度分布进行了归纳总结,发现远震事件、近震事件和数据丢失现象分别具有不同的优势频段和特征,这对后续滤波处理和质量检查具有重要指示意义;最后,研究了背景噪声的时间变化特征,发现台风是导致微震段时间变化的主要原因。     

西太平洋海面风场数据集的建立及其应用

再分析风场数据至今已发展了约30年,目前人们使用区域乃至全球网格化再分析数据集愈加频繁,但风场再分析数据在强天气过程中的强度明显不足,将风场再分析数据同台风观测数据相融合是解决问题的重要途径,本文通过"构建经验台风圆形风场-叠加台风移行风场-流入角修正-叠加背景再分析风场"的基本思路,融合了西太平洋联合警报中心的所有台...     

空间数据挖掘在海域天然气水合物资源评价中的应用

海域天然气水合物早期勘探阶段多使用地震调查方法,利用BSR和速度异常等指标圈定水合物矿体进行资源评价、优选预测勘探目标。阐明了空间数据挖掘技术在天然气水合物早期勘探评价阶段的应用,并通过珠江口盆地东部海域多道地震速度分析中所获速度异常信息,应用核密度估计方法,定量地划分了2个天然气水合物有利分布区(面积分别为18 km2和70 km2),进而为后期天然气水合物试采生产提供了重要依据及基础数据。     

培育密度和投饵量对长牡蛎壳黑选育品系幼虫生长存活及附着变态的影响

为探究长牡蛎(Crassostrea gigas)壳黑选育品系规模化繁育适宜的培育密度和投饵量,本研究以长牡蛎野生群体幼虫为对照组,分析了不同培育密度(3、7和15个/mL)和不同初始投饵量(0.4、0.8和1.6×10~3cells·ind^-1·d^-1)对长牡蛎壳黑选育品系幼虫生长、存活及附着的影响。研究显示,培育密度和投饵量对长牡蛎幼虫的生长速率、存活率和附着率有显著交互作用(P<0.05)。在培育密度3和7个/mL实验组,长牡蛎幼虫生长速率随投饵量增加而显著增大(P<0.05),并在培育密度7个/mL、投饵量1.6×10~3cells·ind^-1·d^-1实验组达到最大值。而在培育密度15个/mL实验组,投饵量增加对长牡蛎幼虫的生长速率无显著影响(P> 0.05)。且在培育密度15个/mL、投饵量1.6×10~3cells·ind^-1·d^-1实验组长牡蛎壳黑品系幼虫存活率和附着率最低。但在培育密度15个/mL实验组长牡蛎壳黑选育品系幼虫的壳高始终高于野生群体幼虫。且除投饵量0.4×10~3cells·ind^-1·d^-1实验组外,长牡蛎壳黑选育品系幼虫生长速率、存活率和附着率均高于野生群体幼虫。研究结果表明,长牡蛎壳黑选育品系幼虫最适培育条件为培育密度7个/mL、投饵量1.6×10~3cells·ind^-1·d^-1,增加投饵量可促进长牡蛎幼虫生长,但过高的培育密度会与投饵量产生拮抗作用,抑制幼虫生长,不利于幼虫存活和附着。与长牡蛎野生群体相比,壳黑选育品系幼虫能适应更高的培育密度环境,在饵料充足的条件下,其幼虫的生长、存活及附着性状均优于野生群体。     

Effects of stocking density on the growth and immunity of Atlantic salmon salmo salar reared in recirculating aquaculture system(RAS)

Atlantic salmon reared in recirculating aquaculture system(RAS) may lead to inappropriately high stocking density, because ?sh live in a limited space. Finding the suitable stocking density of Atlantic salmon reared in RAS is very important for RAS industry. In this paper, the in?uence of stocking density on growth and some stress related physiological factors were investigated to evaluate the ef fects of stocking density. The ?sh were reared for 220 days at ?ve densities(A: 24 kg/m^3; B: 21 kg/m^3; C: 15 kg/m^3; D: 9 kg/m^3 and E: 6 kg/m^3). The results show that 30 kg/m^3 might be the maximum density which RAS can af ford in China. The stocking densities under 30 kg/m^3 have no ef fect on mortality of Atlantic salmon reared in RAS. However, the speci?c growth rate(SGR), ?nal weight and weight gain in the high density group were signi?cantly lower than the lower density groups and middle density groups. Moreover, feed conversion rate(FCR) had a negative correlation with density. Plasma hormone T_3 and GH showed signi?cant decrease with the increase of the stocking density of the experiment. Furthermore, thyroid hormone(T 3), GH(growth hormone) activities were decreased with stocking density increase. However, plasma cortisol, GOT(glutamic oxalacetic transaminase) and GPT(glutamic pyruvic transaminase) activities were increase with stocking density increase. And the stocking density has no ef fects on plasma lysozyme of Atlantic salmon reared in RAS. These investigations would also help devise effcient ways to rear adult Atlantic salmon in China and may, in a way, help spread salmon mariculture in China.     

渤海盐度年代际变异对环流结构的影响

收集并利用1950年代~1990年代后共5个年代的渤海盐度统计资料,诊断计算了不同时期的渤海密度流分布及其变化。通过对比分析,揭示了冬、夏两季渤海盐度的年代际变异特征及其对环流结构的影响。结果显示,自1980年代以来,渤海的盐度格局发生了显著的变化,盐度的水平梯度减小,渤海内部盐度由明显低于海峡区向普遍高于海峡区转变。渤海密度流在冬季较弱,对总环流的贡献较小,而在夏季较强,并在总环流中占优。夏季,渤海密度流随盐度变异有所改变,在1990年代后环流系统在海区中部、渤海湾以及莱州湾呈现出局部的差异,原有流动明显减弱。夏季渤海重要断面的密度流流量和盐通量值整体上呈减小趋势,渤海与外海间的平均水及盐交换量由1950年代的7.85×104 m3/s、2.49×106kg/s降至1990年代后的7.09×104 m3/s、2.27×106 kg/s。     

Distribution of eddy scales for wave current combined flow

This paper illustrates the modulation of the eddy scale distribution due to superimposition of surface wave on only current flow. Time series data of three-dimensional velocity components were measured in a laboratory flume by a three-dimensional (3D) 16-MHz micro-acoustic Doppler velocimeter (Micro-ADV). The velocity time series of only current case and waves following the current were analysed to obtain the phase-averaged mean velocities, turbulent intensities, and Reynolds stress. The probability density function of phase-averaged stream-wise and vertical velocity fluctuations showed bimodal oscillations towards the free surface for higher frequency surface waves. It was revealed that surface waves along the current effectively decrease the intermittency of turbulence of the only current flow. Surface wave changed the intermittent structure of only current flow by modulation of the energy cascade mechanism of the only current flow by introduction of wave induced length scales. Also the scale of the finer dissipative eddies were prominently enhanced by the increase in surface wave frequency. Wavelet analysis of time series of velocity signals provided information on the eddy scale and their frequency of occurrence. It was found that the large eddies are carried by the crest regions of the progressive wave while the small scale eddies are carried by the trough regions.     

A numerical study on the role of wind forcing,bottom topography,and nonhydrostacy in coastal upwelling

The responses of coastal upwelling to different magnitudes of wind stress over a narrow and a wide shelf are studied using a 3-D primitive equation numerical model. The results show that the position of the upwelling front depends on both the strength and the duration of the wind forcing. The comparison between different shelf widths shows that wide shelf will limit the cold water intrusion, so that the corresponding decrease in sea surface temperature is less compared to narrow shelves. Besides, the difference between hydrostatic and nonhydrostatic model results shows that nonhydrostatic effects will enhance the growth of surface meandering, and can be more pronounced near steep fronts. Although difference does exist, our results show that the nonhydrostatic effects are very small at least in this idealized study case.