Consolidation of double‐layered ground with vertical drains

Vertical drains are usually installed in subsoil consisting of several layers. Due to the complex nature of the problem, over the past decades, the consolidation properties of multi‐layered ground with vertical drains have been analysed mainly by numerical methods. An analytical solution for consolidation of double‐layered ground with vertical drains under quasi‐equal strain condition is presented in this paper. The main steps for the computation procedure are listed. The convergence of the series solution is discussed. The comparisons between the results obtained by the present analytical method and the existing numerical solutions are described by figures. The orthogonal relation for the system of double‐layered ground with vertical drains is proven. Finally, some consolidation properties of double‐layered ground with vertical drains are analysed. Copyright © 2001 John Wiley & Sons, Ltd.     

Carbonate aeolianites of western Saurashtra,India: experimental decipherment of the depositional mechanisms

Granular carbonate deposits of Late Pleistocene to Early Holocene age, commonly referred to as ‘miliolite limestone’, occur in a linear belt, parallel to the southern coast of Saurashtra, India. In the present study area these carbonate deposits are found in select valleys between ridges and mounds of pyroclastic material present in the Deccan trap plateau. Two different depositional histories have been proposed for these sediments. The presence of marine bioclasts led to the postulation of a marine origin for these deposits. The second school of thought propounded redeposition of the coastal sediments by aeolian processes. Although a few features could not be explained by the proposed aeolian model, critical comparison of these two views favoured the aeolian origin. The mode of occurrence, lithological and structural attributes, and microscopic evidence presented here, also support a possible aeolian origin for these deposits. Experimental observation indicates that these carbonate aeolianites represent backflow deposits, which accumulated because of the flow separation caused by the presence of topographic highs. The conspicuous concave‐up geometry of the deposit conformed to the shape of the separation bulb. In view of the inferred depositional mechanism, the disposition of the deposits and the signature of the palaeoflow direction suggest that the carbonate particles were derived from the north‐western coast of Saurashtra by strong south‐easterly winds. Massive granular carbonates with outsized basement clasts appear to be the product of avalanching of granular material from the higher contours because of oversteepening of the primary deposit.     

Tidal and seasonal controls in the formation of Late Miocene inclined heterolithic stratification deposits, western Amazonian foreland basin

Upper Miocene strata in the Acre sub‐basin, Brazil, consist dominantly of various types of inclined heterolithic stratification and pedogenic horizons. These strata were sedimentologically and ichnologically described to: (i) study different temporal controls responsible for inclined heterolithic stratification generation and their variation in a distal–proximal trend; and (ii) delineate the depositional setting. For this purpose, nine representative outcrops were sedimentologically and ichnologically studied, and their facies associations described. Thickness variations of the heterolithic strata of various orders (lamina, lamina bundles and beds) were analysed by statistical methods (Fourier transform). The deposits were interpreted as tidally and seasonally influenced estuarine or delta‐related and continental strata. The inclined heterolithic stratification deposits represented vastly different settings ranging from tidally dominated, brackish‐water ichnofossils‐bearing channels to seasonally controlled, articulated Purussaurus (a freshwater alligator) fossil‐bearing channels. Several time cycles were distinguished in the strata, including semi‐diurnal, fortnightly and seasonal. Tidal imprint was best observed in low‐energy brackish‐water settings, whereas seasonal rhythmicity was distinguishable throughout the depositional system. However, the latter was most apparent in riverine channels proximal to the inferred fluvio‐tidal transition. The different temporal controls commonly had distinguishable impact on sedimentological and ichnological properties in the studied sediments. The differing properties included: (i) the degree and nature of lateral variability with respect to lithology and bedforms in inclined heterolithic stratification; (ii) the lateral continuity of inclined heterolithic stratification; (iii) the nature of sedimentary contacts between the inclined heterolithic stratification members; (iv) thickness variation of inclined heterolithic stratification members within a set; (v) the cyclicities observed in inclined heterolithic stratification series; (vi) the degree of bioturbation; (vii) the types of trace fossils observed; and (viii) the distribution of bioturbation in adjacent inclined heterolithic stratification members.     

On the structural evolution of the Central Trough in the Norwegian and Danish sectors of the North Sea

The Central Trough of the North Sea is not a simple rift graben. It is an elongated area of regional subsidence which was initiated in mid Cretaceous times and continued to subside through to the late Tertiary. Its form is not representative of pre-mid Cretaceous tectonics.In Late Permian times the North Sea was divided into a northern and southern Zechstein basin by the E-W trending Mid North Sea-Ringkøbing-Fyn High. The latter was dissected by a narrow graben trending NNW through the Tail End Graben and the Søgne Basin. The Feda Graben was a minor basin on the northern flank of the Mid North Sea High at this time. This structural configuration persisted until end Middle Jurassic times when a new WNW trend separated the Tail End Graben from the Søgne Basin. Right lateral wrench movement on this new trend caused excessive subsudence in the Tail End and Feda Grabens while the Søgne Basin became inactive.Upper Jurassic subsidence trends continued during the Early Cretaceous causing the deposition of large thicknesses of sediments in local areas along the trend. From mid Cretaceous times the regional subsidence of the Central Trough was dominant but significant structural inversions occurred in those areas of maximum Early Cretaceous and Late Jurassic subsidence.     

长江口及济州岛邻近海域温、盐、密度的跃层现象

本文根据CTD观测资料,分析了研究海区的温、盐、密度跃层的分布与变化,讨论了逆温逆盐层的分布区域,并从跃层角度出发,分析了深层水的涌升,黄海冷水团的上边界以及台湾暖流在东海北部的影响范围。     

Geoacoustic Inversion via Genetic Algorithm and Its Application to Manganese Sediment Identification

An acoustic inversion method using a wide-band signal and two near field receivers is proposed and applied to multiple layered seabed models including a manganese sediment. The inversion problem can be formulated into a probabilistic model comprised of signals, a forward model, and additive noise. The forward model simulates wide-band signals, such as chirp signals, and is chosen to be the source-waveletconvolution plane wave modeling method. The wavelet matching technique, using weighted least-squares fitting, estimates the sediment sound-speed and thickness on which determination of the possible numerical ranges for a priori uniform distribution is based. The genetic algorithm is applied to a global optimization problem to find a maximum a posteriori solution for determined a priori search space. Here the object function is defined by an L 2 norm of the difference between measured and modeled signals. Not only the marginal pdf but also its statistics are calculated by numerical evaluation of integrals using the samples selected during importance sampling process of the genetic algorithm.     

Cycladophora davisiana (Radiolaria) in the Okhotsk Sea: A key for reconstructing glacial ocean conditions

Cycladophora davisiana, a radiolarian species dwelling at mesopelagic depths, is known as a representative glacial fauna due to its unique distribution during glacial periods. In the present ocean, abundant production of C. davisiana is only observed in the Okhotsk Sea, indicating an adaptation of C. davisiana for seasonal sea-ice covered conditions. We found pronounced abundant production of C. davisiana during the early to middle Holocene in the Okhotsk Sea, suggesting more favorable conditions for C. davisiana than the present Okhotsk Sea. In order to clarify the reason, oceanographic conditions during the Holocene were reconstructed based on biomarkers, lithogenic grains including ice-rafted debris (IRD), biogenic opal, and total organic carbon (TOC) in two sediment cores from the Okhotsk Sea. These indicators suggest that the pronounced C. davisiana production may be attributed to: 1) a supply to mesopelagic depths under intensified stratification of fine organic particles derived from coccolithophorids, bacteria, and detrital materials; and 2) cold, well-ventilated intermediate water formation.     

悬对沙Mellor-Yamada海洋边界层模型计算结果的影响

为了分析海洋水体垂向水流紊动及紊动交换情况而采用了一维的海洋边界层模型(Mellor-Yamada)并利用数值实验的方法对悬沙、盐度、温度等数据进行分析。原模型未将悬沙考虑在内，本文试将它引入进去探讨由于它的存在对紊动混合特性的影响。2000年4月，Mellor将最初的模型引入了依赖于Richardson数的紊动动能耗散率。本文通过比较具有悬沙和不具有悬沙两种情况下的速度、温度和盐度垂向分布随时间的变化，分析讨论由于悬沙的存在所引发的密度层化对紊动混合作用的影响，并发现悬浮泥沙抑制了部分模拟时间的紊动混合作用。     

渤黄东海混合层化演变规律的研究进展

较详细地综述了渤黄东海混合层化演变过程与规律的研究进展情况，主要包括：混合和层化过程的分布规律与季节变化特性，采用水温垂直剖面自相关函数的半经验预报模式，动力学和热力学的数值预报模式。     

近海海面上水汽向上输送的季节性差异

本文分析了雷达观测结果，发现近海海面上的水汽向上输送随季节而变化，由于季节的变化和不同的天气情况，海表面大气现象在雷达中有不同的显示，根据这些显示得到了不同的信息，由此而得出春秋两季海表面水汽向上输送量的不同。