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781.
Balaena Bay, Wellington Harbour, New Zealand, has a small pocket beach that was covered originally by pebbles and cobbles. In February and October 1982, the beach was nourished with sandy granular gravel, the stability of which was monitored until February 1984. Although isolated from oceanic swell, the new beach readily responded to locally generated wind waves which induced both northwards and southwards longshore drift. The net effect was erosion of the southern beach, aggradation over the central beach, and minor fluctuations at the northern end. Yet despite this mobility nearly all the nourishment sediment was retained in the littoral zone. Beach volumes, calculated for each survey, varied little and sediment distribution patterns revealed negligable transport of nourishment sediment to adjacent beaches and offshore areas. Stability is further confirmed by compositional data which record no preferential loss of the sandstone, argillite, and quartz components. The only compositional changes were the incorporation into the new beach of small (< 10%) quantities of sediment derived from the old beach surface and from biogenic productivity. 相似文献
782.
K. Nagendra Prasad S. Triveni T. Schanz Late T. S. Nagaraj 《Marine Georesources & Geotechnology》2013,31(3-4):181-197
Despite the sophisticated methods employed to obtain high quality samples, they are prone to disturbance, due to stress release, let apart, due to sampling tools and techniques adopted. Critical reappraisal of different methods suggest that any method of sample quality assessment involving strength and deformation parameters would enable easier implementation and correct other engineering parameters for estimated sample disturbance. In this technical paper, sample disturbance index, using merely the slopes of compression paths, (representing mechanical response), in the pre- and post-yield stress regimes under odeometric loading conditions is proposed. This method is based on single oedometer test results on samples of unknown degrees of disturbance during sampling and handling. The unique feature of this approach is that the ideal rigid plastic material behavior is taken as reference. This eliminates the need for any additional experimental data or any calculations from the relationships formulated with any set of assumptions. 相似文献
783.
Abstract This paper describes the results of laboratory tests carried out on model pile shafts in a variety of reconstituted calcareous sands and on silica sand. The factors influencing both the skin friction under static loading and the degradation of skin friction under cyclic loading have been investigated. The grading and crushability of the particles appears to have a significant influence on both, with less favourable performance being found for uniformly graded crushable particles. Relative density and overconsolidation ratio also have some influence. Under cyclic loading, the amplitude of cyclic displacement and, more specifically, the cyclic slip displacement, influence the extent of cyclic degradation of skin friction. 相似文献
784.
AbstractSurcharge preloading consolidation of soft soils often implements a layer of fully arranged aggregate materials. The volume of drained water is abundant at the early stage of consolidation, but it reduces at middle and later stages, during which the fully arranged sand blanket will be a waste. In this investigation, a concept of distributed sand blankets is proposed to save aggregate materials. A series of finite element analyses have been performed on layered soils with distributed sand blankets. A mixed type of drainage boundary is assigned to a representative model, where a half sand blanket is perfectly pervious and a half width of soil among sand blankets is impervious. From parametric study, it has been found that a pave ratio between sand blankets and the total soil width can be selected in a range of 40%–60%, which will save aggregates by approximately 50% but cause an increase of consolidation time by less than 10%. For a fixed pave ratio, more evenly spaced sand strips with smaller width should be employed to optimize the design. The effectiveness of distributed sand blankets is not influenced by the anisotropy of hydraulic conductivity, elastic modulus, Poisson’s ratio, and thickness in multiple soil layers. 相似文献
785.
This paper presents the development of a new remediation technology for contaminated sandy soil using humic acid (HA). Distribution of amount of Cr (VI) in the aqueous or solid system containing humic acid and sandy soil, was studied using batch experiments, es-pecially for effects of reaction time, pH, concentrations, temperature and irradiation on the reduction of Cr (VI), and the optimum reaction conditions. The results indicated a significant increase of the adsorption of Cr (VI) because of the complexion reaction between HA and Cr (VI) that occurred under acidic condition. The reaction mechanisms of HA with chromium on sand surfaces were certified. Thus it came to a conclusion that HA could be used effectively on remediation of Cr (VI)-contaminated soil and groundwater in a wide range of pH, with or without sunlight. These results suggest that the organic-inorganic complex-such as sandy soils coated with humic substances-is important as a metal reservoir in the environment. 相似文献
786.
土结构性是决定土力学特性的一个最为根本的内在因素。基于综合结构势理论的土结构性参数研究是土结构性研究的一种行之有效的方法, 它不仅考虑了土颗粒排列的几何特征和土颗粒联结的力学特征,而且对土结构性进行了综合的、整体的、动态的量化。对已提出的结构性参数进行全面的总结和评述,统一了结构性参数的命名。在此基础上,总结了结构性参数与强度和变形的关系、结构性参数本构模型和结构性参数应用方面的研究现状,并进一步分析了土结构性描述的合理途径以及结构性与固结状态对强度和变形的影响,提出了同一结构性条件下研究结构性土强度、变形本构规律的新观点。 相似文献
787.
788.
789.
The grain‐scale morphology of fluvial sediments is an important control on the character and dynamics of river systems; however current understanding of its role is limited by the difficulties of robustly quantifying field surface morphology. Terrestrial Laser Scanning (TLS) offers a new methodology for the rapid acquisition of high‐resolution and high‐precision surface elevation data from in situ sediments. To date, most environmental and fluvial applications of TLS have focused on large‐scale systems, capturing macroscale morphologies. Application of this new technology at scales necessary to characterize the complexity of grain‐scale fluvial sediments therefore requires a robust assessment of the quality and sources of errors in close‐range TLS data. This paper describes both laboratory and field experiments designed to evaluate close‐range TLS for sedimentological applications and to develop protocols for data acquisition. In the former, controlled experiments comprising high‐resolution scans of white, grey and black planes and a sphere were used to quantify the magnitude and source of three‐dimensional (3D) point errors resulting from a combination of surface geometry, reflectivity effects and inherent instrument precision. Subsequently, a methodology for the collection and processing of grain‐scale TLS data is described through an application to a coarse grained gravel system, the River Feshie (D50 32 to 63 mm). This stepwise strategy incorporates averaging repeat scans and filtering scan artefact and non‐surface points using local 3D search algorithms. The sensitivity of the results to the filter parameter values are assessed by careful internal validation of Digital Terrain Models (DTMs) created from the resulting point cloud data. The transferability of this methodology is assessed through application to a second river, Bury Green Brook, dominated by finer gravel (D50 18 to 33 mm). The factor limiting the resolution of DTMs created from this second dataset was found to be the relative sizes of the laser footprint and smallest grains. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
790.
呼伦贝尔沙质草原风蚀坑形态发育模式分析 总被引:4,自引:3,他引:1
野外调查测量呼伦贝尔沙质草原风蚀坑分布和形态参数,根据不同发展阶段的风蚀坑形态特征的差异、形态参数间相关关系和拟合结果分析了风蚀坑的形态演变和发育、成因、规律。发现不同发展阶段风蚀坑形态参数之间的控制关系和扩展模式不同,各形态参数之间具有较好的幂函数关系。对于风蚀坑的侵蚀坑而言,坑长增长速度最快,其后依次是坑宽和坑深,坑后积沙体具有类似规律。风蚀坑坑后积沙的3个形态参数,受侵蚀坑3个参数的联合控制,但受坑深的控制最为显著。风蚀坑出现的起始形态、地形特征、植被、气流场、气候条件、人类活动的扰动等对其形态和发育具有重要影响,并且形态和发育反作用于植被、气流等,形成形态与气流、植被之间的响应与反馈。 相似文献