渍水麦田土壤水分动态模型研究

根据土壤水分平衡原理,建立了一个反映土壤渍水、可与小麦生长模型耦合的土壤水分动态模型,尤其考虑了因地下水位较浅而引起的毛管上升水量和土壤导水率的变化对土壤含水量的影响。采用盆栽小麦水分试验资料验证了日蒸散量的模拟值,利用湖北荆州农业气象试验站和江苏金坛农业气象试验站的土壤水分历史资料对建立的模型进行了综合测试和验证,结果表明：蒸散量、地下水位和0～50 cm土壤含水量的模拟值与实测值具有较好的一致性,模型能可靠地预测多雨和渍水地区麦田土壤水分的变化动态     

基于SMAP卫星雷达资料的海冰密集度反演技术研究

SMAP是美国于2015年初发射的一颗卫星,搭载了L波段的雷达。它采用圆锥扫描方式,具有固定的入射角、较大的幅宽和千米级的分辨率,在海冰监测方面具有独特的优势。本文利用SMAP卫星雷达资料分别与德国Bremen大学海冰密集度产品和美国国家冰雪数据中心（NSIDC）海冰密集度产品建立3.125 km和25 km匹配数据集,分析了L波段雷达后向散射系数、极化比和归一化极化差与海冰密集度之间相关性,建立基于人工神经网络的海冰密集度反演算法。为了验证SMAP卫星雷达资料反演海冰密集度的精度,本文选择德国Bremen大学和美国冰雪数据中心发布的海冰密集度产品分别与SMAP海冰密集度产品进行对比分析,SMAP海冰密集度与Bremen海冰密集度的偏差为0.07、均方根误差为0.14;与NSIDC海冰密集度的偏差为0.04、均方根误差为0.18,这表明SMAP海冰密集度产品与现有业务化海冰密集度产品具有很好的一致性。     

Behavior of drag anchor in clay with linearly increasing shear strength under unidirectional and combined loading

Drag anchor is a widely used economical anchor option for offshore floating structures. The anchor behavior under unidirectional loading and combined loading is important for anchor selection. The anchor behavior under combined loading, characterized by the yield envelope, can also be used for the prediction of anchor installation, which is still an issue in anchor design. However, most existing studies on anchor capacity are for plate anchors which focused only on the anchor pullout capacity in soil with uniform shear strength. The behavior of drag anchor under unidirectional and combined loading in soil with linearly increasing shear strength profile is seldom investigated. The current 2D finite element studies investigate the anchor behavior for a horizontal anchor fluke in clay with linearly increasing shear strength under unidirectional vertical, horizontal and rotational loadings first. Then based on the results of anchor unidirectional loading behavior, the yield envelopes for anchor under combined loading for both shallow and deep embedded flukes are studied. The effect of anchor embedment depth, soil non- homogeneity, soil overburden pressure and the soil/anchor interface breakaway conditions are studied to provide insight for drag anchor design.     

全球冻融地区土壤是重要的N20释放源的综合分析

Ｎ２Ｏ是重要的温室气体之一，它是微生物硝化作用和脱氮化作用过程的产物。有多种释放源，其中土壤圈是重要的释放源之一。在影响Ｎ２Ｏ释放通量的诸多因素中温度是关键因素之一。本文根据土壤冻融加强有机质矿化作用，以及对微生物群体产生非生物应力的性质，结合冻融地区土壤和冻土带湿地所具有的特征，进行综合分析，论述冻融地区土壤是重要的Ｎ２Ｏ释放源。     

Analysis of resistance factors for LRFD of soil nail pullout limit state using default FHWA load and resistance models

Abstract

Resistance factors for load and resistance factor design (LRFD) of pullout limit state of both permanent and temporary soil nails are calibrated against a wide design space using the current Federal Highway Administration (FHWA) nail load and resistance models. The calculated resistance factors were shown to scatter broadly among design scenarios that differ in wall face batter, soil friction angle, nail ultimate bond strength, and surcharge live load. An important lesson learned from the analysis results is that the current practice of using a single resistance factor for LRFD of nail pullout limit state could not result in uniform reliabilities across different design scenarios. Simple artificial neural network (ANN) models were developed for computation of resistance factors. Design examples demonstrated the ability of the ANN models in providing resistance factors that yield satisfactory and consistent reliabilities in different nail pullout designs.     

A semi-analytical solution for random wave-induced soil response and seabed liquefaction in marine sediments

In this study, unlike most previous investigations for wave-induced soil response, a simple semi-analytical model for the random wave-induced soil response is established for an unsaturated seabed of finite thickness. Two different wave spectra, the B-M and JONSWAP spectra, are considered in the new model. The influence of random wave loading on the soil response is investigated by comparing with the corresponding representative regular wave results through a parametric study, which includes the effect of the degree of saturation, soil permeability, wave height, wave period and seabed thickness. The maximum liquefaction depth under the random waves is also examined. The difference on the soil response under the two random wave types, B-M and JONSWAP frequency spectra, is also discussed in the present work.     

Stability of waterfront retaining wall subjected to pseudo-static earthquake forces

Waterfront retaining walls supporting dry backfill are subjected to hydrostatic pressure on upstream face and earth pressure on the downstream face. Under seismic conditions, if such a wall retains a submerged backfill, additional hydrodynamic pressures are generated. This paper pertains to a study in which the effect of earthquakes along with the hydrodynamic pressure including inertial forces on such a retaining wall is observed. The hydrodynamic pressure is calculated using Westergaard's approach, while the earth pressure is calculated using Mononobe-Okabe's pseudo-static analysis. It is observed that when the horizontal seismic acceleration coefficient is increased from 0 to 0.2, there is a 57% decrease in the factor of safety of the retaining wall in sliding mode. For investigating the effect of different parameters, a parametric study is also done. It is observed that if φ is increased from 30° to 35°, there is an increase in the factor of safety in the sliding mode by 20.4%. Similar observations were made for other parameters as well. Comparison of results obtained from the present approach with [Ebeling, R.M., Morrison Jr, E.E., 1992. The seismic design of waterfront retaining structures. US Army Technical Report ITL-92-11. Washington DC] reveal that the factor of safety for static condition (k_h=0), calculated by both the approaches, is 1.60 while for an earthquake with k_h=0.2, they differ by 22.5% due to the consideration of wall inertia in the present study.     

膨胀土收缩开裂特性研究

在干燥环境中,由于蒸发失水,膨胀土发生收缩,表面容易产生纵横交错的裂隙网络(龟裂)。龟裂的产生会极大弱化土体的工程性质,并导致各种工程问题。随着极端干旱气候的频发,膨胀土龟裂问题将会越来越多,越来越显著。开展龟裂研究对揭示龟裂现象的本质规律和指导膨胀土地区的工程实践有重要意义。龟裂的形成和发展是一个动态的过程,与土中水分的蒸发速率、应力状态、收缩特性等直接相关:龟裂形成时水分蒸发处于常速率阶段; 吸力和抗拉强度是制约龟裂形成的两个关键力学参数,当土体中的吸力引起的张拉应力超过土体的抗拉强度时,龟裂便会产生; 龟裂是孔隙发生收缩的直观表现。总体上,力的作用和收缩空间是土体龟裂形成的两个必要条件。此外,膨胀土龟裂具有非常复杂的发生发展过程,受土质学、土力学、土结构、试验条件和方法等许多因素的影响。龟裂定量分析是龟裂研究的重要内容之一,能为龟裂机理研究及相关理论模型的建立提供必要参数。计算机图形处理技术具有效率高、操作性强、精度高等优点,为龟裂定量分析提供了强有力的工具。目前关于土体龟裂研究还存在许多不足之处,在今后的工作中,应该重视龟裂形成和发展过程的动态特征,围绕与土体龟裂相关的水-土作用关系、力学机制、收缩变形机制、大尺度现场试验和三维观测分析技术等方面开展更多的针对性研究,综合考虑龟裂形成过程中的土质学、土力学和土结构因素,结合宏观现象与微观分析,建立土体龟裂的理论体系。     

土壤天然热释光测量在寻找滑坡体边界中的应用研究

土壤天然热释光测量方法是一种累积型测氡方法。由于累积测氡时间长,其灵敏度和异常的重现性远比一般累积测氡及其子体方法好,因此,在地质领域得到了广泛的应用。在寻找滑坡体边界的应用中,取得的测量效果明显,表明该方法经济有效。     

土结构性本构模型研究现状综述

土本构模型的建立是一个重要而又复杂的问题,到目前为止,国内外学者们已提出数以百计的土本构模型,诸多文献也对这些模型进行了评述和归纳。然而这些土本构模型多是在扰动土或砂土的基础上发展和建立起来的,它们难以描述由于土结构性引起的各种非线性行为,其计算结果与实际情况相差甚远。天然土体一般都具有一定的结构性,所以有必要建立考虑土结构性影响的土本构模型。针对这个现实,目前有些学者已基于各种理论和方法,提出了一些可以考虑土结构性影响的土本构模型,并得了较好的应用。但在目前的文献中还很少有对土的结构性本构模型研究进行归纳,基于此,本文简要介绍了一下目前土的结构性本构模型研究现状,并提出了这些本构模型在应用中所存在的问题。