大兴安岭中部乌兰浩特地区林西组碎屑岩锆石U-Pb年龄、地球化学特征及其构造意义

内蒙古乌兰浩特地区出露一套缺少化石、遭受接触变质作用的厚层碎屑岩。在该套地层采集碎屑锆石样品,进行碎屑锆石U-Pb测年研究。80个锆石分析点的年龄可分为3个主要年龄区间:242～294Ma,年龄加权平均值为263.6±3.3Ma(n=50,MSWD=4.9),峰值年龄为261Ma;301～381Ma,峰值年龄为348Ma;454～530Ma,峰值年龄为487Ma。另有7个锆石分析点的年龄分别为824Ma、836Ma、859Ma、867Ma、1279Ma、1556Ma、2447Ma。261Ma的峰值年龄限定了该地层的沉积下限,即属晚二叠世林西组。主量元素SiO2含量为67.81%,Al_2O_3为18.22%,MgO为1.44%,CaO为0.41%,Na_2O为1.54%,K_2O为3.90%,K_2O/Na_2O为1.15～10.21;A_(12)O_3/(CaO+Na_2O)为4.87～26.38;稀土元素总量介于162.39×10-6～223.46×10-6之间,平均值为200.88×10-6,负Eu异常,Ce为1.00～1.05,轻稀土元素富集,重稀土元素亏损,微量元素以亏损Nb、Ta、Sr,富集Rb、Ba、La、Ce、Pb、Nd、Sm为特征。以上分析表明,林西组形成于活动大陆边缘构造背景。依据碎屑锆石年龄谱值信息,林西组沉积物源具多样性和复杂性,除东北各地块,同时存在华北板块和西伯利亚板块的物源信息,说明林西组沉积时期华北板块与西伯利亚板块可能已经开始俯冲碰撞过程。     

Simulation of long-term thermo-mechanical response of clay using an advanced constitutive model

Acta Geotechnica - There is extensive data to show that heating and cooling produces irrecoverable deformations in clays under fully drained conditions. The effects are most pronounced for normally...     

Fracture grouting and geonails for soft soil tunnelling

To stabilise the tunnel faces and slopes in soft clay for the Airport Link construction in Australia, fracture grouting and glass fibre-reinforced plastic (GFRP) soil nails are proposed for the soil improvement as well as ease of handling. The compensation caused by the fracture grouting and the gain in strength due to consolidation as well as the geonail have stabilised the soft clay during construction. Only a small amount of ground settlement during soft clay box-jacking operation is generated so that the railway traffic above the embankment can be maintained without interference. The design method of the fracture grouting ground improvement study for this difficult project is discussed in this paper. Extensive laboratory and field tests were employed to verify the design assumptions and to fine-tune the ground improvement studies. The success of this project in poor ground conditions results from combined efforts of extensive field tests, an improved ground improvement design method and a realistic numerical analysis to assess the unstable/highly stressed zones for the placement of soil reinforcement.     

Microbially induced calcite precipitation along a circular flow channel under a constant flow condition

Biogrouting is a new ground improvement method that has been studied in recent years. This method involves mainly the use of a microbially induced calcite precipitation process to bind soil particles to increase the strength or to fill in the pores of soil or joints of rock for seepage control. There are two major challenges in the use of biogrout for seepage control through rock joints. The first is how to inject the biogrout solutions, and the second is to understand the mechanisms for the formation of calcite under seepage flow. In this paper, a study on the injection of biogrout solution and the formation of precipitates along a circular 1D flow channel is presented. To minimize the influence of flow, a new one-phase injection method to inject bacterial solution and cementation agents simultaneously was adopted in this study. Factors affecting the formation and distribution of precipitates along the flow channel such as flow velocity, flow rate, and aperture of flow channel were investigated. The experimental results indicated that less calcite was precipitated at locations further away from the injection point due to depletion of the reactants’ concentrations along the flow path. Using the one-phase injection method, the bacterial activity had a major effect on the accumulation of the calcite on the inner surface of the flow channel. The total calcite precipitated on the surface of the flow channel increased slightly with increasing bacterial activity or flow rate. An equation to predict the distance travelled by the biosolution has been derived based on the testing results.

     

史灌河流域水量平衡研究

建立了一个水量平衡模型,并用1998、1999年淮河流域能量和水循环试验(HUBEX)期间获得的史灌河流域(HUBEX水文试验区)加密观测资料来率定模型中的参数.结论表明:(1)水量平衡的要素计算合理;(2)梅山、鲇鱼山、蒋集土壤含水量的平均值系列基本上反映了流域蓄水量的变化过程;(3)流域蓄水量的衰减系数、蒸发能力的折算系数比较稳定,不应通过调整这些系数来实现水量平衡.     

闽江河口地区河道演变及其影响因素分析

比之传统的调查方法,利用遥惑技术进行岸线解译具有范围大、多时段、省时、省力以及快速等优点。根据多时相TM遥惑数据,对闽江河口地区岸线进行解译,结合20世纪60年代地形图和2001年海图,分析了河口地区河道演变情况．对河流岸线和浅滩变化进行对比分析,发现闽江口南部水道多呈淤积状态,北边水道则为弱侵蚀型岸线;南部水下浅滩有新发育,原有的浅滩面积有很大的扩展,北边水道变化较小;文章最后对河道演变的影响因素进行了初步的探讨。     

Wave Slamming on An OWSC Wave Energy Converter in Coupled Wave-Current Conditions with Variable-Depth Seabed

China Ocean Engineering - Coastal wave energy resources have enormous exploitation potential due to shorter weather window, closer installation distance and lower maintenance cost. However, impact...     

1917号台风“塔巴”对浙江沿海风场的影响及其成因分析

通过分析浙江省区域自动站加密资料、常规观测资料、NCEP/NCAR 1°×1°和0.25°×0.25°再分析资料以及卫星TBB (Black Body Temperature)资料,研究2019年第17号台风"塔巴"影响期间,浙江沿海风场分布的特点及其成因,以寻找台风影响时浙江沿海风场预报的着眼点。此次台风大风具有影响时间早、持续时间长、影响范围大和大风强度强的特点。台风环流与浙江沿海地面弱冷空气之间形成一定气压梯度的堆积,以及后续随着台风环流的发展加强,两者之间气压梯度进一步增大,是导致此次台风大风提早出现的原因之一。垂直环流有利于水平的动量输送和高层动量下传,导致此次台风大风范围大、强度强。冷空气在这次台风大风中起到非常重要的作用。随着台风外围环流与冷空气距离拉近,部分干冷空气侵入台风环流,冷、暖气团之间θse等值线密集,环流附近风速增强。由于干冷空气的继续侵入,冷、暖空气相互作用累积并释放斜压能。同时台风低层的暖心结构被冷空气占据,高层暖心结构上抬,形成上暖下冷的中心结构,导致台风开始变性减弱。地形的辐合、阻挡和摩擦作用对风场的再分布也有一定影响。     

A hybrid integrated deep learning model for the prediction of citywide spatio-temporal flow volumes

ABSTRACT

The spatio-temporal residual network (ST-ResNet) leverages the power of deep learning (DL) for predicting the volume of citywide spatio-temporal flows. However, this model, neglects the dynamic dependency of the input flows in the temporal dimension, which affects what spatio-temporal features may be captured in the result. This study introduces a long short-term memory (LSTM) neural network into the ST-ResNet to form a hybrid integrated-DL model to predict the volumes of citywide spatio-temporal flows (called HIDLST). The new model can dynamically learn the temporal dependency among flows via the feedback connection in the LSTM to improve accurate captures of spatio-temporal features in the flows. We test the HIDLST model by predicting the volumes of citywide taxi flows in Beijing, China. We tune the hyperparameters of the HIDLST model to optimize the prediction accuracy. A comparative study shows that the proposed model consistently outperforms ST-ResNet and several other typical DL-based models on prediction accuracy. Furthermore, we discuss the distribution of prediction errors and the contributions of the different spatio-temporal patterns.     

Dynamic responses of unsaturated half‐space soil to a moving harmonic rectangular load

The problem of the dynamic responses of a semi‐infinite unsaturated poroelastic medium subjected to a moving rectangular load is investigated analytical/numerically. The dynamic governing equations are obtained with consideration of the compressibility of solid grain and pore fluid, inertial coupling, and viscous drag as well as capillary pressure in the unsaturated soil, and they can be easily degraded to the complete Biot's theory. Using the Fourier transform, the general solution for the equations is derived in the transformed domain, and then a corresponding boundary value problem is formulated. By introducing fast Fourier transform algorithm, the unsaturated soil vertical displacements, effective stresses, and pore pressures induced by moving load are computed, and some of the calculated results are compared with those for the degenerated solution of saturated soils and confirmed. The influences of the saturation, the load speed, and excitation frequency on the response of the unsaturated half‐space soil are investigated. The numerical results reveal that the effects of these parameters on the dynamic response of the unsaturated soil are significant.