ANALYTICAL SOLUTION OF THERMAL CONSOLIDATION OF SATURATED SOILS WITH TWO PARALLEL CYLINDRICAL HEAT SOURCES1）

基于应力平衡条件、渗流连续方程、能量守恒方程,考虑土颗粒和孔隙水热膨胀系数的不同,建立考虑热水力耦合的饱和土体三维热固结控制方程。利用傅里叶变换和拉普拉斯变换导出变换域上的控制方程,解得点热源在变换域和实数域上的解析解,再利用区域积分给出两平行圆柱形热源热固结土体温度、孔压、位移的解析解,并对其进行分析,发现径距比增大会导致两热源温度相互影响程度减弱,热固结系数减小会导致孔压和位移的峰值增大。     

一种考虑液相惯性的一维准静力固结模型

经典Terzaghi一维固结理论不考虑孔隙流体惯性影响,且该理论在不同时期模型推导和表述结果差别较大,导致当前仍存在诸多困惑甚至认识混乱的现象. 在笔者前期研究大变形动力固结理论框架内,忽略固相惯性而重点考虑液相惯性影响,经过合理简化建立反映孔隙流体惯性的一维小变形固结波动模型. 该固结波模型具有频散和耗散特性. 采用分离变量法,可得到单面排水和瞬时加载条件下无量纲形式固结波解析解答. 算例分析结果表明:固结波发展规律受无量纲数D_{\mathrm{c}}变化影响而呈现不同性态;D_{\mathrm{c}}数值较大时固结波响应会出现阶跃和正负波动现象;当D_{\mathrm{c}}值较小时,可能出现Mandel-Cryer效应等特殊现象. 通过对早期和后期Terzaghi固结模型的分析和对比,初步探明Terzaghi固结理论模型内部的矛盾性,在普通土体坐标和固相体积坐标两种不同解读条件下,早期Terzaghi (1923,1925)模型可以分别诠释为具有小变形和大变形属性的不同固结模型. 在经典一维固结理论模型的不同诠释背景下,固结波模型也可以据此作出相应拓展和表述. 固结波理论揭示缩尺固结试验中土体物理力学参数与固结波响应两种因素之间存在一种不确定性矛盾,据此建议微观土力学研究重视尺度效应. 固结波模型的意义还在于,可为Terzaghi经典固结模型理论精度分析提供新的依据.      

Quasi-Static and Dynamic Behavior of Saturated Porous Media with Incompressible Constituents

In this paper the field equations governing the dynamic response of a fluid-saturated elastic porous medium are analyzed and built up for the study of quasi-static and dynamical problems like the consolidation problem and wave propagation. The two constituents are assumed to be incompressible. A numerical solution is derived by means of the standard Galerkin procedure and the finite element method.     

Numerical solution of a multidimensional sedimentation problem using finite volume-element methods

We are interested in the reliable simulation of the sedimentation of monodisperse suspensions under the influence of body forces. At the macroscopic level, the complex interaction between the immiscible fluid and the sedimentation of a compressible phase may be governed by the Navier–Stokes equations coupled to a nonlinear advection–diffusion–reaction equation for the local solids concentration. A versatile and effective finite volume element (FVE) scheme is proposed, whose formulation relies on a stabilized finite element (FE) method with continuous piecewise linear approximation for velocity, pressure and concentration. Some numerical simulations in two and three spatial dimensions illustrate the features of the present FVE method, suggesting their applicability in a wide range of problems.     

On the service performance of alternative shipment consolidation policies

In order to compare the performances of alternative shipment consolidation policies, we develop closed-form expressions of the distribution of the maximum waiting time and the average order delay. We examine the tradeoff between the expected delivery frequency, as measured by the expected shipment consolidation cycle length, and the average order delay. The previous analytical results regarding shipment consolidation are aimed at optimizing the performances of alternative policies using cost-based criteria whereas our results are useful under service-based criteria.     

变附加应力条件下组合桩复合地基固结理论研究

针对组合碎石桩–不排水桩复合地基固结问题,考虑碎石桩径向和竖向组合渗流、附加应力随时间和深度变化等因素对复合地基固结速率的影响,建立组合桩复合地基固结计算模型,采用解析法推导了变附加应力条件下组合桩复合地基固结解析解。进行固结度解退化研究,与已有解对比分析,验证了此解的正确性。通过算例计算,绘制了不同因素影响下复合地基固结度变化曲线。结果表明：增加地基顶部与底部的附加应力比值、碎石桩与土体的径向渗透系数比值,复合地基固结速率加快;忽略碎石桩的径向渗流,会高估复合地基的固结速率;减小桩径比可显著提高复合地基固结速率;增加外围不排水桩的置换率,对复合地基固结速率的加快效果不明显。

     

竖向荷载作用下半透水边界固结问题解

本文基于Biot固结理论,采用积分变换的方法,获得了竖向点荷载、环形荷载作用下半透水边界固结问题基本解,并求得圆形分布荷载作用下的固结解,计算分析了圆形分布荷载作用下的竖向位移、总应力和孔压的时间效应.     

Exploring the simultaneous existence of Stone-Wales and carbon ad-dimer defects in the zigzag single-walled carbon nanotubes

We have applied density functional calculations to investigate simultaneous existence of Stone–Wales (SW) and carbon ad-dimer (CD) defects in the zigzag (n, 0) n=5, 6, 7, 8, 9, and 10 SWCNTs, with an extensive search by considering two different orientations of defects. According to our results, the adsorption of a carbon dimer on a hexagonal ring of SWCNTs is easier than the rotation of a C–C bond trough the SW rearrangement. Moreover, the formation of a carbon dimer on the exterior sidewalls of an SW defective SWCNT or the rotation of a C–C bond of a CD defective SWCNT is more favorable than those on the perfect ones. Defect formation energy shows a strong dependence on the both SWCNT radius and defect orientation. The reactivity of SW–CD defective SWCNTs through chemisorption of hydrogen atoms on the central bonds of defect sites shows the thermodynamically lower preference of additions for the CD defective sites in comparison to SW defective sites. Histograms of the ¹³C NMR chemical shifts of SW–CD defective SWCNTs exhibit individual signals for defect sites, which can be attributed to azupyrene- and pentalelene-like structures for SW and CD defect sites, respectively.     

Evaluation of polymers for conservation treatments of outdoor exposed stone monuments. Part I: Photo-oxidative weathering

The commercial acrylic polymers, Paraloid B72 and Paraloid B67, and a silicon-based product, Dri-Film 104, commonly used as water repellents/consolidants in the restoration of stone artefacts, have been tested to evaluate their performances when submitted to ageing, simulating the outdoor conditions of treated stone. After full characterization, the three polymers were applied as thin films on slides, as thick film on petri dishes and on marble by brush or by imbibition and the resulting samples were submitted to photo-oxidative weathering (λ = 340 nm). The weathering evolution was checked by ultrasonic and colorimetric measurements and by FT-IR, NMR and SEC determinations. Removability tests were also performed. All the polymers underwent irreversible modifications with reduction of their conservative properties, colour change and, above all, impossibility of their complete removal.