A Review and Update of Analytical and Numerical Solutions of the Terzaghi One-Dimensional Consolidation Equation

Practical resolution of consolidation problems that we often face requires an extensive and solid knowledge of the different parameters highlighted by the Terzaghi one-dimensional consolidation theory. This theory, with its assumptions, leads to a partial differential equation of second order in space and first order in time of pore water pressure. Analytical and numerical resolutions of this equation allow determining the water pressure variation before and after the application of a charge. Numerical modeling has enabled the simulation of the whole results obtained by the two methods of resolution (pressure, degree of consolidation, time factor, among others) to have a physical analysis and a lawful observation that lead to a suitable understanding of the phenomenon of Terzaghi one-dimensional consolidation.

Secondary settlement estimation in surcharge preload subject to time effect of secondary consolidation coefficient

In order to eliminate the settlement underestimation in surcharge preload engineering, a study based on Bjerrum's creep diagram and the tangent slope definition of secondary consolidation coefficient was carried out to analyze the time effect of secondary consolidation coefficient of over consolidated soil, and a time–growth model for it was formulated. As Bjerrum's creep diagram is an idealized model, oedometer tests were performed to improve the above time–growth model of secondary consolidation coefficient for the purpose of achieving a better agreement with the actual ground situations. It is found that secondary consolidation coefficient of over consolidated soil not only decreases with the ratio of historical maximum to current effective stress of soil(OCR), but also increases with the development time of secondary consolidation. No matter how large OCR is, the long-term time effect of secondary consolidation coefficient of over consolidated soil is all significant. Based on the above results, a model for settlement estimation was formulated and a case study to estimate it indicates that the settlement estimated by our method is 2–5 times larger than that estimated by the previous method. Moreover, the larger the OCR is as well as the longer the service life is, the larger the difference between our method and the previous method is. Thus, the post-construction secondary settlement in surcharge preload engineering will be underestimated when neglecting the time effect of secondary consolidation coefficient in over consolidated state.

Sediment settlement rate and consolidation time of flling reclamation in coal mining subsidence land

With the continuous growth of the population and the continuous reduction of cultivated land,China’s food security is greatly threatened.In addition,China’s coal mining has been mainly underground mining,causing land subsidence and damaging existing cultivated land.This efect intensifes the contradiction between the growth of the risk population and the reduction of cultivated land.The reclamation of mining subsidence land with Yellow River sediment is often used as an efective way to improve the recovery rate of cultivated land.Shortening the reclamation time and realizing continuous flling are signifcant issues.The work presented in this paper studied the sediment settlement rate and consolidation time by combining theory,feld flling and reclamation tests and numerical simulations.A feld flling test study was carried out in the lowlands of Jibeiwang Village,Qihe County,Shandong Province,China.By calculating the drainage consolidation time,the consolidation factor of 0.015656 m^(2)/d,and the time factor for sediment consolidation of 0.575 were determined.The sediment consolidation time for this test was 9.18 days.The calculation of sediment deposition rate and consolidation time is of great practical signifcance to guide the Yellow River sediment flling,realize continuous flling,and save reclamation time and cost.

ONE-DIMENSIONAL CONSOLIDATION OF LAYERED SOILS WITH IMPEDED BOUNDARIES UNDER TIME-DEPENDENT LOADINGS

On the basis of Terzaghi's one-dimensional consolidation theory, the variation of effective stress ratio in layered saturated soils with impeded boundaries under time-dependent loading was studied. By the method of Laplace transform, the solution was presented. Influences of different kinds of cyclic loadings and impeded boundaries conditions were discussed. Through numerical inversion of Laplace transform, useful illustrations were given considering several common time-dependent loadings. Pervious or impervious boundary condition is just the special case of the problem considered here. Compared with average index method,the results from the method illustrated are more accurate.

Rigorous Axially Symmetric Consolidation Solution of Vacuum Combined Linear Loading Surcharge Preloading

Vacuum combined surcharge preloading is an effective method which has been used in ground treatment. This study presents the analytical solution of vertical drains with vacuum combined surcharge preloading. The surcharge was considered to be time-dependent preloading due to its reflection of the real situation.Moreover,the free strain,instead of equal strain hypothesis of the surface,was adopted for the mathematical rigor. Both vertical and horizontal drainages,along with the well resistance were considered.Besides,the time-dependent surcharge preloading was resolved with the impulse theorem which has been presented in the study,and the solutions for pore water pressure and degree of consolidation were derived by applying the approach of separation of variables.Furthermore,the solution is compared with previous solutions and numerical solutions,and the results verify the correctness of the proposed model.

Daily Activities and Sleep Durations of Patients with Ischemic Heart Disease Who Were Discharged to Their Homes after Elective Percutaneous Coronary Intervention

The purpose of this study was to examine the relationship between daily activities and sleep durations for patients following elective percutaneous coronary intervention (ePCI) and diagnosed with ischemic heart disease (IHD) after discharge to their homes. The actigraph data were used to collect data from twenty five patients. The duration of night-time sleep (minutes from the start to end of night-time) and actual night-time sleep duration (total sleep duration excluding wake-up durations of night-time) on the seventh day after discharge were divided into three groups;less than 360, 360 to 480, and more than 480 minutes (short, optimal and long respectively). Subsequently, among the three groups of patients, the data were analyzed by Kruskal Wallis H-test with multiple comparison procedures using the Scheffé-test in order to compare differences in daytime activity items at seven days after discharge from the hospital. Total daytime nap duration (p p p p < 0.05). However, the duration of night-time sleep and daytime activity did not significantly differ. If actual night-time sleep duration is improved from 360 to 480 minutes, daytime nap could potentially be decreased. Determining objective sleep conditions for patients and treating sleep disorders may improve overall patient health, facilitating appropriate sleep and wake rhythms.

Solution to 1-D consolidation of non-homogeneous soft clay

In this work, semi-analytical methods were used to solve the problem of 1-D consolidation of non-homogeneous soft clay with spatially varying coefficients of permeability and compressibility. The semi-analytical solution was programmed and then verified by comparison with the obtained analytical solution of a special case. Based on the results of some computations and comparisons with the 1-D homogeneous consolidation (by Terzaghi) and the 1-D non-linear consolidation theory (by Davis et al.) of soft clay, some diagrams were prepared and the relevant consolidation behavior of non-homogeneous soils is discussed. It was shown that the result obtained differs greatly from Terzaghi’s theory and that of the non-linear consolidation theory when the coefficients of permeability and compressibility vary greatly.

Analysis of one-dimensional consolidation of soft soils with non-Darcian flow caused by non-Newtonian liquid

Based on non-Darcian flow caused by non-Newtonian liquid, the theory of one-dimensional (1D) consolidation was modified to consider variation in the total vertical stress with depth and time. The finite difference method (FDM) was adopted to obtain numerical solutions for excess pore water pressure and average degree of consolidation. When non-Darcian flow is degenerated into Darcian flow, a comparison between numerical solutions and analytical solutions was made to verify reliability of finite difference solutions. Finally, taking into account the ramp time-dependent loading, consolidation behaviors with non-Darcian flow under various parameters were analyzed. Thus, a comprehensive analysis of 1D consolidation combined with non-Darcian flow caused by non-Newtonian liquid was conducted in this paper.

惰性浆性能优化及固结时变规律试验研究

针对富水粉细砂地层中由于惰性浆凝结时间长,早期强度低等引起的地层沉降及管片上浮控制难题,开展水泥改性惰性浆配制及固结试验研究,结果表明:随水泥掺量从0增加到40 kg/m^(3),浆体凝结时间从24 h缩短到14 h,3 d强度从35 kPa提高到180 kPa,显著缩短浆体凝结时间,提高早期强度,但同时降低了浆体流动性。另外,在不掺加水泥时,聚羧酸减水剂对惰性浆性能影响不大,而在掺加水泥后,聚羧酸减水剂能提高浆体流动性能,延缓凝结时间,提高强度。水泥掺量从0增加到30 kg/m^(3),浆体渗透系数降低,进而降低固结排水速率,延长孔隙水压力消散时间,减小固结排水量,使固结轴向应变减小。在同一水泥掺量下,增大固结压力提升了固结排水量,使浆体水胶比降低,无侧限抗压强度提高。

预固结对长江漫滩相软土抗剪强度的影响研究

固结快剪试验是获取软土固结不排水抗剪强度的重要方法,长江漫滩相软土具有压缩性高、孔隙比大、含水率高、渗透率低、固结时间长等特点,严重影响了软土固结快剪试验的生产效率。为研究预固结对长江漫滩相软土抗剪强度的影响,并探索提高漫滩相软土固结快剪试验效率的方法,以南京长江漫滩相软土为研究对象,制定了预固结-卸载剪切、正常固结剪切、预固结-卸载-再固结剪切3种试验方案,开展了一系列固结和剪切试验。试验研究表明:长江漫滩相软土是一种前期固结迅速,后期固结稳定缓慢的软土;固结25 min时固结度可以达到95%,而完全固结稳定需要5~8 h;软土抗剪强度均随固结度U的增加呈增大趋势,其增长速度逐渐减缓,各荷载条件下抗剪强度随U提高的增长幅度基本相同;当固结度为70%~80%时,其抗剪强度达到完全固结时的90%~95%。研究成果可为软土固结快剪试验的方法改进提供参考。

时变载荷作用下饱和黏土地基的流变固结特性研究

基于Biot多孔介质理论,利用分数阶Kelvin模型描述土骨架流变效应,引入斜坡、三角形和梯形载荷的时空域解析函数,构建时变载荷作用下饱和黏土地基的三维轴对称固结模型.采用Hankel–Laplace联合变换和张量运算推导控制方程的变换域解析解,利用数值反演得出时空域解.通过算例分析,对模型和计算方法的有效性进行验证,并研究了3种时变载荷作用下饱和黏土地基的流变固结行为和参数影响规律.结果表明,饱和黏土的次固结沉降更为显著.土骨架流变性对孔隙水渗透具有抑制作用,使土体在主固结阶段沉降速率减缓,次固结阶段沉降速率加快,而且长期沉降量增大.加载速率越大,孔隙压力峰值越大.卸载阶段土体发生变形恢复,土骨架弹性扩张产生负孔压,卸载速率越大,产生的负孔压越大.土骨架流变性越强,变形恢复量越小,产生的负孔压也越小.载荷类型和加载路径主要影响固结过程中位移和孔压随时间的变化形态,而土骨架流变性影响土体的长期沉降量.

考虑波次订单动态释放的B2C电商订单合并配送决策方法

本文针对动态释放、异质性强的B2C电商波次订单的物流配送决策难题,以提高车辆满载率、降低配送成本为目标,研究考虑波次订单动态释放的B2C电商订单城区物流合并配送问题。首先,将原动态问题建模为一阶马尔可夫决策过程以表达其多阶段时序序贯决策的特点;其次,基于状态转移具有的时序特征,提出一种基于时序预测的前向动态规划方法用于寻找最优策略,将时序预测信息融入到合并配送决策的模型中,并结合定性启发式规则与定量优化模型以兼顾方法的决策效率与优化能力;最后,基于标准算例下的数值实验和某B2C电商平台的实例分析,验证了所提方法的有效性和实用性。此研究可为B2C电商订单物流配送提供决策支持,同时对于状态转移具有时序特征的马尔可夫决策问题提供了求解的新思路。

基于潜力类型差异化的农村居民点建设用地整治潜力测算及释放——以华南丘陵区某县为例

从其他闲散用地、闲置建设用地及超标准宅基地3个角度对农村居民点建设用地整治潜力进行测算,从经济角度探索区域整治效益,并结合整治潜力、效益确定建设用地整治时序。结果表明,研究区农村居民点建设用地整治潜力充足,其中超标准宅基地整治潜力显著;其他闲散用地及闲置建设用地整治效益优越,超标准宅基地整治收支差异明显;农村居民点建设用地整治潜力释放大小与整治面积、效益、时序相关,由地区能力与需求决定。

一种融合时序特征的网络场景识别算法

针对网络场景识别问题,提出了一种基于语义识别改进的树模型识别算法框架,利用语义分析提取网络时序特征,纵向表达用户活动轨迹,可更加直观地表征办公、宿舍和食堂等场景。同时,通过对数据通信物理模型拟合的网络环境特征(设备之间的路损、干扰等)进行识别,获得网络环境内设备的款型、安装的疏密和用户的负载等信息。进而基于决策树模型框架,耦合上述两类特征生成场景识别算法框架。通过耦合网络环境的流量特征及网络规划特征,全局框架具有智能识别网络场景的特点。算法针对多个数据集样本进行验证,证明所提方案均能对不同场景进行有效识别。

饱和黏性土试样底部孔压时间滞后机理探讨

采用一维固结仪进行饱和黏性土固结试验时,测量的试样底部孔压普遍存在“时间滞后”现象,荷载施加后,孔压随固结时间先增大至最大值,然后开始消散。以往研究发现,测压管式孔压计的刚度不足,导致孔压计腔体体积在施加荷载后发生变化,从而得出孔压滞后可以归结于孔压测量系统刚度的结论。基于已有理论,分析了不同孔压测试系统刚度对孔压滞后性状的影响,发现隔膜式孔压测量系统刚度足够大,固结试验中施加荷载所引起的孔压计腔体体积变形可以忽略不计,测量系统刚度不是隔膜式测量系统孔压滞后的主要影响因素。对比分析三轴固结试验和一维固结试验不同边界排水条件诱发不同的孔压滞后性状,发现一维固结试验中施加荷载时,试样顶部处于自由排水条件,外加荷载引起的水力梯度均匀地分布于试样之前试样顶部便产生排水固结是诱发底部孔压时间滞后的关键因素。基于一维固结试验数据,分析了孔压滞后时间与土体试样固结参数的关系,可以得出:底部孔压峰值滞后时间随着试样渗透系数的减小和压缩指数的增大而增大;渗透系数的影响比压缩指数更为显著。

适用于一般时变荷载情况的一维固结解析解

现有的一维渗流固结解析解只适用于特定的荷载类型,如矩形分布荷载和三角形分布荷载,而工程实际中常见的是更为一般的荷载分布形式,而且荷载往往是随时间而变化的。为更好地便于工程应用,结合前人研究工作,本文在一定的假设基础上,采用理论分析方法明确了一维渗流固结问题对应的基本微分方程和相应的边界条件,然后采用特征函数法,推导出更为一般的随时间变化的荷载分布形式下一维固结解析解,并且对解析解进行编程求解。最后将新解析解与已有的特定荷载类型下的解析解进行对比,结果表明采用新解析解能够快速准确地得出一般时变荷载作用下的一维固结解析解,值得在工程应用中加以推广。

含砂量对湘北湖相软土流变特性影响研究

在室内配制不同含砂量的湘北湖相软土试样,开展了单级荷载下的一维固结流变试验,研究含砂量对湘北湖相软土流变特性的影响。结果表明,含砂量对湘北湖湘软土的固结变形影响显著;主固结完成时间几乎不受固结压力影响;主固结完成时间与砂土比呈线性递减关系;软土中含砂量越高,固结压力越大,次固结系数越小;次固结系数与砂土比存在良好的幂函数关系;软土中粗颗粒含量越高,分形维数越大;次固结系数与分形维数呈线性关系。

基于PXI实时平台铰接式车辆转向轨迹特性分析

根据双油缸“缸体前置式”布置的地下矿用铰接车转向系统的结构特点,获取油缸行程和整车转向角度之间的关系,并对转向过程中前后轮的坐标位置进行分析,获得数学模型。基于Simulink搭建分析模型,获得不同运行速度时的转向轨迹。基于ADAMS建立某铰接车的多自由度分析模型,与转向轨迹模型结合,嵌入PXI驾驶员在环测试实时平台,对整车的转向轨迹进行分析;基于实车测试,选取双移线转向工况,根据结果对仿真结果进行验证。分析可知:车辆运行速度低于6m/s时,行驶稳定性良好,转向过程比较平缓;当速度高于6m/s时,应该先减速,当到达适合转向行驶的速度再实施转向动作;驾驶员在环实时测试模拟、数学模型与实车测试获得转向轨迹,具有较高的重合度,转向角的误差小于3%,进一步地说明转向轨迹分析的准确性,为实际设计提供参考。

南朝位阶制度考释

出于加强皇权的需要,南朝初期复置了很多东晋时期省并的官职,并新设了大量王府僚佐官。在这种情况下,以官品九品为核心的魏晋旧制丧失了实际功能,而新生效的官员位阶制度即为十八班。此制的主体结构在魏晋时期并不存在,其与魏晋官品的差异,实为南朝与魏晋官制体系的不同。不过,官品在南朝并未被淘汰,而是在吸收班制的基础上形成了“陈官品”。南朝官制中共存的班和品,并非散阶与职位的关系。南朝单个官职的位阶高低,以班次而非官品为准。南朝带帖制度与班制关系密切。官员兼领多官时,往往以东、西省官或散号将军作为带帖官,带帖官和主职的班次共同决定了官员位次。