Consolidation considering increasing soil column radius for dredged slurries improved by vacuum preloading method

Soil column is often investigated in the improvement of dredged slurries. Different from the smear zone, the soil column forms gradually and has extremely low permeability. This study presents an analytical solution for soil consolidation considering the increasing radius of the soil column and time-dependent discharge capacity. Based on the solution, the influence of the radius' increase on the consolidation behavior is found significant when the soil column has low permeability and large final radius, and the increase of formation time can lead to the increase of consolidation speed and final consolidation degree.     

Comparative analysis on performance of vertical drain improved clay deposit under vacuum or surcharge loading

This paper presents two well-instrumented large-scale field tests of PVD-improved soft soil with vacuum and surcharge preloading, respectively. The two large-scale field tests were conducted adjacent to each other with the same preload. A comparative analysis was performed to investigate the performance of subsoil (i.e., the ground settlement, the layered settlement, the lateral displacement of subsoil and pore water pressure) under vacuum preloading and equivalent surcharge preloading. Some design methods were verified based on the field data. Cone Penetration Tests (CPT) and Vane Shear Tests (VST) were conducted to assess the improvement effects on subsoil after preloading. The results showed that as compared with surcharge preloading, vacuum preloading mitigated the differential settlement of the ground. The vacuum pressure transmitted into the soil with a minor loss through the PVD length. From a practical point of view, the improvement effects by vacuum preloading and surcharge preloading were similar in terms of influence depth and soil strength based on the in-situ tests.     

Preloading using fill surcharge and prefabricated vertical drains for an airport

This paper presents the field measurements and analysis of a preloading project with the installation of prefabricated vertical drains (PVDs) in Wenzhou, China. At the site, PVDs were installed to a depth of 22?m from the ground surface with a spacing of 1.5?m in a triangular pattern. The preloading fill thickness was 6?m with a unit weight of approximately 18 kN/m³. After a total elapsed time of 310 days, approximately 3?m thick fill was removed. The measured preloading settlement was approximately 1.5?m. The measurements and analytical results indicated that the soil layer with PVD improvement reached almost 100% primary consolidation when part of the fill was removed. After partial unloading, the PVD-improved zone was in an over-consolidated state. After the runway was opened for traffic, a settlement increment of approximately 7?mm was monitored over a period of 11 months. Analysis indicated that the settlement was mainly due to the consolidation of soil layers below the PVD-improved zone and post-surcharge secondary consolidation of the PVD-improved zone. The values of the parameters related to PVD improvement were back-estimated from the field measurements. These findings can be used to guide the design of PVDs improvement along the east coast of China.     

基于ANSYS的双列圆锥滚子轴承预紧力有限元分析

应用赫兹弹性接触理论,首先分析双列圆锥滚子轴承的结构参数、预紧原理及其预紧受力,再运用SolidWorks建立了双列圆锥滚子轴承的三维模型,最后通过ANSYS进行有限元分析计算,得出在不同的预紧载荷下的接触应力和变形,为轴承预紧力分析提供了新的研究方法。     

真空渗流场的形成机理探讨

软基在“真空预压”法处理过程中的固结,不是因其所谓的“真空荷载”进行“预压”所致,而是因“真空渗流场”的形成并在其作用下产生“渗透固结”所致。全文详细探讨了“真空渗流场”的形成机理,包括该场中孔隙水运动的物理模型和土体固结的物理模型。在对土体固结模型探讨的过程中,首次将“有效应力”的概念扩展成“竖直向”有效应力和“水平向”有效应力两种,并在此基础上提出了“双弹簧固结模型”。从有效应力发展过程的角度探讨“真空渗流场”的形成过程时,发现该模型能较好地符合“真空预压”对软基的作用实质。     

真空联合堆载预压加固高速公路软土地基应用及机理分析

详细介绍了真空联合堆载预压法对高速公路软土地基进行加固的基本原理、基本方法和施工工艺等，并以图表的形式对加固效果进行分析评价，结果表明：真空联合堆载预压法是一种既经济又有效的处理软土地基的方法。这种方法值得大面积推广和应用。     

基于Gompertz成长曲线的真空预压软土沉降规律分析

对真空预压软土沉降变化规律进行分析,发现其与社会经济预测中的Gompertz成长曲线变化规律相似。引入Gompertz成长曲线模型,采用3段估计法求解模型参数;同时,结合具体工程实例,对真空预压软土的表面累计沉降数据进行拟合和分析,并与双曲线模型和指数曲线模型进行比较。研究结果表明,Gompertz成长曲线模型拟合曲线与实测曲线吻合良好,采用该模型进行真空预压软土沉降变化规律分析是可行的,并可根据所反映出的沉降发展变化趋势,作出沉降预测,计算工后沉降及确定卸荷时间。与双曲线模型和指数曲线模型比较,Gompertz成长曲线模型适应性较好,趋势预测准确性高。最后指出应用Gompertz成长曲线模型进行分析时应注意抽真空的连续性、实测时间序列数据能等分成3组及保证实测沉降数据已进入弹塑性阶段等问题。     

真空预压地基非饱和带探讨

目前,真空预压研究中将加固地基均视为饱和土,这与工程实测的地基地下水位下降相矛盾。针对这一的现状,通过对真空泵抽水的室内模拟试验和真空预压工程中实测现象进行分析,得出不同外界条件下真空吸力可引起水、空气或气液两相对流:(1)真空预压工程中射流泵提供的真空吸力引起地基中流体气液两相对流;(2)真空预压地基存在非饱和带,真空预压工程实践中密封系统不是绝对密封的,预压地基内存在漏气,液-液气射流泵以气水两相流态抽吸地下水,导致抽真空期间地基地下水位下降;(3)真空预压地基非饱和带类似于群井抽水地基的非饱和带,射流泵抽水量来源于地下水位下以上非饱和带土体的重力排水和地下水位以下饱和土体的弹性释水。同时,提出当前真空预压研究中,理论分析、室内模型试验与实际工程中的地基加固边界密封条件不同是产生矛盾或分歧的根源所在。     

真空排水预压在公路软基加固中的应用

分析真空排水预压技术对软土地基加固机理,介绍该技术在武汉地区的施工应用效果,对其施工影响因素及其在武汉地区的发展前景进行探讨。     

大连港大窑湾吹填区软基的堆载预压处理研究

结合大连港大窑湾吹填区软土地基处理具体工程,通过现场试验与监测比较详细地介绍了堆载预压方法中关于分级堆载设计、施工及监测等各方面的技术问题。通过对监测结果的综合分析,探讨了堆载预压处理过程中地表沉降、深层沉降等关键参数的变化规律及堆载级数、堆载高度与固结时间等参数之间的依赖关系,为吹填造陆地区软基处理提供了经验和依据。