从长期沉降观测资料分析次固结沉降

对一大面积淤泥软基超载预压加固工程,在不卸载的情况下进行了长达4年多的沉降观测。依据实测资料结合理论计算可知,厚11．3～26．4m的淤泥层在荷载作用下会发生最大达35．2cm的次固结沉降,占软基总沉降量的8．8％,次固结沉降的绝对量值超过了一般建筑物对地基的沉降控制要求,不可忽视。对本工程实测沉降数据次固结段进行了拟合分析,推算出该区淤泥土层次固结系数,该值比同地区一些项目实验室获得的次固结系数稍大,可供该区软基处理设计估算工后沉降量计算参考。     

硬盘磁头读写臂动态性能的有限元分析

针对希捷公司ST微型硬盘驱动器磁头读写臂建立了有限元模型,通过模态分析系统探讨了预载荷对磁头读写臂动态性能的影响。结果显示,预载荷引起的磁头读写臂形状改变对其共振频率有显著影响,而预载荷引起的读写臂内应力只对一阶扭转模态共振频率有较大影响,对其它典型模态共振频率的影响有限。     

湿地湖泊相软土加固方案及固结沉降离心模型试验研究

为研究湿地湖泊相软土的软基加固方案及固结沉降规律,分别进行真空堆载联合预压和水泥土搅拌桩复合地基加固湿地湖泊相软土路基的离心模型试验,对比分析2种方案的沉降发展和土压力变化情况。试验结果表明:相同条件下,真空堆载联合预压固结沉降发展更快,第30天固结度达到80%以上,第90天达到90%以上,且各测点土压力值更小;真空堆载联合预压下路堤横断面沉降分布更均匀,但后期沉降差较大,真空堆载联合预压的工后沉降约为水泥土搅拌桩复合地基的一半,加固效果更好;由含水率测试可知,真空堆载联合预压的影响深度至埋深10 m以下;2个模型的沉降拟合公式都为指数型函数,与实际沉降拟合较好,可预测长期的固结沉降。真空堆载联合预压方案优于水泥土搅拌桩复合地基加固方案。     

真空预压地基处理的加固深度研究

随着沿海经济的发展,软土处理的需求加大,真空预压处理软土有着比较大的优势,被广泛运用。但在真空预压的影响深度方面,目前学术界研究的较少,没有给出一个明确的结论。文章从土体三维固结出发,分析土体受力不但在微观上的等向受力,在宏观上受到真空压力差的影响,而且真空压力差增加了真空度的影响深度。同时结合工程实例,分析现场监测数据,得出真空预压影响深度可以达到排水板底部。     

真空预压下土体强度增长机理及其计算方法研究

在真空预压法加固过程中,土体产生等向固结压力。简单地将真空预压等同堆载作用的处理方法不尽合理,将导致计算土体抗剪强度时出现较大偏差而不宜忽视。该文采用摩尔应力圆来阐述土体受等向固结应力和K0固结应力的不同特点,从而导出二者土体抗剪强度增长偏差的解析解。实例分析表明,该方法较常规方法更准确可行。     

堆载预压与强夯在某港区地基处理中的应用

结合工程实例,针对不同的地质及环境条件,介绍和探讨了堆载预压和强夯在深圳某港区软基加固工程中的应用、设计方案、施工参数选取、施工中遇到的技术问题和处理方法,并对两种方法加固效果进行了检验和分析。     

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.     

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.     

复杂地质真空预压压力过低原因探讨

本文结合平潭某建筑场地真空预压地基处理密封膜下真空压力不足的工程实例,通过分析真空压力过低的原因,供有关工程参考。     

Effect of surcharge loading rate and mobilized load ratio on the performance of vacuum–surcharge preloading with PVDs

The results from three laboratory model tests performed under various vacuum and surcharge loads with PVDs are reported. Different SLRs were adopted to investigate the effect on the consolidation of dredged soil. To measure the lateral displacement, a refitted inclinometer was developed and tested. In the tests, the settlement, lateral displacement, and vane shear strength were measured, and the degree of consolidation (DOC), horizontal coefficient of consolidation (C_h), and bearing capacity were calculated. The results indicate that larger SLR values promote consolidation. The largest vane shear strength, settlement, and C_h values were all obtained under the highest SLR, and the bearing capacity under this SLR was more than double that under the lowest SLR. The DOC was found to increase with the growth of the SLR. However, considering the vacuum pressure was higher in Case-III, the influence of SLR on reinforcement effect may not be so significant.