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Measuring stiffness of soils in situ
Published in Fusao Oka, Akira Murakami, Ryosuke Uzuoka, Sayuri Kimoto, Computer Methods and Recent Advances in Geomechanics, 2014
Fusao Oka, Akira Murakami, Ryosuke Uzuoka, Sayuri Kimoto
ABSTRACT: Costal belts are normally composed of highly compressible soils with very low beaning capacity. To avoid excessive settlement of soft soils, vacuum preloading with combination of fill surcharge is frequently adopted in field to accelerate the consolidation progress. This paper presents analytical derivations of excess pore-water pressure and average degree of consolidation distributions of soft soil layers under the effect of both vacuum preloading and fill surcharge. Typical considerations in these analytical derivations involve: (a) both vertical and horizontal drainage conditions; (b) well resistance and smear effect; and (c) three assumed distributions of coefficient of permeability in the smear zone. A case study is presented for discussion of the effect of different parameters. The present analytical results are found to agree fairly well with the measured settlement data of Huanghua Port in China. The analytical solutions and the related comparisons present a better understanding of the significance of different parameters.
Replacement method, stage construction, preloading and drainage
Published in Bujang B. K. Huat, Arun Prasad, Sina Kazemian, Vivi Anggraini, Ground Improvement Techniques, 2019
Bujang B. K. Huat, Arun Prasad, Sina Kazemian, Vivi Anggraini
This technique can be used to limit settlement and increase the shear strength of the sub-soil. Vacuum preloading is often used in conjunction with vertical drains. This technique has one major advantage over the normal preload: no embankment construction is required. As such, the problem of soil instability will not arise. It enables the equivalent construction of a very high embankment on very soft ground to be made over a relatively short period of time by reducing the development of shear strain in the soil (Mitachi et al., 2003).
Ground improvement
Published in Alan J. Lutenegger, Soils and Geotechnology in Construction, 2019
Vacuum preloading is a newer modification to the traditional preloading with wick drains that uses a vacuum to accelerate the consolidation process. Since about 1980, the method has been used in many parts of the world, especially in China, where it has been used to consolidate very soft reclaimed ground (e.g., Chu et al. 2000). The vacuum method eliminates the need to place a surcharge fill on the site and produces the equivalent surcharge load with the vacuum.
Influence of the intermittent vibration ratio on the electro-osmotic consolidation of dredged sludge
Published in Marine Georesources & Geotechnology, 2023
Dikang Zhang, Jing Xu, Hongtao Fu, Xiaobing Li, Ying Cai, Xiuqing Hu
The vacuum preloading method (Kjellman, 1952; Anda et al., 2020; Wang et al., 2020) is widely used owing to its short construction period, low cost, and simple construction technology, but it has various disadvantages, including poor drainage effect on low-permeability clay, long treatment time, and poor reinforcement of deep soil (Cai, Xie, et al. 2018). Compared with the traditional vacuum preloading drainage method, electroosmotic drainage consolidation is considered to be one of the more effective methods and has the advantage of significantly improving the speed of consolidation. In the early 19th century, Reuss discovered electroosmosis in clay. The field application of electroosmosis in soil was demonstrated by Casagrande (1952). Since then, the electroosmosis process has been applied to ground improvement in the field (Bjerrum, Moum, and Eide 1967; Lo, Ho, and Inculet 1991a; Hu, 2004; Zhang et al., 2005; Guo et al. 2007) and embankment stability (Fetzer 1967; Wittle et al., 2008), improving the bearing capacity of piles (Soderman and Milligan, 1961; Butterfield and Johnston, 1980; El Naggar and Routledge 2004). However, Lefebvre and Burnotte (2002) presented the potential losses from the electro-osmotic consolidation experiment. The electroosmosis method (Li et al., 2019; Wang et al. 2019a) is independent of the particle size of the soil, but problems persist such as uneven water content reduction, easy cracking, easy corrosion of electrodes, and large energy consumption (Yu, 1989; Mitchell 1997; Gong 2002).
Vacuum preloading combined with surcharge preloading method for consolidation of clay-slurry ground: A case study
Published in Marine Georesources & Geotechnology, 2023
Shuangxi Feng, Weiwei Bai, Huayang Lei, Xugen Song, Wei Liu, Xuesong Cheng
Vacuum preloading is the process of applying a negative or vacuum pressure in the ground, thereby creating a pressure gradient between drainage channels (usually prefabricated vertical drains (PVDs)) and surrounding soils. The negative pressure continuously draws pore water out of the ground, which can speed up the consolidation of the soils (Saowapakpiboon et al. 2010; Voottipruex et al. 2014). This method was first proposed by Kjellman (1952) to improve the consolidation of soil deposits at the Philadelphia International Airport, USA. Subsequently, a large number of scholars (Chu, Yan, and Yang 2000; Shen et al. 2015; Gangaputhiran, Robinson, and Karpurapu 2016; Wang et al. 2019; Lei et al. 2019; Wu et al. 2021) employ this technology to strengthen weak soft ground. However, with its increasing application, the vacuum preloading method has shown some drawbacks in sustaining desirable performance, especially regarding the treatment of clay-slurry ground. The most prominent problem is that the vacuum pressure cannot break through one atmosphere (100 kPa), which might affect the ground treatment effect. Therefore, vacuum preloading combined with surcharge preloading method is proposed. This method is based on the vacuum preloading system, and the filling materials are loaded on the surface according to the design requirements so that the consolidation pressure can exceed one atmosphere. However, it is necessary to be aware of such problems as soil instability caused by a surcharge rate that is too fast.
Field instrumentation and evaluation of ground treatment by combined air-booster and straight-line vacuum preloading without sand
Published in Marine Georesources & Geotechnology, 2022
The air-booster vacuum preloading system includes an air-booster system and a vacuum preloading system. The vacuum preloading system is composed of a vacuum pump, membranes, horizontal pipes and PVDs. The air-booster system consists of air-injection boosting pipes, booster pumps and plastic hoses that form the air-pressurizing system. The Underground Engineering Laboratory at Tianjin University has independently developed an air injection boosting pipe measuring 4.5m in length for shallow ground treatment. Steel wire is used to form the skeleton of the pipe, which bears the construction load. The outer circumference of the steel wire is wrapped in fibrous cloth.