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Gu C.,Wenzhou University | Wang J.,Wenzhou University | Zhang T.-T.,Key Laboratory of Soft Soils and Geoenvironmental Engineering of Ministry of Education | Cai Y.-Q.,Wenzhou University | Cai Y.-Q.,De Zhou Vocational and Technical College
Yantu Lixue/Rock and Soil Mechanics | Year: 2013

In the process of deep excavation and tunnel design, soils of different sites may undergo different static stress paths. Under different stress paths, soils may behave different static characteristics. At the same time, in engineering practice, the work strain of soils is in the range of small strain; and in the range of small strain, the static characteristics of soils behave more nonlinear and depending the stress paths. In this paper, based on the soft clays which spread widely in the Eastern China and behave many bad engineering properties, a series of static stress paths tests were conducted under undrained condition and drained condition. Test results show that: under both undrained and drained conditions, the stress paths make great influences on the static strength; the stress paths with increasing confining pressure increase the static strength; while the stress paths with decreasing confining pressure decrease the static strength. Meanwhile, the stress paths make greater influences on the degradation of secant Young's modulus; the stress paths with increasing confining pressure decrease the secant modulus; while the stress paths with decreasing confining pressure increase the secant modulus. The influence of stress paths on the secant modulus is more significant in the range of small strain; and it is due to the anisotropy induced by the change of stress path directions.


Liu N.-W.,Key Laboratory of Soft Soils and Geoenvironmental Engineering of Ministry of Education | Liu N.-W.,Zhejiang University | Zhang Z.-M.,Key Laboratory of Soft Soils and Geoenvironmental Engineering of Ministry of Education | Zhang Z.-M.,Zhejiang University | And 3 more authors.
Journal of Central South University | Year: 2013

A series of well-designed full-scale destructive load tests were conducted on six bored piles to investigate the influence of loose debris at the pile tip on end resistance. The results show that soft debris below the pile tip will weaken the mobilization of end resistance. The ultimate tip resistance of post-grouted pile is 2.05 times that of the pile without post-grouting and the ultimate tip resistance in the second load cycle is 2.31 times that of pile in the first load cycle. The relationship between unit end resistance and displacement follows a linear model and a bilinear mode in the first load cycle and the second load cycle, respectively, whereas the unit end resistance-displacement response of post-grouted bored pile can be simulated using a bilinear mode. The critical end resistance ranges between 2 000 kN and 3 000 kN and the critical displacement ranges between 2.5 mm and 4.5 mm in the bilinear mode. As for piles rested on moderately-weathered peliticsiltstone, the socketed length has no effect on the end resistance because of the existence of loose debris. © 2013 Central South University Press and Springer-Verlag Berlin Heidelberg.


Zhou Y.-G.,Key Laboratory of Soft Soils and Geoenvironmental Engineering of Ministry of Education | Zhou Y.-G.,Zhejiang University | Ding H.-J.,Key Laboratory of Soft Soils and Geoenvironmental Engineering of Ministry of Education | Ding H.-J.,Zhejiang University | And 4 more authors.
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2015

Ageing has significant effect on soil liquefaction resistance, and the quantitative characterization of ageing effect is one of the key research themes in assessment of soil liquefaction. An ageing index (AI) characterizing soil ageing effect is proposed based on small strain shear modulus (Gmax) and cone penetration resistance of CPT testing (qc), with further normalization of soil density and stress state. This index is expressed by a function of the ratio between the fabric parameter of small strain shear modulus and that of large strain penetration resistance. The analysis of laboratory test data shows that the reconstituted sand has a stable reference AI value, while the field data reveal that AI increases with the increase of geologic age of the soil deposit. AI is an apparent parameter as it can characterize the extent of soil ageing without the variable of time, which provides a sound basis for further researches on the effect of soil ageing on liquefaction resistance. © 2015, Chinese Society of Civil Engineering. All right reserved.


Zhan T.L.-T.,Key Laboratory of Soft Soils and Geoenvironmental Engineering of Ministry of Education | Mu Q.-y.,Key Laboratory of Soft Soils and Geoenvironmental Engineering of Ministry of Education | Chen Y.-m.,Key Laboratory of Soft Soils and Geoenvironmental Engineering of Ministry of Education | Ke H.,Key Laboratory of Soft Soils and Geoenvironmental Engineering of Ministry of Education
Water Resources Research | Year: 2015

The time domain reflectometry (TDR) penetrometer, which can measure both the apparent dielectric permittivity and the bulk electrical conductivity of soils, is an important tool for the site investigation of contaminated land. This paper presents a theoretical method for evaluating the measurement sensitivity and an improved design of the TDR penetrometer. The sensitivity evaluation method is based on a spatial weighting analysis of the electromagnetic field using a seepage analysis software. This method is used to quantify the measurement sensitivity for the three types of TDR penetrometers reported in literature as well as guide the design improvement of the TDR penetrometer. The improved design includes the use of semicircle-shaped conductors and the optimization of the conductor diameter. The measurement sensitivity to the targeted medium for the improved TDR penetrometer is evaluated to be greater than those of the three types of TDR penetrometers reported in literature. The performance of the improved TDR penetrometer was demonstrated by conducting an experimental calibration of the probe and penetration tests in a chamber containing a silty soil column. The experimental results demonstrate that the measurements from the improved TDR penetrometer are able to capture the variation in the water content profiles as well as the leachate contaminated soil. © 2015. American Geophysical Union. All Rights Reserved.


Zhou Y.-G.,Key Laboratory of Soft Soils and Geoenvironmental Engineering of Ministry of Education | Zhou Y.-G.,Zhejiang University | Li Y.-G.,Key Laboratory of Soft Soils and Geoenvironmental Engineering of Ministry of Education | Li Y.-G.,Zhejiang University | And 9 more authors.
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2014

The results of consolidation tests under K0 condition and cyclic triaxial tests on Fujian sand at a given relative density are introduced, and the mechanism of the liquefaction-induced volumetric strain is revealed, which is composed of the re-sedimentation and the re-consolidation processes. The re-sedimentation is closely related to the cyclic shear strain history, especially that after liquefaction, and the more the accumulated shear strain ratio is, the more the re-sedimentation volumetric is. Besides, the re-consolidation behavior is significantly affected by the previous consolidation history and cyclic stress history, and the post-liquefaction reconsolidation will follow the trend of the previous normal consolidation curve, and the compression index is larger than that of the normal consolidation curve under the same conditions. A post-liquefaction volumetric strain model accounting for both the consolidation and cyclic shear strain histories is proposed, which treats the re-sedimentation as part of the re-consolidation by introducing the concept of assumed initial stress, and the estimation methods for re-compression index and the assumed initial stress are recommended accordingly. Then dynamic centrifuge model tests are performed, and the consolidation settlement and liquefaction responses are monitored, whereupon the mechanisms of liquefaction-induced volumetric strain are observed at the model scale, and the proposed model for post-liquefaction settlement estimation is preliminarily validated.

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