Browsing by Author "Chang, Wen-Jong"

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A mist pluviation method for reconstituting silty sand specimens
(2015-04-07)
Huang, An-Bin
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Chang, Wen-Jong
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Hsu, Huai-Houh
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Huang, Yu-Jie
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土木工程學系
A mist pluviafion (MP) technique was proposed in an effort to develop a practical method for reconstituting silty sand specimens without inducing severe particle segregation. The mist pluviation method includes both air and water pluviation processes, with the addition of a mist zone that mixes soil particles with water droplets while falling through air. The soil and water mixtures have similar particle sizes, thus resulting in significantly reduced particle segregation. A thin water layer on top of the deposited soil mimics the water deposition process, and saturates the soil with little chance for particle segregation. The performance of the MP method was evaluated with regard to homogeneity, repeatability, undrained monotonic compression, and cyclic strength of triaxial specimens with various fines contents. Results have indicated that the MP method can be a promising technique to prepare reconstituted silty sand specimens. (C) 2015 Elsevier B.V. All rights reserved.
Geotechnical reconnaissance and liquefaction analyses of a liquefaction site with silty fine sand in Southern Taiwan
(2011-11-13)
Chang, Wen-Jong
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Ni, Sheng-Huoo
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Huang, An-Bin
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Huang, Yan-Hong
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Yang, Yu-Zhang
Geotechnical reconnaissance of a recurrent liquefaction site at a Quaternary alluvial deposit in southern Taiwan was conducted to establish a comprehensive case history for liquefaction on silty fine sand with high fines content. The liquefaction occurred at a silty fine sand layer with D(50) = 0.09 mm and fines content greater than 35% and was triggered by a M(w) = 6.4 earthquake on March 4,2010, which induced maximum horizontal acceleration up to 0.189 g at the site. In situ subsurface characterizations, including standard penetration test, cone penetration test, and shear wave velocity measurement, were performed as well as cyclic simple shear tests on undisturbed specimens retrieved by a modified hydraulic piston sampler. Comparisons of cyclic resistance ratios (CRRs) indicate that CPT sounding with standard penetration rate could overestimate the resistance ratio and drainage conditions during penetration should be considered for high fines content soil in the liquefaction analysis. Additionally, variations of CRRs from different in situ tests indicate that correlations among in situ tests and CRR could be soil specific and precautions should be taken when using these curves on silty fine sands. (C) 2011 Elsevier B.V. All rights reserved.
Physical simulation of aquifer compression due to groundwater fluctuation
(2017-12-14)
Chang, Wen-Jong
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Chou, Shih-Hsun
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Huang, An-Bin
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土木工程學系
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Department of Civil Engineering
To investigate the compression of granular aquifer induced by fluctuations of pore pressure, series of repeated pore pressure induced loading-unloading tests on specimens made of Ottawa sand mixed with mica were conducted in a K-o-triodal consolidation system. To simulate the stress paths in the field, the vertical displacements of soil specimens were monitored while maintaining a constant total vertical stress and applying sinusoidal fluctuations of pore pressure to specimens under K-o conditions. Shakedown theory is applied to interpret the testing data. The paper describes the laboratory setup, test procedure and findings from the test results. The results reveal that a shakedown behavior existed in saturated granular specimens and the accumulated permanent axial strains are 5 to 56 times of the values for conventional, monotonic loading. The finding evidently proves the significance of aquifer compression to ground subsidence due to repeated ground water fluctuations.
Simplified monitoring and warning system against rainfall-induced shallow slope failures
(2018-10-01)
Wang, Chien-Chih
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Chang, Wen-Jong
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Huang, An-Bin
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Chou, Shih-Hsun
;
Chien, Yu-Chun
A system that involves the use of a low-cost microelectromechanical system (MEMS)-based sensor stick and soil-water characteristic curve (SWCC) inferred from grain-size distribution was developed to assess the factor of safety against rainfall-induced shallow slope failure. The system allows water content at multiple depths to be monitored in the field. The corresponding suction and factor of safety against infinite slope failure are derived based on the estimated SWCC. The new system circumvents the use of tedious and often costly field as well as laboratory procedures while providing a quantitative slope stability assessment on a real-time basis. The paper introduces the background of the new development and describes the application of the sensor stick system in a field test.