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Interpretation of slaking of a mudstone embankment using soil skeleton structure model concept and reproduction of embankment failure by seismic analysis

2016; Volume: 2; Issue: 5 Linguagem: Inglês

10.3208/jgssp.jpn-124

2188-8027

Masaki Nakano, Takayuki Sakai,

Geotechnical Engineering and Underground Structures

In this study, the effect of a slaking on a mechanical behavior of the crushed mudstone specimen is examined through laboratory test and interpreted based on the concept of soil skeleton structure through simulation using SYS Cam-clay model. Furthermore, seismic response on Makinohara highway embankment with slaking under soil-water finite deformation analysis code GEOASIA. The new findings are as follows, (1) After the early shear stage, the crushed mudstone aggregate specimens with a 100% compaction degree show hardening behavior with plastic expansion that follows the critical state line of the remolded sample. This behavior resembles overconsolidated soil. Additionally, a greater number of drying-immersion cycles correspond to a lower maximum deviator stress of crushed mudstone aggregate. Although this aggregate shows similar behavior at a 95% compaction degree, when compared at the same level of slaking progression, it shows an increase in maximum deviator stress with increasing compaction degree. (2) Employing elasto-plastic parameters for remolded samples and evolution rule parameters in calculations using a SYS Cam-clay model of an elasto-plastic constitutive model allowed us to reproduce the mechanical behavior of crushed mudstone aggregate with differing slaking progression levels and compaction degrees simply by changing the initial conditions. These calculations indicated that, given a constant compaction degree of the crushed mudstone aggregate, the structure decays and overconsolidation decreases as slaking progresses. (3) The behavior of the Makinohara Embankment failure was reproduced during an earthquake response analysis using GEOASIA. During the earthquake, large strain occurred at the mudstone–sand and gravel boundary, and at the sand and gravel–mudstone base boundary. After the earthquake, a very large circular arc slip failure occurred, bisecting the crown of the embankment. A typical element of the numerical model of the embankment was examined for behavior during the failure and showed the following. It shows softening behavior accompanying plastic compression and that the effective stress path approaches the point of origin. Simultaneously, there was a positive excess pore water pressure and strain grew to a high level. In a calculation assuming no slaking, there was little softening behavior during the earthquake, and so strain did not develop to high values and the embankment remained stable after the earthquake.