A total of 114 constant rate of strain (CRS) consolidation tests and 15 incremental loading (IL) consolidation tests were conducted for undisturbed Ariake clay samples from three boreholes in the Saga Plain, Kyushu, Japan, to systematically investigate the strain-rate effect on the consolidation behaviour of Ariake clay. The test results show that the consolidation yield stress (p c ) of Ariake clays increased by about 15–16% with a tenfold increase in strain rate, and no clear correlation exists between the strain-rate effect and the clay content or plasticity index I p of the samples. For a given strain level, the strain rate does not influence the compression index C c , which implies that an isotach model is applicable to Ariake clay. It has been newly found that, under a given effective vertical stress, the coefficient of consolidation c v increases with increase of the strain rate, resulting mainly from the increase of hydraulic conductivity k with strain rate. Linear regression gives about a 33% increase in c v with a tenfold increase in the strain rate. For the Ariake clay tested, the p c and c v values of CRS tests with a strain rate of 0·02%/min are comparable with those of IL tests.
Abstract Three types of constant rate of strain (CRS) consolidation tests were conducted on samples of undisturbed Ariake clay, using a newly developed consolidometer, to investigate the anisotropic consolidation behavior of the clay. CRS tests conducted using vertically cut specimens (with respect to the in situ condition) tested with vertical (or end) drainage (with respect to test condition) were designated as CRS-V-V tests. Specimens cut vertically but with radial drainage were designated CRS-V-R, whereas those cut horizontally and tested with vertical drainage were designated CRS-H-V. The test results show that the ratio of the consolidation yield stress of a horizontally cut specimen (pch) to that of a vertically cut specimen (pcv) is in a range from 0.5 to 1.0. Both pcv and pch increased about 15 % with a tenfold increase in strain rate, but there was no clear difference in the degree of strain-rate dependency for pcv and pch. Values of the coefficient of consolidation obtained from CRS-H-V (chh) and CRS-V-R (chv) test are larger than those measured in CRS-V-V (cv) tests, and it has been identified that these differences arise mainly from the anisotropy of hydraulic conductivity (k). The ratio of k in the horizontal direction (kh) measured in a CRS-V-R test to that in the vertical direction (kv) from a CRS-V-V test is about 1.65, and the ratio of chv/cv is about 1.54. The value of kh from a CRS-H-V test is generally smaller than that from a CRS-V-R test.
Along the zone of interaction between land and water, there are continually changes due to dynamic interaction of water and land, so lots of problems occur such as Erosion, flooding, etc. Therefore riverbank and flood protection structures have become useful in the past decades. The National Road NR.01B is built along the mountainous area below the road is a river which flow parallel to the road alignment in soft shale area. There are 4 different stations which were investigated at KM90+600, KM 92+125, KM 92+212.5 and KM92+512.5. Unusually heavy monsoon rains, exacerbated by tropical storms, have caused widespread flooding in more than 60 per cent of the Lao PDR from late June through August. The monsoon rains continued since, and the country endured almost continuous heavy rainfall for some ten weeks. The forensic solution for erosion along the National Road is to use geosynthetic for improving the stability of the erosion protection structures. PLAXIS FEM 2D analysis was utilized to predict factor of safety for each station in case of low water and high water level. In each station of erosion protection structure used same soil parameter due to the same locations. The Slide Software was utilized to predict the value of factor of safety using Bishop, Janbu and Spencer methods in both cases of water level for each flood and erosion protection structure by using the same soil and support parameters which was used in PLAXIS FEM 2D Software. Moreover, comparing the best station between each erosion protection structures were carried out. Furthermore, comparing the results from PLAXIS FEM 2D and Slide Software, the result from PLAXIS 2D seems to have higher accuracy.
The characteristics of clay soil in the Saga Plain in Japan, as well as the effect of the depositional environment on its engineering properties, have been investigated. While the clay was being deposited there were several large-scale volcanic eruptions in the region. A considerable amount of volcanic ash settled into the clay, which had a marked effect on its engineering properties. The soil is strongly structured and the sedimentation compression curves are well above the sedimentation compression line proposed by Burland, which indicates some degree of cementation. The compression index is high – even for soil samples with in situ vertical effective stresses of 200–300 kPa, the index can be as high as 2·3. The rate of permeability reduction with void ratio is higher than most reported data in the literature. The reason considered is that the compression process involves not only gradual compression of the pores but also breaks down relatively large pores into smaller pores, which can cause rapid reduction of permeability. The stiffness is lower, with results of unconfined compression tests showing that the ratio of undrained shear strength to secant modulus is about 150.
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