No abstract

Background: Earthquakes in liquefaction-prone areas are frequently followed by the settlement of surface structures due to subsoil liquefaction. This paper aims to study the influence of geosynthetics along with gravel usage to reduce the vertical soil displacement caused by liquefaction using a shake table equipment. This influence is analyzed by means of measuring soil acceleration, pore water pressures and vertical soil deformation due to the shaking process. Results: Results of a series of 1-g shaking table tests which have been conducted in different initial relative densities which are 50% (loose sand conditions) and 90% (dense sand conditions) to evaluate the performance of proposed mitigation against settlement problem are presented. It is found that ground settlement reduced around 11.4 mm for loose sand conditions, from 20.9 mm in the case with no countermeasure (Case 1) to 9.5 mm in the Case reinforced with gravel and geosynthetics Type II (Case 4). Correspondingly, for dense sand states, the settlement decreased by about 1.8 mm, from 5.6 mm in the Case 1 to 3.8 mm in Case 4. Moreover, a differential settlement between loose sand and dense sand conditions decreased as well, around 9.6 mm, from 15.3 mm in the Case 1 to 5.7 mm in Case 4. Conclusions: By conducted a series of shake table tests, it is confirmed that the vertical ground displacement decreased by the use of geosynthetics and gravel up to 54% and 32% for loose sand and dense sand states, respectively. Furthermore, test results also show that there is a decrease in the differential settlement between loose sand and dense sand conditions, around 62%.

Species of root-knot nematode (RKN) from green pepper fields in Miyazaki, Kagoshima, Kochi, and Ibaraki prefectures were surveyed. Ten to second juveniles (J s) and female adults were collected, respectively, from each field and the species were identified individually by PCR-RFLP method. As a result, all RKN specimens, except one, were Meloidogyne incognita. Then each infested soil sample from of the fields was inoculated to breeding lines of nematode-resistant chili peppers (CM , LS and PI ). Many galls and egg masses were observed after the inoculation in (ca. %) of the infested soils. This indicates that resistance-breaking nematodes dominated at a high frequency in these fields. Nematol. Res. ( ), -( ).

Liquefaction-induced lateral spreading has imposed damages to structures during past earthquakes. This paper presents experimental results of a series of 1-g shaking table tests on models reinforced with gravel and geosynthetics subjected to liquefaction-induced lateral spreading. Firstly, observations linked with the mechanism of lateral spreading based on the test without remedial measures are presented, followed by the results based on the test with remedial techniques by using gravel only and then gravel combined with geosynthetics as well. Furthermore, in order to obtain the additional results from the use of gravel and geosynthetics, further tests were done by varying the position of the geosynthetics in the gravel, which were at the bottom, in the middle, and at the top of the gravel layer. General test results including timehistories of accelerations, pore water pressures and displacements are presented and discussed in this paper. The results indicated that by applying the proposed mitigation measures, the seismic performance of the soil models can be improved by reducing lateral ground displacement, which best results obtained from soils reinforced with geosynthetics at the bottom and in the middle of the gravel layer.