There are various types of instruments to measure the tensile force of ground anchors (hereinafter anchors). In general, the strain-gauge type load meter which substitutes the resistance change of the strain gauge with electric signals to measure the tensile force is used. But affected by thermal expansion and contraction of the strain gauge itself, caused by temperature change, the measurements of the strain-gauge type load meter fluctuate even when external force is not acting on the anchors. The characteristics indicated by the temperature and load meter’s measurements may be used to evaluate the stability of a slope. And the state of the anchor’s tensile force is judged by the changes in the tensile force’s percentage to the designed anchor force. But no definite evaluation method for tensile force that fluctuates continuously due to temperature change has been established. In this paper, we focus on the correlation between the temperature and measured value of the load meter, and evaluate the fluctuations in the tensile force of anchors considering the influence of temperature change.
Shimajiri mudstone distributed in southern part of Okinawa Island is regarded as a good bearing layer because of its characteristics of high N-value. On the other hand, it has been reported that many landslides and slope failures were occurred in the artificial and/or natural slopes founded by Shimajiri mudstone. In addition, many damaged anchors have been observed on the artificial slope founded Shimajiri mudstone, and it has been pointed out that the cause may be related to the physical and chemical weathering of Shimajiri mudstone. Hence, in order to understand the weathering mechanism, it is necessary to study the time-related degradation of Shimajiri mudstone from a perspective of mineral composition, microstructure, and mechanical behavior. In this study, the authors focused on the artificial slope founded Shimajiri mudstone in the southern part of Okinawa Island, and investigated the time-related degradation, the characteristics of its slaking, and the composition of minerals such as clay minerals based on the boring survey in both 1986 and 2016. Then, the physical and chemical weathering mechanism and the weathering progression processes of Shimajiri mudstone were discussed. As a result, it was revealed that the damage of the slope is deeply related to the physical and chemical weathering such as swelling/dissolution of clay minerals and/or oxidation of pyrite.
The stability assessment of river levee against intense rainfall and flooding involves predicting variations of the phreatic surface level and pore water pressure through unsaturated seepage analysis. This study is a summary of collective work conducted by JSCE River Levee Research Committee WG2, which was set up in 2012 to investigate the applicability of unsaturated seepage analysis to the levee wetting problems in practice, and to assess the accuracy and robustness of the analysis implemented with different numerical codes by different users. To this end, three levels of round-robin analysis exercise were conducted, in which different degrees of prescription were imposed to analysis conditions. Amongst the main findings from this exercise is that all the numerical codes, whether commercial or home-grown by the authors, output sufficiently accurate and practically identical solutions when same conditions are input, despite the differences in their discretisation methods, integration methods, etc. When the participants were given a total freedom in modelling the given levee’s cross-section and material data, notable variations in the numerical results came out, confirming that each participant’s engineering judgment in conditioning/modelling, not the sensitivity of numerical codes, is the main cause of the diverse outputs. Nevertheless, the variations are on the whole within a range which can be deemed acceptable for most levee engineering purposes.
When block fields exist on the slope along a road, it is necessary to carry out rockfall surveys and take measures to prevent disasters. But rocks fall because of various, complex causative and triggering factors, and it is difficult to standardize the stability of a block field and evaluate it accordingly. The Rock-fall Vibration Survey method was developed for this reason. The survey is carried out by installing a vibration meter on the block field and using the dominant frequency and subtrahend constant of the recorded vibrations to quantitatively evaluate the stability of the block field. With this method, the vibration meter is installed and removed every time a measurement is taken, and measurements taken for only a short period of time are used to evaluate the stability. But it is possible that block field vibrations change, affected by the environment such as weather conditions. In this study, a facility to monitor the vibrations of unstable block fields is built, and points to keep in mind when evaluating the stability of block fields by analyzing the measured data are indicated.
In order to utilize reclaimed gypsums derived from waste plasterboards as ground improvement materials, thermal behaviors of reclaimed gypsums and reagent gypsums are investigated in this paper. Furthermore, simple heating method of judging quality of reclaimed gypsums was examined to determine gypsum hemihydrate content.
As the results, it was found that gypsum dihydrate is changed into gypsum hemihydrate under thermal condition of 90°C and gypsum hemihydrate is changed into anhydrite under that of 120°C with heating of 24 hours. And determining by calculating gypsum hemihydrate content and gypsum dihydrate content with the decrease in mass under the thermal condition of 90°C from 70°C, effectiveness of the estimation of gypsum hemihydrate content by using heating method was shown. Therefore comparing gypsum hemihydrate content determined by both methods of the heating method and the density measuring method, both results were in substantial agreement.
The improvement effect of the sand compaction pile method can be divided into the increase of density and the increase of earth pressure coefficient K0. In this study, we evaluate the effects of density increase and and increase of earth pressure coefficient K0 in sand compaction pile method by using three-dimensional analysis. And we propose the method to model the effects of density increase and K0 increase on N-value appropriately. Firstly, we evaluated the effects of density increase and increase of earth pressure coefficient K0 by using three-dimensional analysis. Also, we confirmed it to be consistent with the existing measurement example. Then, we proposed modeling for the effects of density increase and and increase of earth pressure coefficient K0 and conducted case study. If the earth pressure coefficient K0 could be set or measured appropriately, we could evaluate the ground improvement effect larger than existing method by using proposed method.
The authors have proposed a new fracture grouting method, which can increase densities of liquefiable ground and increase liquefaction resistance by injecting leaf vein shape grout. Since this method can improve liquefiable ground effectively with low grouting ratio (approximately 10% in volume ratio), widely spreading liquefiable ground can be improved economically within a short period. This paper describes results of experimental studies following brief explanation about a concept of the propose method. At first, 4 cases of trial grouting tests were conducted to validate feasibility of the proposed grouting method using a large-scale soil stratum pit. As a results, it was confirmed that leaf vein shape grout could be injected in loose saturated sand ground by a dynamic grouting method, of which specifications were adequately set. Furthermore, increase in density of the improved ground could be evaluated by some soil investigations conducted before and after grouting, such as the standard penetration test, the in-situ seepage test, the PS logging and so on. Finally, a series of shaking table tests were conducted to confirm effect of the proposed method against soil liquefaction during earthquakes. The test results clarified that the loose liquefiable sand ground could be effectively improved by the proposed method and could show almost the same liquefaction resistance with that of the dense sand ground, which was ideally compacted to have the same density assumed in the improved ground.