Research on the Prediction of Stability for the Excavated Slopes by Using Monitoring Systems

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Prior to construction of retaining walls, slopes are excavated in most of slopes. However, some slopes often lose their stability and slope failure occur. Construction workers were often died by an attack of earth fall from collapsed slopes. Accidents by earth fall are large in number next to falling from higher place, traffic accidents and accidents by construction equipments during construction work. As the results of investigation on 219 slopes in all,it was considered to set up monitoring system by the extensometers on 30 percents of the slopes in order to confirm stability of the slopes. According to the measurement of displacements on the slopes, 6 percents of the extensometers showed some displacements. 2 percents of the extensometers showed the displacements of more than 4mm in a hour and gave an alarm for an earth fall to the workers. 0.4 percents of the extensometers were useful for refuge of workers.It is considered that the number of such a construction work reaches to one thousand in a year in Nagano Prefecture including those along city roads and town roads. Worker's accidents by earth fall usually occur once or twice a year in Nagano Prefecture. It may be reasonable value that 0.4 percents of the extensometers gave useful information. As the results of displacement measurement at many slopes, it has been clear that the monitoring system is effective not only for refuge of workers but also for quick performance of construction work. Also, it is reasonable to give alarm with displacements of 4 mm in an hour.