Yasuo Toyosawa

Development of a New Soil Tensile Strength Test Apparatus

This paper describes a newly developed apparatus for measuring the tensile strength of compacted and pre-consolidated saturated soft to medium clayey soils. This apparatus is simple to use to perform a soil tensile strength. Two types of tensile molds are described and results obtained from them are compared. Repeatability of test results is also verified. Effects of water content, dry density, proportions of particle size and amount of fines present in the soil are also examined. Tensile strength and unconfined compression test results are compared. It was found that the ratio of unconfined compression strength (qu) to tensile strength (qt) for statically compacted Kanto loam soil is around 12.5. In case of compacted Kanto loam, maximum value of qt and qu is obtained around 50~60% of water content for all the samples prepared at three different d ry densities (�d = 0.66, 0.68 and 0.7 g/cm 3 ). Both types of strength decrease on wet and dry sides of this maximum value. In case of mixtures of NSF clay, silt and sand in different proportions , it is observed that with the increase in the amount of finer particles, both qt and qu increase. But with the increase in the size of finer particles , reduction in the strengths is observed. In case of pre-consolidated saturated NSF clay, tensile and unconfined compression tests are performed. Saturated NSF clay samples are prepared under the preconsolidation stresses of 100, 200 and 300 kPa. The ratio of strength (qu/qt) obtained for this saturated NSF clay is around 6.

Factors Affecting Tensile Strength Measurement and Modified Tensile Strength Measuring Apparatus for Soil

In this paper tensile strength measuring apparatus developed by Tamrakar et al. (2005a,b) was used to measure the tensile strength of one dimensionally consolidated saturated NSF-clay and statically compacted unsaturated mixtures of NSF-clay, CFP-silt and Toyoura-sand. Tensile strength (qt) obtained from the tensile tests were compared with the unconfined compressive strength (qu). It was observed that the ratio qu/qt lied within the range of 2 to 3 for saturated NSF-clay and 4 to 16 for compacted mixtures. Effect of specimen thickness within the tensile mold, number of compaction layers and tensile pulling rates on the tensile strength were also examined. Comparing the specimen thickness within the tensile mold, it was found that the specimen having 5 cm thickness gave the minimum value. Also, tensile strength increased with the increase in the number of compaction layers. As in other shear strength, increment in the tensile strength was observed beyond tensile pulling rate of 0.34 mm/min. But below this pulling rate also, some increments were observed.

Failure Mechanism of Anchored Retaining Wall Due to the Breakage of Anchor Head

In this research, a case history of temporary earth support collapse is first illustrated briefly and the mechanisms of accident occurrences are introduced, with the results showing that the shallow penetration of piles mainly caused the sequences of collapse. In order to understand these failure characteristics and mechanisms, centrifuge model tests using an in-flight excavator were carried out. The failure mechanism of the retaining wall in this labour accident was first demonstrated using centrifuge model tests by Toyosawa et al. Failure mechanism of anchored retaining wall, 667–672 (1996). In this paper, we added some viewpoints regarding the mechanism of the retaining wall and it was thus clarified that the active and passive earth pressures in the retaining wall increased during excavation and then the anchor head exceeded the capacity with respect to tensile stress. As a result, the retaining wall and ground behind the wall collapsed suddenly.

Analysis of labour accidents in tunnel construction and introduction of prevention measures.

At present, almost all mountain tunnels in Japan are excavated and constructed utilizing the New Austrian Tunneling Method (NATM), which was advocated by Prof. Rabcewicz of Austria in 1964. In Japan, this method has been applied to tunnel construction since around 1978, after which there has been a subsequent decrease in the number of casualties during tunnel construction. However, there is still a relatively high incidence of labour accidents during tunnel construction when compared to incidence rates in the construction industry in general. During tunnel construction, rock fall events at the cutting face are a particularly characteristic of the type of accident that occurs. In this study, we analysed labour accidents that possess the characteristics of a rock fall event at a work site. We also introduced accident prevention measures against rock fall events.

Analysis of death labour accidents relating with drag-shovels and investigation of the countermeasure for safety

In Japan, we have more than 600,000 drag-shovels and the death labour accidents relating with drag-shovels happened more than 70 per a year until 2006. So that we analysed the accidents relating with drag-shovels in details. As a result, there are 4 types of labour accidents: a drag-shovel falls down due to its unstable condition, a burden hanged hits a worker, slope or trench collapses due to excavation and weight of a drag-shovel, a drag-shovel drives backward or pivots and hits a worker. It is revealed that a drag-shovel becomes unstable condition due to dynamic operation such as driving forward or pivoting in a slope and that a drag-shovel and worker are working together within the maximum excavation radius of the drag-shovel. As the countermeasure for the safety, we recommend the use of a drag-shovel with ROPS (Roll-Over Protective Structure) and fastening a seat belt, to set the maximum stable grade considered with dynamic operation, the system alerting both an operator and worker to their approach. Language: ja