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COVID-19 is around the world. We attempt to apply three-step method in ISO/IEC Guide 51: 2014 to COVID-19 infection control in the workplace. The results show that the COVID-19 infection control measures include the eradication of the virus, the destruction of infectivity, the detoxification and weakening and the elimination of opportunities for infection as “Inherently Safe Design Measures”, the avoidance of contact as “Safeguarding and Complementary Protective Measures” and the reduction of contact and the avoidance of seriousness as “Information for Use”. Among these specific measures, the New Normal, especially in the manufacturing industries, would be “telecommuting” and “unmanned workplaces”, which are part of the elimination of opportunities for infection, and “changes in flow lines” and “changes in airflow”, which are part of the avoidance of contact. Where “telecommuting” and “unmanned workplaces” are feasible, they should be implemented as much as possible, and where they are not, attempts should be made to minimize human-to-human contact by “changes in flow lines”. In addition, in the area of “changes in airflow”, there are high expectations for future research on how to establish a ventilation design for COVID-19, in which but also the source would be workers themselves, not only combustible gases and toxic gases.

Multistep excavations were implemented at the toe of a large-scale slope model, and the surface displacements in the slope were measured to examine the validity of the relationship between the velocity and acceleration proposed by Fukuzono for excavated slopes. The surface displacement increased both during and after slope excavation, among which the latter was due to creep deformation under a constant stress. The rate of increase in the surface displacement was initially high and then decreased to zero during creep deformation after the excavation without slope failure. However, the surface displacement exhibited an accelerated increase during creep deformation after the final excavation prior to slope failure; the surface displacement increased with small fluctuations even before slope failure occurred. The surface displacement velocity and acceleration also fluctuated notably due to variations in the surface displacement. The trendlines for the derived relationships between the velocity and acceleration were in good general agreement with the measured data at certain locations in the model slope. These relationships were unique at different locations on the slope, while the inclination of the relationship trendline suddenly decreased just prior to slope failure. The steeper trendlines predicted an earlier failure time if the displacement was large and close to the failure condition, whereas they resulted in worse predictions if the displacement was small and far from causing slope failure according to the prediction method proposed by Fukuzono.

In February 2012, a serious accident which resulted in five fatalities happened during a TBM-tunnel construction under the seabed in Japan. The cause of the accident appeared to be due to the Key-segment slipping out of the segment ring by the thrusting tailskin (wire brushes) of the TBM into the segment ring. This resulted in the collapse of the rings, causing the seabed ground and seawater to flow into the tunnel. We investigated how thin and thick segments without any circumferential joints behave under isotropic and anisotropic pressures using small-scale physical model. In the model tests, pressures were applied to the surroundings of the segment rings and the strains at each segment were measured in order to evaluate the damage. In addition, cases where lubrication on the contact area between the K- and B-segments was present or not were investigated and their discrete element simulations were also conducted.

In order to prevent occupational accidents during slope excavation work, it is important to include slope stability in all aspects of construction design. In slope excavation work, the two major factors are the excavation height and the gradient, both of which are prescribed by some guidelines and laws. However, accidents often occur during slope excavation work, even with the required safety gradient, because existing guidelines fail to consider the effects of water. In this study, the stability of a slope with rising groundwater was examined for different excavation slopes. The results show that the slope was stable in the absence of water, but it collapsed when the groundwater rose. We also propose a method for predicting landslides using slope movement measurements. The method uses the standard deviation from past measured values to detect data abnormalities on current measurements. Predictions obtained by this method were classified under advisory, warning, or emergency warning based on the deviation rate between the moving average and standard deviation of past data. It was observed that slope failure can be reliably predicted using this method.

In tunnel construction, shotcrete is sprayed on excavated surfaces to strengthen the walls and prevent rocks from falling off the tunnel face. Soon after, workers enter the face to erect the steel arch support. However, before entering, they must know the maximum rock size supported by the early-age shotcrete. This study aims to reveal the resistance and fracture mechanism of early-age shotcrete when a rock exfoliated from the tunnel face punches through shotcrete. To this end, we developed a novel experimental apparatus in which the strength deformation characteristics of shotcrete were evaluated through a laser scanner by punching a disc rock against the shotcrete on the substrate rock. The punching experiment was simulated, and the fracture mechanism was revealed using the discrete element method. The stress state of shotcrete sequentially reached the tensile failure criterion at the elements adjacent to the edge of the loaded zone. The elements of shotcrete progressively failed at the fracture process zone with punching. Finally, the punching strength of early-age shotcrete was formulated based on its fracture mechanism.

This paper presents results from geotechnical centrifuge tests performed at the Japanese Institute of Occupational Safety and Health (JNIOSH) in Tokyo, Japan. A range of shallow footing configurations with different bearing pressures founded on saturated sand in a laminar box on a shake table was studied using harmonic excitations. The free-field condition was also studied as a reference. The study aimed to address the influence of stand-alone and closely adjacent shallow foundations on the dynamic response of the soil-foundation-structure system. A partially drained response of the soil and a minor dilative response for large values of shear strain were observed for the free-field case. In the case with footings, the settlement was found to be largely due to the footing penetrating the supporting sand. A dilative response of the soil beneath the footings was observed for the stand-alone configurations at the beginning of the base motions, this was not observed in the case of adjacent footings. Adjacent footings also tilt inwards consistently while stand-alone footings did not present a clear tilt pattern. In terms of the acceleration recorded in the near-surface soil beneath the footings, a reduction was observed after a few cycles in the free-field case. This reduction was considerably smaller in the case with footings with no significant differences between the response of the stand-alone and that of the closely adjacent footings.

On February 22, 2011, an epicentral a 6.1 moment magnitude (Mw) earthquake with a seismic center near Lyttelton occurred in the suburb of Christchurch, New Zealand, at 12 : 51 p.m. local time, 17 days before the Great East Japan Earthquake struck off the coast of Tohoku. The authors visited and exchanged opinions with Work Safe NZ, a New Zealand government organization, the Canterbury Rebuild Health and Safety Programme (CRHSP), and Site Safe, a nonprofit construction organization, for the purpose of collecting information regarding the safety and health efforts made by the New Zealand government and its pertinent agencies, as well as understanding the current status of rebuilding and recovery efforts after the Canterbury Earthquake (which started as almost in tandem with recovery efforts in the wake of the Great East Japan Earthquake). RESULTS show that there was little difference between New Zealand's countermeasures on safety and similar efforts made in Japan. However, there were some beneficial activities in New Zealand, such as an update to the system of qualifications; use of a tender system (based on an evaluation of safety and health); and partnerships between clients, contractors, and regulatory agencies. These activities should be implemented Japan to improve the nation's construction industry regarding safety and health. Language: ja

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.

There are around 10 casualties due to rock-fall at cutting face annually in conventional tunnel construction in Japan. As from the analysis conducted on the cases involving such casualties, workers were either killed or seriously injured when they works in front of or near the cutting face. For the purpose of evaluating the mechanism of rock fall at tunnel cutting face, this paper performed experimental tests which involved blasting to excavate a model ground of tunnel cutting face, and then analyzed the stress state which is in the cutting face by using Discrete Element Method (DEM) simulation. Based on the results, the tensile stresses remained even when the action of gas expansion due to blasting has completed. Therefore, it is suggested that rock falls might be induced because of the residual tensile stresses. The tensile stresses would gradually open small cracks between rocks and then rocks may suddenly fall after sufficient crack opening due to gravity.

It is important to predict an onset of slope failures or rock falls for the occupational safety because about 15 to 20 workers were killed by these every year in Japan. Approximately half of the victims suffered from slope failure during slope excavation construction. In this research, in order to predict the time of slope failure during an experimental testing on a full-scale model slope was conducted, and the displacements of the slope surface were monitored during the slope excavation. The surface displacements rapidly increased with the elapsed time after the excavation, and the relationship between the displacements and the elapsed time included an exponential function just before the collapsed. We validated that the time of slope failure could be predicted by the relationship between the acceleration and the velocity of the obtained slope surface displacements. However, in order to predict the time of collapse, the data was required to compute only 2 seconds before the collapse. Therefore, we realised the importance of providing advisory and warning signal to give workers enough time to escape the slope failures. We have discovered that by computing the inverse of velocity of slope surface displacement, advisory and warning signals can be provided 2 minutes before the collapse.

It is important to predict an onset of slope failures or rock falls for the occupational safety because about 15–20 workers were killed by these every year in Japan. Approximately half of the victims suffered from slope failure during slope excavation construction. In this research, in order to predict the time of slope failure during an experimental testing on a full-scale model slope was conducted, and the displacements of the slope surface were monitored during the slope excavation. The surface displacements rapidly increased with the elapsed time after the excavation, and the relationship between the displacements and the elapsed time included an exponential function just before the collapsed. We validated that the time of slope failure could be predicted by the relationship between the acceleration and the velocity of the obtained slope surface displacements. However, in order to predict the time of collapse, the data was required to compute only 2 s before the collapse. Therefore, we realised the importance of providing advisory and warning signal to give workers enough time to escape the slope failures. We have discovered that by computing the inverse of velocity of slope surface displacement, advisory and warning signals can be provided 2 min before the collapse.

Pumice occurs widely in New Zealand and is important in infrastructure construction, but is not readily characterized in situ. It is a unique material, the particles of which crush easily under finger pressure, making it arguably the most delicate of the suite of crushable soils found in various locations around the world. In this study, we scanned pumice particles of different sizes using an X-ray computed tomography (CT) scanning machine to investigate particle microstructure. Using image analyses, we were able to determine the solid density of pumice more accurately than the standard method, which showed increasing density as particle size decreased. Results from the CT scanning showed a solid density of about 2.2 g/cm3, which is similar to the highest value obtained using the standard method. On the other hand, the apparent density from CT scanning was 0.89 g/cm3, which is lower than the density of water, therefore confirming that almost all pumice particles float on water. In addition, the volume of surface voids was observed to be much greater than that of internal voids. Moreover, the particle shape of pumice sand was analyzed and compared to other natural sands. Finally, analyses showed that pumice particles are very fragile not only because they are porous, but also because of their angular nature.

The influence of the model footing diameter and embedded depth on the bearing capacity of circular shallow footings was studied by centrifugal model testing in order to determine a model footing size and embedded depth against particle size in a model ground. In the series of 37 tests, the ground was made by river sand whose particle size was adjusted by sieving to a mean particle size of 0.6 mm. The diameter of the model footing and the embedded depth were considered as influential parameters in this study. The diameter of the model footings varied from 5 to 40 mm and the ratio of the footing diameter to the mean particle size was calculated as 8.3–66.7. The ratio of the embedded depth to the footing diameter was 0, 0.5 and 1.0. As a result, the bearing capacity in the same equivalent diameter of footing was not dependent on the diameter of model footing when the ratio of footing diameter to particle size is more than 50 with any ratio of embedded depth to footing diameter. Our results that the proposed relationship between the ratio of footing diameter to the particle size and the ratio of the embedded depth to the footing diameter can be used to choose a reasonable model footing diameter, embedded depth and the particle size of ground material for centrifugal model tests.

Pumice sand particles have a vesicular nature, making them light and crushable. Previous research showed that the in situ relative density of pumice deposits cannot be estimated from conventional cone penetration testing. Because of this, a need exsits for more study of the geotechnical properties of this material. First, to distinguish compression behavior of loose and dense sand, K0 compression tests were performed on pumice specimens at various strain rates, from 0.33% to 1,000%/min, until a final compression of approximately 33% of the original specimen length was achieved. Second, after compression, the maximum displacement was held constant for a period of time during which the relaxation of the axial stress was monitored. After unloading, the particle-size distribution was measured to confirm particle crushing. From these results, the magnitude of stress relaxation of loose sand was found to be slightly larger than that of dense sand. On the other hand, dense sand particles exhibited more c...

The degree of saturation of ground is conventionally measured at discrete points using transducers, soil moisture sensors, etc. In this paper, a novel method was developed to directly measure the degree of saturation of continuous region of ground by noting the variation in color of the ground as the amount of moisture in the soil changes. In this research, a series of experiments was conducted for the purpose of developing a method to measure the degree of saturation of ground by digital image processing. From photo images taken at various soil moisture contents, the colors of the images were converted into numerical values which were then related to known degrees of saturation. The results of the experiments showed that a method to measure the degree of saturation of ground by image processing was possible. The relation between degree of saturation and luminance value can be expressed in terms of second degree function. Good results were obtained for two soil samples with different colors and grain size distributions. The margin of error was in the order of ±5%. The method was validated through vertical seepage tests, where good agreements were obtained between the measured degrees of saturation by tensiometers and those estimated from the proposed method. The method illustrates the possibility of measuring the degree of saturation of a larger portion of the ground, which is difficult to perform using conventional procedures. With this method, contour diagrams of degree of saturation can be produced, making it possible to visualize the propagation of the saturated region.

The properties of the residual clays derived from in situ weathering of the Waitemata group sandstones and siltstones, found around Auckland, are known to be surprisingly variable. In addition, it is known that the permeability of the material decreases rapidly as the effective consolidation pressure is increased. A possible contribution to both the variability and the rapid decrease in permeability might be the void structure of the soil. The advent of micro-CT (computed tomography) scanning equipment provides an opportunity to examine how the shapes and sizes of the voids change with increasing consolidation pressure. This note presents a discussion on some preliminary results on small specimens of Auckland residual clay. These indicate that at low effective confining pressures there are some quite large macrovoids. These are found to be greatly diminished in size when the effective confining pressure reaches about 200 kPa. From very low effective consolidation pressures up to about 200 kPa the permeability decreases markedly.

本研究では，2種類の画像取得方法を用いて，三軸供試体表面を三次元計測し，表面形状の変形過程を追跡する方法を開発した．画像の取得方法は，8台のデジタルカメラを使用する8カメラ法と，1台のカメラを用い供試体を回転させ8方向からの画像を取得する供試体回転法である．いずれの方法においても3次元座標の計測精度は，0.05mmであることが確認された．圧密排水三軸試験において計測された供試体表面の3次元座標からせん断層を抽出できること，推定されるせん断層の間隙比の変化を評価した結果，豊浦砂のせん断層の間隙比は，残留状態に至る過程で最大間隙比以上となることが認められた．加えて，まさ土のせん断層はその幅を狭めながらせん断が進行することを明らかにした．

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.

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