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Pumice-rich soils originating from volcanic eruptions are deposited in various parts of the world, such as in the central region of North Island, NZ. The pumice sand components of these natural pumiceous (NP) soils are known to be crushable and lightweight, resulting in a significant difference in their cyclic resistance ratio (CRR) and small-strain shear modulus (Gmax) when compared to hard-grained (quartz) sands. In this paper, the results of a number of cyclic triaxial and bender element tests performed on reconstituted specimens of three types of NP sands having different pumice contents (PC), as well as on quartz-type Toyoura sand specimens, are discussed. Then, the concept of modified cyclic yield strain, εay,m, which relates the CRR of the specimen to its Gmax, is used. The results indicate that εay,m appears to be dependent only on the soil type, and independent of the confining pressure applied and the relative density of the specimen. All NP sand specimens show higher εay,m when compared to Toyoura sand because of their higher CRR and lower Gmax, with values of εay,m increasing as the PC of the specimen increases. Based on the results obtained, an empirical chart is developed to estimate the CRR of NP sands from their shear wave velocity (Vs) values under field conditions.

In the study of geotechnical hazards, such as soil liquefaction and landslides, the analysis of soil movements is always one of the major preoccupations. An efficient movement sensing technique requires the tracking of subsurface soil for the purpose of examining the mechanism involved. A magnetic tracking system is therefore proposed, with permanent magnets as trackers and magnetometers as receivers. When permanent magnets, deployed within the soil to serve as excitation sources, move with soil body during a geotechnical event, they generate static magnetic fields whose flux densities are related with the positions and orientations of the magnets. Magnetometers are used as receivers to detect the generated magnetic fields, which can be further used in calculating the magnets' locations and orientations based on appropriately developed algorithms. Comparison between situations where the trackers are exposed to air and embedded within soil was conducted to evaluate the influence of soil (wet and dry) on the tracking accuracy. Also, multi-objective tracking is realized by using the particle swarm optimization (PSO) technique combined with interior-point algorithm. The tracking errors are evaluated and applications of the proposed system in small-scale laboratory tests for geohazards are discussed.

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/[cm.sup.3], 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/[cm.sup.3], 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. Key words: pumice, solid density, apparent density, particle shape, void, computed tomography. Resume : La pierre ponce est presente en Nouvelle-Zelande et est importante pour la construction d'infrastructures, mais elle n'est pas facilement caracterisee in situ. C'est un materiau unique dont les particules cedent aisement sous la pression d'un ongle de la main, le rendant probablement le materiau le plus delicat parmi les sols broyables rencontres a differents endroits sur la planete. Dans cette etude, nous avons analyse des particules de pierre ponce de differentes tailles a l'aide d'un appareil de tomodensitometrie (CT) a balayage des rayons-x dans le but d'etudier la microstructure des particules. A l'aide de l'analyse d'images, nous avons pu determiner la densite du solide de la ponce de fa^on plus precise que par la methode standard, et ainsi demontrer que la densite augmente lorsque la taille des particules diminue. Les resultats de l'analyse CT ont demontre une densite du solide d'environ 2,2 g/[cm.sup.3], ce qui est similaire a la valeur la plus elevee obtenue par la methode standard. Cependant, la densite apparente de l'analyse CT etait de 0,89 g/[cm.sup.3], ce qui est inferieur a la densite de l'eau, et confirme que presque toutes les particules de ponce flottent sur l'eau. De plus, selon les observations, le volume des vides sur la surface est nettement superieur au volume des vides internes. Aussi, la forme des particules d'un sable de ponce a ete analysee et compare a d'autres sables naturels. Enfin, les analyses montrent que les particules de ponce sont tres fragiles non seulement parce qu'elles sont poreuses, mais aussi en raison de leur nature angulaire. [Traduit par la Redaction] Mots-cles: ponce, densite du solide, densite apparente, forme des particules, vide, tomodensitometrie., Introduction Pumice deposits are found in several areas of the North Island of New Zealand. They originated from a series of volcanic eruptions centered in the Taupo and Rotorua regions [...]

Large-scale one-dimensional compression tests were performed in order to analyze the influence of gravel on the compression properties of gravel-mixed decomposed granite soils. After adjusting the gravel contents of the said soil, specimens compacted at a certain level of compaction energy and water content were tested. Based on the test results, it was observed that when gravel- mixed decomposed granite soil was compacted at the same energy level, there existed a specific gravel content at which the dry density was maximum and which also produced the minimum compression index. Furthermore, an expression based on two-phase mixture theory was proposed to quantitatively evaluate the effects of gravel content through a material parameter calculated using the theory, and the estimated compression curves agreed very well with the results of the experiments. DOI: 10.1061/(ASCE)GT.1943-5606.0000370 CE Database subject headings: Compression: Density; Gravel; Compacted soils; Granular materials. Author keywords: Compression; Density; Gravel; Compacted soil; Granular material.

In order to simulate the effect of drainage on soils adjacent to gravel drains that are installed as countermeasure against liquefaction, several series of cyclic triaxial tests were performed on saturated sands under partially drained conditions. The condition of partial drainage under cyclic loading was simulated in the laboratory using triaxial testing equipment installed with a drainage control valve to precisely regulate the volume of water being drained from test specimens. Effects of both drainage conditions and loading frequencies on cyclic response were incorporated through the coefficient of drainage effect, [[alpha].sup.*]. Experimental results showed that for sand exhibiting strain softening, the partially drained response was controlled by the critical effective stress ratio while for sand showing strain hardening behavior, the controlling factor was the phase transformation stress ratio. Moreover, test results indicated that the minimum liquefaction resistance under partially drained conditions can be used as a parameter to describe the liquefaction resistance of sands improved by the gravel drain method. From these results, a simplified procedure for designing gravel drains based on the factor of safety ([F.sub.L]) concept was proposed. DOI: 10.1061/(ASCE)GT. 1943-5606.0000051 CE Database subject headings: Cyclic tests; Drainage; Soil liquefaction; Earthquakes; Sand; Soil stabilization; Sand.

A series of undrained cyclic torsional simple shear tests using hollow cylindrical torsional shear apparatus was carried out to investigate the dynamic shear moduli and damping properties of clayey specimens with various sand contents and plasticity indices. The clayey soils used were collected from various sites along the coast of west Japan. Among these clayey soils, a clay sample with intermediate plasticity and another with high plasticity were mixed with silica sand at different proportions in order to examine the dynamic properties of sand-clay mixtures. In addition, experiments were carried out on undisturbed and remolded natural clay specimens with various plasticities. The effects of plasticity, loading frequency and confining pressure on the strain dependent normalized shear modulus and damping ratio were examined. Based on the results, empirical correlations for predicting the normalized shear modulus and damping ratio of remolded sand-clay mixtures at various shear strain levels were proposed. CE Database subject headings: Shear modulus: Damping; Dynamic properties; Material properties; Clays; Mixtures; Cyclic tests; Soil dynamics.

This paper presents the dynamic properties of undisturbed and remolded clays and sand-clay mixtures based on the results of undrained hollow cylindrical torsional cyclic simple shear tests. The clays were obtained from different sites having a wide range of plasticity, covering fluvial and marine sediments. The main focus of this investigation is the dynamic properties of sand-clay mixtures whose properties are intermediate between those of clays and sands. The initial shear moduli are examined in terms of fines content, and conventional plasticity index. An equivalent plasticity index has been defined in the present investigation and a better correlation is obtained between the initial shear modulus of sand-clay mixtures and this parameter than with the conventional plasticity index. Further, a simple method has been suggested to determine the equivalent plasticity index based on the conventional consistency limit tests and grain size analysis. An empirical correlation for predicting the initial shear modulus is also proposed. CE Database subject headings: Shear modulus; Dynamic properties; Material properties; Clays; Mixtures; Cyclic tests: Soil dynamics.

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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.