Stability of a circular tunnel in cohesive-frictional soil subjected to surcharge loading

The stability of circular tunnels in cohesive-frictional soils subjected to surcharge loading has been investigated theoretically and numerically assuming plane strain conditions. Despite the importance of this problem, previous research on the subject is very limited. At present, no generally accepted design or analysis method is available to evaluate the stability of tunnels/openings in cohesive-frictional soils. In this study, continuous loading is applied to the ground surface, and both smooth and rough interface conditions are modelled. For a series of tunnel diameter-to-depth ratios and material properties, rigorous lower- and upper-bound solutions for the ultimate surcharge loading are obtained by applying finite element limit analysis techniques. For practical use, the results are presented in the form of dimensionless stability charts with the actual tunnel stability numbers being closely bracketed from above and below. As an additional check on the solutions, upper-bound rigid-block mechanisms have been developed and the predicted collapse loads from these are compared with those from finite element limit analysis. Finally, an expression that approximates the ultimate surcharge load has been devised which is convenient for use by practising engineers.     

The effect of a thin weak layer covering a basalt block on the impact cratering process

To clarify the effect of a surface regolith layer on the formation of craters in bedrock, we conducted impact-cratering experiments on two-layered targets composed of a basalt block covered with a mortar layer. A nylon projectile was impacted on the targets at velocities of 2 and 4 km s^?1, and we investigated the crater size formed on the basalt. The crater size decreased with increased mortar thickness and decreased projectile mass and impact velocity. The normalized crater volume, π_V, of all the data was successfully scaled by the following exponential equation with a reduction length λ₀: ${\pi }_{\text{V}}=b_0{\pi }_{\text{Y}}^{-b_1}\exp (-\lambda /{\lambda }_0)$, where λ is the normalized thickness T/L_p, T and L_p are the mortar thickness and the projectile length, respectively, b₀ and b₁ are fitted parameters obtained for a homogeneous basalt target, 10^?2.7±0.7 and ?1.4 ± 0.3, respectively, and λ₀ is obtained to be 0.38 ± 0.03. This empirical equation showing the effect of the mortar layer was physically explained by an improved non-dimensional scaling parameter, ${\pi }_{\text{Y}}^1$, defined by ${\pi }_{\text{Y}}^1=Y/({\rho }_{\text{t}}{u}_{\text{p}}^2)$, where u_p was the particle velocity of the mortar layer at the boundary between the mortar and the basalt. We performed the impact experiments to obtain the attenuation rate of the particle velocity in the mortar layer and derived the empirical equation of $\frac{u_{\text{p}}}{v_{\text{i}}}=0.50\exp \left(-\frac{\lambda }{1.03}\right)$, where v_i is the impact velocity of the projectile. We propose a simple model for the crater formation on the basalt block that the surface mortar layer with the impact velocity of u_p collides on the surface of the basalt block, and we confirmed that this model could reproduce our empirical equation showing the effect of the surface layer on the crater volume of basalt.     

Restitution coefficients and sticking velocities of a chondrule analogue colliding on a porous silica layer at impact velocities between 0.1 and 80 m s−1

To study the accretional growth of rimmed chondrules and their agglomerates in the solar nebula, we measured the restitution coefficients, ε, and the sticking velocities to a porous silica layer, v_c, by impacting the silica layer with a glass ball at velocities from 0.1 to 80 m s^?1. We used a porous silica layer covering a basalt block with thicknesses ranging from 1/5 of the glass ball radius to equal to the glass ball radius as a rimmed chondrule analogue, and the porosity of the silica layer was set to be 70%, 80%, 85%, and 90%. Collisional experiments were conducted by means of the free fall method or by the use of a spring gun or a gas gun, allowing us to vary the impact velocity. We used a laser displacement meter to estimate the impact and rebound velocities as well as the acceleration during the collision at impact velocities below 1 m s^?1. As a result, the sticking velocity, v_c, of 90%- and 85%- porosity layers with a thickness equal to 1/2 of the glass ball diameter was 0.44 and 2.4 m s^?1, respectively. On the other hand, we found a distinct barrier to sticking for smaller-porosity layers: the silicate layer with a porosity smaller than 80% never exhibited sticking at any impact velocity below 1 m s^?1. Instead, we observed a rebound effect with restitution coefficients larger than 0.2. In the case of a silica layer with a porosity smaller than 80%, we observed the sub-sticking condition defined by ε < 0.1 at velocities extending from 5 m s^?1 to 70 m s^?1.     

The nationwide investigation of endocrine disruptors in sediment of harbours

Various types of endocrine disruptors or environmental hormones flow from their sources down into harbours through rivers and other watercourses, and are accumulated in sediment on the sea bottom. Tributyltin, which has been used as paint for ship bottoms, is considered one of the endocrine disruptors.In close cooperation with the other ministries and agencies, the Ports and Harbours Bureau of the Ministry of Land, Infrastructure and Transport carried out an investigation in 1999 to determine the actual condition of 12 endocrine disruptors in the sediment of 39 harbours, in order to gather fundamental data to be used in future examinations of policy. Furthermore, in 2000 the bureau chose seven harbours out of the above 39 harbours as subjects of an additional investigation regarding the surface distribution of endocrine disruptors in the harbour areas and the synchronistic change of accumulation of dioxin and other substances. As the result of the investigation regarding the surface distribution of endocrine disruptors accumulated in seven harbours, relatively high concentrations were measured in the innermost parts of harbours and the mouths of rivers. Synchronistic changes in the amount of dioxin and other substances accumulated in sediments of five harbours were determined. Small amounts of dioxin and other substances, including an especially small amount of coplanar-PCBs, were found in the layers formed before or around 1950. Relatively large amounts of these substances were measured in the upper layers formed during roughly 1960-1990, though no significant yearly differences in concentration could be identified. This result coincides with the facts that, during roughly 1960-1980, PCP and CNP were used as agricultural chemicals and full-scale production of PCBs started in 1960.     

Terrestrial heat flow at Hirabayashi on Awaji Island, south-west Japan

Abstract Terrestrial heat flow at Hirabayashi in Awaji Island, south-west Japan, was investigated using the deep borehole penetrating through the Nojima Fault, which was activated during the 1995 Hyogo-ken Nanbu earthquake, by measuring the thermal conductivity of basement rocks. Using the temperature logging data, the value of terrestrial heat flow in Hirabayashi was found to be 56.6 ± 5.2 mW/m². The relationship between cut-off depth of aftershocks of the Hyogo-ken Nanbu earthquake in Hirabayashi and terrestrial heat flow are discussed. The cut-off depth roughly corresponds to isotherms of 300°C.     

Coastal upwelling along the north coast of Papua New Guinea and El Niño events during 1981–2005

We investigate the relationship between sea surface temperature (SST) cooling and upwelling along Papua New Guinea’s (PNG) north coast before the onset of El Niño events using a hindcast experiment with a high-resolution ocean general circulation model. Coastal upwelling and related SST cooling appear along PNG north coast during the boreal winter before the onsets of six El Niño events occurring during 1981–2005. Relatively cool SSTs appear along PNG north coast during that time, when anomalous northwesterly surface wind stress, which can cause coastal upwelling by offshore Ekman transport appearing over the region. In addition, anomalous cooling tendencies of SST are observed, accompanying anomalous upward velocities at the base of the mixed layer and shallow anomalies of 27°C isotherm depth. It is also shown that entrainment cooling plays an important role in the cooling of the mixed layer temperature in this region.     

Geochemical constraints on the depositional environment of the 1.84 Ga Embury Lake Formation,Flin Flon Belt,Canada

The Flin Flon Belt of Canada contains Paleoproterozoic volcanic–sedimentary sequences that are related to the Trans‐Hudson Orogeny. The sequences include island arc volcanic and volcaniclastic rocks (Amisk Group) that are unconformably overlain by subaerial sedimentary rocks (Missi Group), and younger deep facies sediments. In the Flin Flon area, several north–south trending faults divide the sequences into blocks and obscure the depositional environment of the deep facies sediments. Locally, within the Flin Flon area, the Embury Lake Formation is in fault contact with island arc volcanic–sedimentary sequences of the Amisk and Missi Groups. To identify the depositional environment of the Embury Lake Formation, we used lithologic and geochemical approaches. Here, we report carbon isotopic values in organic matter (δ¹³C_org) and sulfur isotopes (δ³⁴S), as well as total organic carbon and total sulfur measurements for the black shale in the formation. Samples were taken from a drill core that contains alternating bands of sandstone and black shale. Pyrite in the black shale is divided into four textural types: euhedral, vein‐type, elliptical, and microcrystalline. Microcrystalline pyrite is typically generated by microbially mediated sulfate reduction. An extremely low S/C ratio (avg. = 0.04) is consistent with lacustrine deposition. The ranges of δ¹³C_org (?36 ‰ to ?27 ‰) and δ³⁴S (+3.0 ‰ to +7.7 ‰) values can be explained by bacterial photosynthesis that involved Calvin cycle and acetyl CoA pathways, and sulfate reduction in a low‐sulfate environment. Considering the depositional age reported in a previous study of < 1.84 Ga, the Embury Lake Formation was likely emplaced in a lacustrine setting during the Trans‐Hudson Orogeny.     

Origin of the Tonaru body in the Sanbagawa metamorphic belt,SW Japan

Zircon U–Pb dating of the Tonaru metagabbro body in the Sanbagawa metamorphic belt, southwest Japan, suggests that igneous events at ca 200–180 Ma were involved in the protolith formation. The trace element compositions of the Tonaru zircons are enriched in U (a fluid‐mobile element) and Sc (an amphibole‐buffered element), and depleted in Nb (a fluid‐immobile element), suggesting that the parental magmas related to the Tonaru metagabbros formed in an arc setting. Integration of our results with previous studies of the metasedimentary rocks in the Tonaru body clearly indicates that the protoliths of the Tonaru body were produced by oceanic‐arc magmatism. With the previous geochronological and geological studies, the tectono‐magmatic–metamorphic history of the Tonaru and other mafic bodies in the Sanbagawa metamorphic belt may be summarized as follows: (i) the protolith formation by the oceanic‐arc magmatic event had occurred at 200–180 Ma; (ii) the protoliths were accreted in the trench at ca 130–120 Ma; and (iii) they were completely subducted into the depth of the eclogite‐facies condition after 120 Ma.