The present study investigated the application of zero valent iron to remediate the arsenic in naturally contaminated groundwater. A performance evaluation was conducted in the laboratory on groundwater contaminated with artificial arsenic using sodium arsenate (Na₂HAsO₄.7H₂O) to simulate the arsenic concentration in the groundwater. Batch and column experiments were performed to evaluate the arsenic removal capacity by zero valent iron and the removal mechanism. The flow rate (up-flow mode) was maintained for 180 days in each column. The results from both the batch and the column experiments showed that more than 99% of the arsenic was removed successfully. In the column experiments, the arsenic was efficiently removed and the arsenic concentration in the treated water decreased to below the limit of 10 μg /L (WHO's standard) even when the columns were packed with only 25% ZVI by volume. We used SEM and XRD to characterize the surface morphology and the corrosion layer which formed on pristine ZVI and arsenic-treated ZVI to elucidate the arsenic removal mechanism. XRD and SEM results revealed that ZVI gradually converted to a magnetite/maghemite corrosion product mixed with lepidocrocite. Adsorption followed by co-precipitation was an important pathway to removing the arsenic by ZVI. Our results suggest that ZVI, combined with sand, is a suitable candidate for the ex-situ treatment of groundwater in the neutral pH range and in the presence of dissolved oxygen.

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In recent years, serious damage has been done to retaining structures because of large earthquakes. In order to establish practical methods for evaluating the seismic earth pressure, which is one of the important external forces acting on retaining structures during large earthquakes, a series of shaking table tests was conducted on retaining wall (RW) models. The experiments revealed that the seismic active earth pressure was considerably smaller than that obtained by the Mononobe-Okabe theory, particularly under a large seismic load. Furthermore, it was demonstrated that the seismic earth pressure had an upper limit, which was determined by the force equilibrium of the soil wedge at the critical state when the RW lost its stability. On the basis of the test results, a new method to evaluate the seismic earth pressure for practical designs under a large seismic load has been suggested. This proposed method provides a reasonable earth pressure as well as an angle of failure plane, those of which depend on the seismic stability of the retaining wall. It has been confirmed that earth pressure obtained by the proposed method agrees well with the measured seismic earth pressure exerted on several retaining walls with different degrees of stability.

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An apparatus has been developed to model the excavation of a tunnel in the laboratory. With this apparatus, 2D model tests are carried out to investigate the surface settlement and the earth pressure brought about by the tunneling. Finite element analyses using an elastoplastic subloading t_ij model are also conducted. The influence of volume loss on the surface settlement and the earth pressure, due to the shallow tunnelling, is illustrated based on the model tests and the corresponding numerical analyses. It is revealed that the surface settlement troughs and the earth pressure distributions around shallow tunnels depend on both the volume loss and the crown drift of the tunnel. The effect of the interaction between the tunneling and existing nearby foundations is also demonstrated in this paper. For existing foundations, the building loads control the surface settlements and the zone of deformation during the tunnel excavation. The behavior of the foundations depends on the deformation mechanism of the ground during the tunnel excavation. The induced axial force and bending moments in the piles of a piled raft are investigated numerically, and it is shown that the axial force changes due to the stress relaxation of the ground. Bending moments are induced in the piles at a lower value of soil cover due to the differential settlement of the piled raft.

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Dynamic centrifuge tests were performed using soil-footing-superstructure models to investigate the effects of the roughness of the soil-footing interface on the uplift and the resulting vertical acceleration of the footings during strong shaking. Four footing models, each of which had a smooth or rough surface and was embedded or not embedded in soil, were subjected to strong shaking. The horizontal shearing and the vertical compressive forces on the base of each footing, as well as the earth pressure and the wall friction forces on the active/passive sides of each footing, were elaborately measured with newly developed 2D load cells. It was shown that (1) the collision impulse of the uplifted footing against the ground induced an extremely high vertical acceleration of the structure, which was much larger than could be induced by the vertical movement of the gravitational center of the structure; (2) the vertical acceleration caused by the collision impulse increased with the induced rotation angle of the footing; (3) if the footing was not embedded in the ground, the rotation angle and the resulting vertical acceleration tended to be larger for the rough footing than for the smooth footing, probably because the larger horizontal sliding of the smooth footing was able to reduce the footing rotation; and (4) if the footing was embedded, by contrast, the rotation angle and the resulting vertical acceleration tended to be smaller for the rough footing than for the smooth footing, probably because the larger wall friction that developed on the passive side in the rough footing was able to reduce the footing rotation.

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Experimental data are presented in this paper to study the instability behavior of sand in strain path testing under plane-strain conditions. K₀ consolidated strain path tests were conducted on Changi sand using a plane-strain apparatus. The test results show that the occurrence of pre-failure instability under plane-strain conditions is affected by the void ratio and the strain increment ratio. This is consistent with previous findings established under axisymmetric conditions. However, instability behavior of medium dense sand in strain path-controlled plane-strain tests can also be affected by shear band formation. In this case, on-failure instability takes place and failure is likely caused by shear band development. This observation is different from that in triaxial strain path-controlled tests where shear bands do not normally occur.

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In tropical and subtropical regions, shallow landslides often occur in residual soil slopes. Short-duration, high-intensity rainfall will increase the pore-water pressure. As a result, the shear strength of the soil in the slopes decreases and the stability of the slopes is affected. In this study, horizontal drains were installed in a residual soil slope in Singapore in order to improve the stability of the slope. The slope was instrumented with tensiometers and piezometers to investigate the effectiveness of the horizontal drains as a slope stabilization method against rainfall-induced slope failures. The variations in water table elevation and matric suction in the slope due to rainfall events were monitored. In addition, numerical analyses of the seepage into the slope brought about by the rainfall were carried out, and the results showed a reasonably good agreement with the data obtained from field measurements. The field measurement results indicated that horizontal drains were indeed effective for lowering the water table and for increasing the stability of the investigated slope. Therefore, horizontal drains are considered to be a useful and economical method for improving the stability of residual soil slopes against rainfall.

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Response of tunnels to earthquake induced loads is a complex dynamic soil-structure interaction problem. While there seems to be a general consensus that tunnels in rock perform adequately during earthquake events, the seismic performance of shallow tunnels in soils is less certain. More experimental and field data is needed to better understand the dynamic tunnel-soil interaction. In this paper, the behaviour of relatively shallow tunnels of square cross-section located in a sand deposit is investigated using dynamic centrifuge modelling and complimentary Finite Element analysis. Emphasis is given on the effect of tunnel axis depth on the seismic response of square tunnels. Dynamic centrifuge tests were carried out on model tunnels at different depths of embedment. Accelerations around the tunnel and earth pressures on the linings were measured. Tunnel deformations were also recorded using a fast digital camera. Particle Image Velocimetry (PIV) analyses were conducted to measure soil and lining deformations. Results show that for the cases investigated, the depth of the tunnel does not effect the deformation pattern of the tunnel significantly during an earthquake event; however it affects the amount of amplification of accelerations through the tunnel, the magnitude of dynamic earth pressures and the magnitude of the lining forces.

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A comparative study of the trapdoor problem is proposed in this paper involving experimental model tests on one side and a Discrete Element Method modelling on the other side. Most of the past studies related to the arching effect and the trapdoor problem were performed under plane strain or axisymetric conditions. The observation of the arching mechanisms is indeed simplified under these special test conditions. In this paper, the trapdoor problem was simulated under three-dimensional testing conditions with a square-shaped trapdoor. The granular layers were made with monodisperse glass beads. The arching mechanisms were experimentally investigated with X-ray Computed Tomography. Based on the images obtained, the propagation in the granular layer of the disturbance due to the displacement of the trapdoor was monitored. On the other side, the intensity of the load transfers in the granular material was evaluated with a force measurement apparatus on the trapdoor. In parallel, a numerical analysis involving the Discrete Element Method was conducted to predict both the qualitative and the quantitative phenomena. The gradual local expansion of the granular layer due to trapdoor displacement and the load transfer amplitudes were very well reproduced. An agreement between the experimental and the numerical results was obtained for small displacements of the trapdoor (high load transfers) as well as for larger displacements of the trapdoor.

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Changes in the pore-water pressure of unsaturated soil slopes due to rainwater infiltration comprise a crucial factor which affects the shear strength of soils and may trigger slope failures. Two residual soil slopes in two main geological formations in Singapore, the Bukit Timah Granite and the sedimentary Jurong Formation, were fully instrumented. Real-time monitoring systems were developed to examine the pore-water pressure, the rainfall and the groundwater level of the slopes for over a year. The characteristics of the pore-water pressure distributions in both slopes during rainfall were highlighted and compared. The monitoring results indicate that the residual soil slope of the Bukit Timah Granite has a thicker unsaturated zone due to a deeper groundwater table than the residual soil slope of the sedimentary Jurong Formation. A higher permeability of the residual soil of the Bukit Timah Granite results in more rapid changes in negative pore-water pressure due to rainwater infiltration than the residual soil of the sedimentary Jurong Formation. Therefore, the residual soil slope of the Bukit Timah Granite differs from the residual soil slope of the sedimentary Jurong Formation in the changes in shear strength and the variations in the factor of safety during rainfall. The differing characteristics of the pore-water pressure responses during rainfall for these two residual soil slopes are analyzed in the present study based on the results of field measurements and numerical analyses.

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This paper evaluates the uplift capacity of belled and multi-belled piles in dense sand. A two-dimensional distinct element (DE) analysis was applied in pullout tests on single piles to investigate the uplift resistance of the piles, the soil behavior around the piles, and the interaction between the soil and the pile surface. It was observed from the DE analysis that the soil mass adjacent to the projections of the belled and multi-belled piles moved vertically, and that the soil movements leaned slightly with the occurrence of relative displacement between the soil and the pile surface. A theoretical solution for predicting the uplift capacity of belled and multi-belled piles was derived from an upper bound limit analysis based on the soil movements in the DE analysis. The solution was able to reproduce the ultimate uplift resistance in the DE analysis using the friction angles in the aggregates and on the pile surface that were evaluated from a simulation of direct and simple shear tests. In addition, a continuity equation that satisfied the relationship between the displacement vector of the soil mass adjacent to the projections and the change in volume around the soil mass was proposed for predicting the uplift capacity of actual piles under axisymmetric conditions. The theoretical solution obtained with the continuity equation was in good agreement with the pullout resistance of the belled and multi-belled piles in centrifuge model tests and full-scale tests conducted in situ.

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A major problem in the geotechnical approach to the stability of natural slopes is that there is usually little information on the in-situ geotechnical conditions, because of the extreme difficulty associated with ground investigations of steep slopes covered with vegetation. In this study, a lightweight dynamic cone penetration test (LWDCPT) has been introduced for a geotechnical survey of natural weathered granitic (Masado) slopes. Based on a series of direct shear tests, the internal friction angle and the apparent cohesion of reconstituted Masado soil were found to be fairly closely related to the void ratio and the degree of saturation in the soil. From the laboratory calibration tests, an equation was created to relate the dynamic cone resistance (q_d) and the void ratio of reconstituted Masado under different degrees of saturation. Equations were developed to calculate the internal friction angle and the apparent cohesion from the value of q_d for Masado at a known degree of saturation. LWDCPT and direct shear tests were carried out on undisturbed samples taken from a natural Masado slope. The estimated internal friction angle and the apparent cohesion calculated with the value of q_d in the LWDCPTs agreed fairly well with those of tests on the undisturbed samples obtained in laboratory shear tests.

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This paper offers five recent case histories of piled raft foundations in Japan. The buildings are 19 to 162 m in height above the ground surface and were completed in 2005-2009. The piled rafts were designed based on a numerical analysis using the simplified method developed by Yamashita et al. (1998) with soil deformation parameters evaluated from the soil's shear modulus at very small strains. To confirm the validity of the foundation design, field measurements were performed on the foundation settlements and the load sharing between the rafts and the piles by monitoring the five structures from the beginning of their construction to 17 to 60 months after the end of their construction. The measured settlements were 19 to 24 mm, and the ratios of the load carried by the piles to the effective load of each structure in the tributary area, α′_p, were estimated to be 0.61 to 0.93 at the end of the observation period. The predicted maximum settlements and angular rotations of the rafts in the design were generally consistent with the measured values, and the ratios of the load carried by the piles to the total load assumed in the design were also consistent with those estimated from the measurements. Based on the measurement results from ten case histories, namely, five previously published case histories and five from the present study, it has been found that the value of α′_p generally decreases as the pile spacing ratio is increased. The value of α′_p seems to decrease gradually with a pile spacing ratio larger than about six, whereas the value of α′_p seems to decrease significantly as the pile spacing ratio is increased from about four to six. Based on the measurement results, it is suggested that piled rafts work more effectively at a pile spacing ratio of larger than about six, where at least 30% of the effective load of the structure can be carried by the rafts.

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The 2007 Niigata-ken Chuetsu-oki (Off Mid-Niigata) earthquake caused the liquefaction of the sandy soil distributed near the coast of the Japan Sea in the middle of Niigata Prefecture. The liquefaction-induced damage occurring in many residential areas was investigated in detail by means of victim interviews, visual inspections, Swedish Weight Sounding tests, Standard Penetration Tests, old topographical map examinations, etc. Based on in situ soil investigations, the liquefied soil layers were estimated for each area. As a result, it was confirmed that the liquefied areas were mainly sand dune hinterlands, flood plains, reclaimed old river channels and sandy fills with high groundwater table. Among them, damage was especially serious on land having an inclined ground surface due to the flow of foundations, on the cut-fill borders of artificially developed land due to landslides and at the toes of sand dune slopes due to the thrust of the sliding soil and/or the collision of the sliding soil with objects. These investigation results also revealed that soil improvement by cement mixed columns is an effective countermeasure against liquefaction-induced damage unless lateral spreading of the subsoil arises.

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In a case history of dip slope failure caused by the 2004 Niigata-ken Chuetsu Earthquake, it has been reported that the slope contained a thin sandy soil layer. The layer may have liquefied if it had been saturated at the time of the earthquake. Undrained cyclic triaxial tests comprise one of the available experimental approaches for evaluating the liquefaction behavior of such thin sandy soil layers. In this study, a series of undrained cyclic triaxial tests was performed on specimens containing an artificial sand layer in order to investigate the effects of system compliance that are possibly induced by partial drainage caused by the changes in volume of the filter paper used to saturate the sand layer and the local drainage at the interface among the specimen, the top cap and pedestal, and the rubber membrane. The observed liquefaction behavior depended on the thickness of the sand layer under otherwise similar conditions, suggesting the significant effect of system compliance. By conducting special tests, while correcting the partial drainage, it was possible to reduce its effect on the liquefaction behavior. Cylindrical specimens with a top cap and pedestal, all having the same diameter, exhibited a smaller effect from partial drainage than prismatic specimens with an oversized top cap and pedestal.

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Normalized, non-dimensional relationships for calculating the depths of embedment of sheet pile walls and soldier pile walls embedded in cohesionless soils are presented. Rankine theory for lateral earth pressures in active and passive conditions are used in the analyses. Relationships are presented for cantilever walls and walls propped at crest. The proposed relationships can be used in dry soil conditions and as well as in saturated soil conditions with steady state seepage. The embedment depth relationships are presented in terms of non-dimensional parameters and can be used for a variety of soil conditions, dimensions and spacing of the walls, and depths of excavation. The presented relationships are simple, easy to use, and do not require tedious calculations.

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