The coastal areas of the Pacific Ocean suffered extensive damage by the tsunami of the 2011 off the Pacific Coast of Tohoku Earthquake. Since then, it was necessary to develop reinforcement methods to strengthen the existing breakwaters against tsunamis. Therefore, the authors proposed a method to reinforce a breakwater against tsunami by backfilling the space between the breakwater and installed steel pipe piles. A series of model experiments was conducted. In the experiment, the embedment length and space between the piles were selected as parameters to improve the horizontal resistance of the caisson. A horizontal loading experiment was conducted to study the horizontal resistance of the model caisson. The model ground was prepared by dry silica sand #5 under 80% of relative density. Strain gauges were attached to the steel piles to measure the bending moment of the piles along the pile length. The experimental results suggest that the horizontal resistance of the caisson remained stable under a certain embedded length of the piles, and the horizontal resistance of the caisson decreases when the space between the piles is long although the flexural rigidity per unit horizontal length was constant.

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Since 1996, pore water pressures have been continuously measured every 10 min at depths of 80 m (GL-80 m), 402 m (GL-402 m) and 403 m (GL-403 m) on the Tsudanuma campus of the Chiba Institute of Technology in Narashino, Japan. For a long period during the measurements, the periodic behaviour of pore water pressures in the span of a year was such that pore water pressures tended to become low in summer and high in winter. Furthermore, pore water pressures were greatly affected by groundwater withdrawal by some cities in the vicinity of the field site. In this study, the permeability in deep sedimentary ground was predicted using two main methods: The Theis and Jacob methods based on the aquifer test theory and Creager’s and Hazen’s empirical equations. For the Theis and Jacob methods, pore water pressure data at the field site and groundwater withdrawal data for some cities surrounding the field site were employed to predict the coefficient of permeability k. For Creager’s and Hazen’s empirical equations, the values of k were calculated using the grain size analysis results of 37 soil samples collected at a field site. The results obtained from these methods were examined for their applicability to the prediction of permeability in deep sedimentary ground.

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A simplified analytical approach is proposed to study on the behavior of the piled raft foundation with rigid raft subjected coupled loads in layered soils. Employing the shear displacement method, based on the transfer matrix, the pile-pile interaction under vertical load is analyzed. Adopting the modified subgrade modulus, the pile head-pile head interaction under horizontal load is analyzed through the finite difference method. Base on solutions for stresses and displacement in layered elastic half space, the interactions between pile head and soil surface, soil surface and pile head, soil surface and soil surface subjected coupled loads are taken into account to determine the flexibility matrix of the pile group-soil system. Then the load-settlement relationship of rigid piled raft foundations subjected coupled loads, load and settlement of the piles along the depth are obtained. Comparison among the results of the finite element and the calculated results is carried out, and the feasibility of the present method for the analysis of piled raft foundation and the superiority of the modified subgrade modulus are proved.

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The bearing capacity of an open-ended pile depends largely on the degree of soil plugging. Many factors including pile diameter, relative density and the end conditions of piles may influence the degree of soil plugging. The degree of soil plugging is mainly described by the incremental filling ratio (0 and 100% of it imply a fully-plugged and unplugged state respectively). In this paper, the effects of pile diameter and height of an inner sleeved attached to the base of an open-ended pile on the incremental filling ratio are discussed. The experiments were conducted on a medium-dense sandy ground using small-scale model piles. The experimental results suggest that the bearing capacity is influenced by the sleeve height for 50 mm diameter piles while it is independent for 30 mm diameter piles, probably due to the influence on the inner frictional resistance. The results also indicate that a longer sleeve produces a shorter soil plug regardless of the pile diameter. The results of the incremental filling ratio show that the penetration of non-sleeved piles is closer to the unplugged state than the sleeved piles. The results of the IFR also reveal that the degree of soil plugging is affected by the sleeve height of a slightly larger diameter piles of 50 mm while it is independent for 30 mm diameter piles. While the degree of soil plugging remains same after a depth of roughly 1D penetration (D is pile outer diameter) for 50 mm diameter piles, it linearly increases (i.e., decreasing IFR) with the penetration for 30 mm diameter piles.

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Scour effect have a significant impact on the dynamic lateral response of composite caisson-piles foundations (CCPFs) because of the removal of soils around the foundation and the change of stress history of remaining soil. Based on the simplified method with the dynamic Winkler model, a computational method for predicting the dynamic impedance of CCPFs influenced by scour is developed. Subsequently, theoretical results for the response of CCPFs are verified by the 3D finite element method with sponge boundary. Finally, results from a case study show that scour has a great influence on the dynamic stiffness and damping coefficient, and the deeper scour depth increases, the more remarkable influence on the results. Besides the removal of soil around CCPFs resulting from scour effect, it also shows that the change of stress history will further weaken the bearing capacity of composite foundation and enlarge the dynamic response. Thus, ignoring the change of stress history would result in an overestimate of the dynamic impedance. And stress history is also proved to be of great significance to increase the resonant response of composite foundation, while has little influence on the resonant frequency.

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In urban areas with extensive peat ground, such as Sapporo, long-term subsidence of shallow buried structures such as backfilled pipelines has been reported to pose chronic engineering problems. In addition to natural ground water fluctuations, pavement overlaying and nearby traffic loads, the load imbalance due to backfilling itself is suspected to aggravate the problem, as the usually very light peat is replaced by heavier, compacted sandy fills. The objective of this paper is to discuss detailed mechanisms behind the subsidence observed in surface peat layers. In this study, subsidence mechanisms are investigated by performing long-term 2-D model tests and soil-water-coupled finite element (FE) analysis using a Modified Cam Clay-type model tuned to express the stiffness and consolidation characteristics peculiar to peats.

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A bridge column integrated by multiple steel pipes and connected directly to piles without a footing has been proposed to design a rational foundation of the column. Based on the past achievements, the proposed substructures possess an excellent advantage of reduction of strain at the column through strain decentration at footing point. In addition, reduction in footing weight contributes to decrease pile strain. On the other hand, the proposed substructure has some disadvantages i.e. increase in strain and displacement of piles. But it has been revealed that the strain generated at piles can be minimised by using a beam in the ground. In this paper, the seismic performance of the bridge column structure grounded in liquefiable sand is evaluated based on the large-scale shaking tests using a bridge column model with the scale of 1/20. Subsequently, a soil-water coupled FE analysis is conducted to reproduce the experimental results and confirm the seismic performance and the detail of the mechanism.

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The Quaternary alluvial deposits was widely distributed in the field of hydropower station, composed of the silty sand with mud, the silty sand and the gravel. The Quaternary alluvial was with the low average standard compaction number and the loose structure, high compressibility and low bearing capacity, particularly its saturated silty sand had the potentiality of liquefaction. According to these characteristics, the single mixed pile foundation was used to improve its bearing performance. There were series of static loading tests in situ with the different conditions including the three different pile’s length and the two different bearing stratums.Combined with the data of numerical analysis, its failure modes were analyzed and both of the vertical ultimate bearing capacity and the characteristic value of bearing capacity were obtained. Study showed that: 1)when bearing stratums was the compacted sands or the gravel, the P-S curve was the gradually falling type with no steep drop and the P-Δs/ΔP curve had plain stage or sharp, 2)when pile length was 14.0m and 19.0m respectively, the pile failuer was resulted by the pile flaw，their ultimate bearing capacity by the static loading test was lower than the ultimate strength value of core of pile and the one calculated by the minimum combination, when pile length was 11.0m, it was controlled by the ultimate bearing capacity by the resistance from the soil surround pile and the resisitance from the pile’s tip. The study was the foundation for the follow up tests of grid structure mixed pile composite foundation and as the reference for the similar engineering.

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The problem that occurs during open-ended steel pipe pile installation is that soil enters the pipe and develops frictional resistance that further prevents soil intrusion, causing plugging and increased piling resistance. The steel pipe pile with tapered tip (tapered tip pile) restrains plugging and piling resistance. To apply the tapered tip pile as end-supported piles, it is essential to clarify the bearing capacity mechanism suitable for tapered shapes. In addition, it is not possible to apply the bearing capacity mechanism of the flat tip pile (straight pile). The purpose of this paper is to reveal the piling performance and the bearing capacity by experiment and to propose the bearing capacity model based on the mechanism in a fully plugged mode. Experiments were conducted on model-tapered pipe piles installed in sands with different soil conditions to investigate the effects of the pile shape on piling performance and bearing capacity. Extending the combination theory of Prandtl and cavity expansion, bearing capacity model and formula incorporating shape parameters were derived. Theoretical values were good agreement with the experimental results.

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Surcharge loading, phreatic level decline and other factors cause negative skin friction on the peripheral surface of piles, which increases engineering insecurity. Negative skin friction has been researched deeply by filed, scale and numerical test. However, few studies have considered the influences of drainage boundary conditions on pile settlement considering consolidation of surrounding soils. Based on 1D perfect elasto-plastic model, this paper demonstrates that pile-soil elastic relative displacement at the position of neutral point is zero, and derives a simplified settlement calculation method. Calculation results show that change of neutral point position makes the pile-soil relative displacement not zero. Finally, the proposed method is verified by FEM method and used to analyze the influence of different drainage cases on the pile settlement.

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When The Tohoku-Pacific Ocean Earthquake occurred on the March 11th, 2011, harbor facilities such as breakwaters and tide embankments suffered serious damages from the Tsunami. The following three mechanisms are considered to be related to the collapse of the breakwater: 1) scouring of the mound due to overflow, 2) the horizontal force originated from the difference of water level between the sea side and the harbor side on the breakwater, and 3) reduction of bearing power of the mound resulting induced by seepage flow. However, the mechanism of the instability of the rubble-mound by overflow and seepage flow induced by tsunami is not fully clarified. In this study, the formula to calculate the stable weight of rubble-mound was proposed in consideration of the overflow and seepage flow, and hydraulic model experiments were conducted on Kamaishi Bay breakwaters as the subject in order to confirm the effectiveness of the proposed formula. Using the results, the stability of the breakwater was evaluated from the geotechnical engineering point of view.

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