Undrained shear characteristics of normally and over consolidated remolded peat are investigated using constant volume (CV) ring shear apparatus. Followings are shown in this paper. That is, the shear stress _˜ displacement curve in CV ring shear test shows a peak shear stress which enable us to decide the undrained shear strength τ_MAX of peat. Shear displacement at failure depend largely on both consolidation pressure σ₀ and over consolidation ratio OCR, but it has a unified relationship with void ratio ^e. The initial part of shear stress _˜ displacement curve can be approximated by a hyperbolic curve, and the stress shown by the asymptote is in proportion to τ_MAX. The relationship between τ_MAX and σ₀ did not pass the origin even if sample was normally consolidated, and shear strength ratio obtained from CV ring shear test was smaller than that obtained from the triaxial compression test. The angle of shear resistance in CV ring shear test was also smaller than that in triaxial compression test. Unprecedented shape was observed in stress pass where the stress pass after peak strength did not converge on a envelope.

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It is important to consider the latent hydraulic property of granulated blast furnace slag in order to appropriately evaluate the stress sharing ratio of pile and clay between piles in the design of low replacement ratio SCP method. In this paper, finite element analysis was applied for the low replacement ratio SCP improved ground where sea sand and granulated blast furnace slag were used. Based on the analytical results, it was proven that the stress concentration ratio was n=3-4 in case of the sand pile and n=8-11 in case of the slag pile. The undrained shear strength calculated by finite element analysis coincides approximately with c_u=q_u/2 by the field sampling. In addition, it was proven that the sensitivity of cohesion of the granulated blast furnace slag was bigger than the permeability of it on undrained shear strength of clay between piles.

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The grid-form ground improvement is one of the countermeasure methods against soil liquefaction. The lattice interval was decided from L/H, the ratio of a lattice interval (L) and improvement depth (H), based on shaking table tests in the conventional design. However, this design method needed to make lattice interval small so that improvement depth was small. In order to determine rational lattice intervals of the grid-form ground improvement, the simple calculation was suggested by conducting the two-dimensional equivalent linear analysis that considered lattice intervals, rigidity, and depth of improvement. Furthermore, the three-dimensional effective stress analysis and centrifugal model shaking table tests were carried out for the propriety of the simple calculation. As a result, correlation was seen between the excess pore water pressure ratios provided from the analysis results or the experiment results and the FL value based on the simple calculation. The simple calculation proposed in this study was effective for preliminary setting for a lattice interval of the grid-form ground improvement.

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Many efforts have been done for introducing the ground friction to the design of caisson type pile foundation under condition of large-sized. Ground reinforcing type foundation which has rigid steel bars for reinforcement of the surrounding ground is very effective for increasing of friction under using contact concrete support. It has developed in order to cut down the cost of the foundation for transmission tower or road bridge foundations, these are determined by uplift or horizontal bearing capacity. In this study, the authors investigate the reinforcement effects for vertical bearing capacity of reinforced and un-reinforced foundations under consideration of experimental viewpoint. The outdoor actual size vertical loading tests show the character of friction and the mechanical effect of the reinforcement. The evaluation method which is proposed on facts of experiment and analysis is appropriately demonstrated.

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Permeability of dam foundation is generally evaluated by Lugeon Water Test (LWT). The LWT is conducted according to the "Guidelines for Lugeon Water Test" in Japan. But, these guidelines do not concretely describe the problems concerning unsteady seepage during the LWTs in unsaturated soft rock foundations and an appropriate evaluation method of Lugeon value considering these problems. In the study, in order to clarify these problems, long-term permeability tests are performed at a dam site composed of weathered soft rocks. In addition, we investigate an appropriate permeability evaluation method based on the combination of the above field tests and saturated-unsaturated seepage analysis. As a result, the Lugeon value by long-term permeability tests (Lu_LPT) is larger than that by common permeability tests (Lu_WPT), and the ratio of Lu_LPT to Lu_WPT, α, ranges from 0.1 to 0.5. Furthermore, we have confirmed that the tendency of unsteady seepage during long-term permeability tests can be reproduced using saturated-unsaturated seepage analysis.

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A new construction control method for a large-scale reclamation project using an echo sounding system was developed. A case study, which applies the developed method to an artificial island constructed on soft ground improved by a sand drain method, is presented. This paper uses bathymetry data to describe the thickness of a sand fill, settlement of the ground, and the magnitude and distribution of the load increment at a site. The main conclusion as follows ;
1) The measurement accuracy of the developed bathymetry survey system is ±10cm which is same accuracy estimated from specification of each instrument.
2) The accuracy of the construction control system is ±0.3 m for 16 m in thickness and ± 0.15 m for 4 m in settlement.
3) From the construction control system, the volume change rate and the unit weight of sand fill can be confirmed and the mean value of the volume change rate and the saturated unit weight is 1.21 and 12.2 kN/m³ respectively.
4) The consolidation parameters which were calculated backward from this system are distributed within range of laboratory test results.

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Because of the topographic and linear condition, the applicability of excavating Shallow Overburden tunnel using NATM on soft ground is increasing. In the mentioned construction field, a phenomenon of equal settlements of the surface, crown and foot called phenomenon of accompanied settlement occurred, which had not been observed in the past. The mechanism of the phenomenon is not clearly understood, and preventing surface settlement has become a significant problem. In this study, the reinforcement effect of preventive system and effect of the length and spacing of preventive system has been clearly understood through experiment and FEM analysis. The results showed that preventive system is effective in preventing surface settlement, and the preventive system can prevent surface settlement by increasing the shear reinforcement and redistribution of load.

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Pull out test on chain set in soil container and construction test in the field are conducted in order to develop a method of earth reinforcement using chain a reinforcing material. From the results of the pull out test conducted to investigate the shape effect of chain on reinforcement it was found that the pulling resistance depends on the diameter of chain more greatly than its shape and the material. The pull out resistance of the chain can be predicted more accurately using the cylindrical model in which the shearing face is modeled as a cylinder and its diameter regarded as several times the actual diameter of the chain. Also, friction correction factor of round steel bar, band steel and band steel with ribs are compared to that of the chain. From the test results, the friction correction factor of chain is 2.2 times that of round steel bar, 3.8 times that of steel band and 1.9 times that of steel band with ribs. In order to verify the construction procedure and its applicability, reinforced soil wall whose height is 3.0 m is constructed in the field using chain. The pull out tests carried out in the field make the pulling out resistance in the field clear.

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