The substructure of YOKOHAMA Bay Bridge is multi-column foundation; for the tower foundation, nine piles are grouped and the tops of each pile are imbedded in a footing. Each pile is constructed by sinking a 10m out dia, open caisson made of reinforced concrete. Those caissons are penetrated about 20m in depth into the soft mud stone bed. To penetrate such big caissons deep into a bearing hardpan, it is necessary to excavate and remove the material under caissons' cutting edge. We have already developed a swing boom type under-water drilling system that can excavate and remove materials under caissons' cutting edge. We hereby explain the progress of the development of the system both of manufacturing shop and working site with the result through actual operation.

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In recent years, the constructions of concrete structures in the underground have been increasing in towns and cities. For these structures, it is required to develop such concrete that will gain sufficient strength within early stage to shorten the construction period with economically reasonable cost for construction.
Experimental tests were conducted to develop a new concrete which will obtain strength more than 60kgf/cm² within 4 hours after placing and will be applied for the lining concrete of the shield construction method. The results of experiments were satisfactory and are reported in this paper. The acceleration of hardening was attained by means of a new type of admixture, regulation of curing temperature and pressure application to the form.

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This article is a report on the results of basic researches conducted as a necessary step in applying shot blasting, conventionally used for the treatment of metallic surfaces, to the construction procedures for bonding of new concrete to hardened concrete structures.
The experiments were conducted to accumulate data by varying the many factors concerned such as the ratio of cement to water for the concrete, types of coarse aggregate, the size of the shot (round particles) and grit (angular particles), blasting velocity, and blasting density.
Studies were mainly conducted to a method for the quantitative evaluation of the degree of surface treatment of the concrete, and to establish a method for the treatment of concrete surfaces to attain the required strength in the construction joints by applying shot blasting.

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The rigidity of steel sheet-pile wall depends mainly upon the degree of connection between each pile and surrounding soil conditions. In order to obtain the section rigidity as a wall, loading tests on jointed steel sheet-piles were carried out. From the tests, following results were obtained:
(1) The force mobilized at each joint can be considered to consist of cohesive force due to connection of each pile and friction type of force.
(2) Section modulus of the wall in soft ground decreases with increase of the stress level.
(3) Both moment of inertia and section modulus of the wall obtained were nearly 30% larger than those of the unit steel sheet-pile.

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For a ripping operation on a bedding rock mass, the determination of an optimum direction of ripping to minimize the excavating force considering the strike and dip of bedding plane is very useful to increase the ripping performance and to reduce the fuel consumption of bulldozer. Here, 32 series of rock mass model made of cement mortar and 3 ripping operation sites have been tested to determine the characteristics of ripping excavation force to its direction and the relation between excavating force and coefficient of penetration of rippertip. As results, the direction of excavation to minimize a ripping force agrees well to that of minimum modules of deformation of rock mass which could be calculated from a coefficient of penetration by a piston-type bore hole test.

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Tomari-ohashi bridge is located at the Naha coastal way connecting four wharves of Naha Harbor, Okinawa. The type of this bridge is three-span continuous steel decked box girder of 170-meter center span. Tomari-ohashi bridge stands fifth in Japan as regards the length of center span of this type. This paper describes leading characteristics of the planning, designing, construction and erection method of Tomari-ohashi bridge, and also a detailed explanation is given showing wind tunnel test results and suppressing methods of wind-induced vibration, which requires particular investigations.

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Characteristics and mechanism of ground displacement during shield thrusting in soft ground were discussed. It is pointed out that the shield machine, auxiliary construction methods, backfill grout and the quality of operation control are the main influencing factors and should duly be taken into account for the prediction of ground displacement. The numerical calculation by two dimensional elastic finite element method with some modeling techniques was confirmed to provide an excellent method to predict the 3-dimensional ground displacement behavior under shield thrusting.

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The present paper is concerned with the prediction for the maximum settlements of ground surface adjacent to open cut. Using many field measurements, statistical analysis were made for the maximum settlement and the distance from wall where more than 2mm settlement occured. It became clear that those values are influenced considerably by the following factors; (1) ground type, (2) cutting depth H and width B, (3) deformation modulus of soils under excavated base, and (4) wall type. The parametric study by the FEM have confirmed the significance of statistically analized results. And it is shown that maximum settlements are influenced by the proposed cutting factor (BH/β_DD). D is the wall length under excavated base and β_D is coefficient related to the wall stiffness and deformation modulus of soil.

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There is a big demand to develop innovative measures to improve the concrete durability, with increasing social interest in the durability of concrete structure.
“Textile-form method” described hereunder, has been developed with an aim to prevent air bubbles and blow holes, using the complex form consisting of special textile and form with tiny holes providing high air and water permeability.
Through the site experiment for practicability in Aseishi-gawa Dam Project, this method proves several merits such as smoother surface and higher surface strength and compressive strength compared with the conventional methods, and is considered to be applicable in a wide range of concrete construction works.

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Tunnel blasting causes several undesirable effects, for example, overbreak at the perimeter and damage to or loosening of the remaining rock at the perimeter. Notched blast hole technique is sometimes employed in order to minimize these undesirable effects.
Model blast tests were conducted in order to simulate the propagation of blast cracks from the notched holes. Through the tests, the following conclusions were summarized.
(1) Notching of blast holes can initiate blast cracks from the notch tips.
(2) The fracture plane from the notch tip is rough when the hole is loaded with high explosive detonation. It is smooth when the hole is loaded with low explosive combustion gas pressure.
(3) When the notched holes are used as perimeter blast holes, underbreak can be reduced remarkably.

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