In order to enable construction of a long and curved small-diameter tunneling system, a new lining method using a plastic material has been studied. After consideration of requirements for the lining material, a hard-foamed plastic was selected. The relationships between the mechanical properties of the plastic and its density were investigated. Furthermore, several exoeriments were carried out to discover the properties of the foamed plastic, for example, the bending strength, the bonding strength and so on.
Experimental and theoretical studies of the hard-foamed plastic showed the potential applicability of the new lining method proposed in this paper.

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This study aims to propose a new predictor of the vibration level of blasting vibrations. The level must be measured by a vibration level meter that satisfies JIS (JIS C1510). We first researched the response characteristics of the level meter, and developed a computer program which could simulate those characteristics. Using the program. we investigated the effect of the delay on the level. In the investigation, we assumed that the delay blasting was made up of a series of single shot blasting with a time delay. Intermitted sine waves were used as idealized delay blasting waves as well as observed waves.
On the assumption that frequency is more than 8Hz, and time delay (T_i) is longer than duration time we proposed a new practical predictor for the vibration level as a function of T_i and peak particle velocity (PPV).The PPV is easily estimated from the well known predictor.

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In this study, the smoothblasting in hard granite tunnel was discussed with reference to the results of three field tests which aimed at the minimization of overbreak and underbreak. In the tests, the drilling was practiced by the aid of automatic drilling machine. Among many factors which effect on the smooth biasting result, particular attention was payed to the drilling precision. Differences between the designed and actual blasted faces were statistically analized and smooth blasting results were discussed from its point of view.
The study revealed that not only the blasting techniques but also the drilling precision give a great effect on the smooth blasting result in hard granite tunnels.

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In order to investigate the effect of top-plates on mechanism of soil-reinforcement of cut-off slope with steel bars, pull-out tests employing top-plates with various sizes, and model tests simulating a sliding force acting on the cut-off slope, were performed.
From this experimental study, it was made clear that not only do the top-plates act as bearing plates for pull-out force, but also they play an important role in mobilization of friction force acting on the reinforcing bars. Thus, followings were concluded; Top-plates are indispensable to soil-reinforcement of cut-off slope with steel bars, and there exists an optimum size of top-plates for causing effectively the friction force on the bars.

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Many arguments have been made on the countermeasures of cracks of inner lining in urban-NATM tunnel, but there are many uncertain points on the selection of countermeasures to prevent cracks at present stage. The purpose of the present investigation is to examine the practical method for selection of the countermeasures on the basis of experimental data on site.
As a results, we wish to propose a selection method of countermeasures by means of actual data obtained through site.

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The laying-down caisson method was adopted to construct the bridge-pier foundation in deepsea such as Honshu-Shikoku connecting bridges.
To secure the quality of under-sea concrete and to prevent contamination of the ocean floor caused by leakage of mortar, it was necessary to seal the clearance between the rock-beds at the sea bottom and cutting edge of the bottom of the caisson without diver work.
Sponge-mat made of special polyurethane foam and special structure was used as the sealing material in constructing the large-scale caisson foundation such as the South Bisan-Seto bridge piers and so forth.
The present paper summarizes the development of the sealing material and its application to construction work.

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It is a general trend to make maintenance free designs for bridge structures. Although the design concept of expansion joints was different from that of bridge structures so far, it will be required to take an expansion joint as a structural element of a bridge as long as the maintenance-free concept is applied to bridge designs.
It is discussed in this paper how expansion joints should be designed and what problems will arise under the maintenance free concept. An experimental study was conducted on a specific expansion joint system (mechanical expansion joint system). Through fatigue tests, several material and structural problems in a joint system were pointed out. Finally, those defects were removed and an improved joint system was proposed.

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