In Japan, three methods as shown below are ususlly adopted as boring technique for piles ; a) the earth drilling method, b) the Benoto method, and c) the reverse circulation merhod. Though these three methods, whose way of excavation and way of protection concrete collapse of surface of excavated well, differ each other, have their own peculiar problems, they have also some problems common to the all three. Among them, there exist the risks as follow ; 1) decline of bearing capacity of pile which may cause in case of lack of care for exclusion of slime deposited at the bottom of the well, 2) collapse of bored well due to the influx of underground water, 3) decline of concrete strength due to the admixture with muddy water which may cause in case of casting in the muddy pool. This report relates principally to the causes and the preventive measures of these problems.

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Reinforced concrete masonry structures were introduced from United States of America soon after World War II, and improved to be adaptable against earthquake motions in Japan. In the 1950's, these structure were adopted extensively for governmental housing projects, and are now widely known and built by many individuals and corporations in all parts of the country. On the other hand, the Building Code for these structures, which was put into effect in 1952 and revised to some extent later, has remained generally unchanged in the main design criteria until now.
Because of increasing building damages caused by several recent large earthquakes, earthquake-proof design methods of all types of structures are now in urgent need for revisions to assure safe and tenable methods. Considering these circumstances, this report describes the earthquake resistant strength of reinforced concrete masonry structures especially from the viewpoint of shear strength and behavior of load-bearing or shear walls under lateral forces parallel to their plane, referring some test results recently obtained in this country.

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The shortage of river sand pushes sea sand into the important and indispensable material for concrete in the past decades in the Kansai areas and westward.
However there are two big drawbacks in using the sea sand as the fine aggregate of concrete, one of which is chlorine content much higher than the concrete construction standard specifications, and the other is the prospect of its supply which is not promising because dredging around the sea bottom too much may disturb the environment and the balance of nature.
To cope with these drawbacks, the use of other materials like rock crushed sand or blast furnace slag sand, or their combined use is considered to be practical. The authers made various experimental studies on the characteristics of fresh and hardened concrete using the combined fine aggregate of sea sand and rock crushed sand or slag sand.
It was found that the concrete using the conbined sand needs more water than the usual river sand concrete does to give the same workability and shows a few different characteristics.
But as a whole the authors concluded that combined sand can be used without notable deficiencies as a fine aggregate for concrete.

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There have been many types of methods for shotcrete and now dry type shotcreting method is widely used, because this is well adapted for the various conditions of each construction site and shotcreting work is carried out easily compared with other methods. On the contrary this method has several defects: large quantities of powdery dust badly affect the working environment, large percentages of rebound cause a loss of materials, quality control is difficult on account of large deviations of strength.
SEC shotcreting system is a quite new method for shotcrete. SEC mortar is substituted for water which is added at a nozzle in conventional dry type method. Thus the defects of dry type method will be eliminated by applying a new shotcreting system.

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