6585844985

Japan

194

te9ts are applicable as In situ tests are predomi-nantly alluvial or diluvial deposits and it i9 rare that they are applied to formations older than the later Piiocene in the Tertlary period. Of course the penetration test is most effectively applied to alluvial deposits. Weak soli layers with tf<2 are widely distributed in the urbanized regions including large cities; notably weak beds with a peat surface layer extend from the central part of the Main Island (Honshu) to its northeastem part.

Table 2 gives the typical JV-values of strata of different ages as obtained from the Standard Penetration Test and the applicabilities of different penetration tests to these strata.

2. STANDARD PENETRATION TEST

2.1 Procedurę for the Standard Penetration

Test in Japan

In Japan the tools and procedurę for Standard Penetration Test were specified in the Japa-nese Industrial Standard in 1961, hased on the Tentative Method of the A.S.T.My Figurę 1 shows a splU spoon sampler for Standard Penetration Test?) which is approximatelyof the same dimensions as that specified by the Tentative Method of the A.S.T.M. The weight and the height of fali of the drop hammer are respective-ly 63.5 kg and 75 cm. Among the four kinds of boring rods ranging from 33.5 nim to 50 mm in diameter, only the 40.5 mm and 42 mm rods are fit for thls sampler. Figurę 2 lllustrates a knocking head to be connected to the boring rod and Figurę 3 a drop hammer?) 2.2 Boring and Standard Penetration Test

In Japan, rotary hand-feed boring machinęs are in common use except for rock drilling; percussion drilling and wash drilling are never practiced. Boring is advanced by rotation of a drilling bit attached to the tip of a boring rod which is forced into the bottom of the hole by the hand lever. The borehole diameter rangęs from 65 mm to 110 mm, and the stability of borewall is maintained by the use of drilling mud.

After the boring has reached the depth for testing, the hole is cleaned by circuiating drilling mud and immediately the sampler is set at the bottom of borehole. The sampler is first driven about 15 cm of its length into the bottom for the purpose of removing the slime remaining at the bottom of borehole and minimizing the effect of disturbance and then, a 30 cm penetration i9 madę by the specified dropping of the hammer. Usually the number of blows for every 10 cm penetration is recorded, but the number of blows is limited at50; the standard method of dropping is free fali. For this purpose, the "Tombl" (a triggerine devlce) illustrated in Figurę 4 may be employed?) but it is common practice to use, in-stead of such a trigger, a cone pulley to lift a hammer and give it a sudden drop.

The Standard Penetration Test is usually carried out at one meter intervals in depth and the results obtained are entered in a boring log in a manner such as illustrated In Figurę 5.

SHoe

Wranch grlp 19*47'

Spili Barrel A__

Wraneh *rip_, Hola Coruiaetor head

f

I o		b	c
1		Kl.lt	-1

	Total length	o-Shoa length	l:Birr«l length	c: Head length	diOhiter )iiafter	* •’ Inner llemotor	>:Anglo of ceper
ptandard	81. Oo.	7. Sm	5S.0®	17. Saa	S. las	3. Sm	19*47'

coupliftg

Rod

Fig. - 1 Split-Spoon Sampler for Standard Penetration Test (J1S)

Fig. - 4 "Tombi", a Trigger used in Japan

2)

Rod eoupling

Knotkin| Htad Rod coopling

(Unit - cen)

Iron ctuio

Teaiing Inierrala of S.P.T.

\ i

Fig. - 2 Knocking Fig. - 3 Drop Hammer Head (J1S)    (J1S)

Fig. - 6 Density for Measuring Depth Interval of S.P.T. and Pattern of fł-curve

gained^)