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2.3 DYNaMIC OONE PENETRATION TEST (65 mm cone wlth and wlthout slurry)

It is a slmple devlcG for pro bing the soli strata and it has an advantage over the Standard Penetration test that maklng of a borę hole is avoided. Moreover, the data obtained provides a continuous reoordof 9oil resl stance.

The Dynamie Obne resl stance (N_c(j) in terras of blows per 3D ot of penetration of the 65 mm dia. cone specified in the Standard and developed by the Central Building Research Institute, Roorkee, has been corrolated quant±tatively to the Standard Penetration value N obtained in accordance to IS: 2131-1963,

Method for Standard penetration test for solls. Studies with a view to establish a definite oorrelation bet-ween N_cbr and N values for different regions of the country are in progress. The Standard covers the procedurę of dynamie driving of the cone and thereby obtaining a reoord of resi stance of the soil. The cone is dlrectly driv® into the ground and for eliminating the friction on the driving rods, bentonite slurry is used. The sluriy may not be used then the investi gation reąuired is upto a depth of 6 m only.

The cone is of mild steel wlth the tip case hardened. The cdLmensions and shape of the cone are shoyn in Fig. 6.

Fbr better drculation of slurry at greater depths, a vane borer consisting of four vahes welded to a driving rod wlth a number of drill holes fbr the escape of slurry are piovided Just above the cone.

The cone is connected to the drlving rods, with the vane borer in position. The driving head is fixed with the guide rod on the drill rods and this assembly is kept in positlon wlth the oone rest-ing yertically on the ground at the point to be tested. Fbr the circula-tion of slurry the guide rod is connected to a water swlvel preferably through a fledble tubę connection and then through another flexible tubę to a reciprocatlng type pump. The swivel assembly is held in position by a ropę passlng over the pulley provided for that purpose. The slurry tank is fllled \Ath bentonite slurry of suitable oonsistency. (A five percent solution of bentonite in water has beaa fbund generally useful in practice). The sluriy should generally be prepared separately and sto red in druns. Suitable protection against entzy of debil s is tak&i. The 65 Kg. hammer slides over the guide rod and rests on the drlving head. A typical assonbly of the eauipment for test using a portable tripod with manually operated geared wlnch is shown in Fig. 7.

150 mm

VANES

A SIZE DR0.L ROD

3 mm 6 H0LE5

SOnwn

Smm4 HOLES 10 mm

lOmm

THREADED OR PUSH FTT

PULIEY FOR HOLOING SWIVEL

PORTABLE TRfPOO HOłST

WATER SWIYEL BUIT N LA00ER

ROPĘ FOR

HOLOING

SW1VEL

RH/ING ROD VANE BORER

FK3. 6. CONE ASSEMBLY

FI6. 7. DYNAMIC CONE PENETRATION TEST

ASSEMBLY