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Fig. 12

Princlple of separating skin friction from point resistance at the SGI penetrometer.

Sweden

The penetrometer rod with 20 mm diameter 1s rota-ted at the same time as 1t is pushed down into the soil. Maximum turnlng moment 1s 250 Nm and penetration forces can be recorded up to 10 kN. Hlgher forces are possible to apply wlthout re-

?1stration dependlną on the weight of the truck Fig. 11).

Fig. 11

Static Sounding Machinę, type SGI, mounted on a Mercedez Unimog jeep.

The penetration ratę 1s approximately 3 m/min. Intermptions for extension of rods are not required. The point is free to rotate relatiye the rod. The diameter of₂the point is 25 mm (cross sectlon area 5 cnr) or alternatively 40 mm (cross sectlon area 12.5 cm^z). The penetration is 12.5 mm per revolution of the rod which corresponds to a pitch of 1:5. The skin friction resistance is eva1uated from the measured torque assuming a constant relationship between the horizontal and vertical skin friction resistance. Point resistance is determined by subtracting the skin friction resistance from the total resistance (Fig. 12). This is done automatically by the machinę. The point resistance is plotted directly as a function of depth (scalę 1:100). Skin friction is indicated separately by a pointer.

Nil eon Static Sounding Method

The Nilcon penetrometer has been used extensive1y 1n Sweden during the last 20 years. This penetrometer is characterized by the slip coupling close to the penetrometer point as shown in F1g. 13. This slip coupling 1s used to determine the skin friction resistance along the rods. This is done by pulling the penetrometer a d1stance (5 to 10 cm) which corresponds to the play of the slip coupling. Then the penetrometer is pushed down agaln and the corresponding force 1s measured. This force corresponds to the skin friction resistance. The pulling and the subsequent push-1ng of the rod is indicated by two horizontal lines on the recording paper as indicated in the diagram in Fig. 14. The vertical scalę of the diagram is 1/lOOth of the real penetration of the point. The points in the diagram which corresponds to the force required to push down the

Fig. 13

Point of the static penetrometer, type Nilcon.

rod and thus to the skin friction resistance,are then connected. The distance between this linę and the measured total penetration resistance corresponds to the point resistance. However, the accuracy of the results can be Iow, especially in stratlfied soils.

When the penetration resistance exceeds the capaclty of the machinę (10-20 kN),the point, with a square cross section (10 cnr) is rotated. The yertical force Is reduced to 3 to 5 kN at the same time. If the penetrometer then goes down further the test is continued without further rotation.