6585844935

125

Sweden

Fig. 14

Draughtlng of static sounding results according to the SGF standard.

Recently, Nilsson (1973) has described a new penetrometer whlch uses the same principle as the SGI sounding machinę (the rotation ratę is adjusted to the penetration ratę), so that the pitch is constant. The skin friction resistance is subtracted automatically from the total resistance. Only the point resistance is registered by the machinę. The rotation of the penetrometer rod is regułated by two ballscrews, which are ntechanically coupled. The maximum penetration and puli-out force is 140 kN, the maximum penetration yelocity 6 m/min, the maximum torque 750 Nm and the maximum rotation 200_?rpm. The conical point (Fig. 15a) with 10 cnr cross sectional area, is either fixed or free. The

F1g. 15

Points of the new static penetrometer, type Nilcon: a) Normal point, b) pgint for soft soils (cross sectional area A*50 cm²) with an inner point (A=10 cm²) for hard soils. c) Point (A=

10 cm2)for hard soils.

local skin friction resistance can be measured ₂ immediately behind the conical point by a 250 cnr sleeve, which is released when the skin friction resistance is measured. Experiments have also been carried out 1n soft clays with a 50 cm2 point (Fig. 15b). The point in Fig. 15c is pro-vided with three ribs of hardened Steel with a pitch which corresponds to the resultant move-ment of the penetrometer rods. This point is used when the penetration resistance exceeds about₂30 KPa. A combination point composed of a 50 cnr point and the 10 cnr ribbed point, described above, has also been developed. The smal-ler point can be released from the larger point (see Fig. 15b) when the penetration resistance becomes exces$ive. The penetrometer is provided with a mechanical recorder which registers vertical forces up to 30 kN and turning moments up to 750 Hm. The penetrometer is mounted on a tractor weighing 35 kN.

Borros Static Sounding Method

An electric static sounding apparatus has been developed by Borros AB with which the point resistance is measured directly with strain gauges. The strain gauges are connected with a recorder unit (Fig. 16 left) at the ground surfa-ce. The penetrometer point (Fig. 16) is conical (apex angle equal to 60°). The diameter of the penetrometer rods is 32 mm.

Recorder unit and point for the static penetrometer, type Borros. Kechanical jack (crank-dr1ver) for driving and pulling.

The point resistance is recorded automatically as a function of depth (scalę 1:10 or 1:100). The instrument has at present four load ranges. The maximum load Is 1 MPa at the lowest load rangę and 40 MPa at the highest rangę.

Maximum penetration is governed by the capaclty of anchoring system (earth screws) or by the weight of the truck. The penetrometer is driven manually (Fig. 16 right), in which case the penetration velocity is about 0.8 m/min or hyd-