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FIG.2.3. A new weight sounding machinę.

terrain. The method is very much used by the geotechnical division of the State Highway Laboratory, in connection with their investigations in highway planning.

Percussion -drill machinę

irr

W

ITT

ITT

22mm rods

A new semi-automatic working weight sound-ing machinę has been constructed last year at the Geotechnical laboratory of the Norwegian Institute of Technology. This hydraulic operated device is shown in Fig. 2.3. The vertical load of the moving part of the machinę is 100 kg. If it penetrate by a weight less than 100 kg, the hydraulic piston makes it possible to registrate to what weight the drilling string is forced down (with a definite ratę of penetration). The rotation of the machinę is started when the sinking by 100 kg is nearly stopped. The half turns pr. 0.2 ra depth is recorded. The bali cone clamp of the machinę, rotated by the hydraulic motor, grip and rotates the string in 0.5 m intervals. The only thing the operator has to do is to lengthen the drilling string, to operate the handle for up and down movement and to read half turns pr. 0.2 m. To with-draw the rods is easy. It is necessary to change the bali cone clamp, then the string is pulled up in 0.5 meter inter-vals. It is possible to apply a pulling force of 34 kN. The power is developed from a gasoline motor (right side of Fig. 2.3). The drilling machinę can of course be apfcłied in connection with a tractor or truck, then the hydraulic power can be taken from their hydraulic pumps.

2.2 Percussion sounding (soil-rock sounding)

A useful sounding method is the percussion sounding. It is generally used only for preliminary investigations to estimate the depth to bed rock or dense layers. The method may also give some useful inforraations about the soil it-self, if the drilling pass through clay, sand or gravel per example. The main advantage is that the eąuipment is light, easy to handle and bring around in the

Point :

25 x 25 x lOOmm or

V diam . 25mm

FIG.2.4    Percussion sounding.

Fig. 2.4 shows a schematic drawing. The eąuipment consists of the same 22 mm Steel rods as for the weight sounding method. The end rod is provided either with a square point (25 x 25 x 100 mm) or with a 25 mm diameter point of the same length. The drilling rods are forced down by a portable percussion-drill machinę. There are different types of this machines, mainly madę in Sweden.

To find reliable indications of contact with bedrock is often difficult>especi-ally if the soil depth is considerable. Some research have been carried out by the State Highway Laboratory, to find an electronic device, by which the size of the reflected impulses can give indications of bedrock or not.

The generał practice is, when the drilling has come to a stop, to hit with a sledge hammer, trying to find indications of solid rock.

2.3 Machinę sounding

(drill-pressure sounding)

Until 5-10 years ago, the soil investiga-tions in Norway have to a little degree been mechanized. Especially the sounding methods used was hard labor. Besides, the demand of ąuicker and morę economic-al investigations led to heavier and morę mechanized eąuipment.

The problem was tackled by the Norwegian Geotechnical Institute and The State Highway Laboratory. The discussions led to the construction of an all round drilling machinę mounted on a tractor.