6585844936

Sweden

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raullcally in which case the penetration ve1ocity can be adjusted within wide limits.

Geotech Sta tle Sounding Method

A new static penetrometer developed by Geotech AB has been described by Jonell (1973). With this method signals from a vibrating w1re gauge at the penetrometer point are transmltted acoustically through the penetrometer rods to the ground sur-face. Ampliflcation of the signals is required due to the damplng at the joints. The signals are ampllfled by a battery driven unit of the type used in transistor radl os. The batteries will last for at least one days work. The force measuring unit and the amplifier with a diameter of 35 mm and a total length of 700 mm are built into the penetrometer point. The penetratlon res1stance is recorded at the ground surface as a function of depth. The main advantage of the acoustical static penetrometer is the wireless transmission of the signals from the point.

The penetrometer has four load ranges. The maxi-mum load is 5 MPa at the lowest load rangę and 40 MPa at the highest rangę. On the diagram is also shown the load rangę which is used in addltion to the measured point resistance. The point resistance can be measured with an accuracy of 1* of the maximum load for each load rangę. A temperaturę change of 20° will affect the readings less than 0.1% of the fuli rangę.

A hydraulically driven, 11ght boring rig, which can be mounted on a tractor or a band wagon is used to push down the penetrometer. The stroke of the hydraulic cylinder is 1.1 m. Maxiraum penetratlon force 1s 30 kN and the max1mum puli-out force 100 kN. The maximum turning moment is 1400

Nm.

The Swedish Ram-Sounding Method

The current standard for the Swedish ram-sounding method was adopted by the Swedish Geotechnical Society (SGF) in 1971. At that time a new proce-

Fig. 17

Tradltional ram-sounding device (method B) with motor tri pod.

dure (Method A) was standardized in addition to the traditional method (Method B). These two methods are described below.

In method B (Fig. 17) sounding rods with 32 mm diameter and a cyligdrical point (0 45 mm) with 90 mm length and 90° apex angle are used. The point is either fixed or loose. The sounding rods are driven down mechanically by a ram weighing 63.5 kg with a helght of fali of 60 cm. The ram strikes an anv11, which consists of a pair of wedges and a jacket. The penetration resistance 1s taken as the number of blows requ1red to dr1ve the penetrometer 20 cm.

The penetration resistance is affected by such factors as variations in the height of fali of the ram. (The ram is manually regulated.) Also friction 1n the cables affects the energy deli -vered by the ram and thus the test resuIts.This friction varies with air temperaturę and with the generał condition of the machinę. The sounding rods are usually rotated to prevent lateral deviat1on of the rods when the test is tempora-rily stopped for splicing of the rods. This ro-tation decreases temporarily the penetration resistance when the test is continued. The anvi1 moves slightly when it is struck. This slipage can reduce appreciably the intensity of the blow as indicated by shock wave measurement. The slip of the anv1l is large just after it has been reset every 1.0 - 1.5 m and is then

METHOD A    METHOD 8

0 100 200    0 100 200

blows; 20c/*    blows; 20cm

Fig. 18

Draughting of ram-sounding test results according to the SGF standard.

Notations:    (Method A) * Test interrupted for

morę than 5 min. (Method B) — Anvil reset and rod rotated at this level, * other causes for interruption, vr rotation of rod according to Method A from this leve1, uvr No rotation of rod according to Method A from this level. Com-pare also Fig. 9.