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Sweden

tratlon. A soundlng diagram is shown in Fig. 9.

The penetrometer is today (1974) often rotated by machinę (Fig.9) to facilitate the test. This mecha-nization affects,however, the measured penetration resistance. The difference between manuał and machinę rotation has been 1nvestigated (Bergdahl, 1969) for both cohes1ve and cohesionless solls as summarized in Table 2.

Table 2

Relationship between penetration resistance and rotation ratę.

Modę of		Ratę	Halfturns (%)
rotation		(rpm)	Cohesive soil	Cohesionless soil
Manuał1y		17	100	100
By machinę		24	103	128
H	II	50	116	98
U	II	125	122	126

Fig. 9. Also the noise and the vibrations in the soundlng rods during a test can be used to iden-tify the soi! penetrated (clay, sand or stone). These observations should also be shown on the drawing. However, this possibility to eva1uate the sol 1 conditions can usually not be utUized when the rod is rotated by machinę.

Push Soundings

Push sounding is carried out with weight soundlng rods. The rods and the screw point are turned and pushed down by hand. In order to increase the penetration depth the penetrometer may be dr1ven by sledge hammer. Noise and yibrations In the penetrometer rod are observed during a test as well as dlfferences in the penetration resistance at different leve1s. From these obserya-tions the soli conditions and the relatiye den-s1ty of the penetrated layers can be estimated. The number of blows, the maximum penetration depth and 1eve1s of temporary high resistances should be recorded. If handled by an experien-ced person push soundings can be very useful and besides 1nexpensive.

Static Sounding Machinę, type SGI

- GE AR BOX

SPRING FOR

TORQllE

SPRINGS FOR VERTICAL LOAO

CONICAL POINT

NOT ROTATING

POINT 0 40mm

Rules for mechanical weight soundings were intro-duced flrst in the 1970 Standard. The rotation ratę should, according to this standard, not exceed 50 revolutions/min (rpm) and should pre-ferably be between 15 and 40 rpm with 30 rpm as guide va1ue. The machinę should be removed or the motor be stopped, when the penetrometer sinks under its own weight, so that the yibra-tions from the machinę do not influence the test results.

If a firm or hardlayer is located close to the ground surface (fili or thick dry crust) the frlction resistance along the penetrometer rod withln this layer can affect appreciably the measured penetration resistance. In that case the standard prescribes preboring 1n order to obtain comparative results.In the standard is also polnted cut the importance of a suitable criteria when the soundlng should be termlnated.

A penetration test could for example be termlnated when a certaln penetration resistance has been reached or at certaln depths. Firm bottom is defined, according to the above mentioned specifications, when the penetrometer does not ,sink notably when turned or driven by at least 10 blows of a 3.0 kg sledge hammer. (The two top 25 kg weights can be used Instead. They should be dropped from a height of 20 cm.) If this criteria has not been satisfied the penetration test can be termlnated when two adjacent 20 cm layers are accounted with an increasing penetration resis-tance exceeding 40 halfturns/20 cm and the penetration is less than 1 cm/blow after 5 blows with sledge hammer or with the weights.

If the penetration is larger than 5 cm/5 blows or the penetration resistance decreases the penetrometer rod should be rotated again before the dr1v1ng is contlnued. (The high resistance may be caused by a stone or by a boulder.) The depth of penetration due to drlying should be shown on the drawing. If refusal is met relati-vely close to the ground surface this level should also be shown. An examp1e is shown in

A hydraulically operated static sounding appara-tus was deve1oped by the Swedlsh Geotechnical Instltute (SGI)in about 1950. The functlon of the penetrometer is schenatically shown in Fig. 10.

FLOATING__

PtVOT

ROTOR

ROTATING

POINT fi 2Smm

Fig. 10

Static Sounding Machinę, type SGI. Principle