6585844932

Sweden

121

PENETRATION RESlSTANCE

Fig. 7

Depth of penetration related to penetration reslstance and total cost.

POINT RESISTANCE. q_c. MPa 0    4    8    12    16

A B

Fig. 8

Different types of soil as indicated by static soundings. A) Dry crust clay, B) surface layer of frictional soil, C) clay,"gyttja" or loose sand, D) fili or "gyttja", E) medium dense silt, sand, gravel or peat, F) dense silt, sand or gravel, 6) dense gravel or till, H) transition stage towards till, J) interpretable sounding curve rich in contrasts, K) sounding curve with-out elear contrasts, difflcult to Interpret,

L) transition from postglacial clay to glacial clay (varved clay). Source: T Kailstenlus,1973.

1evel within an area is an indlcation of the stone and boulder content of the soil. However, the probability that the penetrometer point en-counters a single stone or a single boulder 1s smali, if the stone or boulder content is Iow to medium.

Specifications regulating the quality requirements of soil investigations and the payment for borings and soundings have been worked out by a committee composed ot geotechnical consultants, boring contractors and consumers of geotechnical services. The specifications for soundings and penetration testing will certainly be modified in the near futurę due to further developments in this field.

The cost for a penetration test depends on such factors as the characteristic of the soil, the penetration depth, the variations of the penetration resistance and the requirements for the termination of a borę hole.

The diagram in Fig. 7 shows the penetration re-sistance for a soil profile consisting of a rather stiff surface layer (dry crust), a layer of clay andatgreater depths sand and gravel with a relative density wich increases with depth. The cost of this investigation will be dependent on the penetration. If the object of the investigation is to locate the lower bounda-ry of a clay layer (leve1 A in Fig. 7), it is wasteful to terminate al1 the borę hol es at level 3. may, however, be desirabie to extend a few borę holes to maximum depth to obtain complete information of the layer sequence. A borę hole which is terminated at 1eve1 A will give no Indications of the sand layer,which may be of interest as foundation level for spread footings. If the object is to predict the length of end-bearing piles some types of penetrometers may be inadequate due to their limited penetration ability.

Interpretation of test results

Soundings are primarlly used to determine the layer sequence or the laterał extent of a particular layer. The soundings are generałly combined with sampling.

The special soil conditions in Sweden influences the interpretation of the test results. The present practice is to combine soundings with sampling. The sampling is often concentrated to the weak layers located by the soundings In order to decrease the cost of the invest1gation.

The shape of the sounding curve and the magni-tude of the penetration resi stance are often used to evaluate the soil type. Typical sounding records and their interpretation are shown in Fig. 8. By recognizing typical features of such diagrams it is possible to determine the layer sequence.

The above mentioned method of uslng the results from penetration tests is dominating. Transla-ting the penetration reslstance into piąte or pile bearing capacity by using principles com-mon abroad occurs mainly when one deals with loose frictional solls. Within certain areas the penetration reslstance has been related to relat1ve density, shear strength or modulus of compressibillty as determined by other methods.

Interpretation of ram sounding tests for the estimation of lengths of point bearing piles are madę from the number of blows per