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Spain

This point is drivcn by a 32 mm rod to which it may be fixed or simply supported, in which case it is lost in the ground at each site, what is pre-ferable becausc time is saved.

The hammer weighs 65 kg and has a free drop of 50 cm. applied at a ratę of 15 to 30 blows per minutę. The number of blows necessary to pene-trate each consecutive 20 cm is taken as the pe-netration valuc, n£g, and the results are drawn in a continuous graphic.

2.4. Number of tests. - It is difficult to know even approximately what is the number of test of each kind which are performed in Spain. But in order to get an idea of what is the relative pro-portion for each type of test we summarize below the answers we havc received from a few Compa-nies, which may be considered representative of the average firm working on soil surveys; we al-so include the total figures for the services of the Dirección General de Carreteras, D. G.C. (General Directorate of Roads).

Company S P T Cone Test6 Borro's Tests _ numb./vear m/vear    m/vcar

A	5.000	3. 000	12.000
B	2. 000	no	9. 000
C	3. 000	no	no
D	2.500	9.000	no
DGC	4.000	1.500	13.000

As it is seen from these figures, the SPT test is used by everybody. The cone test is cither not used or not very much used, but in one case. On the contrary the Borro's test seems to be very often used by the companies which have the equip-ment. Even though the number of answers is vc -ry limited to draw generał conclusions, our per-sonal impres8ion coincides with the results. Ne-vertheless we also think, as we already said, that the use of the static cone test will increase during the next years, at least for detailed foun-dation studies.

3. INTERPRETATION AND EVALUATION OF TEST RESULTS.

3.1. Reliability of the different tests. - We think that before entering into the topie of how to inter-pret the results of the tests, it will be useful to make some considerations about which are their shorteomings and therefore how reliable the working data may be.

a) Standard Penetration Test. - The SPT is usual-ly run in cohesionless soils, at least if ąuantitati-ve data are intended to be obtained. Very often sands are submerged at a certain depth and then the troubles may be serious if very careful pre-cautions are not taken to avoid piping or loosening at each testing levei. We have described above the precautions we usually take to avoid such dif-ficulties; we should mention an additional one: very careful supervision. And we may add that even that way the reliability is ąuestionable: a designer will always feel very unsafe if he has to dimension his foundations only on the basis of the SPT results*

In order to illustrate this assertion I will mention one case personally experienced by the author of this Report during the last years in San Sebastian, when preparing a gcotechnical study for the new building of the Caja de Ahorrcs Provincial de Guipuzcoa.

The dimensions in plan of the plot are of appro-ximately 30 x 60 m. The soil profile is formed down to elevation *18 m by silty sands with D50 between 0, 25 and 0, 35 mm and C_u between 2 and 4 and from 3 to 10% passing n9 200 sieve; down to elevation -12 there are occasional layers of silt or peat of the order of a few millimeters to a couple of centimeters thickness. Below elev. -18 there are interbedded layers of sand and silt, again with thin peat layers, down to about elev. -40 or -43 m , where gravelly sands are found. The water table is at elcv. -5.50 m.

The soil survey consisted of 7 borings perfora-ted by percusion drilling and piston sampling with SPT tests in between; 9 static cone tests were performed, three of them at a short distan-ce from the corresponding borings (l to 4 m ) and the rest uniformly distributed in plan. Both the SPT and the cones showed a remarkable uni-formity of the deposits at each given elevation.

The works were directed by the author, who was in close connection with the field supervisor. One year before taking carc of this job three borings had bcen performed by the same Contractor without our supcrvision and SPT test had been run by a different foreman. It was very surpri-sing to see how the SPT values of the new cam-paign were much lower than the previously obtained (of the order of one half to one fourth). As the company is one of the most reliable in the country they became very worried and asked their foreman to oyerstress all short of precautions in perfect collaboration with our supervi-sor. Neverthele88 all the new SPT repeated very well the results in depth at the diferent points.

In Fig. 2 all the SPT performed in all the borings for this new survcy have bcen plotted;as it can be seen the repeatability is quite remarkable. In Fig. 3 the SPT of the three borings of the first campaings havc also been plotted; evidently there is a much greater dispersion but they still show to some extent the right layering of the soil.

We felt very happy to see how we had discovered a serious sistematie error committed in the first campaign, which scemed to be due to the fact that the casing had been hammered down for a considerable length without cxtracting the sand simultaneously.