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Penetration testing in Portugal    esopt

J. Folque    State-of-the-art report

1    - Geological background - Nearly through-out the Portuguese territory rock or tertiary soils (clay and clayey sands), formations with very high strength characteristics, occur. Recent-soil overburden is thin. Even so, whe-never boring is done in non-rocky soils, SPT penetration tests are carried out as a routine.

The biggest urban centers and industrialpłants are located in the litoral, by large r i v e r inlets. Such is the case with Viana do Caste-lo, Porto, Aveiro, Lisboa and Setubal. As the ancient valleys, now filled up by alluvia,have steep slopes in these zones, alluvium formations are narrow in plan and present conside rabie thickness. In these urban centers, the-refore, most of the building areas show outcrops of ancient soils with good mechani-cal characteristics. Nevertheless a large num ber of buildings, plants and, of course, har-bour facilities are concerned by alluvia which have been actively investigated by means of penetration tests together with other field tests (mainly vane-test) and tests carried out on undisturbed samples.

In what concerns some dams, either in pro -ject or in construction, which are located nearer to the finał reach of watercourses, the need has been felt of studying alluvia that fili up valleys, for which penetration tests have been conducted. Most of these cases have been connected with loose sands studies.

2    - Penetrometers used in Portugal -The most current penetration tests is the ^łstan -dard penetration test* (SPT). The type and weight of the rods in this test are not stan-dardized as well as the device that releases the hammer causing it to fali freely.

Deep soundings (with Dutch penetrometers) are very often carried out. Entreprises en-gaged in this type of work are provided with the standard eąuipment available in the market (10 t capacity).

The Laboratório Nacional de Engenharia Ci-vil is eąuipped with a point-resistance reading apparatus using a vibrating-wire celi. A celi for measuring pore-pressures can be coupled to this apparatus at its point. As a rule, porę -pressures developed during tests have been judged to be irrelevant.

For preliminary exploration studies a ligth percussion penetrometer is widely employed which consists of a eonie point with 90° in the vertex and in which the diameter of the base is 3 cm. It is coupled to rods 2,5 cm in diameter and 2 kg/m in weight. Operation is carried out by means of a 10 kg hammer with a free fali of 50 cm. As a rule the quan tification is performed in terms of point-resis tance, using dynamie formulae, usually the Eytelwein formula. Very often, however,this penetrometer is used only to ascertain the depth at which lies a bed-rock whose strength strongly contrasts with the strength of t h e overburden. Attempts at correlating the results of light penetrometer tests with those obtained with other penetrometers or deduced from tests on samples have led to marked scattering. This shows that accidental errors not detected by the operator are likely to occur in the results obtained from light pene trometer tests.

3 - Test procedurę - SPT tests are always carried out in combination with percussion soundings for which casing is systematically used.

Drilling muds, usually consisting of bentoni-te suspensions, are used when tests are carried out on loose sands. Correlations between results of SPT tests and Dutch pene trometer tests have proved well in generał. But as regards loose sands, even if one resorts to drilling muds, the SPT tests ha-ve given results in disagreement with obser vations of actual structures.