6585845021

France

48

shows that the approximatc distribution of surface exposurcs, over a total ₀ piane projectIon arca of 550 000 km“ i s as foliows :

Pre cambrian    20    %

Pa Ioozo i c    10    %

Mcsozoic Triassic    5    °/j

Ju rass i c    20    %

Cretaceous    20    %

Tcrtiary    15    /o

Ouaternary or various

other surface cxpressions    10    %

100 %

At first glance, one may be tempted to simpIy concludc that the penctrometer can efficiently be uscd over about 10 % of the total area of France, that is in the rcccnt sedimentary deposits.

This would be a vcry inaccurate deduction. It is true howevcr that all unconsolidated sedimentary deposits, be they sands, clays, pcats or yravels, etc. of uny age or origin arc capable of bcing pcnctrated by one or morę of the dcviccs prcsently availabie.

On the other hand, it is extrcmcly interesting to thoroughly invcstigate such deposits bccause they may cxhibit important heterogeneiti es both in the horizontal and vcrtical pIanes.

Penetration is not possiblc in highly over-consoIidated sediments or strongly cemcnted by prccipitati on of silica or calcium carried in ground waters.

It can be stated that the geologie age of soils is not a criteria to select the penctrometer for soi I investigati on * A good example of this is givcn by many regions in France (Esterel Coast on Kediterranean shore, Massif Central, Massif Armoricain,

Vosgcs, Pyrenees and, to a Iarge extent, Alps) which are essentially paleozoic zones and consist of metamorphic or cristalline rock formations. In most cascs, these zones are covercd by rcsidual soils due to the weathering in place of the parent bedrock of the order of ten meters in thickncss (except for somc rock outerops) • Penctrometer tests are possible in such areas on to the bcdrock hor i zon (cxamplc : gron i te arenas in Brittany and in Vendee and the altered schists of Angers, etc.)•

The heavy duty modern dynamie penetrometers are capable of penetrating into Iayers of vcrv high rcsistanccs which were unattainablc some t i me ago•

A correct evaluation of the possibility of use of penetrometers could only be ac’iievcd by a statistical survey with the engineers having expcriencc in certa in areas. Such a survey was carried out in which 60 engineers geograph i ca I I y, scattercd over France and Cors ipart icipated • This survcy showed that the areas amenablc to the penctrometer varied from 50 to 90 % of the areas availabie for construction with a few exceptions in the 25 ? or 95 J rangę. The avcragc was about 71 % • Little change in the average occurs with the overseas areas wherc the perccntage varies from 50 % (Martiniquc) to 90 % (GuadcIoupc) •

It is of interest to noto that the answers to the survey were boscd most Iy on the performance of light duty dynamie penctrometers or that of static penetrometers. To that extcnt they give conservative estimates.

One outstanding case to i Ilustrate this point is that of the Parisian region which was renewned to be difficult for penetrometers unti I a few years ago. Numerous engineers and architects or contractors assumed that little penetration could be achicvcd. Howcvcr, sińce the availability of hcavy duty penetrometers on the market, a greater varicty of soils at greater depths can now be investigated • It can now be said that in most of the Parisian region, heavy duty penetrometers can be uscd.

In the Rhone-AIps region the static penetration is rather limited in scope, but rarely is the static dynamie penctrometer found wanting. For this type of penetrometer, expericnce shows that 7 to 10 % of the tests must be madę by dynamie method and that in 80 % of the cases, alternating both the static and dynamie methods is required. Similar expcricnce was obscrved in the Parisian region.

III- PENETROMETERS USED IN FRANCE

Practically all of the penetrometers prcsently in use in France have bcen dcscribed by Sanglerat in the book ''The Penctrometer and Soi I Exploration" (Ref. 1). Only the modifi-cations madę sińce 1972 are therefore presented herc, or, as the case may be, the deviccs used in certain localities.

The three main types commonly in use are :

-    static penetrometers

-    dynamie penetrometers

-    stet ic-dynamic penetrometers