ABSTRACT:

The Lugeon Test, or Water Pressure Test, has, in general, been used for more than15 years as a basis for determining the hydraulic properties of rock masses. Nowadays, as there is more need to understand better the behaviour of the flow in rock masses, the test has become obsolete because of the unreliable results obtained when using it. This paper presents a critical analysis of the test, in an attempt to show the incongruities, contradictions and lack of precision of this technique, and as a replacement, introduces the tests called "Teste de Registro Hidraulico" - TRH (Hydraulic Register Test), "Ensaio de Injecao d''agua sob Pressöes Decrescentes"-EIPD (Water Injection Test under Decreasing Pressures) and "Ensaio Direcional"-ED(Directional Test), which for their simplicity and low cost, together with their ability to give reliable information, have become the tools most suitable for studying the hydraulic properties of rock masses.

INTRODUCTION

In 1933, when Maurice Lugeon published ''''Barrages et Geologie" after a conference at the swiss society of Engineers and Architects in Lausanne, he could never have imagined that, on the subject of determining hydraulic properties in rock masses, he would be not only the most quoted, but also, for many years, the only one mentioned in all publications on the subject and that, as time went by, the specialists would attempt to collect pos- use and impossible results in order to his recommendations. The most incredible thing of all is that Lugeon was only concerned with studying ce- ment groutlng, and therefore his objectives were others. He made the following recom- mendaton: ''''Aujourd''urd''hui, voici'' la methode que je. fais appliquer partout. C''est la methòde dite par phases descendantes. On fore 5m. On place un joint d ''etancheite à 3 m et on essaye Ie coefficient de porosit de la roche. On ap- pele coefficient de porosite la quantite d''eau. absorbee par minute et ''par mètre lineiare sous une pression cholsle. La presmi sion doit s''exercer pendant 5 à 10 minutes" And further on:"Voici les valeurs que je e Pour tout barrage qui depasse 30 m: L''absorption en eau par la roche ne devra pas depasser 1 litre/minute par metre lineaire sous une pression de 10 kg pendant 10 minutes. Telle est la perte que l''on peut tolerer". As one can understand, Lugeon spoke of a loss that can be accepted for one coefficient of the rock porosity, thereby referring to the tolerable water loss for cement grouting in the impermeabilization of the rock mass. Lugeon''s recommendation was modified in the USA only with regard to the pressure of 10 kgf/cm2• The pressure used had lower values, which took into account the weight of the rock on the section being tested,so as to avoid the harmful deformations in the foundation rock mass. It was in 1967, with Guerra et alii, when they said "Si ces absorptions sont mesurees a plusieurs pressions, on peut etablir les relations entre hauteur de charge e debits, et en tirer des conclusions sur le regime de l''ecoulement laminaire ou turbulent". After this statement all subsequent authors began to analyse the test, based on what can be seen in figure 1; that is,they showed in graph form the ratio flowrate x pressure of the test.

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