Hidrológiai Közlöny 1970 (50. évfolyam)

12. szám - Galli László: Kötött talajok minősítése a vízépítésben

552 Hidrológiai Közlöny 1970. 12. sz. Galli L.: Kötött talajok minősítése [21] Kezdi Árpád: Stabilizált földutak. Akadémiai Kiadó, Budapest. 1967. [22] Lyon L. T.—Buckman H. O.—Brady N. C.: The Nature and Properies of Soils New York. 1952. [23] Marjay Gyula: Öntözőcsatornák vízveszteségének vizsgálata. Mérnöki Továbbképző Intézet, Jegyzet, 1959. [24] Marjay Gyula: Öntözőcsatornák vízveszteségének vizsgálata különös tekintettel az eredmények gyakorlati felhasználására. Hidraulikai Konferencia, Budapest, 1960. [25] Mihályfalvy János: Időszakosan üzemelő öntözőcsatornák szivárgási vesztesége és a termésre való kihatása. Öntözési Konferencia, Budapest, 1961. [26] Szepesy Károly—Máyer János: Neuartige Sedimentations Analyse. Tonindustrie Zeitung, 1963. [27] Szepesi Károly—Székiné (Fux V.) : Az alföldi lösz szerepe a szikes talajok képződésében. Földtani Közlöny, 1969/1. [28] Szepesi Károly: Az árvédelmi földművek anyagának időbeli változása. VITUKI, Téma beszámoló. 1969. [29] Szilvágyi Imre: Korszerű talajmechanikai laboratóriumi vizsgálatok. Mérnöki Továbbképző Intézet, Jegyzet, 1955. [30] Szilvássy Zoltán: Árvízvédelmi töltések tömörségi feltárása VITUKI, Közbenső jelentés, 1965. [31] Szilvássy Zoltán: A déldunai árvízvédelmi töltések feltárása Vízügyi Közlemények, 1967/1. Classification of Cohesive Soils in Hydraulic Engineering Galli, L. Experience gained with earth structures in hydraulic ongineering, such as flood levees, irrigation and drainage canals has shown cohesive soils to be susceptible to structural transformation, eaused by x'epeated cycles of drying and wetting, freezing and thawing, but especially by the chemical action of water in contact with these soils. In response to changes in environment they may become crumbly, structured, whereas in other cases their volume-change properties may be increased. These transformations are always influenced by two factors: the mineralogical and chemical character of the soil and the nature of the change in environment. For this reason the mineralogical and chemical stability of a particular soil, and thus the constancy of engineering properties can be evaluated only by eonsidering both factors simultaneously. These transformations can be traced back to reasons of colloid cheitaistry and their potential occurrence, and probable sense are difficult to determine exactly, with an accuracy required for the reliable designing of hydraulic structures. In Hungárián hydraulic designing practice a simple test has been developed for estimating the character and susceptibility to changes of soils. The test consists in determining the sediment volume of an air-dry powdered sample. For the settling test the sample is wetted and dried repeatedly and then settled, using the water with whieh the soil will come into contact in the completed structure. The pore volume of the sediment volume thus obtained is the so-called critical pore volume (ejif), on the basis of which the soil can be classified into four groups of hydraulic stability. The soil is regarded as hydraulically stable, i. e., its engineering properties are expected to remain constant in a changing environment if the critical pore volume ranges from 2 to 3.5. The soil is of a loosening character, i. e., considerable swelling and loss of strength may be anticipated if the critical pore volume is from 3.5 to 6. The soil will tend to show flowing properties if the critical pore volume of the sample is higher than 6, or cannot be determined at all. The transformation may be, however, alsó of an opposite trend, i. e., the repeated drying and wetting, freezing and acidic water may cause the soil to become crumbly if the critical pore volume is smaller than 2. In this case it will develop structure and assume properties similar to sand. Aceording to experience gained with the classification by hydraulic stability values the sediments in river beds, flood plains and lakes belong usually to the stable group, but may belong to the loosening, of flowing groups if they have become alkaline. Clays when excavated to the surface show usually „loosening" properties. Depending on the parent material and the stage of weathering attained, slope debris may belong into the loosening, but alsó into the crumbling group. The „crumbling" transformation is perhaps of the greatest engineering interest. In this process the soils tend to become structured. Similar transformations are likely to occur in flood levees, and may take place in the vicinity of irrigation- and drainage canals. Unter the influence of repeated cycles of drying and wetting, leaching and freezing the soils may become crumbly, permeable, embankments loose their sealing properties and there is a considerable loss of water from canals. Consequently, when designing such structures, allowance must be made for similar transformations. Classification on the basis of hydraulic stability may greatly facilitate engineering-geological mapping for hydraulic engineering purposes. In fact, in areas where the surface is covered by loose sedimentary rocks, the genefal hydraulic stability properties of cohesive soils are approximately the same over larger areas even if there are appreciable differences in the partiele size or sand content of the sediment and consequently the plastic and liquid limits of the soils show considerable scatter. In the classification of cohesive soils on the basis of hydraulic stability many questions are still uncleared. Systematical experiments are required to obtain better understanding on these transformations.