Lœss are sedimentary deposits.
They cover nearly 10%of the earth’s surface area 1. They are mainly composed of fine and angular grainsof silt, fine sand, and of calcite. They contain relatively smaller amounts ofclay. Many researchers described the lœss as uniform yellow silt, or as homogeneoussilt not laminated slightly yellow in color. However, its color can vary from thedark gray, brown, red, yellow to the white color. They are mainly producedunder periglacial conditions, and transported by the permanent action of thewinds 2.
Smalley and vita-finzi 3 defined the lœss asa windblown deposit. It is mainly made of silica and carbonate of calcium (CaCO3),and is composed primarily of the grains ranging between 10 and 50 ?m. Itcontains a less proportion of sands and clays.
In order to clarify it better,Pye 4 described the lœss as a windblown deposit of silt. Healso noted that it consists of quartz, feldspar, mica, minerals of clay, andcarbonate grains in varying proportions. According to Pye 2, a typical lœss oftencontains 10% to 20% clay minerals, and up to 10% of fine sand. However, Grabowska-Olszewska has stated that, ingeneral, lœss contains 11 to 19% of sand, 73 to76% of silt and 8 to 10% of clay. From the mineralogical viewpoint, quartz is theprincipal mineral. It represents 40 to 70%, with 15% feldspar, and up to 30% ofclay minerals 5. They play the role of the binder at the level of theinterparticle contacts, and give lœss whenit is dry a certain resistance 6.
According to Smalley 7, the calcium carbonateis present in the lœss as a cementing material. Its contentcan vary between 4 and 20% and can slightly help to bind the particles of theground 6. Lœss ischaracterized by liquid limits ranging from 25% to 35%. Exceptional values??reaching 45% are observed for clayey lœss.The plasticity index is included in the range of 5 and 22%. Lœss canbe classified as sandy, silty or clayey lœss6. In their natural state, it is characterized by low water content, and ahigh porosity 8. The bulk density varies between 1.
5 and 1.8 g / cm³, and thespecific gravity between 2.1 and 2.75 9. This type of soil is mainlylocated in arid and semi-arid regions. It is found in large quantities around theworld. The most important deposits are located in China 10-11-12-13. Theycover an estimated area of 630000 km² 11.
In central Europe, themost important areas of lœss arefound in the Danube basin, in Bavaria, the Rhine, Belgium, northern France, theChannel Islands and the South of England 2, which covers 30 to 50 meters inheight and reaches up to 180 km in length 14-15.In Great Britain, some deposits are mainly found in the East of England. Other deposits were recordedin Scotland, in Wales, in the North-West and the South-west of England 16.In Poland, the cover of the lœss islimited to the latitudinal belt in the southern part of the country, withthickness values ??reaching 30 meters 5-14.In addition, in the United States, the principal lœss depositsare indicated in the areas of Nebraska, Kansas, Iowa, Wisconsin, Illinois,Tennessee and the Mississippi.
Other lœss depositswere located in the South of Idaho and Washington. Sometimes the thicknessexceeds 60 meters 17-6-18-19.In Canada, the lœss reaches 100 meters in thickness 20.
In South America, lœss deposits cover 30% of the total area of ??the Pamparegion in Argentina.The thickness reaches approximately 30meters 21.Other peri-Saharan type of lœss depositswere founded in North Africa. It has been noticed that the Sahara is one of themain sources of dust 22-23.
Coudé-Gaussen 24 reviewed theperi-Saharan lœss. He reported that the peri-desert lœss is less known than the periglacial lœss.The lœss ofMatmata in southern Tunisia can present a well example of these deposits. This lœss depositexceeds 20 meters in thickness 24.Some lœss deposits are also known in the Southern PiedmontAtlasique of Morocco and in the Canary islands. The Moroccan dust deposit is located on the north shore of the wadi ofMassa.
It is mainly silty, witha carbonate content ranging from 25% to 40% 25. On the Scheidig map 26, the only distribution of lœss found in Africa is indicated in the north of Libya. Although this card is very old, it stillremains a useful one. In the area of Tripoli (North-west of Libya),particularly in the Jefara plain, lœss is characterized by a particle sizehigher than 100 ?m. Assallay et al 27 concluded that the Libyan lœss can be classified as silty lœss in the Tripoli region, and clayey lœss in the Ghat region.The work of Coudé-Gaussen 24 indicated that the lœss of North Africa can have a coarser particle size, shift towards thecoarse silts even fine sands. In Algeria, some lœss depositswere observed in the Ghardaïa region.
Till today, no thorough study was carriedout to determine the distribution, the characterization and the possible use ofAlgerian lœss. It is hoped that the lœss deposits which exist especially in theSouth of Algeria may present opportunities with the consideration of economicaland ecological effects. In this article, the results of the laboratory testsare presented and discussed. These tests allow us to characterize, from ageotechnical viewpoint, the lœss samples collected from two sites belonging to theGhardaïa region (South Algeria).