Strength erosion of a fine-grained gypsiferous soil during soaking

Abstract EN

In most regions of the world, especially in the Middle East, natural soils and aggregates contain varying quantities of soluble salts [1–3].

Gypsum is one of the soluble salts that could have a detrimental effect on pavements, buildings, and earth structures [4–6] if and when these soils are subjected to long-term soaking.

Bjerrum [7] studied the effect of leaching of soluble salts from the soil on the shear strength of a Norwegian marine clay using the Vane test, and he found out that the undrained shear strength in the leached zone was only 50% of the shear strength of the unleached clay.

Torrance [8] carried out direct simple shear tests on marine clays, and he found out that the shear strength of a leached marine clay was less than that of a similar high salt marine clay.

Recent advances in irrigation have made it possible to open up many of the gypsiferous regions to farming and industrial development.

These developments include industrial and urban complexes, and require the use of water in large quantities.

When salt bearing soils, are subjected to soaking, increases in moisture content can take place causing dissolution of some of the gypsum.

In practice, soaking can take place in different ways such as local shallow wetting, deep local wetting, slow and uniform rise of ground water level, and the increase of the moisture content of a thick layer of soil resulting from condensation of steam and accumulation of moisture caused by changes in the evaporation process [9, 10].

In the case of brief flooding of gypsiferous soils, the soils are not very compressible, but in the case of long-term flooding, piping settlement can develop.

The magnitude and character of such development depend on the type of soil, initial gypsum content, relative amount of leached salts, soil properties, and acting loads [11].

Abduljauwad and Al-Amoudi [3] examined the effect of soaking and leaching on the structure, compressibility, collapse and settlement of sabkha soil.

Their results indicate that the percolation of distilled water through the sabkha causes destruction of the natural cementation leading to collapse, increase in permeability, reduction in strength, and increase in settlement.

Razouki and El-Janabi [12] studied the effect of long-term soaking on the CBR (California Bearing Ratio) of a granular gypsiferous soil, and they concluded that the normal soaking period of 4 days can lead to serious overestimation of the CBR values of gypsiferous soils.

Similarly, Razouki and Kuttah [13] studied the effect of long-term soaking on the resilient modulus of gypsiferous soils, and they suggested an empirical formula to predict the effect of long-term soaking on the resilient modulus of different gypsiferous soils.