Reliability of Shear-Box Tests Upon Soaking Process on the Sand Soil in Al-Najaf City

Abstract

Accurate prediction of the soil shear strength parameters is essential in the reliable geotechnical design of civil engineering structures. This recent paper investigates the effect of the dry testing condition on the shear strength parameters of the sandy soil using the direct shear apparatus and compared with the saturated condition tests in previous researches on the same soil. The dry soil, usually above the water table, is the principal condition of the Al-Najaf city soil in Iraq. Samples are selected from the site of the University of Kufa, which represents the sandy soil of the city. For reliability purposes, the soil is exposed to different pre-soaking durations (one, two, and four weeks) then air-dried for shear tests. The main results revealed that the angle of internal friction (Φ) tested as a dry sample decreases about -6% up to two-weeks soaking then recovered upon four-week soaking about +6%. Compared to the saturated testing, there are increases in F between 6%-17% from saturated tests. Finally, it is recommended to aware in the selection of testing conditions for calculations of the angle of internal friction.

Effect of Matric Suction on Deformation of Gypseous Sand Using Modified Oedometer

“…The soils' bearing capacity is decreased by about 50% due to the soaking process [19]. The shear strength of the soil can be improved by advancing the soaking time (long term) before shearing [20,21]. The settlement of the gypseous soils is increased and continued relating to the increase of the gypsum content due to wetting [17].…”

Numerical Evaluation of Slope Stability for Construction and Seismic Loads: Case Study

“…The soil's shear strength can be enhanced by the long term soaking method [13]. The risk of collapse in all soil groups rises due to a drop in soil matric suction [14][15][16].…”