Acta Geodyn. Geomater., Vol. 18, No. 2 (202), 209–230, 2021 DOI: 10.13168/AGG.2021.0015 journal homepage: https://www.irsm.cas.cz/acta ORIGINAL PAPER ASSESSMENT AND IDENTIFICATION OF THREE TYPES OF DIFFICULT SOILS Tahar AYADAT Prince Mohammad Bin Fahd University, Al-Khobar, Saudi Arabia *Corresponding author‘s e-mail: tayadat@pmu.edu.sa ABSTRACT The soil engineer needs to be able to readily identify difficult or problematic soils and to determine the amount of settlement that may occur. This paper deals with the assessment and identification of three types of difficult soils: collapsible soils, swelling soils, and liquefiable soils. In the first instance, the study investigates the effect of some soil properties on wetting-induced collapse strain and the swelling potential of soils. Also, two new methods for predicting soil collapse and swelling potential are developed. The proposed relationships correlate between collapse strain and swelling potential and some soil parameters which are believed to govern soil collapse and swelling. Validation of these two relationships with some data reported in literature is also examined. Furthermore, the paper describes the different steps suggested in a new procedure for soil liquefaction assessment. The procedure was presented in the form of an evaluation guide. In addition, a relationship was suggested for computing the potential for liquefaction. An application of the proposed procedure to a practical case is included in order to validate and illustrate the different steps to be followed in the suggested evaluation procedure. ARTICLE INFO Article history: Received 5 January 2021 Accepted 6 April 2021 Available online 21 April 2021 Keywords: Identification Prediction Collapsible soil Swelling soil Liquefaction Difficult soils Cite this article as: Ayadat T: Assessment and identification of three types of difficult soils. Acta Geodyn. Geomater., 18, No. 2 (202), 209– 230, 2021. DOI: 10.13168/AGG.2021.0015 1. INTRODUCTION AND BACKGROUND Difficult soils are those that make the construction of foundation extremely difficult. Due to the increase of land development all over the world, the need to deal with difficult soils has become essential. The best-known difficult or problematic soils are collapsible soils, expansive soils, liquefiable soils, sabkha soils, compressible soils, peat, etc. This investigation is concerned with three types of difficult soils: collapsible soils, expansive soils, and liquefiable soils. Expansion, liquefaction, and collapsibility of soils give rise to many geotechnical difficulties, including inadequate bearing capacity, the potential for unacceptable settlements, and slope instability. In the following, some details about these three different soils are summarized. Collapsible soils are defined as any unsaturated soils that go through a radical re-arrangement of particles and a great volume decrease upon wetting, with or without additional loading. The most extensive deposits of collapsible soil are aeolian or wind-deposited sands and silts (loess). However, in addition to these deposits, there is a wide variety of other types of deposits which have been identified as having an unstable structure. These are in alluvial flood plains, fans and mudflows, colluvial deposits, residual soils, volcanic tuffs, and man-made fill. Most of the work carried out on the parameters governing the collapse of partially saturated soils have focused on the initial dry density, moisture content, degree of saturation, and overburden pressure. The influence of these factors on the amount of collapse has been investigated by several researchers. Most of them have agreed that for a given moisture content, the amount of collapse increases with the dry density. Meanwhile, for any given dry density, the magnitude of collapse decreases with increasing moisture content, and there is a critical moisture content above which no collapse occurs (e.g., Booth, 1975; Lefebvre et al., 1989; Lawton, 1989). At a given dry density, the overburden stress level at which the maximum amount of collapse takes place varies inversely with the compaction water content (e.g., Booth, 1975; Cox, 1978; Lawton, 1989). Moreover, there is a critical degree of saturation beyond which the soils do not appear to be susceptible to collapse. Booth (1975, 1977) and Geneshan (1982) proposed a critical degree of saturation of 50–60 %. Markin (1969) and Prusza and Choudry (1979) suggested slightly higher values, between 60 % and 65 %. For the identification of collapsible soils, different criteria have been adopted or established by different investigators. Most of the criteria reported in the literature before 2010 were reviewed by Ayadat et al. (2011). Many other research works were carried out in the last decade to investigate the parameters affecting soil collapse and to develop empirical equations in order to correlate the amount of soil collapse to soil properties (e.g., Lommler and Bandini, 2015; Li et al., 2016; Bigdeli and Siddiqua, 2016; Ping