Document Type : Research Paper


Civil Engineering Dept., University of Technology-Iraq, Alsina’a street, 10066 Baghdad, Iraq.


The main objective of this study is to determine the appropriateness of unsaturated gypseous soil as a subgrade layer for carrying foundations. A comprehensive laboratory testing program was implemented to investigate the geotechnical characteristics and behavior of unsaturated gypseous soil. Tests that are physical included specific gravity, classification tests, relative density, Proctor compactions, single and double oedometer collapse potential, and static triaxial compression (CU-test). Chemical testing, Scanning Electron Microscopy (SEM), and Electronic Dissipation x-ray Scanning (EDS) analyses were also carried out. The tests were performed for samples prepared at 70% relative density of the natural gypseous soil. Tests are performed on the natural, unsaturated at degrees of saturation (30%, 60%, and 80%) and fully saturated gypseous soil to investigate the gypseous soil behaviors. In both single and double oedometer testing, it was discovered that the degree of specimen collapse is (Moderate) at 70% relative density, with a collapse index value ranging from (4%). The angle of internal friction for both total and effective stresses (f' and f) decreases as the moisture content of the gypseous soil increases at all saturation levels. In contrast, it was found that the strength of soil cohesion for both total and effective stresses (c' and c) increased with increasing gypseous soil moisture up to saturation (60%), which led to a rise in soil shear strength. The reduction value ranged from (38.50° to 7°) in respect of effective stresses and between (34.50° and 7°) with respect to total stresses. Effective stress increase varied from (10.0 – 26.0 kPa), and total stress increase ranged from (12.50 – 28.0 kPa). Then the strength started gradually decreasing at the saturation degrees 80 and 100%, respectively. As a result, the shear strength of the soil decreases with the value of reduction ranging from (20.0 – 11.50 kPa) for effective stresses and (21.50 – 11.50 kPa) for total stresses.

Graphical Abstract


  • Tests on gypseous soil include standard Proctor compactions and consolidated undrained triaxial compression.
  • The soil was either natural, unsaturated at degrees of saturation (30%, 60%, and 80%), or fully saturated.
  • Increasing the humidity of the gypseous soil at saturation degrees causes a decline in the internal friction angle.
  • The soil cohesion for effective and total stress increased with gypseous soil moisture up to (60%) saturation degree.


Main Subjects

  1. G. Fredlund, H. Rahardjo, Soil mechanics for unsaturated soils, Wiley and Sons Publishers, Inc. New York, 1993.
  2. H. Pereira, D. G. Fredlund, Volume Change Behavior of Collapsible Compacted Gneiss Soil, J. Geotech. Geoenvironmental Eng., 126 (2000) 907-916.
  3. M. Futai, M. S. S. Almeida, W. A. Lacerda, The shear strength of unsaturated tropical soils in Ouro Preto, 4th Int. Conf. Unsaturated Soils, Brazil, (2006) 1200-1211.
  4. Solis, J. Zhang, Gypsiferous Soils: An Engineering Problem, 11th Multidisciplinary Conf. on Sinkholes and the Eng. and Envir. Impacts of Karst, ASCE, Florida, 2007.
  5. A. Al-Mufty, Effect of gypsum dissolution on the mechanical behavior of gypseous soils, Ph.D. Thesis, Civil Engineering Department, University of Baghdad, Baghdad, Iraq, 1997.
  6. K. S. Al-Saoudi, M. Sh. M. Al-Shakerchy, S. A. Al-Janabi, Water infiltration characteristics for suggested artificial lake in bahr al-najaf, 1st Int. Conf. for Geotech. Eng. and Transportation, Baghdad, Iraq, Eng. Tech. J., 31 (2013).
  7. H. Nashat, Engineering characteristics of some gypseous soil in Iraq, Ph.D. Thesis, Civil Engineering Department, University of Baghdad, Baghdad, Iraq, 1990.
  8. D. Salman, Soaking Effects on the shear strength parameters and bearing capacity of soil, University of Baghdad, Iraq, Eng. Tech. J., 29 (2011) 1107-1123.
  9. Y. Fattah, M. M. Al-Ani, M. T. A. Al-Lamy, Studying collapse potential of gypseous soil treated by grouting, The Japanese Geotechnical Society, Soils Fdn. J., 54 (2014) 396–404.
  10. S. Mahmood, Effect of Time-based soaking on shear strength parameters of sand soils, App. Res. J., 3 (2017) 142-149.
  11. S. Razouki, M. S. Al-Azawi, Long–term soaking effect on strength and deformation characteristics of a gypsiferous subgrade soil, Eng. J. Univ. Qatar, 16 (2003) 49-60.
  12. H. Moula, N. K. Al- Saoudi, Predication collapse of gypseous soils due to wetting, J. Tech., Iraq, 23 (2010) 157-164.
  13. O. Abbas, S. M. Muarik, Behavior of compacted gypsiferous sandy soil during soaking and leaching process, J. Wassit Sci. Med., 5 (2012) 165-176.
  14. Y. Fattah, M. K. Hameedi, M. F. Aswad, Determination of collapse potential of gypseous soil from field and laboratory tests, Diyala J. Eng. Sci., 10 (2017) 75-85.
  15. N. Ibrahim, A. Khosravifar, Remedial method for collapse soil foundation of Mosul dam, DFI Annual Conf., New Orleans, LA, USA, (2017) 557-568.
  16. Sh. Mahmood, L. J. Aziz, A. M. Al-Gharrawi, Settlement behavior of sand soil upon soaking process, Int. J. Civ. Eng. Technol., India, 9 (2018) 860-869.
  17. H. Obead, H. A. Omran, M. Y. Fattah, Implementation of Artificial Neural Network to Predict the Permeability and Solubility Models of Gypseous Soil, Pertanika J. Sci. Technol., 29 (2021) 107-122.
  18. S. A. Al-Gharbawi, M. Y. Fattah, M. R. Mahmood, Effect of magnesium oxide and carbonation on collapse potential of collapsible gypseous soil, Int. J. GEOMATE, Japan, 22 (2022) 48-55.
  19. L. Hayal, A. M. B. Al-Gharrawi, M. Y. Fattah, Effect of nanomaterials on shear strength of gypseous soil, Kufa J. Eng., 12 (2021) 1-14.
  20. K. Jha, P. V. Sivapullaiah, Role of Gypsum on Microstructure and Strength of Soil, Environ. Geotech., 3 (2016) 78–89.
  21. K. Jha, P. V. Sivapullaiah, Susceptibility of Strength Development by Lime in Gypsiferous Soil-A Micro Mechanistic Study. Appl. Clay Sci., 115 (2015) 39–50.
  22. Ebailila, J. Kinuthia, J. Oti, Role of Gypsum Content on the Long-Term Performance of Lime-Stabilised Soil, Materials, 15 (2022) 5099.
  23. ASTM D 854-00, Standard test method for specific gravity of soil solids by pycnometer, American Society for Testing and Materials.
  24. ASTM D 2216-00, Standard test method for laboratory determination of water (Moisture) content of soil and rock by mass, American Society for Testing and Materials.
  25. ASTM D 4318-00, Standard test methods for liquid limit, plastic limit, and plasticity index of soils, American Society for Testing and Materials.
  26. ASTM D 422-00, Standard test method for particle size-analysis of soils, American Society for Testing and Materials.
  27. ASTM D 2487-00, Standard practice for classification of soils for engineering purposes (Unified Soil Classification System), American Society for Testing and Materials.
  28. ASTM D 4253-00, Standard test method for maximum index density and unit weight of soils using a vibratory table, American Society for Testing and Materials.
  29. ASTM D 4254-00, Standard test method for minimum index density and unit weight of soils and calculation of relative density, American Society for Testing and Materials.
  30. ASTM D698-00a, Standard test methods for laboratory compaction characteristics of using standard effort (600 kN-m/m3), American Society for Testing and Materials.
  31. A. Al–Mufty, I. H. Nashat, Gypsum content determination in gypsum soils and rocks, 3rd Int. Jordanian Conf. on Mining, Amman-Jordan, (2000) 500-506.
  32. British Standard Institution, Method of testing soils for civil engineering purposes, B.S. 1377, 1990.
  33. ASTM D5333, Standard test method for measurement of collapse potential of soils, Annual Book of ASTM Standards, Vol. 04.08, Philadelphia, PA, ASTM, USA. Copyright, ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States, 2003.
  34. A. J. Al-Obaidi, Hydro-mechanical behaviour of collapsible soils, Ph.D. Thesis, Civil and Environmental Engineering, Ruhr-Universität Bochum, Germany, 2014.
  35. ASTM D 4767-04, Standard test method for consolidated undrained triaxial compression test for cohesive soils, American Society for Testing and Materials, West Conshohocken, PA, 2004.
  36. S. Al-Gharbawi, Collapse Behavior of Carbonated Collapsible Gypseous Soil Admixtured with Reactive Products, Ph.D. Thesis, Civil Engineering Department, University of Technology, Iraq, 2022.
  37. J. Zidan, M. A. Hussein, Behavior of square footing subjected to gypseous soil under eccentricity-inclined load, J. Tikrit Eng. Sci., 20 (2013) 1-15.
  38. K. M. Gan, D. G. Fredlund, Shear strength Characteristics of two saprolitic soils, Canadian Geotech. J., 33 (1996) 595-609.
  39. Zhang, R. Solis, Fly-ash-stabilized gypsiferous soil as an embankment material, Geotech. Eng. Disaster Mitigation and Rehabilitation, (2008) 809-814.
  40. J. Lewry, J. Williamson, The setting of gypsum plaster: part I, the hydration of calcium sulphate hemihydrates, J. Mater. Sci., 29 (1994) 5279–5284.
  41. Al-Daood, M. Bouasker, M. Al-Mukhtar, Geotechnical properties of lime treated gypseous soils, Appl. Clay Sci., 88-89 (2014) 39-48.
  42. Y. Fattah, Y. J. Al-Shakarchi, H. N. Al-Numani, Long –term deformation of some gypseous soils, Eng. Technol. J., 26 (2008) 1461-1485.
  43. Lu, W. J. Likos, Unsaturated soil mechanics, John Wiley & Sons, Inc., Hoboken, New Jersey, 2004.