Behavior Study of the Gypsiferous Sand Soil of AlNajaf City with Presence of Matric Suction Using Unsaturated Triaxial Device

Document Type : Research Article


1 Civil Engineering Department, Engineering Faculty, Ferdowsi University of Mashhad, Iran

2 Civil Engineering Department, Engineering Faculty, Ferdowsi University of mashhad,Mashhad,Iran

3 Civil Engineering Department, Engineering Faculty, Kufa University, Iraq


Al-Najaf city is considered one of the gypsiferous rich soils cities in Iraq. When a building is constructed on a gypsiferous soil in the unsaturated state, no effective settlement will be distinguished. When a gradual saturation has occurred, the soil gives a clear deformation and may be collapsed. This paper presents how the degree of saturation can affect on the deformation of a gypsum sand soil. A triaxial test device has been modified to have the ability for unsaturated tests. The soil samples were taken from Al-Najaf city in Iraq. Disturbed samples with two different gypsum contents; 14% and 29%, are tested with the presence of different matric suctions, initial matric suction, 60% initial matric suction, 30% initial matric suction and zero matric suction. A loading-path was adopted to symbolize when construction is built on a gypsiferous sand soil in a specific matric suction (specific degree of saturation). In addition to the previous tests, two conventional saturated tests (CD) were added under the above mentioned of confining stresses. The results were when increasing matric suction, the stiffness and shear strength are reduced and the volumetric strains increase significantly. The percentage increases are 60% and 50% under confining pressure of 100 kPa and 200 kPa, respectively for the two selected gypsum contents. The results of this study can be used to estimate the settlement that results from decreasing matric suction due to water table rise or other phenomena.


Main Subjects

  1. [1] Fredlund, D.G. and Rahardjo, H. 1993. Soil mechanics for unsaturated soils, John Wiley & Sons, Canada.

    [2] Lu, N. and Likos, W. J. 2004. Unsaturated soil mechanics,

    1st ed, Wiley, Canada.

    [3] Fredlund, D. G., and Morgenstern, N. R. 1977. “Stress state variables for unsaturated soils”. Journal of Geotechnical Division, 103(5), pp. 447-466.

    [4] Handoko, L., Yasufuku, N., Oomine, K., and Hazarika, H.

    1. “Suction controlled triaxial apparatus for saturatedunsaturated soil test”. International Journal of Geomate, 4(1), pp. 466-470.

    [5] Escario, V., and Saez, J. 1986. “The shear strength of partly saturated soils”. Geotechnique, 36(3), pp. 453-456.

    [6] Rassam, D. W., and Freeman, C. 2002. “Predicting the shear strength envelope of unsaturated soils”.

    Geotechnical Testing Journal, GTJODJ, 25(2), pp. 215–

    220, DOI: org/10.1520/GTJ11365J

    [7] Guan, G. S., Rahardjo, H., and Choon, L. E. 2009. “Shear strength equations for unsaturated soil under drying and wetting”. Journal of Geotechnical and Geoenvironmental

    Engineering, 136(4), pp. 594-606, DOI: 10.1061/(ASCE)


    [8] Tami, D., Rahardjo, H., and Leong, E. C. 2007. “Characteristics of scanning curves of two soils”. Soils and Foundations, 47(1), pp. 97-108, DOI: org/10.3208/ sandf.47.97

    [9] Liu, Q., Yasufuku, N., Omine, K., and Hazarika, H. 2012. “Automatic soil water retention test system with volume change measurement for sandy and silty soils”. Soils and Foundations, 52(2), pp. 368-380, DOI:10.1016/j. sandf.2012.02.012.

    [10] [Mendoza, C. and Colmenares, J. (2006). “Influence of the suction on the stiffness at very small strains.” 4th Int. Conf. on Unsaturated Soils, ASCE, pp. 529-540, DOI: 10.1061/40802(189)40

    [11] Nyunt, T. T., Leong, E. C., and Rahardjo, H. 2011. “Strength and small-strain stiffness characteristics of unsaturated sand”. Geotechnical Testing Journal, 34(5), pp. 551-561, DOI: 10.1520/GTJ103589, ISSN 0149-6115

    [12] Shen, Z., Jiang, M., and Thornton, C. 2016. “Shear strength of unsaturated granular soils: three-dimensional discrete element analyses”. Granular Matter, Springer, 18(3), pp. 37, DOI: 10.1007/s10035-016-0645-x

    [13] Haeri, S. M., Garakani, A. A., Khosravi, A., and Meehan, Ch. L. 2014. “Assessing the hydro mechanical behavior of collapsible soils using a modified triaxial test device”. Geotechnical Testing Journal, 37(2), pp. 190–204, DOI: 10.1520/GTJ20130034, ISSN 0149-6115

    [14] Ng, Ch. W. W. and Menzies, B. 2007. Advanced unsaturated soil mechanics and engineering, 1st ed., Taylor & Francis Group, Canada.

    [15] Aldaood, A., Bouasker, M. and Al-Mukhtar, M. 2013. “Stability behavior of lime stabilized gypseous soil under long-term soaking”. 2nd Int. Conf. on Geotechnical and Earthquake Engineering, pp. 170-177.

    [16] Solis, R. and Zhang, J. (2007). “Gypsiferous soils: an engineering problem.” 11th Multidisciplinary Conf. on Sinkholes and the Engineering and Environmental Impacts of Karst, ASCE, Florida, U.S.A., DOI: 10.1061/41003(327)72

    [17] Al-Shakerchy, M. Sh. M., 2007. “Geotechnical properties of Al Najaf city soil with emphasis on the infiltration and strength characteristics”. PhD Thesis, Building and Construction Dept., University of Technology, Baghdad, Iraq.

    [18] Al-Saoudi, N. K. S. and Al-Shakerchy, M. Sh. M. (2010). “Statistical analysis of some geotechnical properties of Najaf city.” Proc. Int. Geotechnical Conference, Vol. 3, Moscow, Russia, pp. 1173-1180.

    [19] Al-Saoudi, N., Al-Khafaji, A. and Al-Mosawi, M. (2013). “Challenging problems of gypseous soils in Iraq.” Proc. 18th Int. Conf. on Soil Mechanics and Geotechnical Engineering, France, pp. 479-482.

    [20] Razouki, S. S., and Al-Azawi, M. S. 2003. “Long–term soaking effect on strength and deformation characteristics of a gypsiferous subgrade soil”. Engineering Journal of the University of Qatar, 16, pp. 49-60.

    [21] Salman, A. D. 2011. “Soaking effects on the shear strength parameters and bearing capacity of soil”. Eng. & Tech. Journal, University of Technology, Baghdad, Iraq, 29(6), pp. 1107-1123.

    [22] Mahmood, M. Sh. 2017. “Effect of time-based soaking on shear strength parameters of sand soils”. Applied Research Journal, Iran, 3(5), pp. 142-149.

    [23] Mahmood, M. Sh. 2018. “Effect of soaking on the compaction characteristics of Al-Najaf sand soil”. Kufa Journal of Engineering, Iraq, 9(2), pp. 1-12.

    [24] Razouki, S. S., and Salem, B. M. 2014. “Soaking–drying frequency effect on gypsum-rich roadbed sand”. International Journal of Pavement Engineering, 15(10),

    1. 933-939, DOI:10.1080/10298436.2014.893326

    [25] Razouki, S. S., and Salem, B. M. 2015. “Impact of soaking–drying cycles on gypsum sand roadbed soil”.

    Transportation Geotechnics, 2, pp. 78-85, DOI:10.1016/j. trgeo.2014.11.003

    [26] Akhtarpour, A., Mahmood, M. Sh., Almahmodi, R. and Abdal Husain, M. M. (2018). “Settlement of gypseous sand upon short-term wetting.” Proc. Int. Cong. on Engineering and Architecture, Alanya, Turkey, pp. 18071820.

    [27] Ahmed, K. I., 2013. “Effect of gypsum on the hydromechanical characteristics of partially saturated sandy soil”. PhD Thesis, Cardiff University, UK.

    [28] Abdal Husain, M. M., Akhtarpour, A. and Mahmood, M. Sh. 2018. “Wetting challenges on the gypsiferous soils.” Proc. 4th Int. Cong. on Sustainable Development, Shiraz, Iran.

    [29] Aversa, S., and Nicotera, M. 2002. “A triaxial and oedometer apparatus for testing unsaturated soils”. Geotechnical Testing Journal, 25(1), pp. 3-15, DOI: 10.1520/GTJ11075J, ISSN 0149-6115

    [30] Cabarkapa, Z., and Cuccovillo, T. 2006. “Automated triaxial apparatus for testing unsaturated soils”. Geotechnical Testing Journal, 29(1), pp. 21-29, DOI: org

    /10.1520/GTJ12310. ISSN 0149-6115

    [31] Padilla , J. M.,  Houston, W. N.,  Lawrence, C. A., Fredlund, D. G.,  Houston, S. L.  and Perez, N. P. (2006). “An automated triaxial testing device for unsaturated soils.” 4th Int. Conf. on Unsaturated Soils, ASCE, pp. 1775-1786, DOI: 10.1061/40802(189)149

    [32] Haeri S.M., Zamani A. and Garakani A.A. 2012. “Collapse potential and permeability of undisturbed and remolded loessial soil samples”. Unsaturated Soils: Research and Applications, Springer, Berlin, Germany, pp. 301-308, DOI: 10.1007/978-3-642-31116-1_41

    [33] Ahmad, F., Said, M. A., and Najah, L. 2012. “Effect of leaching and gypsum content on properties of gypseous soil”. International Journal of Scientific and Research Publications, 2(9), pp. 1-5.

    [34] Al-Dabbas, M. A., Schanz, T., and Yassen, M. J. 2010. “Comparison of gypsiferous soils in Samarra and Karbala areas, Iraq”. Iraqi Bulletin of Geology and Mining, 6(2), pp. 115- 126.

    [35] Barazanji, A. F., 1973. “Gypsiferous soils of Iraq”. DSc Thesis; State University of Ghent, Belgium.

    [36] Nashat, I. H., 1990. “Engineering characteristics of some gypseous soil in Iraq”. PhD Thesis, University of Baghdad, Baghdad, Iraq.

    [37] Al- Mufty A. A., 1997. “Effect of gypsum dissolution on the mechanical behavior of gypseous soils”. PhD Thesis, University of Baghdad, Baghdad, Iraq.

    [38] Ladd, R. S. 1978. “Preparing test specimens using undercompaction”. Geotechnical Testing Journal, GTJODJ, 1(1), pp. 16-23.