# Introducing Cement-Enhanced Clay-Sand Columns under Footings Placed on Expansive Soils
###### Abstract  
The risk posed by expansive soils can be lessened by placing foundations at a more deep level below the surface. Structures are able to withstand uplift forces because overburden pressure partially suppresses swelling pressure. In order to transfer the forces to a sufficiently deep depth, this study suggests introducing shafts of a low-expansion overburden material. Soil improved with cement is chosen for this purpose. This study suggests using sand with added excavated natural clay and cement. The expansive clay is added to sand in ratios of 10, 20, 30, 40 and 60%. The clay-sand mixture is then enhanced by cement of 1, 2, 4 and 8% by the weight of the mixture under four curing periods of 1, 7, 28, and 90 days. This material is recommended for use under lean concrete to transfer the loads to lower levels below the foundation depth. The thickness of this material depends on the stresses exerted, the type and the properties of the subsurface soils. The cement-enhanced clay-sand shaft's properties are examined in this work with regard to the swelling potential, compressibility, and the unconfined compressive strength for different clay contents and curing conditions. Stiff shafts were formed and found to support stresses from 600 to 3500 kPa at cement additions in the range of 1% to 8%. Clay content above 30% is found to be not suitable for Al-Qatif clay due to the compressibility and low strength of the mixture. When two percent or more of cement is added, the swelling potential is significantly reduced. This is reliant on the pozzolanic interactions of soils and cement as well as the clay mineralogy. Determining how cement affects clay-sand combinations in regions with expansive soils would facilitate the introduction of a novel, inexpensive technology to support loads applied by the superstructure. c 2024 2  
Significant parts of Saudi Arabia are covered with soils rich in expansive minerals. The areas of Al-Ghatt, Tabuk, Tayma, Al-Jawf, Sharoura, Al-Medina, Al-Qatif, and Al-Hafuf reported the presence of the expansive soil formations. In the distribution of expansive soil in the Kingdom of Saudi Arabia, Al-Qatif clay is the most expansive clay in the country and was selected for use in this study. When encountering expansive soil, the excavated material can be mixed with sand for reuse as a backfill material. This mix can be further enhanced with cement to exclude the adverse effect of clay within the mix and reduce the costs that include waste disposal. It is customary to combine clay material with coarse-grained or medium-grained sand. The prevailing belief is that the mixture's coarser fraction results in a comparatively strong shear strength and high compacted density, whereas the proportion and index characteristics of the finer fraction determine the soil's hydraulic conductivity [8]. A sand-sized fine aggregate mixed with clay improved the mechanical characteristics and compaction, according to [PERSON] and [PERSON] [9]. The effectiveness of sand-natural clay combinations employing locally accessible clay resources has been the subject of a small number of recent studies [10; 11; 12; 13; 14]. The idea of applying cement-stabilized columns for expansive soils is derived from the studies by [PERSON] et al. [15] in which ground improvement is obtained using soil-cement column-reinforced foundations. Figure 1 below is showing the method of stabilization. In order to widen this approach to cover footings supporting a light structure resting on expansive soil, columns can be enlarged to cover the entire area below the footings. In this study, the focus is not directed towards the geometry but towards the stabilized material and the depth needed to add a sufficient surcharge load. The use of cement-stabilized columns is a technique that can be used in real-world applications for geographical areas and zones of expansive soils where damage to structures and pavements were reported.