## 1 Introduction
Modern penetration devices have become very sophisticated in recent years and are supplied with state-of-the-art sensors that are capable of measuring water pressure, moisture content, seismic parameters, and others. Many studies have confirmed direct and indirect correlations between these measurements and some geotechnical parameters [11; 12; 13]. These parameters include moisture content, plasticity, index properties, and shear strength. The stiffness of the ground in coastal zones or swamp areas was assessed in early times using the feel or resistance to the penetration of a steel rod or wood. This can either be dynamic or by continuous pushing. The initial penetrometers were dynamic until recent technologies introduced control units to measure the response to pressure or the rate of penetration. For gravly and coarse formation, a cone attached to a heavy hammer is recommended. This can be similar to the German Standards, DIN 4093-4 [14], which specifies a 50 kg hammer falling over a 50 cm distance on a 43.7 mm diameter cone. When advancing a cone into the ground, pressure is needed to create a hole by pushing the soil aside and exerting point load pressure. The pressure applied to advance the cone can be equated to the resistance to penetration, and the soil strength measured this way depends on several parameters that include but are not limited to the soil water content and the bulk density. These two parameters influence the resistance to penetration and need to be reported in all penetration profiles presented. The cavity expansion theory is an analytical approach conducted to determine the pressure-expansion relationships. Assuming an incompressible solid with a plastic region surrounding the cavity and a linearly infinite deformable solid zone beyond that region, [PERSON] [15] studied the cavity expansion of cavities using the Mohr rupture condition to determine the spherical and cylindrical cavity expansion stresses. The application of cavity expansion theory may not correctly model the strain path followed by the clay under pressure. [PERSON] [16] suggested a strain path method that accounts for the complex history of the soil during penetration. Solutions for unsaturated soils are more complex than those for saturated soils. [PERSON] et al. [17] presented a solution for the pressure-expansion relationship in pressure-emergers considering small strain deformations in cylindrical and spherical cavities in clayey sand soils. [PERSON] et al. [18; 19] analyzed cavities based on [PERSON] et al. work for pressure-emergers. Advanced models that have been presented by other researchers include those in [20; 21; 22]. Reference [23] presented a dynamic analysis of a smooth penetrometer free-falling into uniform clay. [PERSON] and [PERSON] [24] also studied SWCCs using cone penetrometers for two sites of low- to high-plasticity clayey material. Reference [25] used a penetrometer to evaluate the compaction in levees. They claimed that simple penetrometers can be used successfully in the evaluation of the degree of compaction in compacted partially saturated fine-grained soils. Utilizing this test method can be a quick and reliable approach to assessing the quality of clay-sand liners. In order to use it, several measures need to be taken into account; these include the following:  
The weight of the hammer;  
The geometry of the cone;  
The uniformity of the moisture content within the site;  
The composition of the soil material. Without considering the above conditions, the field shear-strength data may be erroneous and are not likely to reflect the true measurements. However, it can still be used for comparison purposes within the site and can enable the easy recognition of poorly compacted zones. As the material used in clay-sand liners is uniform and does not include gravel or boulders the assessment using the cone penetration method can be ideal.