This work presents a study on the behaviors of diatomaceous soils. Although studies are rarely reported on these soils, they have been identified in Mexico City, the Sea of Japan, the northeast coast of Australia, the equatorial Pacific, and the lacustrine deposit of Bogotá (Colombia), among other locations. Features of this kind of soil include high friction angle, high initial void ratio, high compressibility index, high liquid limit, and low density. Some of these features are counterintuitive from a classical soil mechanics viewpoint. To understand the geotechnical properties of the diatomaceous soil, a comprehensive experimental plan consisting of more than 2400 tests was performed, including physical tests such as grain size distribution, Atterberg limits, density of solid particles, and organic matter content; and mechanical tests such as oedometric compression tests, unconfined compression tests, and triaxial tests. Laboratory tests were complemented with scanning electron microscope (SEM) observations to evaluate the microstructure of the soil. The test results show that there is an increase in liquid limit with increasing diatomaceous content, and the friction angle also increases with increasing diatomaceous content. In addition, several practical correlations were proposed for this soil type for shear strength mobilization and intrinsic compression line. Finally, useful correlations were presented, such as the relationship between the state consistency and the undrained shear strength, the friction angle and the liquid limit, the void ratio at 100 kPa and the liquid limit, the plasticity index and the diatomaceous content, among others.

CBR testing, developed before the Second World War, is still the most commonly used experimental procedure for pavement design. Today, CBR tests are correlated with the resilient modulus, which is a key parameter in current mechanistic pavement design methods. However, results of these correlations have been scattered, indicating that other variables are ignored. The purpose of this study is to show how the value of the CBR test is a function of other variables such as particle size and shape, crushing, and the elastic behaviour of the material. These variables were evaluated through FEM (Finite Element Method) simulations while varying several geotechnical parameters known in practical geotechnics. These FEMs include a linear elastic model and a failure criterion (elastoplastic model) and were prepared for granular soils under drained conditions. The evaluations show that the CBR not only depends on Young’s modulus (the parameter commonly used to correlate with the CBR), but also appears to depend on compressibility due to particle crushing. This appears to be a predominant parameter that can affect the CBR in the elastic domain as much as Young’s modulus does. Finally, this paper provides insights that improve the understanding of variables leading to high or low CBR values for granular materials. In addition, FEM simulations have been compared to the AASHTO Mechanistic-Empirical Pavement Design Guide (MEPDG) and other methodologies used in road geotechnics.

This study presents an innovative procedure to derive the ultimate load capacity of a pile system by considering the natural (intrinsic) variability of a tropical soil. The tropical soil has high aluminum and iron content due to processes of lixiviation of the upper soil layers. As a consequence, this soil has a porous cemented structure, high void ratio, high permeability, and high variability of the geotechnical parameters in its depth. Soil layers are experimentally characterized via standard characterization, a triaxial test, standard penetration test, and flat dilatometer tests. Also, the load test of the standard groups (PG) and pile plus pile-cap (PC), which had self-drilling piles, were performed at real scale. Afterwards, simulations using a three-dimensional finite-element method (3D FEM) considering variations in soil parameters were performed for a hypothetical piles-plus-pile cap system under vertical loading using the random finite-element method. Mean parameters were verified through laboratory and field tests. Results from the load test simulations were compared with real-scale tests conducted in this study. The relative importance of variability of several geomechanical parameters was analyzed in terms of their effects on the contribution of the pile cap to the ultimate bearing capacity of the full system and found to be 18%; the minimum contribution is 2% of the total load. Finally, it is shown that reasonable savings in construction costs accompanied by a modest reduction in the safety factor ($\mathrm{FS}=1.8$ ) may occur when the variability of parameters is taken into account.