# Influence of the Diatomite Specie on the Peak and Residual Shear Strength of the Fine-Grained Soil
## 1 Introduction  
The soil constitutes the support of many infrastructures such as buildings, bridges, highways, and dams, among others; therefore, understanding the various elements that are part of it seems to be an interest topic in the recent years. Due to the heterogeneity of the soil, the shape of distinct particles conditions some properties, including volumetric properties, permeability, suction, compressibility, shear strength, and cyclic loading [1, 2, 3]. Diatoms are unicellular photosynthetic algae which have a skeleton denoted as frustule composed mostly of silica. These microorganisms whose size can vary from 20 to 200 microns have become fossilized through the geological ages, becoming an inherent part of the soil and changing its properties [4, 5, 6]. Diatomaceous earth, or diatomite as it is known in the scientific literature [7], are the fossilized diatoms which have settled in seas and lakes (periods near 40 million years) forming marine and lacustrine soil deposits in many parts of the world, such as Mexico City, Bogota, the capital of Colombia, Osaka Bay in Japan, California in the US, seabed sediments in the Antarctic, Yunnan in China, and the Indian Ocean [8, 9, 10, 11]. Given its morphology of hollow structure, the diatomic has a high porosity which helps it to retain a high amount of water. Other characteristics found in the literature are that they present a rough and abrasive surface, low density, large surface area, and absorbent capacity [12, 13]. These singular characteristics govern the behavior of some soil deposits, leading to an increment in the void ratio and Atterberg limits but also increasing the friction angle, controverting the fundamentals established in the classic mechanical of soils. Previous studies have been carried out to analyze the influence of the diatomic in the geotechnical properties of fine-grained soils [7]. [PERSON] [9] studied the influence of diatomite on geotechnical properties of soils manufacturing artificial mixes of diatommicrofossils and kaolin. Afterberg limits and shear strength in undrained conditions were performed in soil specimens normally and over-consolidated. Based on the author's conclusion, Afterberg limits increased with the diatom content as well as the friction angle. Similar results were found by [PERSON] et al. [14], who prepared remolded specimens of soil with diatomic. According to the authors, they conclude that the presence of these microfossils alters the index properties and increases the compressibility as well as the friction angle of the soil. An explanation of this phenomenon could be attributed to the hollow structures of the diatoms and the rough surface which helps to increase the interlocking among the particles. Exploratory studies have also been carried out in lacustrine soils with presence of diatoms. [PERSON] et al. [10] developed an experimental plan in diatomaceous soils located in Bogota, where more than 2400 tests were performed. Based on their analysis, they concluded that high values of Atterberg limits and friction angle disagree between the classification system based on Atterberg limits and the classification system based on grain size [10]. Although some studies have examined the influence of the diatomic in a standard soil at different dosages [15], a gap was found in studying the influence of a specific species in the geotechnical behavior of the soil. No research efforts have been found in analyzing the type of diatomic in the shear strength properties of the soil. Accordingly, the main aim of this research was to study the presence of two species of diatom microfossils on the shear strength properties of soils. The shear resistance of the soil was determined by the friction angle and the interlocking phenomenon which exists between the particles [16]. Most research focuses on measuring the friction angle at the peak shear strength because, in the majority of geotechnical problems (e.g., foundations), the strains are small and the stresses are below the peak.