1 INTRODUCTION TO SOIL GEOTECHNICAL ENGINEERING - A branch of Civil Engineering concerned with the engineering behavior of earth materials. It uses the principle from soil mechanic... 1 INTRODUCTION TO SOIL GEOTECHNICAL ENGINEERING - A branch of Civil Engineering concerned with the engineering behavior of earth materials. It uses the principle from soil mechanics and rock mechanics in solution of engineering problems and in the design and construction of buildings and other structures. SOIL MECHANICS - A scientific field of the civil engineering discipline that studies the physical properties and utilization of soil. It is critical in civil engineering as it describes the principles that govern the way civil infrastructure projects such as buildings, bridges, tanks, embankments, dams, and tunnels, are supported by the soil. HISTORY OF SOIL MECHANICS - Soil Engineering Prior to 18th Century. The record of the first use of soil as a construction material by mankind is lost in antiquity. In true engineering sense, there is no ‘Soil Engineering’ prior to the 18th century. For years, the art of soil engineering and geotechnical engineering was based only on past experiences through a succession of experimentation without any real scientific character. Based on those experimentation, many structures were built – some of which have crumbled, while others are still standing. The hanging gardens of Babylon were supported by huge retaining walls, the construction of which should have required some knowledge, though empirical, of earth pressures. The large public buildings, harbors, aqueducts, bridges, roads, and sanitary works of Romans certainly indicate some knowledge of the engineering behavior of soil. (Ex. Aqueducts, Pantheon, Roman Roads) One of the most famous examples of problems related to soil bearing capacity and foundations in the construction of structures prior to 18th century is the Leaning Tower of Pisa in Italy. The construction of the tower began in 1173 and lasted over 200 years. This is due to lack of sufficient knowledge of the behavior of compressible soil in those days. Pre-Classical Soil Mechanics. Henri Gautier (1660 – 1737) - A French Royal Engineer, investigated in 1717, the physical slopes of the soil just before overturning a pile. As a result, he formulated the design procedure of a retaining wall. The term angle of repose is today related with the natural slopes. Bernard Forest de Belidor (1671 – 1761) - A French Engineer who extended the theory which was presented in 1717 by Gautier for the lateral earth pressure appearing on retaining walls. He also published in France a textbook for civil engineers and military. Francois Gadroy (1705 – 1759) - French engineer who observed the existence of slip planes in the soil at failure. In 1746, he also reported the 1st laboratory model test results on a retaining wall built with sand backfill. Jean Rodolphe Perronet (1671 – 1761) - A French Engineer who investigated the stability of slopes, offered in this period an additional significant contribution around 1769, distinguishing it between intact ground and fills. Classical Soil Mechanics. Charles Coulomb (1736 – 1806) - A French physicist and engineer who undertook the first scientific study on soil mechanics and published a theory of earth pressure in 1773. He first studied the problem of lateral earth pressures on retaining structures. He used limit equilibrium theory, which considers the failing of soil block as a free body in order to determine the limiting horizontal pressure. Wiliam Rankine (1820 – 1872) - A Scottish mechanical engineer who contributed to civil engineering, physics, and mathematics. He published Coulomb’s work and theory of earth masses in 1857. In the field of civil engineering, he is famous for his lateral earth pressure theory and the stabilization of retaining walls. Alexander Collin (1808 – 1890) - An engineer who introduced in 1846, the details for deep slips in slopes of clay, cuttings, and embankments. He considered that in each case the failure appears when the mobilized cohesion of the soils is greater than the existing one. He determined profiles of slip surfaces in clay slopes and approximated the actual failure surfaces by arcs of cycloids. Otto Mohr (1820 – 1872) - A German scientist who improved Coulomb’s theory of impulses and developed the necessary techniques for depicting graphically a two-dimensional stress-strain situation through the famous Mohr’s circle. Jean Victor Poncelet (1788 – 1867) - An engineer and professor who determined graphically the magnitude of lateral earth pressure and provided the theory of the first ultimate bearing capacity of shallow foundations. Modern Soil Mechanics. Karl Terzhagi (1883 – 1963) - An Australian mechanical engineer, geotechnical engineer, and geologist known as the father of soil mechanics and geotechnical engineering. He is famous for his formulation of the effective stress principle and its influence on settlement analysis, strength, and permeability of the soil. Albert Mauritz Atterberg (1846 – 1916) - A Swedish soil scientist and chemist. He understood the significant role of clay particles in the soil. He justified the cohesion of cohesive soils, depending on the water level of clay and defined the limits of shrinkage, plastic, and liquid. He further defined the index of plasticity as the difference between limits of plastic and liquid. Arthur Casagrande (1902 – 1981) - An American civil engineer who was the inventor of an ingenious worldwide soil testing apparatus, along with the fundamental research on seepage and liquefaction. IMPORTANCE OF SOIL MECHANICS. Soil - Defined as the uncemented aggregate of mineral grains and decayed organic matter (solid particles) with liquid and gas in the empty spaces between the solid particles. Soil is used as a construction material in various civil engineering projects and it supports structural foundation. Application of Soil Mechanics. Foundation - All foundations for any structure that a civil engineer constructs are bound to rest on the soil. The bigger the building or structure, the bigger the foundation and consequently the more important it is for a civil engineer to take into consideration the soil mechanics of the site. Earthen Dams - Dams are among the largest and consequently, some of the most expensive civil engineering projects in the modern world. Soil to be used for constructing these earthen dams must be suitable enough to use in its construction. Their construction requires that one comes up with a proper design to ensure that they can withstand the pressure from water and other elements to serve their purpose. Embankments - Embankments are usually constructed to raise the level of a road, railway or land above ground level to prevent chances of flooding as well as it is required to keep the foundation of the pavement above the water table. There is a need to design an economical embankment which is possible by studying various soil properties. Canals or Other Retaining and Underground Structures - Factors such as shear strength of the soil should be taken into consideration to ensure that the canal that is put up can withstand the force of water that flows through and minimize seepage as much as possible. The retaining walls, whether made of compacted soil or concrete, should also be designed accordingly having taken into consideration the soil mechanics that will be at play depending on the given surroundings soil type. ENGINEERING PROPERTIES OF SOILS. Cohesion - Cohesion of soil is the tendency for particles of soil to stick together. It is used in describing the shear strength of soil. Cohesiveness is one measurement to consider when evaluating the type of soil and quality of the soil. Ex. Clay Soil; Sand Soil. Compressibility - Compressibility in soil is the decrease in volume of soil when subjected to loadings. Elasticity - A soil is said to be elastic when it suffers a reduction in volume while the load is applied, but recovers its initial volume immediately after the load is removed. Permeability - The property of soil which permits the water or any liquid to flow through its voids is called permeability. Capillarity - The process by which soil moisture may move in any direction through fine pores of the soil, under the influence of surface tension forces between the water and the soil particles. Read more