Geotechnical Engineering and Earth’s Materials and Processes
WHAT IS GEOTECHNICAL ENGINEERING What do skyscrapers bridges and tunnels have in common Rocks and soil support them all Earth’s materials are beneath everything from homes to landfills Geotechnical engineers sample study and test these materials They design foundations and supports to suit the ground conditions They consider the natural processes that affect new and developed sites Their work helps make buildings stable and safe for the people who use them To create strong foundations geotechnical engineers include materials such as steel bars in their designs Engineering and science Many closely related science and engineering fields focus on Earth’s materials and processes Each field has a different goal For example geologists are scientists who want to discover as much as they can about how Earth and its materials formed Geotechnical engineers also investigate Earth’s materials However they apply what they learn and find practical solutions For example when they study soil it is so their designs work with the properties of that soil These properties include soil texture how it holds water and how it compacts or joins together under pressure Geoenvironmental engineers specialize in solving environmental problems created by people’s use of Earth’s materials One area of focus for these engineers is improving polluted soil 4
Eight steps to success Geotechnical engineers follow a series of steps to design build and test solutions such as innovative foundations The process for creating strong safe designs is as follows Steps in the design process Define the problem Identify criteria and constraints Brainstorm ideas Select a solution Build a prototype Improve the design Test the prototype Communicate the solution KARL VON TERZAGHI The Massachusetts Institute of Technology MIT in the United States built on a new site in 1916 Within a few years it faced a big problem The new buildings were sinking into the soil John Freeman was one of the lead engineers working with MIT He knew exactly whose help they needed Austrian Karl von Terzaghi had written the first book about soil mechanics in 1924 It described what happens to soil under different conditions MIT offered von Terzaghi a one-year teaching job in the United States They hoped that he could also explain why their school buildings were sinking The professor stayed for an extra three years and advised MIT on its soil issues During that time soil mechanics gained attention around the world It marked the beginning of the modern field of geotechnical engineering Karl von Terzaghi studied mechanical and structural engineering before focusing on soil mechanics 5
MINERALS AND ROCKS Geotechnical engineers study minerals rocks and soil so they can design strong safe foundations Minerals are the main substances in rock and soil For example sandy soil and rock called granite often contain the mineral quartz Minerals rocks and soil are the materials that make up Earth’s outer layer called the crust The crust covers the mantle a dense layer of minerals and rocks Where these layers meet heavy rocks push against each other and intense pressure builds The extreme heat and pressure slowly change solid minerals and rocks trapped in this boundary into liquid magma Look at the rock cycle diagram opposite Can you see why heat pressure and magma are important to rock formation Core samples Geotechnical engineers study and test the rocks and bedrock found at new and existing building sites Bedrock is the solid layer that lies beneath the soil It may be shallow or very deep Engineers drill into the rock with hollow tubes that pull out core samples The samples give them a lot of information such as the minerals the bedrock contains Knowing what the bedrock is made up of helps with planning foundations and structures Engineers also test core samples for strength Labs have technologies and equipment that put increasing amounts of pressure on solid rock samples until they break This shows what forces the rock can bear which is important to know before starting the design process 6 These tubes contain core samples of rock that will go to a lab for testing
1 Heat and pressure cause underground metamorphic rock to melt It becomes magma When magma cools it hardens into igneous rock Underground temperatures and 2 pressure that are not high enough to create magma can cause igneous rock to change into a new solid form called metamorphic rock Over time agents such as wind and 3 water break down metamorphic rock on Earth’s surface Sedimentary rock forms when pieces of metamorphic rock and sometimes materials such as broken shells compact under pressure and cement together Hot temperatures and pressure cause 4 underground sedimentary rock to change form and become metamorphic rock 5 Underground sedimentary rock becomes magma due to very intense heat and pressure When the magma cools and hardens it becomes igneous rock THE ROCK CYCLE There are three main kinds of rock igneous metamorphic and sedimentary They are always moving through the rock cycle These changes can take a long time even millions of years The numbers in the diagram are different ways in which a type of rock may change to another type 6 3 1 2 Igneous Rock 5 Magma 6 Agents such as wind and water cause pieces of igneous rock to break away and become sediment This cements and compacts into sedimentary rock Sedimentary Rock Metamorphic Rock 4 7
