Geotechnical Engineering
Geotechnical engineering is a branch of civil engineering that focuses on the behavior of earth materials, such as soil, rock, and groundwater, and their interaction with structures built on or in them. Geotechnical engineers use their knowledge of the physical and mechanical properties of soil and rock to design and construct safe and stable structures, such as buildings, roads, bridges, tunnels, dams, and levees. Every construction design infrastructure that is supported by foundations, above or below ground such as bridges, dams, plants, slopes, structures, tunnels, etc. uses geotechnical engineering.
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The work of a geotechnical engineer typically involves site investigation and analysis, soil and rock testing, foundation design, slope stability analysis, and groundwater assessment. They use a variety of tools and techniques, such as borehole drilling, geophysical surveys, and laboratory testing, to gather data about the properties of the soil and rock at a construction site.
Geotechnical engineering is an important field because the behavior of earth materials can have a significant impact on the safety and longevity of structures. By understanding the properties of the soil and rock, geotechnical engineers can design structures that are stable and safe, even in challenging conditions such as earthquake-prone areas or sites with difficult soil conditions. They also play a key role in environmental engineering, where they study the behavior of soil and groundwater to ensure that contaminants are properly contained and remediated.
- See Articles - List of Tags, List of Categories, List of Articles, List of Glossaries, Nomenclature and Symbols, (See Geotechnical Glossary)
Soil Types (OSHA)
Stable Rock - Natural soil material that can be excavated with vertical sides and remain intact whole exposed. It is usually identified by a rock name such as granite or sandstone. Determining wheather a deposit is of this type may be difficult unless it is known wheather cracks exist and wheather or not the cracks run into or away from the excavation.
Type A - Cohesive soils with an unconfined compression strength of 1.5 tons per square inch or greater. Includes clay; sandy clay; silty clay; clay loam; and in some cases, silty clay loam and sandy clay loam. No soil is Type A if it is fissured; is subject to vibration of any type; has previously been disturbed; is part of a sloped, layered system where the layers dip into the excavation on a slope of four horizontal to one vertical or greater, or has seeping water.
Type B - Cohesive soils with an unconfined compression strength greater than 0.5 tons per square inch but less than 1.5 tons per square inch and granular cohesionless soils. Includes angular gravel; silt; silt loam; sandy loam; and unstable rock; previousely disturbed soils unless otherwise classified as Type C; soils that meet the unconfined compressive strength or cementation requirements of Type A soils but are fissured or subject to vibration; dry unstable rock; and layered systems sloping into the trench at a slope less than four horizontal to one vertical.
Type C - Cohesive soils with an unconfined compression strength of 0.5 tons per square inch or less. Includes granular soils such as gravel; sand and loam sand; submerged soil; soil fron which water is freely seeping; and submerged rock that is not stable. Also included in this classification is material in a slope, layered system where the layers dip into the excavation or have a slope of four horizontal to one vertical or greater.
Multi Type Soil - Layered geological strata. Whlere soils are configured in layers. where a ayered geological structure exists, the soil must be classified on the basis of the soil classification of the weakest soil layer. Eacs layer may be classified individually if a more stable layer lies below a less stable layer, where a Type C soil rests on top of stable rock.
Soil Types
Clay - Clay soil is composed of tiny particles that are hard and able to become easily compacted. This compaction makes it difficult to plant or even shovel within the soil.While clay soil can be difficult to work with, it can be beneficial to the growth of certain plants. It is able to hold onto the roots of plants better and provide a more stable environment than many other types of soil.Clay Loam - A fine-textured soil that breaks into clods or lumps that are hard when dry. When the moist soil is pinched between the thumb and finger, it will form a thin ribbon that will break readily, barely sustaining its own weight.
Loam - Soil comprised of almost equal amounts of sand and silt and a little less clay. Of the three components, sand particles are the largest. Sand does not hold onto moisture, but it provides good aeration. On the opposite end, clay particles are much smaller and easily compact. That makes clay a great material for building bricks, but not so great for allowing water, air, and plant roots through.
Loamy Sand - This soil type is normally made up of sand mixed with a majority of silt and clay. Many people prefer loamy sand soil for their gardening because this type of soil normally allows for good drainage.
Silty - Silty soils have a distinct silky and soft feeling, typically quite fertile, and have the ideal balance of decent nutrient density without terrible drainage. Silt soils are usually easy to grow most crops in, although amendments for drainage may be needed for optimal crop performance. Silty soils don’t compact as easily as clay soils and they are softer and lighter, however, they do lack a robust structure in their soil profile that can be improved through the planting of perennial crops whose root presence holds them together.
Silty Clay - Silt has larger particles than clay and is mainly inorganic in nature. A silty clay soil has a higher percentage of clay than silt.
Sand - This type of soil is easy to cultivate but, since it allows for more drainage than needed, it is important to water it regularly, especially during summer days. As sandy soils don't allow the water to pool around the roots, they are a good choice for plants that have a tendency to suffer from root decay.
Sandy Loam - Sandy loam soils have a high concentration of sand that gives them a gritty feel. In gardens and lawns, sandy loam soils are capable of quickly draining excess water but can not hold significant amounts of water or nutrients for your plants. Plants grown in this type of soil will require more frequent irrigation and fertilization.
Soil Mechanics (OSHA)
Tension Cracks - This usually form at a horizontal distance of 0.5 to 0.75 times the depth of the trench, measured from the top of the vertical face of the trench.
Sliding or Sluffing - May occure as a result of tension cracks.
Topping - In addition to sliding, tension cracks can cause toppling. Toppling occurs when the trench's vertical face shears along the tension crack line and topples into the excavation.
Subsidence or Bulging - An unsupported excavation can create an unbalanced stress in the soil, which, in turn, causes subsidence at the surface and bulging of the vertical face of the trench. If uncorrected, this condition can cause face failure and entrapment of workers in the trench.
Heaving or Squeezing - Bottom heaving or squeezing is caused by the downward pressure created by the weight of adjoining soil. This pressure causes a bulge in the bottom of the cut, as illustrated in the drawing above. Heaving and squeezing can occur even when shoring or shielding has been properly installed.
Boiling - The evidenced by an upward water flow into the bottom of the cut. A high water table is one of the causes of boiling. Boiling produces a "quick" condition in the bottom of the cut, and can occure even when shoring or trench boxes are used.
Soil Weight - Unit weight of soils refers to the weight of one unit of a particular soil. The weight of soil varies with type and moisture content. One cubic foot of soil can weigh from 110 pounds to 140 pounds or more, and one cubic meter (35.3 cubic feet) of soil can weigh more than 3,000 pounds.
