Isobars and Vertical Pressure Contours

The question asks for the specific term used to describe a line or curve that connects points of equal vertical pressure beneath the ground surface. Understanding how pressure distributes within the soil is crucial in geotechnical engineering.

Let's look at the options provided and define each term to identify the correct one.

• Isoseismic line: This term is related to seismology, the study of earthquakes. An isoseismic line is a contour connecting points on the Earth's surface where the intensity of an earthquake is the same. This is different from pressure below ground.
• Isolates: This is not a standard geotechnical term for a contour connecting points of equal value. It generally means to separate or set apart.
• Stress block diagram: A stress block diagram is a graphical representation used to show the state of stress at a specific point within a material. It illustrates the normal and shear stresses acting on perpendicular planes. While it deals with stress, it is not a curve connecting points of equal pressure across a region.
• Isobars: This term is derived from 'iso' meaning equal and 'bar' referring to pressure (as in barometric pressure or bars as a unit of pressure). In soil mechanics and geotechnical engineering, isobars are indeed curves or contours that connect points of equal vertical stress (or pressure) below the ground surface caused by applied loads (like foundations). These diagrams help visualize the pressure distribution in the soil mass.

Based on the definitions, the term that specifically describes a curve connecting points of equal vertical pressure below the ground surface is Isobars.

Imagine applying a load on the ground surface, such as from a building. This load causes pressure (stress) in the soil beneath it. The pressure is highest directly under the load and decreases as you move away from the load horizontally and as you go deeper into the soil. An isobar maps out all the locations under the ground where the vertical pressure is exactly the same value.

Therefore, the correct term for a curve connecting all points below the ground surface of equal vertical pressure is Isobars.