In the SI (metric) system of units, kilograms are used for mass, and newtons for weight. There is no confusion as the units are different. However, in the US system, pounds are used for both mass and weight. Confusing? You didn't think it was going to be easy did you? To differentiate between the two, I have developed the following … [Read more...]

## How to Calculate Void Ratio

The void ratio is the ratio of the volume of voids (open spaces, i.e. air and water) in a soil to volume of solids. $$e = \frac{V_v}{V_s}\newline\newline =\frac{V_g + V_w}{V_s}$$ Where: e = Void Ratio Vv = Volume of voids (m3 or ft3) Vs = Volume of solids (m3 or ft3) Vg = Volume of air (m3 or ft3) Vw = Volume of water (m3 or ft3) The void ratio is thus a … [Read more...]

## What is the Torsion Constant?

In structural steel design, the Torsion Constant, J, represents the ability of the steel beam to resist torsion, i.e. twisting. It's units are mm4 or inches4. Equation The bending resistance formula, in which the torsional constant is used, is: $$\theta = \frac{T\cdot L}{G\cdot J}$$ Where: θ = Angle of Twist T = Applied Torque (N·m or lb·ft) L = … [Read more...]

## How to Calculate the Centroid

The centroid of an area is the geometrical center, i.e. the average of all of the points in an area. It is always the same, regardless of how you turn the shape. It is also the center of gravity of a three dimensional object. Basic Shapes The centroids of common shapes are shown below: Shape Centroid Square/Rectangle Right-Angle … [Read more...]

## How to Determine Soil Compressive Strength with a Pocket Penetrometer

A pocket penetrometer is a fantastic little invention which geotechnical engineers and technologists find very handy. It is a small handheld gauge which contains a telescoping rod which can be pushed into the soil. The distance the rod goes into the soil corresponds to a compressive strength on the dial. Measurement of Soil The pocket penetrometer measures the … [Read more...]

## The Standard Penetration Test (SPT)

The Standard Penetration Test is an in-situ test that is useful in site exploration and foundation design. It produces an N-value, which represents the number of blows of a standardized sampler driven into the soil a standardized distance. How the Test Works The sampler is 51 mm O.D. (outside diameter) and it is driven into the soil with a 63.5 kg weight having a … [Read more...]

## How to Design a Radial Gate

Radial Gates, also known as tainter gates (after the structural engineer who popularized them) are the most common type of spillway gate in use today. It is classified as an undershot gate because water flows under the gate. It consists of a curved skin plate supported by a structural steel frame. A hoist system is used to raise or lower the gate. Advantages Better … [Read more...]

## How to Calculate the Hydraulic Grade Line

The Hydraulic Grade Line is a graph of the pressure and gravitational heads plotted along the position of the pipeline or channel. HGL Elevation = hp + hz Where: hp = pressure head (m or ft) hz = gravitational head (m or ft) Energy Grade Line Th Energy Grade Line is related to the hydraulic grade line in that it contains the velocity head as well. EGL Elevation = … [Read more...]

## Swell Factors for Various Soils

A cubic yard of earth measured in its natural position swells to more than a cubic yard after it is excavated. This occurs because of an increase in voids. Swell is expressed as a percentage of natural volume, for example, if 10 yd3 in the ground becomes 13 yd3 after excavation, the swell factor is 30%. The following table lists swell factors for various … [Read more...]