Author Archives: Conrad
Trench Excavation Slope
Banks and excavations greater than 4 feet MUST be sloped or otherwise retained. If you have the room to slope the amount of slope must not exceed the maximum allowed.
To determine the maximum allowable slope for an excavation you need to know the soil type in the area. Remember that ALL of these sloped excavations have a maximum depth of 20 FEET, any deeper than that and you must use some form of shoring or layering.
| Soil Type | Max Allowable Slope (H:V) |
| Rock | Veritcal |
| Type A | 3/4 : 1 |
| Type B | 1 : 1 |
| Type C | 1 1/2 : 1 |
accordng to OSHA the slope can never exceed 1 : 2.
Rock
Solid mineral material that remains upright, stable, and intact when it is excavated.
Type A (compressive strength $$1.5 \dfrac{tons}{ft^2}$$ or greater)
These are cohesive soils that contain a good amount of clay. A soil cannot be Type A if:
1. it has cracks
2. there is vibration from traffic or some other source nearby (factory)
3. It has been disturbed recently (geologically recently, like a hundred years)
4. soil is part of a sloped + layered system Click here to continue reading
Soil Classification
There are two main methods of soil classification: AASHTO, and the Unified Soil Classificaiton System (USCS). Both methods involve finding the appropriate soil class given some parameters like passing a certain sieve size, liquid limit, plastic limit, significant makeup, and other ratings.
AASHTO classification returns an A-1 through A-8 rating. A-1 is the best all-round and A-8 is not really suitable for building.
USCS classification returns a two-digit group symbol for the soil such as GW for gravelly well-graded, SM for silty sand, CL for low plasticity clay etc.
You will need to be familiar with the sieve sizes (e.g. #200 allows up to 0.075 mm grains to pass) and how to determine what percent of the soil passes through that sieve, find the charts for this in your reference.
The Plasticity Index (PI) is equal to the Liquid Limit (LL) minus the Plastic Limit (PL):
$$ PI = LL – PL $$ Click here to continue reading
Concrete Mix Design
Concrete is made from different proportions of cement, fine aggregate (sand), coarse aggregate, and water. Cement usually comes in 94 lb sacks, water is measured by gallons (volume), and coarse and fine aggregate by weight. These are all over the place.
There are two main methods of measuring concrete ingredients, the Absolute Volume Method, and a method using Proportion ratio of components
Absolute Volume
With Absolue Volume the components are measured out using their densities or specific gravities to calculate the volume that each ingredient will use in a given unit of concrete.
$$V_a = \frac{W}{G_s \gamma_{water}}$$ Click here to continue reading
Acceleration and Deceleration
Acceleration is measured in velocity change per second, so miles per hour per second (mphps), feet per second per second (fpsps or fps/s) etc. Deceleration is negative acceleration, so I probably won’t use that term from here on out and simply stitch with acceleration.
If you are starting from zero with an acceleration of 3 fps/s, your velocity will increase by 3 for every second from then on. So 0, 3, 6, 9, 12 etc.
There is one equation relating velocity(v) and acceleration(a):
$$ v_f = v_0 + at$$
Use this equation for any problem with initial and final velocity, and acceleration. Click here to continue reading
