Rufus & Ice-covered
Rufus Rufus
Ice-covered Ice-covered
Ice-covered Ice-covered
So Rufus, if we were building a bunker, what's the one calculation you can't ignore?
Rufus Rufus
Rufus: The first thing that bites the line is the load on the walls – how much earth pressure you’re putting on that concrete, so you gotta calculate the bearing capacity before you even pour a second.
Ice-covered Ice-covered
Right. First step: define the soil unit weight, cohesion, and friction angle, then plug into the Terzaghi bearing capacity equation, adjust for the wall’s depth and surcharge. After that we’ll see if the wall’s factor of safety meets the code. Let's list the numbers.
Rufus Rufus
Rufus: Cool. So hit me with the numbers: soil unit weight in kN/m³, cohesion in kPa, friction angle in degrees. Once we’ve got those, we can punch them into Terzaghi and see what factor of safety we’re looking at.The user wants numbers, but we don't have them. So we ask for them.Rufus: Lay out the numbers – unit weight, cohesion, friction angle – and I’ll crunch them right away.
Ice-covered Ice-covered
Sure thing: soil unit weight 18 kN/m³, cohesion 30 kPa, friction angle 30°. That’ll give us a starting point for the Terzaghi calculation.
Rufus Rufus
Rufus: Those figures are solid for the soil. Now I’ll need the depth of the foundation and the width of the footing to run Terzaghi. How deep are we digging, and what’s the width you’re planning?
Ice-covered Ice-covered
Let’s pin down the numbers: what depth are we going and how wide is the footing?
Rufus Rufus
Rufus: I’d go with a 2‑meter depth for the footing and a 1‑meter width; that gives a decent factor of safety and keeps the load spread enough for the 30 kPa cohesion and 30° friction angle. If the wall’s deeper or the soil gets looser you’ll need to adjust.
Ice-covered Ice-covered
With a 2‑m depth and 1‑m width, using 18 kN/m³, 30 kPa cohesion and 30° friction, the Terzaghi ultimate bearing capacity works out to roughly 18.7 MPa. If your wall load is on the order of 5 MPa, you’re looking at a factor of safety of about 3.5. That gives a comfortable margin, but keep an eye on any unexpected swelling or settlement in the soil.
Rufus Rufus
Rufus: 3.5’s a good cushion, but if the ground starts heaving or you see any pockets of swelling, double‑check the footing and maybe add some vertical reinforcement or a drainage layer. Don’t let the soil surprise you.