Learn about hydrostatic pressure, forms and your basement. #learn #concrete #basement #formwork

This is your standard foundation. This gets poured in two sections. You have a footing and a stem wall. Because of hydrostatic pressure, there are some steps that have to be taken. Hydrostatic pressure will be low up here and high down here. The lowest one has the most pressure and as the water column comes down, it still stays that way. Because this pressure increases at the bottom, these braces hold the top from horizontal movement and through your forms you'll have snap ties that holds the bottom together. Snap tie spacing will have to be increased. On the top, you'll have less snap ties and the lower you go, it requires more snap ties. This helps hold the bottom together when there's pressure. Here's your basement or crawlspace. You'll have your footing in block or concrete for your foundation wall. This here is a keyway. This helps your stem wall from lateral movement. This is also a capillary break. As it rains, water will run down your gutter or get driven towards your house and this water will start to soak your soil. If you have clay, these pressures will be a lot higher than say sand or other types of soil. Once this water makes it to your footing, it'll travel down and hit your drain tile. This drain tile is typically connected to a sump. If this drain tile gets blocked or you have an excessive amount of water, it'll create high pressure in the bottom of your foundation. This pressure causes water to go like this and follow your keyway and go back into your basement or it can cause cracks in your foundation or splits in your block and this can cause your wall to bow. These cracks can also allow water through them. It'll go through and drain down your wall. This is why you want good grade and to extend your gutters out so the water will stay away. Let's demonstrate what happens when you get too much soil pressure. Water pressure is determined by column height, not by volume. A smaller tube will push out as much water as a bigger tube, but the bigger tube can keep the stream longer. Same size hole and same column height of water. As you see the small tube dies faster and this has more continual pressure. So, just because you have wider forms does not mean that you have more pressure. At the same height, both of these have the same pressure. Thanks for watching.