Machine excavation to the foundation footing explored
Machine excavation to the foundation footing is seldom good. 2. One of the more common discussions that I have with homeowners concerning their home drainage problems , which almost always is a rainwater, groundwater created groundwater issue, is the foundation footing drain concept, and a contractors desire to machine excavate with a backhoe, or by hand, all the way down to the foundation footing. Seldom is this the right solution to attempt. My opinion is that unless the surrounding strata around the home is all rock that groundwater runs right through, and if there is soil at the foundation footing to hand excavate for a french drain with a grade of 2″ Per 10 lineal feet to pull the groundwater away from the foundation footing, you are much better off collecting the groundwater in the top 2 feet of the soil around the foundation thereby preventing the saturation and hydrostatic pressure that causes the leaking.
This type of contractor usually has a backhoe and finds the days work with his butt parked on the backhoe much more profitable than getting that same posterior out of the seat and into the hand excavated french drain with a shovel.
Let’s discuss the common logic given to the homeowner in this case.
Usually it starts with the conclusion advanced to the homeowner by the contractor that an underground spring exists. No talk of rainwater/groundwater saturation and hydrostatic pressure causing the leaking. This contractor will use the word “spring” over and over with the fervor of a preacher at the sunday sermon.
His whole concept hinges on the homeowners acceptance of the premise that there is a spring that runs year round and that it is located way down where only a guy with a backhoe can get to it. This is journey to the center of earth folks. He is likely to damage your foundation in the process too. This is just plain terrible home drainage. Here is why.
If the site was one of those extremely rare home sites that contain rock backfilled around the exterior foundation for many feet away from the foundation, the correct method would not be to dig the foundation to the foundation footing with a backhoe or by hand and put a perforated pipe at or below the foundation footing with no grade and no drywell. The correct thing to do from my perspective would be to dig out the rock around the foundation and replace it will dirt and clay, compacting it in lifts of about 6 inches up to the desired foundation grade needed. After the rock was replaced with dirt and clay for many feet away from the foundation, at least 15-20 feet, install hand excavated french drains to collect rainwater that turns into groundwater on the surface layers of dirt around the foundation footing and gravity flow it away from the home to a daylighted vent or drywell. That will prevent the saturation, hydrostatic pressure and leaking.
The proposal mentioned above comes up all the time. The proposal consists of a plan to machine excavate down to the foundation footing or below and place gravel, sand or river rock on the foundation wall, with a perforated pipe laid at the foundation footing, or below.
These contractors use the term footing drain.
It may include placing a layer of tar on the foundation as well. Sealing a foundation wall with tar has it’s benefits, but I usually do not advise this without the installation of hand excavated french drains. In addition I almost never advise this unless there is sufficient foundation concrete repairs that need to be completed. Digging the soil around a foundation will not produce the best surface on which to run groundwater even if the soil is compacted when it is backfilled. It disturbs the bearing soil that makes a hand excavated french drain work most effectively.
Machine excavation with the foundation backfilled with rock is a method favored by some. I do not like the method because it removes too much soil and replaces it with rock that makes groundwater run directly down the foundation. Not a coincidence that the same type of contractor who said there were springs down there and that you needed to do this, also probably is ready with the proposal for the sump pump installation as part of this sell as well. After all, this guys starts to look pretty good to a homeowner, like a deer, caught in the headlights of home drainage hysteria. He said there would be groundwater there and as part of his prediction, there is indeed the groundwater that he promised. So add more more for another layer of failed home drainage science that does not address how to stop the groundwater entry in the first place. This type of groundwater proposal conveys the groundwater below grade from then on because they replace the soil which can run lots of water away from the home with a splash block and hand excavated french drain, with river rock.This stores water against the foundation wall and foundation footing causing worse groundwater drainage problems and foundation damage, as well as crawlspace and basement moisture and groundwater forever.
In other words, the footing drain must continue deeper than 8 feet from the base of the foundation footing, and get 2″ deeper per 10 feet and still vent to a place where the groundwater can spill out on the ground surface below the home, or you need a huge drywell that the groundwater can vent into while maintaining the suggested grade. OSHA will not let you put a man in a hole over 4 feet deep without supporting sides for worker protection from cave ins. A machine cannot make straight clean sides and an engineered flat clean bottom grade. Checkmate. This is most often just not even possible to accomplish even for the best of the best. Some contractors may be able to get it done, but they are “quality contractors” all the way. Did you get all that? Not an easy thing to do.
And even tougher to do with a machine, except the huge drywell that is. This is a loser idea most of the time. It doesn’t remove any groundwater at the grade level, like hand excavated french drains do, and therefore conveys water to the foundation footing forever because the groundwater doesn’t run away from the exterior foundation walls, within the top layers of the soil, in depths of 8″-18″, thereby cutting off the groundwater to the below grade areas.
As a consequence of this type of construction done wrong, the groundwater just runs down the foundation wall to the below grade areas at the foundation footing and lays there. This happens whether you tar the foundation wall or not.
If there actually is an underground spring, which is very uncommon, a footing drain may be the answer, but even then you need a clean slope for the hand or machine excavated footing drain, and a clean down hill vent for groundwater removal and flow of the groundwater. Perhaps even a silt collection box installed as well.
As I have said, this is very rarely needed. Hand excavated french drains within the top layers of the earth around the exterior foundation wall collect more groundwater quicker, and cut off the drainage problem where it begins.
Subdivisions are created with geotechnical surveys that along with geology reports identify and exclude problem groundwater spring areas that become common area to the subdivision and are not granted lot status.
It is very unlikely you own a lot with groundwater problems caused by springs, or the home would never have been built there. Sure maybe your lot slipped through the cracks of county due diligence, but that is on the rare and not common side of reality.
You want to collect that rainwater/groundwater at the surface when it is raining. Hand excavated french drains reduce the hydrostatic pressure and leaking. Your groundwater never gets below grade as a result, and therefore the footing drain is seldom needed unless a true underground source of water is always actually present, year round. Ask yourself this question. Do I see the groundwater entering year round, or when it has rained hard for many days? If you cannot answer the question with a yes to year round constant groundwater to some degree, you do not have a spring. Rains do accelerate springs through saturation, and that is why a problem area leaks when heavy rains are happening.
When the rains slow down or stop, the so called spring also slows down and stops. Remove the groundwater from the surface layers of the soil around the exterior foundation wall and reduce the weight of the groundwater on the soil that becomes the hydrostatic pressure.
Compacting a good slope away from the foundation wall is necessary as well for proper groundwater removal against the foundation. Foundation footing drains on hillside homes make sense if they are installed and vented properly.
Many contractors just own a backhoe, and all they do is advise these types of machine excavations of the exterior foundation on every home. It is their bread and butter deal.