Digging through hardpan

Digging through hardpan is never fun. Too bad I didn't think of renting a demolition hammer. Oh well. Instead, I hired a laborer to swing a pick axe. Poor guy. Hope he didn't break his back. He looked strong, though. This is on the side of the driveway opposite the new tree location, which was luckily much easier to dig. Emerald Gaiety Euonymus will be planted here.

The floor of the trench is practically waterproof, so to improve drainage I installed a perforated pipe — sometimes called a french drain. I sloped mine gradually, running it under the driveway as a solid pipe, then perforated again to a sump bucket that discharges to the street. The direction of flow to the sump is secondary as a backup measure because I also sloped the floor of the trench. The important parts of a subsurface drain like this is to wrap all the drain rock with soil fabric, not just the pipe, the holes should face downward and it should NOT tie into the roof runoff pipes because of potential backflow. Sloping is not absolutely necessary, but the outlet must always be clear. The type of drain fabric should be the large sheets — available at Truitt and White (but not Home Depot). And rigid pipes are far better than corrugated ones.

Landscape soil

There's always a cost-to-convenience breakeven point between getting trucked soil or bagged soil for minor landscaping. Trucked soil is delivered in cubic yard quantities, and there's often a minimum for an order, like three cubic yards. It costs about $40 per cubic yard and most vendors charge for delivery. Bagged soil is mostly 2-cubic-foot each, so you have to consider how many trips to make and how many bags can fit your largest vehicle.

I decided the convenience of getting the whole batch at once was worth it. A tree was waiting for it.

Drain outlet

The drilled hole at the street curb went only as deep as the thickness of the concrete, so the soil under the sidewalk had to be dug out horizontally from the other end. It's a common solution. Breaking the public sidewalk then patching it afterwards would be too much unnecessary work. The ABS (Acrylonitrile Butadiene Styrene) sleeve protecting the opening added a clean professional appearance.

Pipe transition

A short piece of 4" O.D. (outside diameter) ABS pipe fits the curb hole snugly. The transition to the 3/4" PVC (Polyvinyl Chloride) pipe was made with an ABS clean-out plug and threaded cap (all the black pieces in the photo are ABS, the white is PVC). A 3/4" hole was then drilled in the ABS cap for a snug fit with the PVC. Sleeves were cemented to lock the joint. After pushing the PVC pipe through under the sidewalk, the threaded connection created a tight assembly.

Sump pump

The pump itself is a small one that I got second-hand from my brother. It has the usual float switch, inlet connection that fits a common garden hose, and a grounded AC (alternating current) plug. These units are designed to be submersed for a long time. For good measure, my outlet is GFCI (ground-faulted circuit interrupter). The hole in the sump pit for the electrical conduit should be installed as high as possible to keep water away from electrical connections.

Sump pit

A sump pump is hardly ever needed at any distance from a building. They help with discharging water in poor drainage conditions that can cause foundation problems, so they're often installed right next to the foundation.

Nevertheless, I installed a cheap version way out near the sidewalk as a secondary measure because I have super-hard clay soil conditions. The water table here hits the hardpan like it's a waterproof wall and flows around it, causing underground rivulets during storms and leaving air voids when it's dry. Large cracks in the concrete ground are sure signs of air voids below the slab. I suspected poor drainage at the isolated location for the new tree.



The sump pit is just a 33-gallon waste bucket with three holes: drain inlet, discharge outlet, and power conduit. The cover handle is rot-resistant redwood because the whole thing will get buried.

The big dig

Concrete removal was the most expensive part of this project. A simple 9'x15' section of driveway was to be broken up and taken away. However, a utility trench was needed to cross under the driveway for a drain pipe, an irrigation pipe, and an electrical conduit. Concrete cutting was required, not just concrete removal. The trench was eventually covered with paver bricks dry-grouted with crushed granite for appropriate semi-permanence.



Lessons learned
Hiring the concrete-removal contractor should have been better planned. I had to schedule them within just a few days due to friends and hired labor helping me on a specified day. Contractors with diamond-tipped concrete saws were important, too, not just concrete haulers (guys that can just swing a sledge hammer and drive a dumptruck). In addition to the 135 sq ft section and trench, I asked for a 4" hole at the curb (for a drain outlet) and two 14" diameter borings elsewhere (for future post footings).

Concrete removal cost: $800. Ouch.