Pond Boss Forums POND CONSTRUCTION Building a dam Core Trench

At the base of a hill on my land I have a large flat area that water puddles in during rains. It' about 500 feet long and around 200 feet deep. I'm planning on taking out the trees and moving the dirt across the area to build a long, low dam.

I figure a 4ft dam and digging about 3 feet will give me 6 foot of water and a foot of freeboard.

I have a Case 1550 dozer to do this, so the work itself shouldn't be a problem.

My question is about the depth and width of the core trench. Is there a formula for this? My dozer blade is 12 feet wide. If I dig it that wide, am I creating more problems than I'm solving? I have a backhoe that I could use for this, but it's bucket is only 2ft wide. I was also thinking that I could lift the blade at the place I want the core trench, but don't think It would be the best solution.

Thanks,
Eddie

Eddie,

The primary objectives of a core trench are to: (1) Remove grass, tree roots and other debris that could compromise the structure and (2) Create a "keyway" that anchors the dam in place. In other words; The downhill pressure exerted on the structure from water will not tend to slide the structure down hill.

Given your planned structure height is only 4 ft., I would still doze out a 12 ft. wide core (matching dozer) about 2.5 ft. deep. Remember to slope the sides on the core no steeper than 1:1. A vertical cut will NOT allow for proper compaction when you begin to fill the core with proper earth material.

Ed

ED, if you make the core twelve foot wide you will not compact the center of the core , with your dozer , unless you use a sheep foot roller. You have to make it wider than twelve foot so you can split your tracks to compact it in.Put in six inches of dirt at a time and track it in.

troll

If I understand this correctly, the core trench needs to be below grade deep enough to lock the dam in place from horizontal movement.

This makes sence, along with the angle of the slope. I'm gonna put a 2:1 slope on both sides.

Could I cut the core trench at an angle with the far side being the deep side?

Yes, you are correct in saying a 12 ft. wide dozer would not compact the center portion of the core. However, it has been my experience that a dozer does not do a very good job of compacting earth fill anyway. Pounds (psi) of force exerted downward by a 35,000 lb. dozer does not exert nearly the same force as a 7,000 lb. farm tractor! The surface area in square inches of a dozer's tracts is quite large compared to a rubber tired piece of equipment. Dozers are designed to "bouy" themselves and therefore do a poor job of compacting soil. A small 8 ft. wide Earth Scraper, Sheepsfoot Packer, Vibratory Packer or even a small Farm Tractor will do a much better job on a core trench in my opinion.

Ed