Hmmm--- Any clues as to what is going on in Big_Ponds dam?
Guessing and speculation on my part.
1. Equipment used in construction included; Track hoe, dozer and two dump trucks.
Was adequate soil compaction achieved using this combination of equipment?
Again I am guessing but was dirt brought to the site with dump trucks and spread and compacted using the dozer? There has been a lot of discussion on this site regarding the use of a dozer for compaction. I believe adequate compaction can be achieved by using a dozer if lifts are kept less than 6 inches, adequate soil moisture is maintained and the dam is a low head structure. (20 - 30 ft. is not a low head structure IMHO.)
If you can take a shovel and push it into the dam fill------you do NOT have adequate compaction. Digging a hole 8 inches deep with a shovel in a properly compacted dam fill, should be very difficult.
Mother Nature generally deposits our soils at 70 – 80% compaction in a natural environment. A 627 Cat scraper fully loaded weighs in at about 120,000 lbs. That’s a lot of weight distributed on 4 tires. At proper soil moisture content and 9 inch maximum lifts a 95% compaction can be achieved with one pass.
2. Was quality assurance employed throughout the entire work process?
In other words, did the landowner and contractor assure that proper moisture and compaction were employed each day? At the beginning of each day soils can dry out on the dam fill. So was there a good contact from previous days work to the next days work. (No dry seams.)
3. Core trench?
Core trench was probably plenty deep on this project (10 ft. I think)
Was water present in the core and pumped out?
Were side slopes of the core trench sloped at least 1:1. Vertical slopes are not stable and will not accept compaction when core is re-filled. This is a very important step and should not be short changed.
4. Situations beyond landowners control?
Perfect soils for dam construction are not always available throughout the entire process.
Water seeping through the existing upstream banks and exiting downstream.
Un-foreseen gravel and sand layers just under the excavated area.
A personal note on possible over-reaction? If this structure at 25 ft. of pool height is only loosing 20 gpm from seepage……I would be tickled!
Hope I didn’t step on any toes.
Ed
