Somerset Dam Improvement Project, Queensland, Australia

Prepare and plan for a proposed upgrade to Somerset Dam that will raise the Dam crest, construct downstream buttress, modify the gated spillway, and replace eight each 8x12 sluice gates. Work is expected to take 5-10 yrs.

An invited member of an independent consulting board to review the design and ongoing installation by DWR and Stantec Engineering for the installation of the replacement of the lower outlet at Oroville Dam. There are two new 72” spherical valves with a capacity of roughly 3,000 to 4,000 cfs. The valves are under 600 ft. of head and located in a tunnel beneath the dam 

Offering alternative ideas and constructability considerations in the decommissioning & removal of this dam.

 Provide constructability reviews of AECOM’s Draft 30% and 65% design packages. Offer alternative conceptual ideas. 

Constructability reviews to install post-tensioned, 91-strand vertical anchors on 1650 ft. wide Ogee crest spillway to address stability concerns. Possible crest raising & abutment buttressing. Spill capacity 2.3 million cfs or 64,600 m3/sec.  

AECOM was contracted to stabilize the remaining structure before Spring 2021. Gary provided constructability reviews and scheduling assistance.   

Constructability planning for removal of 5 meters from the 1,000 ft. wide RCC ogee crest of the Paradise Dam Spillway.  Member of a design-build team working with General Contractor: CPB Contractors of Fortitude Valley, QLD.  

Constructability review for demolition & replacement of concrete dam crest.

 Installation of silt diversion system which required careful, in-stream work. Excavation of 12,000 cy’s of silt from within the drained lake basin. Material hauled, placed, and graded to fill a ravine  

Mill off existing asphalt and repave dam face. (Includes asphalt disposal & reclamation and on-site asphalt batch production .) Excavate and rebuild dam crest. Demo existing 5’x7’ slide gate and replace with new one. Rehabilitate dam outlet works including two 42” horizontal slide gates, one 42” butterfly valve, and one 42” fixed cone valve. Homestake Tunnel intake gate and outlet improvements. Work to occur on slopes of 1.6H:1V at elevation of 10,260 ft. 

Drilling holes in the upstream face of thin arch dam to intersect vertical contraction joints & then injecting 3 types of chemical grout. Also included, cutting grooves at concrete block lift lines & installing backer rod & sealant.  All work performed from floating barges.  

Demolition of the upper 30’ high X 150’ long section of the concrete dam & center spillway, reconstruction of entire dam & spillway crest with 675 cubic yards of overlying concrete, extension to existing valve house, and installation of air-vacuum and blow-off valves on the pipeline. Additional work included access road improvements and silt removal.  

 The project involved the construction of a new 155 ft. tall RCC gravity dam, including on-site aggregate and concrete production, river diversion, new outlet works installation, and appurtenant features. The dam’s location significantly impacted construction methods in a steep-sided canyon with no downstream access. The project was completed in two short construction seasons(May-October), with a winter shutdown. Project features included 220,000 tons of on-site aggregate crushing from an alluvial deposit and foundation excavation 45 feet below stream level. These activities were accomplished under very strict water quality standards (10 ntu limit,) which required rigorous monitoring. 

 Furnish and install steel sheet piling cutoff walls, steel channel, outlet works, excavate, load, haul, place, compact Government furnished earthfill for sheet piling. Furnish/place bedding for riprap and place riprap and seeding 

 Removal of existing dam, structures and excavation for dam foundations and structures. Placing earthfill zones in dam embankment. Placing riprap on the upstream and downstream slope of dam embankment. Constructing a concrete spillway. Furnishing and placing sandy gravel filter and drain. Furnishing and placing miscellaneous reinforced concrete for dam structures. Furnishing and installing outlet works conduit and 4’ X 5’ heavy duty high pressure slide gate for outlet works.