The Yuncán Hydropower Project, in the Eastern Andes of Peru, includes 16 miles of tunnel, two concrete gravity dams, and an underground powerhouse.

The Yuncán Hydropower Project is located in the Province and Department of Pasco 200 miles Northeast of Lima, Peru. The project includes two concrete gravity dams that divert water from the Paucartambo and Huachón rivers. The water will flow through 16 miles of tunnels before reaching the underground powerhouse. The project is expected to provide 133 MW of power.

The project has encountered numerous difficulties. Headrace tunnel number 4 collapsed on the head of the tunnel-boring machine (TBM), requiring a rescue tunnel bypass to be built. Headrace tunnel number 2 encountered a buried valley with associated poor ground conditions. Tunnel number 1 has had to deal with significant water inflows, which have slowed mining and muck transport. Water inflow has also caused problems and delays in other areas of the project.

Because of both political delays and geological difficulties, the contractor has submitted a large number of claims. D&A staff were hired to analyze and evaluate eight specific claims in regards to validity and true costs. D&A staff had previously been retained to advise the client on the TBM collapse and associated bypass tunnel.

Numerous claims were made by the Contractor, and D&A served as expert witnesses for the Peruvian Government.

Client: Empresa de Generación de Energia Eléctrica del Centro S.A.
Project Cost: $117 million

The project involved 2.3 miles of TBM mining through Cambridge Argillite and 0.4 miles of drilling and blasting. D&A staff worked on the differing site condition claims for the contractor. By mapping the tunnel and conducting a rock coring and laboratory exploration program, we were able to establish that stronger than expected rock was encountered. We also established a relationship between fracture spacing and penetration rate. Our efforts helped the contractor negotiate equitable settlements with the owner. We were also instrumental in the installation of ductile iron pipe and backfilling of the tunnel and shafts.

Client: Modern Continental

D&A staff served as the independent technical consultant to both the owner and contractor. The project included 20 km of 7 m diameter TBM tunnel, underground powerhouse, and two dams.

Client: CE Casecnan Water and Energy Company

Effluent Outfall Diffusers
Massachusetts

The effluent outfall diffuser system consisted of fifty-five FRP lined shafts connected to a concrete diffuser heads. The diffuser heads were placed into dredged pockets that were armored with riprap. These diffusers are located in 110 feet of water, with shaft that are 250 feet deep. D&A staff helped the construction management team and had an active role in all aspects of the work including drilling, dredging, grouting, riprap placement, offshore surveys, underwater concrete repair, onshore construction, and onshore preassembly. D&A staff was also involved in the planning for making the underground connection to the Outfall Tunnel.

Effluent Outfall Tunnel
Massachusetts

The project involved 9.5 miles of TBM mining beneath the Atlantic Ocean and through Cambridge Argillite. Precast tunnel segments were used for initial and final support. D&A staff helped the construction management team and had an active role in all aspects of the work including mining, contact grouting, cut off grouting, drill & blasting, precasting of the segments, shaft lining, and surface works. D&A staff was also involved in assessing the impact of ground water inflows on mining in general and specifically the effects on the contact grouting program.

Inter-Island Tunnel
Massachusetts

D&A staff staff oversaw the smaller soft ground tunnel portion of this project. The tunnel was advanced through Boston blue clay, glacial till and boulders. The tunnel was temporarily supported by steel liner plates, with the final support being cast-in-place concrete. D&A staff also inspected the cut off grouting operation for the longer hard rock TBM tunnel drive through Cambridge Argillite.

Laramie-Poudre Tunnel Rehabilitation
North of Fort Collins, Colorado

This project involved rehabilitating 2 miles of water supply tunnel that was constructed in the early 1900's. Several aspects of the project were difficult, including the location and a major cave-in at the midpoint of the tunnel. The tunnel is located at an elevation of 8,400 feet, 45 miles up a narrow canyon in the Rocky Mountains, and its location in a National Forest resulted in stringent environmental restrictions.

Client: Tunnel Water Company

Manapouri Second Tailrace Tunnel
Manapouri, New Zealand

The second tail race tunnel consists of a 6 mile, 33-foot diameter, tunnel through hard rock. The contractor had difficulties with penetration rate and utilization of the TBM due to unexpected rock conditions. D&A was brought in by the owner to develop a comprehensive rock sampling and laboratory testing program in order to evaluate the actual conditions being encountered. D&A's presentation of the rock properties was instrumental in reaching a favorable settlement for the owner.

Client: Meridian Energy Limited

Puerto Rico Highway 53 Tunnels
Maunabo and Yabucoa, Commonwealth of Puerto Rico

The PR-53 highway tunnel project is currently under construction using drill and blast methods to advance through the tonalitic and metavolcanic rock. We are currently providing consulting services during construction. Previously we oversaw the subsurface investigation, and prepared the Geotechnical Baseline Report for the project. The investigation work consisted of geologic mapping, horizontal core drilling, laboratory testing, and analysis of the rock properties.

Client: Barrett, Hale and Alamo

San Vicente to Second Aqueduct Pipeline
California

We prepared a pre-bid evaluation for a 13 mile emergency water supply tunnel in San Diego, California. The San Vicente to Second Aqueduct Pipeline Tunnel requires mining through a variety of geologic formations including very weak cobble conglomerate to very strong granitic rock. Our evaluation of the geotechnical conditions is helping the contractor select the appropriate tunneling methods and ground support.

Seven Oaks Dam
California

Consulted to contractor during construction of a 560-foot high rockfill dam. Investigated slope failure of rock abutment during excavation for dam and served as experts during claims negotiations. Performed detailed rock slope stability analysis of 600-foot high intake tower excavation and prepared design recommendations.

Standley Lake Dam Improvement: Shaft and Tunnels
Westminster, Colorado

Standley Lake Dam required the complete replacement of the outlet works. D&A staff prepared the Geotechnical Baseline Report and designed the 12-foot diameter multi-level microtunnel lake taps, the 35-foot diameter valve shaft, and a 12-foot diameter pressure tunnel. We also provided construction engineering for all underground work.

Client: FRICO, Cities of Westminster, Northglenn, Thornton

WMATA E2C, E3B, E4B Projects
Washington DC

D&A staff provided a pre-bid analysis of the tunnel alignments, and consulting services for one of the contracts involving a twin 20-foot diameter subway tunnel in soft flowing ground. Our services included mapping the geologic conditions as they were encountered, and conducting a soil exploration and laboratory testing program ahead of the digger shield. We advised the contractor on dewatering methods, the effectiveness of chemical grouting, and geologic conditions that required special consideration.