Presa de Casasola

Casasola Dam Construction Overview

Project Background and Timeline

• The Casasola Dam was constructed by FCC for the Confederación Hidrográfica del Sur de España, with a budget of approximately 21 million euros.

• Construction began in January 1994 and concluded in October 2000, facing delays due to extraordinary floods over three consecutive years.

Challenges Faced During Construction

• Two main issues arose: geotechnical instability on the left slope halted work for 13 months, and destruction of access roads and equipment required reconstruction.

Purpose of the Dam

• Initially proposed in the early 20th century, its dual purpose is flood control along the Guadalhorce River and enhancing water supply quality for Málaga.

• The dam's operation aims to eliminate historical flooding problems in Campanillas and increase water supply reliability for Málaga.

Dam Structure Details

Geographical Location and Design

• The dam is located at a bend in the river, with its right abutment resting on a high hill that can absorb horizontal forces effectively.

• It features an arch-gravity design with specific dimensions: a crest elevation of 160 meters and a triangular section vertex at 170 meters.

Structural Features

• The dam has three levels of horizontal galleries accessible from the top via an elevator and emergency stairs.

• An overflow system includes three fixed weirs integrated into the dam structure, designed to manage significant inflow events.

Water Management Systems

Overflow Mechanisms

• The central overflow threshold is set at an elevation of 153.5 meters; side weirs are positioned higher at 156 meters to handle extreme flow scenarios.

Drainage System Specifications

• A bottom drainage system consists of two parallel rectangular conduits leading to chambers equipped with valves for controlled water release.

Construction Techniques

Rock Stabilization Efforts

• Significant rock treatment was necessary due to fracturing; this involved extensive cement grouting through drilled holes to stabilize the foundation.

Construction and Instrumentation of the Dam

Impermeabilization and Drainage Screens

• A waterproofing screen was constructed from the galleries using 25 mm diameter drills, with a length of 2.5 m between holes and a 15-degree inclination upstream.

• Following the impermeable screen, a drainage screen was installed with 80 mm diameter perforations covering the entire dam body, extending 15 m into the foundation.

Monitoring Instruments for Dam Parameters

• Various instruments were placed to monitor key parameters: temperature control via thermometers, joint movement through external and internal gauges, and deformation measurements using concrete extensometers in high-stress areas.

• The dam's movement was tracked using leveling campaigns on surface and gallery levels, along with direct and inverse pendulums.

Key Structural Data

• Significant structural data includes:

• Height of the dam above foundations: 76 m

• Maximum normal reservoir volume: 23.64 HM³

• Upstream face length: 29.70 m

• Rock excavation volume: 130,800 m³

• Concrete volume used: 2,933 m³

Site Preparation for Concrete Production

• A platform at elevation Cota 110 was prepared for cement silos, concrete plants, aggregate hoppers, and ice flake manufacturing equipment due to topographical advantages upstream.

• The use of tower cranes became essential due to challenges in mobile support placement on slopes; thus silo usage was decided for transporting manufactured concrete.

Construction Logistics and Water Management

• An upstream cofferdam was built to facilitate smooth transportation of concrete from plant to loading docks while allowing water storage for mixing during dry periods.

• The cofferdam's crest elevation matched that of facility grading (Cota 110), enabling water retention up to Cota 105 for curing purposes.

Excavation Techniques Employed

• Excavation required blasting techniques with benches approximately seven meters high; pre-cutting methods minimized impact on surrounding structures.

• For foundation excavations under challenging conditions (high vertical jointing), hydraulic hammer-equipped backhoes were utilized alongside explosives for efficient material removal.

Material Handling and Quality Control

• Mini loaders were employed to transport excavated materials into gallery entrances; bolting systems anchored with resin ensured stability during construction phases.

• Aggregates used in concrete production were classified into six granulometric fractions ensuring quality control throughout the process.

Aggregate Supply Chain Management

• An adjacent area next to the concrete plant secured a week’s supply guarantee by preparing an adequate stockpile of aggregates sourced from San Miguel quarry located about 25 km away.

Concrete Production Process Overview

Water Consumption and Recycling

• The concrete production process utilized 230 cubic meters of water per hour, with an impressive recycling rate of approximately 80% through a clarifying tank.

• Coarse sand was directly stored on the site due to its easy drainage, while fine sand required three storage lines of 500 tons each for effective management.

Concrete Plant Specifications

• The concrete plant employed was an Intec Granier model CDM HBP 5000, capable of nominally producing 144 cubic meters per hour, averaging around 115 cubic meters.

• It featured four hoppers for gravel and two for sand, equipped with weighing mechanisms and conveyor belts.

Cement and Aggregate Management

• Two silos were used for cement storage (50 cubic meters each), alongside a water reservoir; the total installed power was 200 kW at 380 V.

• A mixture of type 145A cement and fly ash from a thermal power plant (55% cement to 45% fly ash ratio) was prepared during batching.

Cooling Measures in Hot Months

• During hot months (May to September), ice flakes were used instead of water in the mixing process to cool the concrete effectively.

• The ice factory produced up to 62 tons daily, with a refrigerated storage capacity of 125 tons available for concrete loading.

Transportation and Placement Techniques

• Concrete transport utilized pneumatic systems; hoppers received mixed concrete from mixers before being loaded onto trucks.

• Tower cranes transported buckets holding up to four cubic meters of concrete using pneumatic opening mechanisms, achieving a nominal output rate of 50 cubic meters per hour.

Block Construction Strategy

• The dam construction was divided into 17 blocks, with a maximum width at the upstream face measuring up to 15 meters.

• Each layer (or "tongada") had a height limit set at two meters, requiring specific waiting times between placements: minimum of 72 hours within the same block and 48 hours between adjacent blocks.

Environmental Considerations

• Significant attention was given to aesthetics and minimizing environmental impact throughout construction; all water used was treated before returning it to the river.