The impressive Hoover Dam, built 80 years ago, continues to stand as a testament to engineering excellence, still serving the United States in areas such as irrigation, flood control, and power production. Even during heavy rainstorms, the dam remains resilient, never overflowing or causing destruction. Welcome to the engineering secrets behind the Hoover Dam! In this video, you’ll step into the shoes of John Savage, the visionary engineer who designed and constructed this monumental dam along Arizona’s Colorado River.
John Savage’s surveying team selected Black Canyon, located alongside the Colorado River, as the ideal site. The canyon’s elevated terrain and narrow gaps offered significant savings on construction materials. Despite these advantages, numerous design challenges remained for Savage and his team.
The dam’s design began with the creation of a straight concrete wall with uniform thickness. However, the immense water pressure causes the wall to bend and deform. This deformation leads to elongation in the outer fibers of the concrete, while the inner fibers are compressed. As a result, tension builds on the downstream side, and compression occurs on the upstream side. Concrete, under tension, tends to crack easily. While modern buildings use steel bars to address this issue—since steel can handle high tensile stress—Savage had a more ingenious solution: arch dam technology. By introducing curvature, the dam takes on the characteristics of an arch.
When water pressure is applied, the dam deforms in such a way that both the upstream and downstream sides experience compression. This compression is key, as concrete can withstand substantial compressive forces. This is the beauty of the arch dam design. However, to ensure the dam remains stable and doesn’t topple due to water pressure, it is necessary to gradually increase the dam’s width toward its base. This approach lowers the center of gravity, improving stability. This design is known as a gravity-arch dam, which addresses both tensile stress and stability challenges. The increased width near the base also enables the dam to resist shear forces. Notably, the water pressure exerted on the dam’s body is triangular in shape, with pressure increasing as it moves downward. As the dam’s base widens, shear stress remains consistent at all levels.
Another significant challenge Savage faced was determining the dam’s height. A taller dam allows for greater water storage, which benefits electricity generation and flood control. But could they construct a dam as tall as the surrounding mountain walls? The first step was to calculate the maximum flood discharge that could occur over the dam’s lifetime, using regional rainfall data and catchment area analysis. If the dam wasn’t filled to capacity during extreme river flow, it would be considered over-designed. Additionally, taller dams require more materials, increasing construction costs. Savage opted for a height of 726 feet, which struck a balance between cost-effectiveness, meeting the water needs of nearby cities, and offering sufficient flood control.
With the main design completed, the next challenge was the construction itself. As an arch-gravity dam, Hoover required strong mountain walls to transfer its weight. Initially, workers removed weathered, weak rocks from the canyon walls to reach the more solid, “virgin” rocks underneath. They used jackhammers and dynamite to blast through the rocks. Once the blasting was done, workers, equipped with ropes, scaled the mountain walls to clear any remaining loose rock. Excavated material was then hauled away by trucks.
The connection between the dam and the mountain walls needed to be incredibly strong, so workers dug deep into the canyon walls in an arch-like shape, using dynamite to create this strong joint. The next concern was ensuring the ground could support the weight of the massive dam. To address this, workers excavated the riverbed to a depth of 135 feet to reach a solid foundation layer known as hard strata. The riverbed was dug out to match the dam’s base width.
Before all this work began, however, the river itself had to be diverted. This diversion was a crucial first step in the construction process.
