Alchatek details spillway void-fill fix

Spillway repairs are one of those infrastructure jobs that sound small until you picture the failure mode. Water gets under a concrete chute, erodes the soil beneath it, and suddenly the slab is no longer sitting on ground — it is bridging a hidden cavity. That is how cracking starts, leaks show up through joints, and a structure built to safely pass water starts helping water do damage instead. Alchatek’s newly circulated case study is useful because it shows the fix in a very concrete way — inject structural polyurethane into the voided zone, cut off the seepage path, and give the slab support again. (alchatek.com) ### What was actually broken? The case centers on a leaking retention pond spillway that discharged into a creek through a concrete spillway. Over time, water worked through the earthen dam and under the spillway, washing out soil and creating large voids beneath the concrete. That left the slab cracked and unsupported — basically the classic “water found a path, then made the path bigger” problem. (info.alchatek.com) ### Why are voids under a spillway such a big deal? A concrete spillway only works if the slab and the foundation act together. Once seepage removes support, the slab can crack, lift, or collapse into the void. In bigger dam settings, that can escalate into scour, progressive slab loss, and even spillway breach if high flows get into(info.alchatek.com) very different consequences. (damfailures.org) ### What did Alchatek say the crew used? The repair material was AP Fill 720, a single-component, water-reactive, closed-cell hydrophobic polyurethane injection resin. The point of that chemistry is speed and reach — it flows into the problem zone as a liquid, then reacts and expands when it meets water, which helps both fill the voi(damfailures.org), because the enemy is moving water. (info.alchatek.com) ### How did they get the material under the slab? The crew first used soil probing to map the weak zone. Then they injected from the pond side next to the spillway and also drilled 5/8-inch holes through the concrete along the pond border to inject directly beneath the slab. The injections went 4 to 5 feet deep. That tells you the jo(info.alchatek.com)on had actually happened. (info.alchatek.com) ### Why not just tear out the concrete? Because excavation is slow, disruptive, and often overkills the immediate problem. If the slab is still salvageable, a void-fill and seepage-cutoff repair can stabilize the structure much faster. In this case, Alchatek says the spillway was about 15 by 15 feet, the work was completed within a d(info.alchatek.com)rvention, quick return to service. (info.alchatek.com) ### What is the catch with this kind of fix? The catch is that grout injection is only as good as the diagnosis. You need to know where the water is traveling, how far the voiding extends, and whether the slab itself is still structurally viable. If the root cause is broader drainage failure or continuing internal erosion elsewhere i(info.alchatek.com)d work sits halfway between concrete repair and geotechnical repair. (damfailures.org) ### So why does this case study matter? Because it turns an abstract failure mode into an execution example. Engineers and contractors talk all the time about seepage, loss of support, and slab stabilization, but field details are usually the missing piece. This one gives a clean sequence — identify the seepage-driven voiding, inject(damfailures.org)damage. (alchatek.com) ### Bottom line? This is not a glamorous infrastructure story. But it is a practical one. Hidden voids under spillways are dangerous precisely because they stay invisible until the concrete starts telling on them. Alchatek’s case study shows the repair logic clearly — stop the water, fill the emptiness, and give the slab ground to sit on again. (alchatek.com)