Stabilizing the Pump Truck
Wood and aluminum pads and layers of 4X4- or 4X6-inch boards (called cribbing) are often used under the pump trucks outriggers to spread out its load. This requires determining the load bearing capacity not only of the soil, but of the cribbing, as well. Calculating Pressures on Ground Surfaces (mathematical) In order to stabilize the concrete pump truck, it must be determined if the proper support is being given for the type of surface the truck is mounted on. One way to do this is to calculate the pressure placed on the soil by each of the trucks outriggers by dividing the maximum force on the outrigger leg by the area of soil contact. The area of soil contact is either the area of the wood or aluminum pad, or the cribbing, if used, on each outrigger. The pressure from each outrigger must be less than the load bearing capacity of the soil. (See Table: Allowable Pressures for Various Surfaces, below) Calculating Pressures on Ground Surfaces (physical) Since operators often don't know the soils bearing capacity, a physical test is often used. This involves laying cribbing on a firm spot of ground and positioning the outriggers on them. One at a time, the operator extends the boom out over each outrigger, checking to see if the cribbing sinks. If it does, it means the boom must be refolded, and a larger area of cribbing put in. Table of Allowable Pressures for Various Surfaces
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