A stable foundation is critical for the long-term success of newly constructed pavement or building foundation projects. For this reason, lime-stabilized layers are carefully designed in the laboratory to meet specific criteria. It’s important that these layers are built properly to ensure that those performance criteria are met.
Most acceptance criteria consist of limited moisture and density checks located in a small number of representative locations throughout the project. However, there are numerous documented cases of foundation failures even though they passed those checks. This is evidence that meeting moisture and density requirements alone does not guarantee layers are stable enough to meet the intended design purpose. Proof rolling should be considered as an additional quality control tool.
What is Proof Rolling?
Proof Rolling is a method of examining the entire subgrade or base surface as a complement to standard random acceptance testing. A selected heavy vehicle is driven over designated areas of the soil surface as a simple, low-cost method to ensure prepared subgrades or base layers are adequate prior to the next layer placement. It helps identify areas that need to be reworked, and while it’s referenced in some specifications, it’s an often overlooked tool.
How to Perform Proof Rolling
The recommended equipment includes a tandem-axle rear dump truck or a tri-axle rear dump truck (with a raised third axle) loaded to a minimum gross weight of 20 tons. Another option is the chariot-style roller loaded to a minimum gross weight of 40 tons.
Proof Rolling should be conducted by a single pass in each traffic lane and the criteria should be a 1.0” deflection (i.e., that includes both recoverable and non-recoverable deformation) for new construction and 0.5” deflection for reconstruction or stabilized subgrade. There should also be an absence of pumping and cracking.
Although many specifications recommend a minimum of 2 roller passes, field observations have shown that additional passes are often needed. Multiple slow passes are necessary to reveal instability due to the presence of free water that rises through capillary action under heavy loading. Proof Rolling will mimic the effects of future pavement loading that can be identified in localized areas prior to the placement of subsequent pavement layers. By identifying these in advance, you can avoid expensive future repairs due to poor performance in the pavement foundation.
