A New Bearing Capacity Design Method Using Multi-Axial Geogrid

The design of foundations using geogrid stabilized rafts typically involves the calculation of a two-layer bearing capacity analysis. Existing calculation models are empirical with imprecise input parameters, while other methods have tended to involve multiple design charts and are suited to either strip or circular foundations only. It has also been difficult to quantify the benefits of geogrid materials. The recently developed "T-Value Method" defines bearing capacity in terms of the ratio of strengths of the two layers. It allows realistic integration of the benefit of multi-axial stabilizing geogrid through the enhanced shear strength of the upper granular layer. The recently developed "T-Value Method" is leading to significant cost savings due to thinner working platforms designed in a safe and scientifically rigorous way. Additionally, the geogrid stabilized raft offers a more constructible and quantifiable alternative compared to the Colorado Department of Transportation's (CDOT's) woven raft standard below mechanically stabilized earth (MSE) walls and behind abutment retaining walls. This paper summarizes the development of this innovative design method and describes a case study of a multi-axial geogrid stabilized raft constructed as part of a value engineering alternative on the I-25 South Gap: Monument to Castle Rock.