Challenges and solutions to model-scale testing for composite deep foundations and existing foundation enhancement

Laboratory testing for foundation design offers advantages over field-testing, especially, where existing installations preclude easy accessibility. Advantages include a homogeneous soil, ability to place instrumentation throughout the soil mass, and capacity to bring the system to failure, as well as control over the failure mechanism. Repeatability is also achievable. Laboratory work, however, has its own challenges. For model-scale work, a main impediment is scaling: strength, dimensions, and boundary conditions hinder accurate modeling of the soil and brings a difficulty in representing scaled foundations. This paper describes the construction-oriented solutions pioneered for meeting the geometric requirements of ⅛th scaled laboratory testing of composite deep foundations for existing foundation enhancement, including drilled shafts, helical piers, and grouting. Results of the testing program are included as verification of the usefulness of the techniques.