A concept and preliminary design are presented for a special testing capability to be added to an existing large laboratory geotechnical testing chamber. The modified chamber is intended to allow, through comparative testing, the reasonably rigorous evaluation of methods for providing detailed information, for soil deposits, on in situ undegraded nonlinear inelastic shear stress vs strain characteristics needed for dynamic geotechnical earthquake engineering analyses. Basically, the added capability is to be a large resonant column-like torsional testing system that tests the entire chamber sample and allows access to the center of the sample for the testing of the method to be evaluated. The main features of the modified test chamber are meant to be that 1) tests of methods to be evaluated and comparative tests are to be conducted on the same sample and 2) the comparative testing method is to provide the information of interest
