A Cyclic True Triaxial with Rigid-Rigid-Flexible Boundary for Determination of Cross-Anisotropic Nature of Geomaterials

Aydin C., Hatipoğlu M., Cetin B., Ceylan H.

Geotechnical Testing Journal, vol.46, no.1, 2022 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 46 Issue: 1
  • Publication Date: 2022
  • Doi Number: 10.1520/gtj20220049
  • Journal Name: Geotechnical Testing Journal
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus, ICONDA Bibliographic, INSPEC, DIALNET
  • Keywords: cyclic true triaxial testing, anisotropy ratio, cross-anisotropy, resilient modulus, base, subbase, subgrade, stress-hardening, stress-softening
  • Istanbul Technical University Affiliated: Yes


Copyright © 2022 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.This paper describes a custom-designed Soil Poly-Axial Test System, SPAX-3000, developed to investigate the cross-anisotropic material properties of geomaterials under varying loading conditions. SPAX-3000, a mixed-boundary type of large-scale cyclic true triaxial apparatus (CTTA), is capable of applying a wide range of principal stress combinations on prismatic specimens of dimensions 152 × 152 × 304 mm. Two vertical and two horizontal load actuators on two opposite faces apply principal major (σ1) and intermediate (σ2) stresses independently to evaluate the performance of pavement structures under anisotropic stress states through resilient modulus (MR) testing. SPAX-3000 is controlled through software (CATS Software, provided by the manufacturer to provide advanced digital servo control of stresses and deformations). In this study, SPAX-3000 capabilities were evaluated through MR testing of both isotropic (urethane rubber) and cross-anisotropic materials (base, subbase, and subgrade) for the development of stress histories. The test results showed that SPAX-3000 is capable of determining MR independently of the anisotropy characteristics of the tested materials. Stress-hardening and stress-softening behaviors were observed for the coarse- and fine-grained geomaterials under different loading conditions. Anisotropy ratios (ratio of horizontal MR [MhR] to the vertical MR [MvR]) were determined for the base, subbase, and subgrade materials. MR test results showed that higher MvR results were obtained than that of MhR regardless of the loading conditions. The anisotropy ratios ranged from 0.08 to 0.21, 0.38 to 0.87, and 0.05 to 0.50 for the base, subbase, and subgrade materials, respectively. The highest MvR values (200–590 MPa) were obtained for the base material, whereas subbase material yielded the highest MhR (35–169 MPa). In general, stress-hardening behavior was observed for the geomaterials tested in both directions except for the stiffness of subgrade and subbase materials in the vertical direction.