Limited blast liquefaction testing, vibration testing, and centrifuge testing suggest that vertical drains can be effective in preventing earthquake-induced soil liquefaction and associated settlements or lateral spreading. However, no full-scale drain installation has been subjected to earthquake-induced ground motions. This lack of performance data under full-scale conditions has been a major impediment to expanding the use of this technique for mitigating liquefaction hazards.
To determine the viability of large diameter (4 in.) prefabricated vertical drains for preventing soil liquefaction and associated settlements under full-scale conditions, the pooled fund study no. TPF-5(244) was initiated in 2013 by UDOT, Brigham Young University (BYU), and other state DOTs from California, New York, and Alaska, in conjunction with the National Science Foundation’s George E. Brown Jr. Network for Earthquake Engineering Simulation (NEES) Facility at the University at Buffalo (UB) of The State University of New York.
In August and September 2014, two test series with vertical drains in liquefiable (loose and saturated) sand were completed using the laminar shear box and high speed actuator system at NEES-UB. Tests involved level ground conditions with two drain spacings: 4 ft for the first series and 3 ft for the second series. For each drain spacing, the soil profile was subjected to a total of nine sinusoidal motions at increasing peak base accelerations of 0.05g, 0.10g, and 0.20g. The settlement of the soil profile was measured using surface settlement plates, string potentiometers, and Sondex profilometers. Pore pressure transducers were used within the sand at various depths to measure pore water pressures. Accelerometers and LVDTs were located along the height of the shear box to define the acceleration and deflection profiles induced by the shaking at the base. Example data plots are shown below.
A few video recordings from the first series of tests at NEES-UB are available for viewing at this link. Progress reports and the overall scope of work for the study are provided on the web page for study no. TPF-5(244).
Remaining tasks on the project include data analysis, comparison with previous tests on untreated sand, evaluating predictive methods, and preparing the final report regarding drain effectiveness. If full-scale tests prove the effectiveness of the drainage technique, significant time and costs savings can be achieved for both new construction and for retrofit situations, as compared to other mitigation techniques.
This guest post was written by Kyle Rollins, PhD with Brigham Young University and David Stevens, PE with UDOT Research Division and was originally published in the UDOT Research Newsletter.