Scale Model Shake Table Testing of Underground Structures in Soft Clay

Abstract

Underground structures perform an important role in transportation systems in many seismically active regions around the world, but empirical data regarding the seismic behavior of these structures is limited. This research works towards filling that empirical gap through the use of scale model shake table testing. Underground seismic soilstructure interaction (USSSI) effects were investigated for a stiff rectangular tunnel crosssection embedded within soft clay. San Francisco Young Bay Mud was used as a prototype soil for developing a scale model soil mixture consisting of kaolinite, bentonite, class C fly ash, and water. A single cell Bay Area Rapid Transit (BART) cut-and-cover subway tunnel was used as the prototype for the 10 th scale model subway cross-section.A flexible walled test container originally developed for a pile study at UC Berkeley was modified for use at Cal Poly, San Luis Obispo. The flexible container allows for close approximation of one-dimensional (1D) free-field site response by significantly limiting the rigidity of the boundary conditions and allowing the soil to deform under simple shear. The study was conducted over two shake

Scale Model Shake Table Testing of an Underground Tunnel Cross Section in Soft Clay

“…This paper focuses primarily on the testing and numerical model results. A brief summary of testing equipment and procedures are presented here, but for a full discussion see Crosariol (2010).…”

“…The Ostadan and Penzien (2001) model provides a range of section dimensions, which promotes the method of implied prototypes for the model section design. Meymand (1998) describes the method of implied prototypes as “an iterative procedure in which an acceptable range of prototype behavior is identified, and models are built and tested to verify similarity” (Crosariol 2010 p. 62, after Meymand 1998). This method provides flexibility in model design by allowing the physical model to dictate the prototype, within an acceptable range of prototype characteristics.…”

“…The decision to run simulations at the prototype scale, as opposed to the model scale, was motivated by the desire to assess the validity of the scale relations used in the development of the model, and improved resolution of medium-to-high frequency response at the prototype scale free of the model scale time-history compression. For the input variables the soil unit weight was measured and shear wave velocity profiles (Figure 9) were derived using T-bar pull-out testing and hammer blow testing (Crosariol 2010).…”

“…Only a limited number of well-documented case histories exist demonstrating the behavior of underground facilities under seismic loading (Crosariol 2010), and much of the research in the area of USSSI effects has focused on finite element modeling of a limited number of tunnel failures. Physical testing has mainly focused on the dynamic response of reinforced concrete structures in sand, but underground infrastructure built in soft clay is not uncommon in seismically active regions.…”

Measuring Liquefied Residual Strength Using Full-Scale Shake Table Cyclic Simple Shear Tests

“…The T-bar penetrometers used herein have previously been used in research by Crosariol (2010) and Kuo (2012). Both researchers used the Tbar penetrometers in a soft clay exposed to cyclic motion.…”