Search

Shake table experiments are conducted to assess the potential of the polymer injection technique as a liquefaction countermeasure. A large 2.9 m high (10 ft) laminar soil container on a 3.9×1.85 m (13×6 ft) shake table is employed. Mitigation of liquefaction-induced settlement for a shallow foundation is explored. In a series of two shake table experiments, the system response is studied first without (baseline) and subsequently with polymer injected into the liquefiable stratum. Each test is densely instrumented to provide insights into the dynamic response of the soil and foundation system. Furthermore, cone penetration tests (CPTs) are performed pre- and postinjection to assess the extent of soil improvement. Strong base excitation is imparted by the shake table, resulting in liquefaction and excessive foundation settlement in the original baseline test. In the second test, with the polymer injection countermeasure, a significant reduction is observed in the tendency for liquefaction and the resulting foundation settlement. After this test, careful excavation provided additional insights into the polymer's configuration within the deposit, increasing overall soil relative density, confinement and creating solidified paths for the shallow foundation load toward the lower, more competent stratum. As such, these mechanisms have the potential to allow for: (1) an increase in soil resistance to liquefaction, and (2) a significant reduction in settlement of overlying shallow foundations. [ABSTRACT FROM AUTHOR]

The damage caused by seismic shaking and liquefaction-induced permanent ground deformation has conventionally been assessed as two separate problems often by different engineers. However, the two problems are inherently linked, since ground shaking causes liquefaction, and liquefaction-induced soil softening affects ground shaking. Modelling both problems within a single numerical model is complex for both the engineer and the software, and most finite element software only have the capabilities to address one of them. To improve the estimates of the seismic performance of buildings on liquefiable soil, a new sub-structuring approach is proposed called the macro-mechanism approach. This approach allows the soil-liquefaction-foundation-structure interaction to be considered in a series of sub-models accounting for the major nonlinear mechanisms of the system at a macro level. The proposed approach was implemented in the open-source finite element software OpenSees and then applied to a case study of a building where significant liquefaction- and shaking-induced damage was observed after the 1999 Mw 7.4 Kocaeli Earthquake. The case study building was also simulated using two different commercial software programs, the finite difference software FLAC, and the finite element software PLAXIS, by two different research teams. A comparison between the results from the macro-mechanism approach compared to full numerical models shows that the macro-mechanism approach can capture the extent of the foundation deformation and provide more realistic estimates of the building damage than full approaches since the FLAC and PLAXIS models consider elastic elements for the building. [ABSTRACT FROM AUTHOR]

The mechanisms that control the seismic liquefaction performance of shallow foundations are identified for the special, still common case of a clay crust separating the foundation from the liquefied ground. For that purpose, foundation response is first analyzed with the nonlinear dynamic finite-difference method and consequently evaluated in connection with published field and experimental evidence. Insight is given into the excess pore-pressure buildup under the foundation, the seismic settlement accumulation, the static-bearing capacity degradation, and the inertia-induced interaction with the superstructure. It is thus shown that a naturally or artificially created nonliquefiable soil crust may effectively mitigate the detrimental effects of liquefaction and allow for a performance-based design of surface foundations, without additional improvement measures. [ABSTRACT FROM AUTHOR]