CAREER: Cyclic Behavior of Cemented Sands: Testing, Field Verification, and Modeling

University Of Notre Dame, Notre Dame IN

Investigators

Abstract

Large seismically induced landslides in cemented materials, such as the landslides occurring during the 1989 Loma Prieta and 1994 Northridge earthquakes, and the well-documented case of liquefaction in cemented soils at Apra Harbor during the 1993 Guam earthquake have increased awareness of the damage that can occur in cemented soils. However, most of the geotechnical engineering tools used to evaluate seismic hazard and predict damage are applicable only to clean, unstructured sands. Since cemented sands are common in many seismically active areas of the world, it is important to extend these tools to the case of cemented sands. To do this, a better understanding of the response of these sands to cyclic loads is needed. The response of artificially cemented soils is important as well, due to their role in ground modification: admixtures such as lime and cement have been used to increase soil strength, and promising methods to mitigate liquefaction risk in built-up areas are being developed based on grouting techniques. The main objectives of the proposed research are to improve the fundamental understanding of cemented sands, and to develop methods to predict their response to monotonic and cyclic loads. To achieve this objective, an extensive series of monotonic and cyclic tests will be performed to evaluate the effect of pressure, density, soil grain size and gradation, type and level of cementation, and method of sample preparation on the response of cemented sands. In order to compare samples that are grouted in the laboratory to soils grouted in situ, a field test program will be undertaken. Examination and testing of field grouted samples will be used to develop and validate a method of grouting samples in the laboratory that is representative of the grouted soils at the field test site. An environmental scanning electron microscope will be used to characterize the grouted soils and to examine how and where the cementation bonds were broken. Using the results from the field and laboratory testing programs in conjunction with the principles of damage mechanics, an existing constitutive model that describes the response of unstructured sands to monotonic and cyclic loading will be extended to describe the response of cemented sands. The educational plan includes outreach activities, such as expanding the 'Shakes and Quakes' program, and using it to introduce K-12 students to geotechnical engineering, as well as to increase interest in civil engineering careers. Semester-long projects involving problem-based and active learning will be incorporated into the geotechnical courses as a way to maintain interest in civil engineering at the undergraduate level. In order to increase the number of students pursuing advanced degrees in civil engineering, especially women and minorities, a lab shadow program will be developed that introduces undergraduates to research underway in the department, and aspects of the proposed research will be integrated into undergraduate classes. In addition, the research program will involve and foster collaboration with practicing engineers, leading to increased exchange between academia and engineering practice.