2022 Fiscal Year Research-status Report
Significance of nonlinear soil-structure interaction (SSI) on the seismic performance of micropiles-retrofitted pile foundations
| Project/Area Number |
22K04280
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| Research Institution | Saitama University |
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Principal Investigator |
Goit Chandra 埼玉大学, 理工学研究科, 助教 (10782732)
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| Project Period (FY) |
2022-04-01 – 2025-03-31
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| Keywords | 1g model testing / SSI / impedance functions / kinematic responses |
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| Outline of Annual Research Achievements |
Various seismic retrofitting techniques and strategies have been developed and employed over the years to ensure the seismic performance of existing bridges built prior to the revision of seismic design codes. For retrofitting, however, focus is often given to the bridge piers while lesser attention is paid to the foundations. Out of the many reasons for such attention to the foundations, one can be attributed to the relatively lesser-known seismic performance of the retrofitted foundations. Damage seen in 2016 Kumamoto earthquake revealed the failure of a bridge foundation even though the pier of the bridge was seismically retrofitted, highlighting the necessity of seismic retrofitting of foundations. In practice, for foundation retrofitting, micropiles are often preferred over the traditional piles for its several merits. The behavior of micropiles-retrofitted foundations considering the effects of nonlinear soil-structure interaction (SSI) under dynamic loading, however, is still largely unknown.
To this end, 1g model testing of micropiles-retrofitted pile foundations embedded in soil is considered under a range of static and dynamic loads. Results are quantified in terms of kinematic interaction factors and lateral pile-head impedance functions. A 1/20 model of retrofitted foundation based on the law of similitude is considered. For soil, dry Gifu sand is selected.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
As a first step of the experimental framework, the static pile-head stiffnesses and pile head impedance functions were obtained for 2×2 fixed-head floating pile groups (spacing to diameter ratio of 5.0) reinforced with micropiles; micropiles were placed only on the sides parallel to the applied uni-directional loading. Length of micropiles is considered the same as the length of piles, while three inclinations (0°, 5°, 10° with respect to vertical) are considered to evaluate the influence of micropiles inclination on the pile head stiffness. Results obtained show a distinct influence of the presence of micropiles on the pile head response. Additionally, both the soil nonlinearity and the angle of micropiles inclination are found to show significance. To highlight the governing factor among these, nonlinear three-dimensional finite element modelling is being carried out to simulate the experimental setup and loading conditions.
Secondly, kinematic response of soil-foundation system was obtained in the form of kinematic interaction factor. Similar to the pile head response, influence of the presence of micropiles is clearly seen on the footing response. Moreover, both the effects of soil nonlinearity and the angle of micropiles inclination show a distinct influence on the results. In addition, both the bending and axial strains generated along the depth of piles and micropiles are obtained.
The third phase of the experiments will be the seismic response of the total system, i.e., considering superstructure to represent a bridge pier and associated loads.
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| Strategy for Future Research Activity |
Two types of works will be carried out simultaneously: (a) numerical modelling to elucidate the governing mechanism leading to the experimentally obtained pile head responses, and (b) experiment testing of the soil-foundation-superstructure system under low-to-high level of loading amplitudes.
In relation to the experimental testing, the design of the experimental model is already complete and is ready to be tested, which is planned to be carried out this year. results are expected to be obtained in the form of amplification ratios for both the foundation and superstructure for harmonic excitations while time-history responses will be obtained for actual earthquake loading data. Both the bending and axial strains generated along the depth of piles and micropiles are expected to be obtained.
Finally, an analytical framework to cater experimentally obtained pile head response, kinematic response, and total response is expected to be formulated.
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| Causes of Carryover |
Continuation of current experiments and purchase of relevant items. International conference and publications.
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