Evaluation of the parameters affecting the seismic response of underground cavities considering earthquakes in near and far fault fields

The existence of underground cavities such as aqueducts and water supply pipelines causes changes in the estimated seismic response on the ground. Since the characteristics of an earthquake are different near and far from the seismogenic source and the corresponding regulations have not considered near- and far-field effects on loading, it is necessary to study and compare such effects. This study has used the finite element method and the two-dimensional Plaxis software to investigate seismic responses on the ground while there are underground circular cavities. To this end, a set of near- and far-field accelerograms belonging to Bam, Landers and Loma Prieta were selected. Those recordings were different in terms of frequency. To examine the effect of soil type, four types with different mechanical characteristics were selected, and the seismic responses on the surface of the ground were studied in the presence and absence of an underground cavity. The effect of the buried depth of the cavity was evaluated with regard to two different buried depths (H/R = 1, 3). The results showed that the presence of an underground cavity leads to an amplified response of the ground. For instance, the amplification index of the displacement on the ground with and without cavities in the most critical conditions (Landers earthquake) was found to be 4.8 and 6 as recorded in near-field and far-field accelerograms, respectively. Moreover, the farther from the cavity center (X/R > 4), the less amplification was clearly observed on the ground under different loadings. The selected parameters also proved to have significant effects on the acceleration and displacement on the surface of the ground. To gain more insight about these effects, further research is needed.