Seismic behavior of dry sandy soils improved with Block-Type Deep Soil Mixing in near-fault regions

Document Type : Research Article

Authors

1 School of Civil Engineering, College of Engineering, University of Tehran, Tehran, Iran

2 School of Civil Engineering, College of Engineering, University of Tehran, Tehran, Iran.

Abstract

The Block-Type Deep Soil Mixing (BDSM) method is widely recommended for enhancing soil in sensitive geotechnical projects. Nevertheless, previous studies have predominantly focused on alternative DSM techniques, particularly grid-type methods, with an emphasis on liquefaction mitigation, while the dynamic and seismic performance of BDSM—especially under high-frequency and near-fault excitations—has received limited attention. Considering the high-frequency content of nuclear power plant structures and the stiffness enhancement introduced by BDSM, a precise seismic evaluation is essential. This study investigates the seismic response of dry Nevada sand treated with BDSM under Ricker waves and near-fault earthquake records, including scenarios with and without pulse effects. Plane-strain modeling of the sand layer was conducted in GID, and numerical analyses were performed in OpenSees using the PDMY02 constitutive model. Lateral and bottom boundaries were modeled with semi-infinite free-field columns and viscous dampers. Results indicate that BDSM effectively reduces horizontal accelerations at higher frequencies; however, increasing its thickness can amplify vertical accelerations due to rocking. A thickness equivalent to one-fifth of the shear wavelength is recommended as an initial design criterion. While increasing the DSM width has minimal effect on horizontal accelerations, it can moderate vertical rocking-induced responses. The relative density of sand increases horizontal accelerations, whereas its impact on vertical response depends on input frequency and the dynamic properties of both the soil and BDSM. These findings underscore the critical importance of project-specific design and performance evaluation of BDSM, particularly for sensitive, high-frequency structures such as nuclear facilities, to optimize seismic performance and mitigate dynamic effects.

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AUT Journal of Civil Engineering
Volume 10, Issue 1
in progress
February 2026

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