Experimental Study of Rubble Mound Behavior on the Very Soft Soil Seabed
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Experimental Study of Rubble Mound Behavior on the Very Soft Soil Seabed Hamed Ghazi 1 & Hadi Shahir 1 & Abbas Ghalandarzadeh 2 Accepted: 21 September 2020/ # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract The construction of rubble mound structures such as a breakwater or access road on a very soft seabed is essential to the development of maritime transportation. This process can result in significant settlement that causes the rock particles to sink into the seabed, leading to loss of material. In the current study, several case studies on breakwaters facing large settlements, which resulted in the use of excessive amounts of rubble, were surveyed. A series of physical models were developed to study the deformation and volume loss of rubble mound breakwaters on very soft clayey soil during construction. It was found that most deformation occurred early in construction. The primary mechanisms influencing settlement were rock penetration into the soft bed, flow of clay material into the porous body of the rubble mound, and lateral deformation of the soil beneath the breakwater, which is associated with soft bed heave at the breakwater toe. During testing of very soft beds, the ratio of material loss to the design weight of the rubble mound increased up to 27%, and the proportion of penetration to total material loss was as high as 56%. The results of the experiments and case studies were used to develop an empirical relation with which to predict settlement. Keywords Settlement . Penetration . Material flow . Material loss . Rubble mound structure
. Soft bed
1 Introduction Very soft layers of soil that are frequently observed on sea beds along coastal areas are formed by active deposition. The rapid rate of sedimentation and repeated wave-
* Hadi Shahir [email protected]
1
Department of Civil Engineering, Faculty of Engineering, Kharazmi University, Tehran, Iran
2
School of Civil Engineering, College of Engineering, University of Tehran, Tehran, Iran
Transportation Infrastructure Geotechnology
induced loading lead to the formation of an under-consolidated seabed (Sangrey 1977). The design and construction of rubble mound structures on this type of seabed are associated with issues such as the sinking of the rubble into the seabed, shear failure and instability of the seabed, and significant settlement and complex behavior of the seabed under seismic loading (Memos et al. 2001; Chung et al. 2006; del Campo and Negro 2011; Yan et al. 2018; Jafari et al. 2018). As the rubble is spread during construction, rock particles may sink into the soft soil and prevent the formation of a foundation (Mobarrez et al. 2004). The penetration of individual rock particles into the soft seabed is the primary mechanism of settlement in an unreinforced breakwater and is greater than elastic or consolidation types of settlement (Bayesteh and Mansouriboroujeni 2019), which can cause excessive settlement and instability of a structure. In addition to the penetration of the rubble into the soft soil,
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