Separation as a solution for deformation control and material loss reduction in rubble mound structures constructed on v
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TECHNICAL PAPER
Separation as a solution for deformation control and material loss reduction in rubble mound structures constructed on very soft clayey bed Hamed Ghazi1 · Hadi Shahir1 · Abbas Ghalandarzadeh2 Received: 28 May 2020 / Accepted: 23 September 2020 © Springer Nature Switzerland AG 2020
Abstract In many cases, the construction of rubble mound structures such as breakwaters over soft beds is inevitable in coastal areas. The common problems arising from these structures include sinking of the rubble into the seabed, shear failure, general seabed instability, severe settlement, and soft material flow into the rock pores. The present study investigated the use of sand mattress and geotextile as separation layers through physical-model testing. The results of the model without a separation layer showed that the individual penetration of aggregates into the soft bed and flow of soft clay into the rubble mound pores is the effective mechanisms in wasting rock materials. The results are suggestive of the 25% share of penetration in total material loss. Further, mud flow accounted for a 49% share compared to foundation settlement. It was shown that placing a separation layer under the rubble mound can help significantly reduce material loss and offers control over deformations. Using a sand mattress or a geotextile layer enabled a considerable reduction in material loss—26 and 39%, respectively—by controlling penetration and mud flow. The better performance of geotextile over the sand mattress can be attributed to its capacity for withstanding tension and its reinforcing role, helping reduce lateral deformations. Keywords Rubble mound structure · Separation · Reinforcement · Geotextile · Sand mattress · Physical modeling
Introduction Due to active sedimentation, a very soft bed is more likely to be found in coastal areas than regions away from the sea. The high rate of sedimentation and cyclic loading by the waves is the culprits behind the under-consolidated bed in these circumstances [1]. Very soft clay beds are particularly notable for their difficult consolidation and the ineffectiveness of conventional improvement methods or their high costs. Low soil shear strength and higher compressibility are common features of an under-consolidated bed [2]. Moreover, geotechnical problems, such as landslides, can be caused and affected by the particular properties of clay, including its sensitivity [3]. In this light, soil type mapping * Hadi Shahir [email protected] 1
Department of Civil Engineering, Faculty of Engineering, Kharazmi University, Tehran, Iran
School of Civil Engineering, College of Engineering, University of Tehran, Tehran, Iran
2
(using conventional site characterization methods or new approaches such as artificial-neural-network-based models [4]) is essential for selecting a convenient site for coastal structures. Construction of embankments upon very soft soils is challenged by settlement, lateral spreading of the fill, extrusion of the foundation, overall rotational failure, and instabili
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