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Showing 2 results for Physical Models
Investigation of Local Scour Process around Marine Pipelines with Respect to Submereged Impermeable Base Plate beneath the Pipe
S.m.r. Miralizadeh Orang, M.a. Lotfollahi Yaghin, A. Hosseinzadeh Dalir, H. Hakimzadeh,
Volume 13, Issue 4 (12-2013)
Abstract
  The main aspect of this research study is investigation on scour phenomenon around marine pipelines with respect to submerged impermeable plates beneath the pipe. So far, numerous investigations have been done but the main difference of this study with them is installation an impermeable base plate under the pipelines. Installing these impermeable plates mainly causes that the developed streamlines under the bed, located under the pipeline, are lengthened and accordingly the pressure gradient reduces across the pipe. Reduction of the pressure gradient may be considered an important issue since one of the most important criteria of establishing and progressing of scour under pipelines is the formation of piping phenomenon under the pipelines. This phenomenon is due to dominance of the pressure gradient on floating weight of the bed materials. For this research study, firstly scour phenomena under the pipelines were investigated both for unprotected pipelines and protected pipelines with submerged impermeable plates, with the piping phenomenon under the pipelines were being considered for both cases. The experiments were carried out in a channel with 10m length, 0.25m width and 0.5m depth. P.V.C. pipes with four diameters (i.e., 2cm, 3cm, 4cm and 5cm) and 0.5cm thickness were investigated. The bed materials were consisted of sediment particles with median size of 0.50 mm and geometric standard deviation of 1.43. The specific gravity of bed materials was 2.65. All experiments were run at clear water conditions. For each test the steady approach flow was adjusted so that the ratio of velocity to critical velocity was equal to about 0.85 on the centerline of the flume. A number of rectangular galvanized iron plates with 25cm in length, 0.7mm thickness and various dimensions of breadths were selected as countermeasure tools for scouring phenomenon. Then, the scour depth beneath two parallel pipelines with side by side arrangements and their interaction on scouring process were investigated. Finally, with installing impermeable base plates under the pipelines, the effect of these plates on scour phenomenon were studied for any arrangements of the parallel pipelines. The experimental results showed that installation a plate under the pipeline could prevent the formation of scour hole to some degrees and protect them from scour hazards. For all test cases of unprotected pipelines, the maximum dimensionless scour depth beneath the pipelines decreased when the pipe diameter increased. For side by side arrangement of two parallel pipelines, the formed scour depth decreased when the distance of pipelines increased. Then, for practical purposes, in order to reduce the maximum scour depth it is recommended that the distance of two parallel pipelines increases as far as possible or a submerged base plate may be used beneath the under pipeline. For all test cases of pipelines with impermeable base plates, the scour process will not further occur unless due to wake vortices
Determining of Sand behavior through model tests of Strip Footing with Micropile Skirts
Behrad Bakhtiari, Arash Razmkhah, Hassan Ghasemzadeh, Faradjollah Askari,
Volume 24, Issue 6 (11-2024)
Abstract
Recently, the modification of bearing capacity and the reduction in settlement of existing foundations and buildings has become one of the important topics in the field of geotechnical engineering. Also, the foundation of the buildings on the problematic and flowing sand bed, especially in the coastal strips is inevitable. In general, when faced with problematic soils such as loose soils with low load-bearing capacity, high settlement, liquefaction, disturbed soils, etc., there are two ways for geotechnical engineers, one of which is to use bearing elements in the soil and the other is to improve and modify the physical-mechanical properties of the soil mass. In addition to acting as a bearing and settlement-resistant element, the micro pile also improves the bearing strength of the surrounding soil due to the injection of cement slurry. In many projects, micro piles are used as structural elements. In fact, micro piles are small replacement piles (usually less than 300 mm in diameter) that are often accompanied by steel reinforcement and cement grout injection. Micro piles can be designed and used at any angle and for different purposes, including bearing axial and lateral loads, replacing conventional piles, or as part of a soil-pile system, depending on the purpose of the design. In this study, by physical modeling, the effect of using micro piles on the edge the foundation on sand bed was investigated. For this purpose, the effect of the boundary conditions of the chamber was first investigated. The parameters included the width of the foundation (B), the distance of the foundation from the end surface of the tank (Z), the distance of the foundation from the right/left wall of the chamber (X, X'), unreinforced bearing capacity (Q0) and unreinforced sand settlement (S0). Also, the investigation of the effect of the distance of the foundation from the lower surface of the steel chamber to the width of the foundation (B) showed that when the distance of the foundation from the lower surface of the chamber was less than twice the width of the foundation, the lower boundary affected the results of physical modeling. The evaluation of the lateral boundaries given the distance of the foundation from the chamber wall (X) to the width of the foundation showed that for X/B≥5, the lateral boundary had no effect on the results. Influences of various micropile skirt configurations were investigated, including micropile length (L) and spacing between two consecutive micropiles (S) on bearing capacity-settlement. The micropile skirts improved the bearing capacity of shallow foundations, depending on the L/B ratio and spacing between micropiles depending on the S/D ratio. Analysis of the results indicated that improved bearing capacity upon increasing the length of micropile skirt and reducing the spacing between two consecutive micropiles. Comparison of the pressure-settlement curves showed that in constant micropile lengths, the optimum Bearing Capacity Ratio (BCR) was in S/D=2. Further, the skirt piles reduced the settlement of strip footing. The Micropile Skirted Strip Footing (MSSF) led to increased failure surface and, depending on the pile length and spacing micropiles, it changed the failure pattern of the soil.
 
 
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