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<p>In studying the upheaval buckling of buried offshore pipelines, one key variable that has received less attention, is the effect of non-plastic fines on the uplift behavior of pipes embedded in silty sands. The Makran coast, located in southern Iran adjacent to the Oman Sea, contains carbonate sands with a wide range of marine silt contents. This study employed centrifuge tests with monotonic loading to investigate the influence of marine silt on the uplift behavior of pipes buried in saturated carbonate sand-silt mixtures. Six silt contents, ranging from 0 to 50% by weight, were investigated through uplift tests conducted in two groups: drained (slow uplift rate) and undrained (fast uplift rate). To account for the influence of non-plastic fines in conventional analytical models, a fine-grain correction factor (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(FCF\)</EquationSource> </InlineEquation>) is introduced and formulated. The <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(FCF\)</EquationSource> </InlineEquation> is defined as the ratio of the breakout resistance for a sand with a given silt content to that of pure sand. The experimental results revealed two distinct trends. Under drained conditions, silt addition enhanced uplift resistance (<InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(FCF&gt;1\)</EquationSource> </InlineEquation>) up to 25% silt content, but reduced resistance (<InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(FCF&lt;1\)</EquationSource> </InlineEquation>) beyond this threshold. In contrast, under undrained conditions, uplift resistance increased significantly (nearly twice that observed in the drained tests) due to the generation of negative excess pore pressures during pipe uplift. Generally, the maximum pipe uplift resistance and lowest soil porosity were obtained near the threshold silt content (<InlineEquation ID="IEq5"> <EquationSource Format="TEX">\({FC}_{th}\cong 20-30\%\)</EquationSource> </InlineEquation>).</p>

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Non-plastic Fines’ Effect on the Uplift Behavior of Offshore Pipes Buried in Chabahar Carbonate Sand: Centrifuge Modeling

  • 期刊论文

  • 发表日期：

    2026年7月14日

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  • Hossein Salehzadeh,
  • Ali Akbar Heshmati Rafsanjani,
  • Mojtaba Aani

摘要

In studying the upheaval buckling of buried offshore pipelines, one key variable that has received less attention, is the effect of non-plastic fines on the uplift behavior of pipes embedded in silty sands. The Makran coast, located in southern Iran adjacent to the Oman Sea, contains carbonate sands with a wide range of marine silt contents. This study employed centrifuge tests with monotonic loading to investigate the influence of marine silt on the uplift behavior of pipes buried in saturated carbonate sand-silt mixtures. Six silt contents, ranging from 0 to 50% by weight, were investigated through uplift tests conducted in two groups: drained (slow uplift rate) and undrained (fast uplift rate). To account for the influence of non-plastic fines in conventional analytical models, a fine-grain correction factor ( \(FCF\) ) is introduced and formulated. The \(FCF\) is defined as the ratio of the breakout resistance for a sand with a given silt content to that of pure sand. The experimental results revealed two distinct trends. Under drained conditions, silt addition enhanced uplift resistance ( \(FCF>1\) ) up to 25% silt content, but reduced resistance ( \(FCF<1\) ) beyond this threshold. In contrast, under undrained conditions, uplift resistance increased significantly (nearly twice that observed in the drained tests) due to the generation of negative excess pore pressures during pipe uplift. Generally, the maximum pipe uplift resistance and lowest soil porosity were obtained near the threshold silt content ( \({FC}_{th}\cong 20-30\%\) ).