【摘要】：隨著海洋石油工業(yè)的蓬勃發(fā)展,作為石油、天然氣運(yùn)輸?shù)妮d體—海底管線得到越來越廣泛的應(yīng)用,管線與土體相互作用問題也越來越引起關(guān)注�；谄矫鎽�(yīng)變假定,本文采用模型試驗(yàn)和離散元(DEM)數(shù)值模擬的方法對(duì)砂土中埋設(shè)管線在單調(diào)和循環(huán)荷載作用下的抗拔力特性進(jìn)行了研究。在循環(huán)荷載試驗(yàn)的加載段,管線上拔,下方的空隙可能被周圍土體填充,而卸載時(shí)管線無法回到初始位置最終產(chǎn)生累積位移,這種現(xiàn)象稱為棘輪效應(yīng)。本文的主要內(nèi)容如下：(1)進(jìn)行了中密砂和粗礫石中不同埋深以及不同管徑管線在單調(diào)荷載作用下的上拔試驗(yàn),并采用PIV圖像識(shí)別技術(shù)分析了砂土的流動(dòng)破壞機(jī)制。結(jié)果表明中密砂中管線抗拔力-位移曲線可分為發(fā)展階段、峰值后軟化階段和殘余穩(wěn)定階段。在抗拔力發(fā)展階段,砂土剪切帶由管線肩部向上擴(kuò)展并發(fā)展至土體表面,峰值時(shí)剪切帶同豎直方向的夾角約為2倍砂土剪脹角；在抗拔力軟化階段剪切帶擴(kuò)展角逐漸減��；在殘余穩(wěn)定階段剪切帶擴(kuò)展角為零,即豎直向上。根據(jù)試驗(yàn)結(jié)果分別提出了三階段的抗拔力預(yù)測模型。(2)采用離散元方法對(duì)管線上拔過程進(jìn)行了數(shù)值模擬。數(shù)值分析得到的峰值承載力系數(shù)同模型試驗(yàn)結(jié)果吻合很好。綜合數(shù)值分析、標(biāo)準(zhǔn)砂模型試驗(yàn)和粗礫石模型試驗(yàn)結(jié)果,分析了粒徑對(duì)管線抗拔力-位移關(guān)系變化特性的影響。(3)采用模型試驗(yàn)和數(shù)值分析的方法研究了循環(huán)荷載作用下管線的棘輪效應(yīng)特性。結(jié)果表明循環(huán)荷載應(yīng)力幅值是影響管線累計(jì)位移發(fā)展特性的重要因素。循環(huán)荷載試驗(yàn)中卸載階段土體流動(dòng)機(jī)制同加載和再加載階段類似,都是呈向上擴(kuò)展形狀的剪切帶,但卸載階段剪切帶內(nèi)土體向下運(yùn)動(dòng)。次數(shù)較少但位移幅值較大的循環(huán)荷載作用下,土體對(duì)管線的約束力可以回歸到單調(diào)荷載作用下的抗拔力-位移曲線上。
[Abstract]:With the rapid development of offshore oil industry, as a carrier of natural gas transportation, submarine pipeline has been more and more widely used, and the interaction between pipeline and soil has attracted more and more attention. Based on the assumption of plane strain, the pull-out behavior of buried pipelines in sand under monotone and cyclic loads is studied by model test and discrete element (DEM) numerical simulation. In the loading section of cyclic load test, when the pipeline is pulled out, the voids below may be filled by the surrounding soil, but the pipeline can not return to the initial position and eventually produce cumulative displacement when unloading. This phenomenon is called ratchet effect. The main contents of this paper are as follows: (1) the uplift test of pipeline with different buried depth and different diameter in medium dense sand and coarse gravel under monotonic load is carried out, and the flow failure mechanism of sand is analyzed by PIV image recognition technique. The results show that the drawing load-displacement curve of pipeline in medium dense sand can be divided into development stage, post-peak softening stage and residual stability stage. In the development stage of tensile force, the shear band of sand soil extends upward from the shoulder of the pipeline to the soil surface, and the angle between shear band and vertical direction is about 2 times at the peak value, and the expansion angle of shear band decreases gradually at the stage of tensile softening. The spreading angle of the shear band is zero in the residual stabilization stage, that is, vertical upward. Based on the experimental results, a three-stage pull-out prediction model is proposed. (2) numerical simulation of the pipeline pull-out process is carried out by using discrete element method (DEM). The peak bearing capacity coefficient obtained by numerical analysis is in good agreement with the model test results. Comprehensive numerical analysis, standard sand model test and coarse gravel model test results, In this paper, the influence of particle size on the relationship between pullout resistance and displacement of pipeline is analyzed. (3) the ratchet effect of pipeline under cyclic load is studied by model test and numerical analysis. The results show that the amplitude of cyclic load stress is an important factor affecting the cumulative displacement characteristics of pipeline. In the cyclic load test, the flow mechanism of soil in unloading stage is similar to that in loading and reloading stage, and it is a shear band with the shape of upward expansion, but the soil moves downward in the shear zone during unloading stage. The binding force of soil on pipeline under cyclic load with less frequency but larger displacement amplitude can be regressed to the pull-displacement curve under monotonic load.
【學(xué)位授予單位】：大連理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：TE973

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本文編號(hào)：2264596