筒型桩靴在饱和砂土中的贯入阻力研究          下载免费PDF全文

吴曲楠  刘润  张海洋  王宇飞 《地震工程学报》2018,40(6):1183-1190

桩靴贯入阻力的准确预测是自升式钻井平台安全作业的前提。通过小比尺模型试验,研究饱和砂土中桩靴贯入速度对筒型桩靴插桩性能的影响,并基于地基承载力理论提出筒型桩靴贯入阻力的计算方法,进而采用CEL有限元方法模拟筒型桩靴的贯入过程,并与试验结果进行比较。研究发现:当模型试验中桩靴贯入速度在0.1～0.3mm/s时,桩靴的贯入可看作是准静态过程,此时贯入阻力变化不大,采用基于地基承载力理论中的Hansen公式和Vesic公式可较为准确地计算出对应某一深度的贯入阻力;CEL有限元方法可有效模拟筒型桩靴的贯入过程,当桩靴的贯入速度为0.1～0.3mm/s时,数值模拟结果与试验结果吻合较好。  相似文献   

Enhanced bed load sediment transport by unsteady flows in a degrading channel     

Zhijing Li  Honglu Qian  Zhixian Cao  Huaihan Liu  Gareth Pender  Penghui Hu 《国际泥沙研究》2018,33(3):327-339

Laboratory flume experiments were done to investigate bed load sediment transport by both steady and unsteady flows in a degrading channel. The bed, respectively composed of uniform sand, uniform gravel, or sand-gravel mixtures, always undergoes bulk degradation. It is found that both uniform and non-uniform bed load transport is enhanced greatly by unsteady flows as compared to their volume-equivalent steady flows. This enhancement effect is evaluated by means of an enhancement factor, which is shown to be larger with a coarser bed and lower discharges. Also, the fractional transport rates of gravel and sand in non-uniform sand-gravel mixtures are compared with their uniform counterparts under both steady and unsteady flows. The sand is found to be able to greatly promote the transport of gravel, whilst the gravel considerably hinders the transport of sand. Particularly, the promoting and hindering impacts are more pronounced at lower discharges and tend to be weakened by flow unsteadiness.  相似文献   

Bed-load transport rate based on the entrainment probabilities of sediment grains by rolling and lifting     

Jun-De Li  Jian Sun  Binliang Lin 《国际泥沙研究》2018,33(2):126-136

A function for the bed-load sediment transport rate is derived. This function is obtained by using the entrainment probabilities of the rolling and lifted sediment grains, and by introducing two travel lengths, respectively. The predictions from the new bed-load function agree well with experimental results over the entire experimental range and show significant improvement over the commonly used formula for the bed-load transport rate. The new function shows that, in terms of contributing to the bed-load transport rate, the total entrainment probability of the sediment grains is a weighted summation of those for the lifted and rolling grains, rather than a simple addition of the two. The function is also used to predict the total entrainment probability, saltation length, and the bed layer thickness at a high bed-load transport rate. These predictions all agree well with the experimental results. It is found that, on average, the travel length for the rolling sand grains is about an order of magnitude less than that of the lifted grains.  相似文献   

九江市网纹红土标准贯入击数与力学参数关系分析          下载免费PDF全文

蒋兵 《探矿工程》2020,47(10):89-92

针对九江市网纹红土层标准贯入试验实测锤击数与试验孔深、土的压缩模量、抗剪强度关系之间进行了相关性分析。结果表明：网纹红土标准贯入击数与试验孔深为正显著线性相关关系，与土的压缩模量为正弱线性相关关系，与抗剪强度为正弱线性相关关系。分析成果对在九江市开展岩土工程勘察活动具有很好的指导和借鉴意义。  相似文献   

粉土中筒型基础贯入阻力的研究     

马文冠  刘润  练继建  郭绍曾 《岩土力学》2019,40(4):1307-1312

筒型基础在海洋工程中应用广泛，贯入阻力的准确计算是筒型基础成功应用的关键。在海洋工程中，粉土是介于砂土与黏土间的特殊土，现有计算方法中将粉土等同于砂土，忽略了黏聚力c对贯入阻力的影响。开展了粉土中筒型基础的现场贯入试验，观测了自重下沉阶段与负压贯入阶段筒型基础贯入阻力与贯入深度的关系，提出了粉土中计算沉贯阻力的方法，并对不同筒端形式的减阻效果进行了深入分析。研究结果表明，采用现有规范方法计算粉土中筒型基础的贯入阻力值较实测值偏小20%，提出的两种方法不仅适用于计算粉土中筒型基础的贯入阻力，而且能够反映负压贯入阶段的减阻效果；尖筒端可使筒端阻力减少50%，减阻环可使筒侧摩阻力减少50%，但减阻环会破坏筒壁周围土体，形成渗流通道，导致负压失效。  相似文献   

插拔桩靴对临近桩靴承载力的影响研究     

刘润  曹添铭  陈广思  张海洋  李成凤 《岩土力学》2020,41(9):2943-2952

自升式钻井船桩靴的插拔过程将会对临近井口平台的桩靴基础产生不利影响。开展了室内模型试验研究，将试验结果与理论分析结果相结合，得到了桩靴插拔的影响范围及影响范围内土体强度的变化规律，并推导了桩靴插拔影响区内临近桩靴承载力的计算方法，与模型试验结果进行了对比验证。研究表明，桩靴插拔后砂土相对密实度降低，其降低程度随距桩靴距离的增加而逐渐减小，影响范围约为1倍桩靴直径。受桩靴插拔影响，临近桩靴的承载力下降，降低比例随两桩靴相对间距的增大而减小，随桩靴相对插深的增加而增加。当两桩靴相对间距大于2倍插拔桩靴直径时，可认为桩靴插拔对临近桩靴基础承载力无影响。  相似文献   

Peak discharge increase in hyperconcentrated floods     

《Advances in water resources》2014

The peak of river floods usually decreases in the downstream direction unless it is compensated by freshwater inflow from tributaries. In the Yellow River (China) the opposite is regularly observed, where the peak discharge of river floods increases in the downstream direction (at a rate far exceeding the contribution from tributaries). This flood peak discharge increase is probably related to rapid morphological changes, to a modified bed friction, or to a combination of both. Yet the relative role of these processes is still poorly understood. This paper aims to analyze the relative contribution of bed erosion and friction change to the peak discharge increase, based on available data and a recently developed numerical model. Using this high-resolution, fully coupled morphodynamic model of non-capacity sediment transport, two hyperconcentrated floods characterized by downstream peak discharge increase are numerically reproduced and analyzed in detail. The results reveal that although erosion effects may contribute to the downstream discharge increase (especially in case of extreme erosion), for most cases the increase must be mainly due to a reduction in bed friction during peak discharge conditions. Additionally, based on the concept of channel storage reduction, the effects of decreasing bed friction and (very strong) bed erosion can be integrated in explaining the peak discharge increase.  相似文献   

Study on changes in bed characteristics and friction factor in the presence of wash load in suspension     

N K KHULLAR  Jaspal SINGH 《国际泥沙研究》2014,29(4):501-508

Results of an experimental study on the effects of different concentrations of wash load on the size of bed features and resistance to flow in a laboratory flume are presented. The experiments were carried out under different hydraulic conditions in a 30 m long, 0.204 m wide and 0.5 m deep tilting flume under clear water condition and in the presence of different concentration of wash load in the flow. The bed material used consisted of uniform sediment of size 0.96 mm. Analysis of the data indicates that the characteristics of the bed features change and friction factor increases in the presence of different concentration of wash load in the flow. The reasons for changes in the characteristics of the bed features and increase in friction factor in the presence of wash load are identified and a relationship for predicting friction factor in the presence of wash load has been established.  相似文献   

强夯法加固夹砂粘土吹填场地的现场试验研究     

江舜武  ;王宝善  ;岳喜兵  ;邓永锋 《地震学刊》2014,(4):429-435

江苏省连云港赣榆港区陆域采用航道和港池的疏浚土方吹填形成作业港区,吹填工艺以绞吸式疏浚为主,疏浚涉及土层为粘土和砂土,由此形成了粘土和砂土的混合土地基。为了提高地基承载力和均匀性,采用了强夯法对地基进行加固,但是目前对夹砂粘土地基强夯加固的理论和实践较少。为此,以砂夹粘土构成的混合土地基为对象,测试了多种能量单点夯击时的地基土夯沉量、孔压和夯坑周围土体强度等参数,探讨了强夯法加固该类地基的加固深度和水平影响范围。结果表明：对于该类地基而言,有效加固深度修正系数取0.35~0.5为宜;强夯过程中,孔压与强度的增长范围不对应,即孔压影响范围远大于强度影响范围。  相似文献   

基于孔压静力触探的岩土参数正态性检验方法对比     

林军  蔡国军  刘松玉  邹海峰  侯新宇 《吉林大学学报(地球科学版)》2021,51(5):1408-1415

岩土参数的正态分布是岩土工程可靠分析的基本假定之一。目前,岩土工程参数的正态性检验以KS （Kolmogorov-Smirnov）检验为主,然而诸多研究表明,对于小样本数据,KS检验的正态性检验结果并不可靠。本文以废黄河泛滥沉积相粉土中的孔压静力触探（CPTU）锥尖阻力q_t数据为研究对象,首先采用ANOVA （方差分析）检验,从CPTU测试资料中进行总体的样本筛选,然后应用SW （Shapiro-Wilk）检验、KS检验、LF （Lilliefors）检验和AD （Anderson-Darling）检验等4种正态性检验方法,在不同样本容量条件下,对测试数据进行正态性检验评价。当测试数据的样本容量充足时,分析结果表明：SW检验结果最为严格,KS检验结果最不保守,而LF检验和AD检验的严格性介于两者之间;对于常规岩土工程设计,采用KS检验结果即可满足稳定性分析要求,对于复杂岩土工程设计,采用SW检验对设计参数进行正态性检验,可降低设计的不确定性。  相似文献