Characteristics of Pore Water Pressure of Saturated Silt Under Wave Loading

The characteristics of dynamic stress in the seabed under wave loading are constant principal stress and continuous rotation of the principal stress direction.Cyclic triaxial-torsional coupling shear tests were performed on saturated silt by the hollow cylinder apparatus under different relative densities,deviator stress ratios and vibration frequencies to study the development of pore water pressure of the saturated silt under wave loading.It was found that the development of pore water pressure follows the trend of "fast～steady～drastic".The turning point from fast to steady stage is not affected by relative density and deviator stress ratio.However,the turning point from steady to drastic stage relies on relative density and deviator stress ratio.The vibration cycle for the liquefaction of saturated silt decreases with increasing deviator stress ratio and increases with relative density.The vibration cycle for the liquefaction of the saturated silt increases with vibration frequency and reaches a peak value,after which it decreases with increasing vibration frequency for the relative density of 70%.But the vibration cycle for the liquefaction of saturated silt increases with vibration frequency for the relative density of 30%.The development of pore water pressure of the saturated silt is influenced by relative density and vibration frequency.     

波浪荷载作用下饱和粉土反正弦孔压拟合参数影响因素分析

为探寻波浪荷载作用下饱和粉土振动孔隙水压力发展规律,试验选用近海地区广泛分布的粉土为研究对象,在不同的相对密实度、偏应力比及振动频率下,利用空心圆柱仪进行了一系列模拟波浪荷载的循环三轴-扭剪耦合试验,探讨饱和粉土在不排水条件下的孔压增长规律。试验结果表明,归一化后的振动孔隙水压力比与振次比之间的关系可以用反正弦三角函数来拟合。通过对不同相对密实度、偏应力比及振动频率下归一化孔压发展曲线的分析可知,随着偏应力比的增大,拟合参数θ呈线性趋势减小,随着相对密实度的增大,θ呈线性趋势增加,振动频率的变化对拟合参数θ影响不大。     

塔里木盆地西南部昆仑山前下白垩统沉积相特征及石油地质意义

塔里木盆地西南部沿昆仑山前分布一套逾千米厚的下白垩统碎屑岩,岩相以浅红色中、细砂岩,褐红色砂砾岩、砾岩为主,夹浅红色泥岩和薄层浅灰色细砂岩。按生物组合及岩性特征,自下而上可划分5个岩性段。第1段为灰绿色泥岩段,沉积环境以湖相和前扇三角洲沉积为主;第2段为砂砾岩段,沉积环境以扇三角洲前缘和平原沉积为主;第3段为含砾粗砂岩段,沉积环境以辫状河－辫状河三角洲平原沉积为主;第4段为细砂岩夹泥岩段,沉积环境以辫状河三角洲前缘水下分流河道沉积为主;第5段为泥岩夹砂岩段,沉积环境为辫状河三角洲前缘、前辫状河三角洲和滨浅湖相沉积。沉积环境由快速堆积的扇三角洲-冲积扇向辫状河-辫状河三角洲演化,沉积厚度达1000余米。构造背景为强烈拉张的构造环境,是断陷盆地发育的重要时期。中细砂岩达70％以上,砂岩孔隙类型为原生粒间孔,孔隙度10％~20％,渗透率1~1000×10－3μm2,是塔里木盆地中生代油气勘探的重要目的层系。     

主应力方向变化路径下等压固结粉土强度特性差异和能量评价方法研究

主应力轴方向旋转变化是地基在波浪、车辆等荷载作用下经受的一种复杂而典型动力路径特征,为研究粉土在不同主应力轴方向变换条件下的强度特性差异,以初始密实度为70％的长江入海口饱和粉土空心试样为对象开展主应力轴旋转、拉压交变动三轴和双幅扭剪三轴试验。试验发现,等压固结条件下3种路径均使试样出现小应变崩塌液化破坏,且崩塌应力状态,可在p’-q空间中用近似平行的一组准不稳定相态线归一。而在液化和崩塌振次上,以同剪应力峰值的动扭剪下最高,动三轴次之,主应力轴旋转最低。在此基础上,提出采用崩塌损耗能对不同路径下土体动强度进行评价,结果表明,崩塌损耗能与剪应力幅值无显著关系,而在上述3种动力路径中,试样崩塌损耗能依次降低,这与3种路径下得到崩塌时刻递增的有效围压特征相匹配。崩塌能强度标准的采用,克服了复杂动力路径下由于剪应力恒定或循环变化造成应力水平无法统一而干扰强度评价的不足     

主应力轴旋转下小偏压固结密实粉土崩塌特性及孔压模型研究

为研究主应力轴旋转复杂动应力对偏压固结粉土的性状演变影响,以空心圆柱试样为对象,开展具有不同初始固结比的密实粉土（Dr＝70%）在不排水主应力轴循环旋转下的系列试验。结果表明：①初始固结比不大于1.5时,主应力轴旋转导致试样发生中低应变崩塌,进而液化的脆性破坏模式;而固结比大于1.5时,试样变为应变持续稳定开展至高应变,孔压最终进入动态平衡的延性破坏模式,且不同固结比下试样发生崩塌液化和稳态延性破坏的孔压峰值间不存在交叉。②小偏压固结试样的液化峰值孔压和崩塌孔压均随固结比增加而有规律地下降,但受动剪应力水平影响很小,这与等压固结试样的崩塌孔压值受控于剪应力水平有很大差异。③相同初始球应力水平下,崩塌振次反映的小偏压固结试样强度高于等压固结试样,但在偏压条件下强度与固结比不存在单调变化关系,表明小偏压固结试样崩塌除受制初始围压水平外,很大程度上还取决于偏压程度。④基于上述试验结果,提出了主应力轴循环旋转下小偏压固结粉土的孔压预测模型,该模型不仅突显了崩塌状态对相变及液化破坏的重要预测作用,还反映了固结比和动剪应力对孔压开展的综合影响。     

微生物胶结在防治堤坝破坏中的应用研究

为防治漫顶引起侵蚀造成堤坝破坏,将微生物诱导碳酸钙沉淀即MICP技术应用于加固堤坝表层。通过向堤坝表层喷洒微生物细胞以及营养盐,最终在砂土孔隙中快速析出碳酸钙胶凝结晶,以改善堤坝表层砂的力学性能。首先,采用喷洒法处理堤坝表层;其次,对处理好的堤坝模型进行水槽试验,研究其抗侵蚀性;最后,对堤坝表层的试样进行强度与渗透试验。试验结果表明,采用MICP技术加固堤坝模型表层可有效提高其抗侵蚀力,防治由漫顶引起的堤坝破坏。对加固后的表层取样进行测试,结果表明：无侧限抗压强度可高达9 MPa,渗透系数从4×10?4 m/s 降低至7.2×10?7 m/s。试验说明,微生物胶结技术在加固堤坝表层方面具有潜在的工程实用价值和广阔的应用前景。     

A New Method of Combination of Electroosmosis, Vacuum and Surcharge Preloading for Soft Ground Improvement

As a rapid and effective ground improvement method is urgently required for the booming land reclamation in China’s coastal area, this study proposes a new combined method of electroosmosis, vacuum preloading and surcharge preloading. A new type of electrical prefabricated vertical drain (ePVD) and a new electroosmotic drainage system are suggested to allow the application of the new method. This combined method is then field-tested and compared with the conventional vacuum combined with surcharge preloading method. The monitoring and foundation test results show that the new method induces a settlement 20% larger than that of the conventional vacuum combined with surcharge preloading method in the same treatment period, and saves approximately half of the treatment time compared with the vacuum combined with surcharge preloading method according to the finite element prediction of the settlement. The proposed method also increases the vane shear strength of the soil significantly. The bearing capacity of the ground improved by use of the new proposed method raises 118%. In comparison, there is only a 75% rise when using the vacuum combined with surcharge preloading method during the same reinforcement period. All results indicate that the proposed combined method is effective and suitable for reinforcing the soft clay ground. Besides, the voltage applied between the anode and cathode increases exponentially versus treatment time when the output current of power supplies is kept constant. Most of the voltage potential in electroosmosis is lost at electrodes, leaving smaller than 50% of the voltage to be effectively transmitted into the soil.     

塔里木盆地英买力地区志留系储层构造挤压及火山热液改造效应

针对构造挤压、火山热液发育区的砂岩储层特征及其物性空间变化,依据露头、岩芯、实验分析、测井等资料,基于砂岩动力成岩理论,提出了构造挤压和火山热液作用对砂岩储层性质的定量影响效应。研究表明:塔里木盆地英买力地区志留系柯坪塔格组为临滨亚相石英砂岩沉积,英买35井区构造压实减孔比英买34井区多7%~8%,海西早期构造挤压及海西晚期火山热液作用产生的裂缝改善了英买35井区储层性质。石英砂岩储层性质受构造挤压和火山热效应影响明显,构造挤压成岩效应受控于构造作用时间、构造样式和砂岩原始沉积组构;火山热液对砂岩储层性质的影响具有空间分带性,影响范围为侵入岩体厚度的一半,变质矿物的广泛发育是储层性质遭受破坏的见证。     

基于分数阶微积分的粗粒料静动力边界面本构模型

分数阶微分理论在土体静力黏弹性本构模型中得到了广泛应用,然而,其在动力弹塑性模型中的应用尚不多见。为此,基于分数阶微积分理论分析了粗粒料在循环荷载下的变形特性,提出了粗粒料在循环荷载下的分数阶应变率;并以此为基础,进一步建立了粗粒料受静动力荷载作用下的边界面塑性力学本构模型。所提出模型包含10个参数,均可以运用常规三轴试验获得。为了验证所提出模型,选取了几种已有不同文献中的不同粗粒料试验数据进行了模拟,发现,所提出的模型可以较好地模拟粗粒料在静动力加载下的应力-应变行为,对于循环荷载下的长期变形也能较好地预测。     

粗粒土的分数阶应变率及其与分形维度的关系

在波浪荷载、潮汐作用下砂土等粗粒土常常经受长期动力变形。运用分数阶微积分理论,分析了5种不同粗粒土在不同加载条件下的累积变形特性及粗粒土的分数阶应变率,传统的整数阶应变率随着加载次数的变化而变化,而粗粒土的分数阶应变率在同一加载条件下保持为常数。通过粗粒土颗粒破碎的分形理论,尝试建立分数阶应变率与土颗粒分布的分形维度之间的关系,分析土体分形维度对分数阶应变率大小的影响,发现随着分形维度的增加,分数阶应变率的数值降低。