击实能对击实试验结果影响的探讨

采用单位体积击实功相同,但单击功不同的三种击实标准,对土样进行试验,分别测出击实土样的每层层厚、含水率、密度以及干密度,从而得到不同单击功下土样的击实曲线以及密度的变化规律,进而反映出击实能对土体密实度的影响规律,可对现场压实中击实能的选择提供相应的参考建议。     

西安黄土地基浸水后变形范围的试验研究

黄土是第四纪地质时期里的特殊沉积物,在天然状态下它具有较高的孔隙率(一般在45～50％以上),但是,由于天然状态的黄土颗粒间具有较强的加固粘聚力,能够承担一定的压力而不至产生很大的变形,因而浸水后发生湿陷。一般建筑物建成后地基是否会浸水和浸水的程度,往往难以予计,所以黄土地基实际湿陷值的确定也就变得很复杂而难以估计,但是,如果能从黄土地基浸水后变形的分布情况和范围以及其与一系列影响因素间的关系加以研究,无论在实际工程中或是为了进一步探讨黄土湿陷性的理论方面,都     

浸水对湿陷性黄土工程性质影响的试验研究

以湿陷性黄土为研究对象,本文通过室内试验和现场试验,探讨湿陷性黄土在浸水条件下对其工程性质的影响。分析了其抗压强度、抗剪强度、渗透性和湿陷性在水作用下的变化规律,试验结果表明,水的参与改变了土的物理状态,抗剪强度指标在浸水初期急剧下降,湿陷完成后逐渐恢复,湿陷量减少了90%以上。根据现场试验资料绘出了绝对湿陷量和湿陷速度随时间变化的曲线,拟合得出具有一定精度的表示公式,为研究预湿黄土处理提供参考。     

定向剪切应力路径下击实黄土各向异性试验研究

为了研究在定向剪切应力路径下击实黄土的各向异性对其强度和变形特性的影响,利用空心圆柱扭剪仪对击实黄土进行了沿不同主应力轴方向的定向剪切试验,重点探讨中主应力系数b、主应力方向角?对剪切过程中击实黄土强度和变形的影响。试验结果表明,随着主应力方向角的增加,强度呈现出先减小后增大的变化规律,说明击实黄土存在显著的各向异性。在不同b值条件下,广义剪应力–应变曲线的割线模量在0°~30°随着?角增加而降低,在60°以后逐渐增大。通过分析广义剪应力–剪应变曲线变化规律和已有的研究成果,建议采用峰值广义剪应力作为定向剪切下击实黄土的破坏标准;当广义剪应变达到15%仍未出现广义剪应力峰值时,取15%广义剪应变对应的广义剪应力作为击实黄土的破坏标准。击实黄土各向异性特性还表现在b=0.5时各主应力方向上的强度较b=0.0时的强度低。     

湿陷性黄土间歇浸水试验

<正> 在湿陷性黄土地区,湿陷是一种相当普遍的现象。湿陷变形的充分完成需要足够的浸入水量和浸水时间。实际上,地基浸水往往是断断续续多次进行的,地基大多处于间歇浸水条件之下。根据土层每次侵水的饱和程度以及湿陷发展程度的不同,间歇浸水可分为四种情况。沿用以往的提法,本文所说的“间歇浸水”系指“土层的压力不变,每次浸水都达到饱和并使湿陷变形达到稳定”这一特定情况,以下将“浸水饱和并使湿陷变形达到稳定”简称“充分湿陷”。     

非饱和原状黄土边坡浸水试验研究

 非饱和黄土的渗流问题,由于其理论的复杂性和测试手段的滞后,至今发展很慢。通过大型现场试验,得到水在边坡中的渗透范围,分析在浸水试坑下部2～3 m范围内土体每日含水率的变化规律,讨论暂态饱和区的形成和水在边坡土体中的运移过程,得出本次试验水在非饱和原状黄土边坡中渗透范围的形成机制和运移规律。结果表明：水在非饱和黄土中的渗流过程是暂态饱和区不断下移扩大的过程;浸润角不是定值,随着水入渗总量增加而增大;水在非饱和黄土中的渗透范围分为四部分：第一、第二部分为水的横向运移段,第三部分为水的竖向渗透段,第四部分为暂态饱和区的湿润锋面;水在非饱和黄土中的渗透范围是一个闭合的近似椭圆形区域。     

土的击实试验影响因素

击实试验是土木工程中不可缺少的试验项目,对击实标准、试样制备、润滑剂、余土高度及土的重复使用5个影响击实成果的因素做了对比试验;同时,对试验结果进行了分析.通过土的击实影响因素对比试验,得出如下结论：随着击实功的增加,最大干密度增大,最优含水量反而减小;土样应采用未使用过的天然土或风干土制备,不允许采用使用过的土进行击实试验;余土高度应控制在4 mm之内;在击实试验中,应在击实筒及护筒内壁均匀地抹上一薄层凡士林,这些研究成果对击实原理的研究及击实试验均有一定的指导作用.     

影响击实试验结果的诸因素研究

击实试验是填土工程中不可缺少的试验项目，在相同的试验方法和标准下，对影响击实试验质量的因素进行了探讨。     

昔格达土浸水压缩试验研究

通过对19%,21%,23%,25%不同含水率的昔格达土进行不同标准的固结试验,得出昔格达土在快速固结法和标准固结法下固结参数的差异性,并通过浸水压缩试验得出了不同含水率下昔格达土的湿陷系数及自重湿陷量,判定其仅在25%含水率下具有轻微湿陷性,最后通过对昔格达土添加水玻璃改性后得出改性后昔格达土的湿陷系数,结果显示改性后的昔格达土湿陷性显著降低,研究成果有一定的实践价值和社会意义。     

邯郸击实膨胀土变形规律的试验分析

采用室内实验对邯郸击实膨胀土的膨胀变形进行测试,根据试验结果对击实膨胀土变形规律及膨胀变形速率进行了定性分析,分析得出膨胀率与初始含水率、初始干密度、竖向压力相关关系,并给出了膨胀率与它们的综合定量关系。     

Experimental Study on the Behavior of Unsaturated Compacted Silt Under Triaxial Compression

Most of the experimental investigations conducted on unsaturated soil have been performed under a constant air pressure. Changes in air pressure during deformation are in some cases important in practice. For example, in order to explain the stability problems of embankments during earthquakes and seepage flow, and grounds containing gas associated with the dissociation of methane hydrates, it is necessary to consider the interaction between the soil and the pore fluids. In the present study, we carried out fully undrained tests as well as drained tests, namely, constant water and constant air shearing tests. We performed the fully undrained tests using an air-controlled valve to measure the pore air pressure. For the stress variables of the unsaturated soil, skeleton stress values were used to describe the experimental results. From triaxial compression tests on silty soil, we found that the initial suction, the confining pressure, and the strain rate of unsaturated soil strongly influence the stress-strain behavior of unsaturated silt.     

Experimental Study of the Effect of a Compacted Lime-Treated Loess on Its Hydraulic Conductivity

Soil Mechanics and Foundation Engineering - In this paper, the influence of the lime content on the compaction characteristics and saturated hydraulic conductivity of lime-treated loess is studied...     

干湿循环过程中压实黄土的胀缩变形特性研究

为了研究干湿循环过程中压实黄土的胀缩变形特征,利用自主设计的黄土增减湿过程模拟装置,制备了初始含水率为10％,干密度分别为1.45、1.55、1.65 g/cm3的土柱,首先将其浸水饱和,然后在自然条件下干燥收缩至初始状态,如此进行3次反复干湿循环试验.结果表明:浸水直至土体饱和过程中,土体会持续膨胀,膨胀应变ε随时间...     

非饱和黄土受压过程中结构变化的CT描述(英文)

The triaxial compression tests of compacted loess samples with different lateral pressures arc mmducted with a new set of modified triaxial compression apparatus which. With the new apparatus, the soil sample can be scanned with CT machine at the same time during compression process. The different damage process of compacted loess ssmple is directly observed for the first time with CT images and CT numbers. The initiation mechanisms of soil micro-crack during different processes are analyzed with CT images.     

振动荷载作用下黄土应变增长特征试验研究

以WF12440型空心圆柱扭剪仪为实验平台,通过室内饱和黄土动三轴液化试验,探讨了饱和兰州黄土液化过程中残余应变的发展规律:应力-应变滞回特性随着振动次数的增加发生变化,塑性逐步增大;当残余应变小于2％时,增长缓慢;此后,残余应变上升速率加大,3％应变一般出现在“初始液化”前;3％应变后,应变大幅增加,孔压有可能达到初...     

结构性黄土湿压屈服损伤特性试验研究

通过侧限压缩试验系统研究了原状黄土在湿压条件下的结构屈服特性及结构损伤演化过程。针对利用饱和重塑土模拟正常固结土性质的不足,介绍一种制备正常固结土的方法。结合原状黄土及正常固结黄土压缩曲线提出一种确定原状黄土结构屈服压力的新方法,该方法具有作图简便、精度较高等特点;并指出原状黄土结构屈服压力随着含水量的增大而降低,其与含水量的关系可以近似用幂函数进行拟合。同时确定出原状黄土结构屈服临界点,并指出原状黄土结构稳态线(SSL)的相对位置。最后,根据原状黄土压缩曲线、结构稳态压缩线(SSL)及正常固结线(NCL)的相对位置,结合损伤力学思想,提出原状黄土结构变形损伤比的表达式,为评价黄土地基的湿陷变形量提供一条较为可行的途径。     

非饱和原状黄土的变形及屈服特性试验研究

对不同吸力非饱和原状黄土进行了等应力比三轴压缩及常规三轴剪切路径下的试验,研究了偏应力比q/p(q及p分别为净平均应力及偏应力),吸力及净围压对不同应力路径下变形及屈服特性的影响。研究结果表明:在等应力比三轴压缩及常规三轴剪切过程中,孔隙比e与净平均应力p关系(e-lnp)皆位于二条相交的直线上,吸力、偏应力比及净围压对弹性指数的影响很小,对屈服应力及压缩指数的影响较大。等应力比三轴压缩路径下,偏应力比一定时,屈服应力及压缩指数皆随吸力的增大而增大;吸力一定时,随偏应力比的增大而先增大后减小。常规三轴剪切路径下,吸力一定时,屈服应力及压缩指数皆随净围压的增大而增大;净围压一定时,随吸力的增大,屈服应力增大,压缩指数减小。以塑性体应变作为硬化参数时,q-p平面上的初始及后继屈服面皆为对称于饱和土K₀线的倾斜椭圆,吸力及应力增大时,屈服面没有旋转,而是产生等向扩大。     

循环荷载下冻结兰州黄土变形性质的实验研究

对温度为-1 ℃的冻结兰州黄土在围压为0.6 MPa和不同动荷载振动频率条件下进行动三轴试验,试验采用分级加载,每一级荷载振动十次,加载波形为正弦波。实验结果表明:冻结兰州黄土的累积应变在整个加载过程中逐渐增大;当动荷载加载级数增加时,累积应变率逐渐变大。动应变幅随加载频率和振次的增加而减小;当频率小于或等于1 Hz时,动应变幅随加载级数的增加而增大;当频率大于1 Hz时,动应变幅随加载级数变化不大。随着加载级数的增加,滞回曲线的面积和密集程度越来越小,整体斜率和不闭合程度越来越大。用动模量来描述滞回曲线的整体倾斜程度。当频率小于或等于7 Hz时,动模量随加载级数的增加而增大;当频率大于7 Hz时,动模量随加载级数没有明显的规律。     

普通混凝土三轴压强度和变形试验研究

利用大连理工大学海岸和近海工程国家重点实验室的大型混凝土静、动三轴试验系统,对普通混凝土进行了应力比为0.1∶0.25∶1、0.1∶0.5∶1、0.1∶0.75∶1和0.1∶1∶1的常规三轴和真三轴试验,测得了混凝土的强度和变形,并根据试验结果,系统地探讨了处于常规三轴和真三轴受压下混凝土的强度和变形的性能,在八面体应...     

Residual Deformation of Geosynthetic-Reinforced Sand in Plane Strain Compression Affected by Viscous Properties of Geosynthetic Reinforcement

A series of plane strain compression (PSC) tests were performed on large sand specimens unreinforced or reinforced with prototype geosynthetic reinforcements, either of two geogrid types and one geocomposite type. Local tensile strains in the reinforcement were measured by using two types of strain gauges. Sustained loading (SL) under fixed boundary stress conditions and cyclic loading (CL) tests were performed during otherwise monotonic loading at a constant strain rate to evaluate the development of creep deformation by SL and residual deformation by CL of geosynthetic-reinforced sand and also residual strains in the reinforcement by these loading histories. It is shown that the creep deformation of geosynthetic-reinforced sand develops due to the viscous properties of both sand and geosynthetic reinforcement, while the residual deformation of geosynthetic-reinforced sand during CL (defined at the peak stress state during CL) consists of two components: i) the one by the viscous properties of sand and reinforcement; and ii) the other by rate-independent cyclic loading effects with sand. The development of residual deformation of geosynthetic-reinforced sand by SL and CL histories had no negative effects on the subsequent stress-strain behaviour and the compressive strength was maintained as the original value or even became larger by such SL and CL histories. The local tensile strains in the geosynthetic reinforcement arranged in the sand specimen subjected to SL decreased noticeably with time, due mainly to lateral compressive creep strains in sand during SL of geosynthetic-reinforced sand. This result indicates that, with geosynthetic-reinforced soil structures designed to have a sufficiently high safety factor under static loading conditions because of seismic design, it is overly conservative to assume that the tensile load in the geosynthetic reinforcement is maintained constant for long life time. Moreover, during CL of geosynthetic-reinforced sand, the residual tensile strains in the geosynthetic reinforcement did not increase like global strains in the geosynthetic-reinforced sand that increased significantly during CL. These different trends of behaviour were also due to the creep compressive strains in the lateral direction of sand that developed during CL of geosynthetic-reinforced sand.