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1.
钙质砂在我国南海有广泛的分布。随着海上石油工业和海洋资源的开发利用,钙质砂问题日益得到重视。用室内试验的方法,采用相同级配的南海钙质砂和阿拉伯湾钙质砂进行了分析,结果显示,相同级配的南海钙质砂和阿拉伯湾钙质砂的最大最小干密度存在明显差异,南海钙质砂均低于阿拉伯湾钙质砂。同时在级配以及密实度相同的条件下,南海钙质砂的应力-应变关系表现为硬化,而阿拉伯湾钙质砂表现为软化;两者在Dr=0.3时,内摩擦角接近,均为33°左右,但随着相对密实度的增加,南海钙质砂内摩擦角增长速度更快,在Dr=0.8时达到37.7°,明显高于相同密实度的阿拉伯湾钙质砂的34.9°。电镜分析显示,在微观结构上,南海钙质砂的颗粒多棱角,内孔隙更加发育,这是造成南海钙质砂与阿拉伯湾钙质砂物理力学性质差异的重要原因之一。 相似文献
2.
利用大连理工大学的“土工静力-动力液压-三轴扭转多功能剪切仪”,针对相对密实度为70％的福建标准砂,在不排水条件下控制试验过程中的中主应力系数保持不变,进行了不同初始固结应力条件下不同主应力方向的单调剪切试验.以此着重探讨了主应力方向及初始固结应力对饱和密砂单调剪切特性的影响,研究表明,主应力方向和初始固结应力对于密砂的有效应力路径和应力-应变关系均具有十分显著的影响.通过与饱和松砂不排水单调剪切特性的对比分析,探讨了初始相对密实度对砂土剪切特性的影响,研究表明随着主应力方向角增大,密砂的应变硬化效应逐渐减弱,但未出现松砂对应的应变软化现象. 相似文献
3.
曹妃甸围海造陆区吹填了高厚度的粉细砂,粉细砂在地震荷载作用下可能发生液化,威胁吹填区码头和堆载场地的稳定性。采用等体积循环单剪试验,研究了吹填粉细砂在循环荷载作用下的强度和等效超静孔压发展。随着荷载循环次数的增加,粉细砂中超静孔压的发展呈现"快-慢-快"趋势。当累积孔压达到初始固结应力的80%时,超静孔压快速增加,土体达到破坏,液化的发生具有突发性。根据单调和循环单剪试验数据,提出了曹妃甸吹填粉细砂动强度的归一化表达式。结合场地液化评估简化方法,对曹妃甸场地进行了液化判别:在7级地震作用下,中密粉细砂场地的液化深度能达到10 m。 相似文献
4.
通过纤维加筋来加固南海钙质砂对我国南海岛礁海岸带边坡防护的安全稳固具有重要意义。本文将南海钙质砂掺入不同含量(0.2%、0.5%、0.8%、1.1%、1.4%和1.7%)的椰丝纤维，通过室内三轴试验，对椰丝纤维加筋钙质砂的应力-应变关系、纤维掺量对峰值强度及割线模量的影响进行了研究。试验结果表明：加筋钙质砂的抗剪强度和割线模量随椰丝掺量先增大后减小。当椰丝纤维掺量为1.4%时，加筋钙质砂的峰值强度和割线模量分别为293 kPa和2.85 MPa,此时纤维掺量为最佳；当椰丝纤维掺量为1.1%时，加筋钙质砂峰值强度所对应的应变最大，此时椰丝在砂土中分布较为均匀，延性效果最好。研究成果可对纤维加筋钙质砂应用于南海岛礁海岸带边坡防护提供试验数据和理论依据。 相似文献
5.
《海洋地质与第四纪地质》2017,(5)
天然气水合物上覆层不排水抗剪强度是水合物试采过程中导管喷射设计、地层沉降和井壁稳定性分析的关键参数。孔压静力触探(CPTU)为地层强度参数纵向分布规律研究提供了有效途径。本文基于南海北部神狐海域W18/19站位水合物上覆层的CPTU测试结果和室内实验数据,建立了该区经验锥头系数的确定方法,并基于确定的经验锥头系数求解上覆层不排水抗剪强度。结果表明:W18/19站位水合物上覆层由上至下为强度逐渐增大的钙质黏土,基于总锥尖阻力、有效锥尖阻力、超孔隙压力求解钙质黏土不排水抗剪强度的经验锥头系数分别为13.8、4.2、14.4。水合物上覆层不排水抗剪强度随着深度的增加逐渐增大。基于CPTU建立的不排水抗剪强度计算方法能反映钙质黏土不排水抗剪强度的纵向分布规律。 相似文献
6.
浅层沉积物不排水抗剪强度（Su）是深水作业的关键参数之一。为了获取南海神狐海域首次海域天然气水合物试采区W18-19框体的基本工程地质特征，试采工程准备阶段开展了原位孔压静力触探测试（CPTU）及大量的室内实验。本文将主要基于CPTU计算不排水抗剪强度的基本模型，采用微型十字板、电动十字板、袖珍贯入仪及不固结不排水三轴实验，确定该区域不排水抗剪强度的基本模式，并提出适用于南海神狐钙质黏土层的不排水抗剪强度纵向分布规律计算模型，对该区域水合物上覆层的不排水抗剪强度进行预测。 结果表明，基于总锥端阻力、有效锥端阻力、超孔隙压力的模型系数分为13.8、4.2、14.4。综合考虑地层压实效应和含气情况，本文提出的分段函数预测模型与室内结果的一致性较好，可用于工程设计阶段进行工区不排水抗剪强度纵向分布规律的预测。另外，基于有效锥端阻力的不排水抗剪强度经验模型适应于浅层极软-较硬压实的钙质粘土层，基于超孔隙压力的不排水抗剪强度模型适用于较硬-坚硬的不含气层，而基于总锥端阻力的不排水抗剪强度计算模型则适用于坚硬含气的钙质黏土层。本文提出的分段函数模型有效的提高了经验模型在南海神狐水合物赋存区的适用性，计算结果可为工程安全评价提供支撑。 相似文献
7.
利用单剪SHANSEP试验方法测定了南海某石油平台场址两种粘性土层的不排水剪切强度。通过对比单剪SHANSEP试验结果、原位静力触探(CPT)试验结果和三轴不固结不排水(UU)试验结果,表明通过单剪SHANSEP试验确定的粘土不排水强度与现场CPT解释结果更趋于一致,同时也表明了SHANSEP方法适合于中国南海粘性土强度的评价。因此利用单剪SHANSEP试验能够克服土样扰动对粘土强度的影响,更加客观评价粘性土的强度,为工程设计提供可靠的数据。 相似文献
8.
低围压水平下砂的排水行为(英文) 总被引：2，自引：1，他引：2
采用干样沉降法制备样品 ,选用静三轴仪对松砂和密砂样在 10 k Pa至 10 0 k Pa的低围压下的排水行为进行了实验研究 ,并对实验结果作了橡皮膜校正 ,在围压为 10 k Pa的密砂实验中 ,轴向应力的校正值可达到 12 %。实验研究表明低围压下松砂的剪胀性非常明显 ,且存在剪应力极值 ;围压越低 ,松砂和密砂的剪应力极值越小 ,达到最大剪应力所对应的剪应变越小。同时还表明低围压范围内相对密度不同 ,砂的应力应变特性不同 ;此外 ,低围压下砂的内摩擦角高于高围压下的值 ,从而在工程上应重视低围压水平下砂土工程参数的合理选取 相似文献
9.
针对海床在波浪荷载作用下的应力状态,利用大连理工大学的"土工静力-动力液压-三轴扭转多功能剪切仪",针对相对密实度为70%的福建标准砂进行了一系列应力控制式轴向一扭转双向耦合的不排水循环剪切试验试。通过分别控制轴向与扭转应力幅值,研究了椭圆形主应力轴旋转应力路径下两个剪切分量对饱和砂土的动强度及其剪切特性的影响。结合所得试验结论,说明了目前广泛用于动强度分析的循环剪应力表达式无法正确反映椭圆形主应力轴旋转应力路径下的动强度,并提出了一个新的动应力表达式用于分析复杂应力路径的动强度特性。 相似文献
10.
利用带误差控制的显式积分算法,将一种适用于饱和砂土排水循环动力分析的边界面塑性模型编写成可供有限元软件调用的用户自定义材料子程序。建立土体单元有限元数值模型对Toyoura砂的静、动排水三轴试验进行模拟,验证了模型具备合理描述砂土在不同荷载条件下力学响应的能力。建立饱和砂土中板锚循环承载分析的数值模型,针对板锚在砂土中的单调抗拔特性和循环承载特性进行数值分析,得到了与模型试验一致的荷载—位移响应规律。考察循环荷载要素对板锚循环承载特性的影响,结果发现,随着循环荷载的施加,板锚永久位移逐渐累积,循环荷载会导致板锚持续移动,循环幅值越大,初始位移和位移变化率越大;循环均值越大,初始位移越大,但位移变化率越小。 相似文献
11.
ABSTRACTThe behavior of loose anisotropically consolidated calcareous sand obtained from an island in the South China Sea was investigated under undrained monotonic and cyclic loading in a hollow cylinder torsional apparatus. The tests were conducted on specimens which consolidated under various initial effective confining pressures and consolidation stress ratios. The monotonic test results show that the failure and phase transformation line are essentially independent of the consolidation conditions, while the initial contractive tendency of the specimens decreases with an increasing consolidation stress ratio. During monotonic loading of the anisotropically consolidated specimens, a same major principal stress direction is observed at the constant stress ratio lines up to the phase transformation line, irrespective of initial effective confining pressure. The cyclic strength of the sand increases with an increasing consolidation stress ratio. Moreover, a pronounced stress dependence is observed in the sand with higher consolidation stress ratio. During cyclic loading, the generated excess pore water pressure presents considerable fluctuations. The normalized terminal excess pore water pressure is described as a function of consolidation stress ratio. The tests show that the particle shape, rather than particle crushing, plays an important role in the monotonic and cyclic behaviors of the calcareous sand. 相似文献
12.
The shear strength and dilatancy of typical uncemented calcareous sand from the South China Sea are investigated by soil lab tests. According to drained triaxial tests at various relative densities and confining stresses, it is found that the constant volume friction angle is approximated as 39° and the traditional Bolton’s equations can be modified to estimate the peak friction angle and dilation angle. The reliability of the equation proposed for the peak friction angle is verified in terms of calcareous sands from more onshore and offshore sites worldwide, while the errors of the predicted dilation angles scatter in a relatively large range. Totally, the dilation angles of sands in the South China Sea are estimated by the equation presented with an error of ±30%. The peak friction angle measured by the undrained is similar to that by the drained tests as the relative density smaller than 60%, while the former is slightly lower for denser samples.
相似文献13.
Noureddine Della Ahmed Arab Mostefa Belkhatir 《Marine Georesources & Geotechnology》2013,31(3):218-229
In order to study pore water response and static liquefaction characteristics of silty sand, which has previously experienced liquefaction, two series of monotonic triaxial tests were run on medium dense sand specimens (RD = 50%) at confining pressure of 100 kPa. In the first test series, the influence of the soil saturation under undrained static loading has been studied. It summarizes results of monotonic tests performed on Chlef sand at various values of the Skempton's pore pressure coefficient. Analysis of experimental results gives valuable insights on the effect of soil saturation on sand response to undrained monotonic paths. In the second series of tests, the overconsolidation influence on the resistance to the sands liquefaction has been realized on samples at various values of overconsolidation ratios (OCR). It was found that the increase of overconsolidation ratio (OCR) increases the resistance of sands to liquefaction. 相似文献
14.
AbstractHollow cylinder torsional shear tests on loose isotropically and anisotropically consolidated calcareous sand were conducted to investigate the cyclic behavior under three different linear stress paths, including horizontal line, oblique line, and vertical line stress paths, in a coordinate system of the normal stress difference and the horizontal shear stress. The dominant strain components of the isotropically consolidated specimens are affected by the stress paths. With increasing consolidation stress ratio, axial strain gradually becomes the dominant strain component under the three different stress paths. The cyclic strength of the isotropically consolidated specimens under the three different stress paths are almost the same, while for the anisotropically consolidated specimens, the cyclic strengths are strongly affected by the stress paths. These results indicate that conventional cyclic triaxial tests may overestimate cyclic strength in some cases. Irrespective of the stress paths and cyclic stress ratios, the terminal residual excess pore pressure ratio decreases with increasing consolidation stress ratio. Moreover, an empirical equation is proposed to describe the relationship between the normalized shear work and the normalized residual excess pore pressure ratio. The comparative study reveals that the relationship proposed for silica sand is not suitable for the dynamic analyses of calcareous sand. 相似文献
15.
Two marine calcareous deposits as crushable soils and a siliceous sand as a noncrushable soil were used in this study to compare their monotonic response. Undrained monotonic triaxial tests were conducted on samples, which were prepared in different relative densities and consolidated under various confining pressures. The location of phase transformation point in undrained response of the sands in different initial conditions was evaluated. The effect of important parameters including relative density, confining pressure, particle shape, and particle breakage on phase transformation point was assessed. The input energy applied per unit volume of the soils was used to interpret the shearing response of crushable and noncrushable soils. The results showed that calcareous sands have more tendencies in contraction. Particle shape and breakage play a key role in engineering behavior of crushable soils. 相似文献
16.
Shen Yang Xue Shen Hanlong Liu Huayang Ge Xiaoxi Rui 《Marine Georesources & Geotechnology》2020,38(6):706-715
AbstractConstruction of the reefs in the South China Sea is a significant foundation to the secure stability and economic development of China. The construction of an airport runway is necessary for this realization. The calcareous sand is the main primary material in the runway construction. A certain type of calcareous sand near a certain reef of the South China Sea was studied in this paper. To investigate this specific calcareous sand, quartz sand was used as a reference for comparison. Microscopic 3-D imaging, compression and triaxial tests were conducted to test the micro, squeezing and shear properties. The effect mechanism of gradation on the calcareous sand’s compressibility and shear characteristics are discussed from a mesoscopic viewpoint using 3-D morphology. Calcareous sand particles are multiangular and flatter in comparison with quartz sand. The larger the particle sizes are, the more different the two sands’ morphologies are. The compressibility of calcareous sand is greater, and the effect of the coarse fraction (5–1?mm) content in the gradation plays the most significant role in this feature. When the coarse particles’ content is less than 25% and the mass ratio of the middle and fine particles (M) is constant, there is the worst coarse fraction content causing the calcareous sand to be most likely compressed. The worst coarse fraction content decreases with the increase in M, and an empirical formula is proposed. When the gradation, relative density and confining pressure are the same, the peak shear stress and strain of calcareous sand are all at a high level. The effect of confining pressure is manifested in calcareous sand. The shear strength and dilation of calcareous sand are also most affected by the medium coarse fraction (5–0.25?mm) content. 相似文献
17.
Mohammed Derkaoui Karim Bendani Fethi Belhouari 《Marine Georesources & Geotechnology》2016,34(7):668-680
In recent years, interest in understanding the mechanisms of mechanical instability of porous media, leading to catastrophic failure has been continuously revised to include, new porous media parameters generating the phenomenon of liquefaction under static or dynamic loadings. Results from experimental test programs have concluded too many physical concepts based on material intrinsic properties, initial states, and other characteristics. Despite the great progress on the subject, these concepts do not allow a unified treatment of such porous media. The assessment of critical shear strength of sandy soils as porous media under undrained conditions is a major challenge in stability analysis. Such strength serves to evaluate the occurrence of flow deformation under liquefaction phenomena. The determination of the critical undrained strength is essentially fundamental for the design of soil structures such as earth dams, bridge supports, building foundations as well as soil densification process to avoid catastrophic failure due to soil instability manifested by failure or large displacement such as settlement. In this work, experimental program on reconstituted loose and medium dense specimens of terrigenous silica sands with different specified fine contents was carried out to analyze its mechanical behavior under undrained conditions. The present article is an attempt to experimentally describe mechanical behavior and theoretically justify such response of loose and medium dense sand by means of critical state soil parameters. 相似文献
18.
The post-cyclic behavior of biogenic carbonate sand was evaluated using cyclic triaxial testing through a stress control method under different confining pressures between 50 to 600 kPa. The testing program included a series of isotropically and anisotropically consolidated, undrained triaxial compression and extension tests on samples of remolded calcareous Bushehr sand. Grading analyses (before and after each test) were used to examine the influence of particle breakage on post-cyclic behavior of Bushehr sand. The particle breakage commonly occurred in these soils even in lower values of confining pressure, yet there was not a clear correlation between the post-cyclic responses and particle breakage. Based on the present study, a concept is suggested for post-cyclic behavior of carbonate sand. It was observed that post-cyclic strength has a good correlation with cyclic stress ratio, type of consolidation, and value of residual cyclic strain. For all specimens, it is clear that the post-cyclic strength is greater than monotonic strength, irrespective of confining pressure and relative density. 相似文献
19.
Undrained strength behaviour of a cemented marine clay under monotonic and cyclic loading 总被引：1，自引：0，他引：1
The paper presents the results of a series of monotonic and cyclic triaxial shear tests carried out to study the influence of the strain effect and load cycles on the undrained shear strength of a cemented marine clay from the East coast of India. The undrained shear strength of Indian coastal marine clay has been established from a detailed shear testing carried out in three phases. Undisturbed soil samples taken out from the seabed were used in the test. In the first part, a comprehensive monotonic shear testing has been carried out under both stress-controlled and strain rate-controlled conditions. In the second phase on identical soil specimen, undrained cyclic shear tests were carried out at various cyclic stress ratios (CSR) and these stress levels are chosen in such a way so that no failure occurred during testing. In the final phase post cyclic monotonic shear testing was conducted to qualitatively evaluate the damage caused by cyclic loading. The monotonic shear test results bring out the influence of cementation that can be detected by the stress-controlled test. The cyclic stress results are analysed in terms of CSR. Further, the results are correlated in terms of stress path. 相似文献
20.
Noureddine Della Mostefa Belkhatir Ahmed Arab Jean Canou Jean-Claude Dupla 《Marine Georesources & Geotechnology》2013,31(6):487-495
A series of undrained monotonic triaxial compression tests were performed on natural, medium-dense (relative density (RD) = 50%) Chlef sand containing 0.5% of non-plastic fines, under different confining pressures of 50 kPa, 100 kPa, and 200 kPa. This article focuses on distinctive states of the monotonic undrained response of sands, namely the critical state, the phase transformation state, the quasi-steady state, and the state of undrained instability (onset of flow liquefaction). Specimens were prepared using dry funnel pluviation and wet deposition to investigate the effect of the initial sand fabric on these states. The present data suggest that the initial fabric of the sand appears to have a significant effect on the undrained behavior in the early stages of shearing, with its influence vanishing at large strains. Wet deposition specimens demonstrate considerably larger undrained instability state strength than their dry funnel pluviation counterparts, and a unique critical state locus is reached by both dry funnel pluviation and wet deposition. 相似文献