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1.
E. Rojas A. Zepeda M. L. Pérez-Rea J. Leal G. Gallegos 《Geotechnical and Geological Engineering》2011,29(2):193-202
One of the most prevalent relationships for effective stresses on unsaturated soils was proposed by Bishop in the middle of
the last century. However, only recently Bishop’s effective stress equation has been implemented in various constitutive models
for unsaturated soils. These models have the advantage of naturally including the hydro-mechanical coupling that has been
experimentally observed on these materials. Unfortunately, the problem of properly evaluating Bishop’s parameter χ still remains unsolved. This paper presents the results of a solid-porous model used to determine the value of Bishop’s parameter
χ and evaluate the strength of unsaturated soils. These theoretical results are compared with a series of triaxial test performed
on a silty sand subjected to different suctions in wet and dry paths. These comparisons show that the porous model proposed
herein can be used to estimate the strength of unsaturated soils for both the wetting and the drying paths. 相似文献
2.
Geotechnical properties of municipal sewage sludge 总被引：3，自引：0，他引：3
Brendan C. O’Kelly 《Geotechnical and Geological Engineering》2006,24(4):833-850
The geotechnical properties of municipal sewage sludge, in particular those pertinent to the handling and landfilling of the
material, are presented. Index, drying, compaction, shear strength and consolidation tests were conducted on the material
at different states of biodegradation. The organic content and specific gravity of solids were found to be inversely related,
with typical organic contents of 50–70% and specific gravity of solids values of 1.55–1.80. The density of the compacted material
was low in comparison with mineral soils. Standard Proctor compaction yielded a maximum dry density of 0.56 tonne/m3 at 85% water content. Laboratory vane-shear and triaxial compression tests indicated that, below about 180% water content,
the shear strength of the sludge material increased exponentially with reducing water content. Consolidated-undrained triaxial
compression tests on the pasteurised sludge material indicated an effective angle of shearing resistance of 32° for the moderately
degraded material and 37° for the strongly degraded material. Biogas was produced at rates of up to 0.33 L/day/kg slurry due
to ongoing biodegradation and the resulting pore pressure response must be taken into account in any stress analysis. Consolidation
tests using the hydraulic consolidation cell, oedometer and triaxial apparatus indicated that the sludge material was highly
compressible although practically impermeable, for example the coefficient of permeability for the moderately degraded slurry
was of the order of 10−9m/s. However, creep deformation was significant with typical coefficient of secondary compression values of 0.02–0.08 for
the compacted material. A more free-draining material was produced at higher states of biodegradation. 相似文献
3.
It is universally known that residual soils behave very differently from sedimentary soils. While the latter is widely known as cross-anisotropic, little is known regarding the strength anisotropy of residual soils. This study presents how the inherent anisotropy affects the strength of natural granite residual soils under generalized conditions, where intact specimens were carefully prepared and sheared under triaxial compression, extension, simple shear, and hollow cylinder torsional shear tests. The strength of natural residual soil, in terms of ultimate stress ratio M and undrained shear strength Su, is found to be significantly anisotropic in a different way from normally consolidated clays with the maximum strength obtained under triaxial compression and the minimum under simple shear or at intermediate principal stress direction. As a result, the existing method failed to measure the anisotropy degree of the studied soil. Two parameters were proposed accordingly to quantify the anisotropic strength under general conditions, taking the special strength anisotropy pattern and cohesive-frictional nature of GRS into account. The proposed parameters enable the direct comparison of strength anisotropy among soils. This study serves as a data set to better understand residual soils regarding their anisotropic behaviors under generalized conditions. Although specific to granite residual soils in China, this study is expected to be more widely applicable to other weathered geomaterials.
相似文献4.
《Geomechanics and Geoengineering》2013,8(4):285-296
ABSTRACTIn this study, uniaxial compression experiments with seven different bedding angles and six numbers of freeze–thaw cycles were conducted to investigate the influences of freeze–thaw cycles on the elastic parameters and the uniaxial compressive strength of slate. The laws of the elastic parameters, uniaxial compressive strength and failure characteristics were analysed, and a new uniaxial compressive strength prediction model that considers the bedding angle and the number of freeze–thaw cycles as control variables was established and verified using the experimental data. The results showed that the uniaxial compressive strength, elastic modulus and shear modulus decreased exponentially with an increasing number of freeze–thaw cycles. However, the Poisson’s ratio increased linearly with an increasing number of freeze–thaw cycles. The uniaxial compressive strength initially decreased and then increased with increasing bedding angle. There are three forms of failure occurred during the tests: when the bedding angle was 0°≤β ≤ 26.6°, the splitting failure and shear failure occurred at the same time; when the bedding angle was 26.6°≤β ≤ 83.0°, sliding failure occurred along the bedding plane; and when the bedding angle was 83.0°≤β ≤ 90°, splitting failure occurred along the axial direction of sample. 相似文献
5.
In this paper, the shear strength with respect to the matric suction of unsaturated soils was studied. For this purpose, unsaturated
triaxial testing procedures were applied to the undisturbed residual soil specimens. An apparatus for performing triaxial
tests was designed and constructed. In the tests, matric suction was controlled by using the axis translation technique, and
pore water volume changes were measured by means of a volume change transducer with 10−8 m3 sensitivity. The test results indicated that the matric suction contributes to the shear strength of unsaturated soil specimens,
and this contribution called suction strength varies non-linearly with respect to the matric suction. The logarithmic model
needing to know the air-entry value and the internal friction angle of a soil specimen for prediction of the suction strength
were presented and compared with the test results. It was found that suction strength values predicted from the proposed model
were in satisfactory agreement with the experimental results. 相似文献
6.
应力路径对土的强度和变形性质具有重要影响。相对于饱和土而言,控制吸力条件下的非饱和土三轴压缩状态的应力路径研究更加复杂。随着非饱和土本构理论的不断发展,理论和试验研究结果表明,非饱和土弹塑性本构模型可以用来近似地描述非饱和土的强度和变形性质。因而,运用非饱和土弹塑性本构模型对控制吸力条件下的3种非饱和土三轴压缩应力路径试验进行数值模拟是一种有效的理论研究手段。采用Barcelona模型能够对此类试验进行较好的数值模拟,其研究结果表明,在控制吸力条件的三轴压缩状态下应力路径对非饱和土的强度和变形性质具有重要影响。 相似文献
7.
In this paper an experimental study was planned on rock mass model with three joint sets under triaxial and true-triaxial
stress states to assess the influence of joint geometry and stress ratios on deformational behaviour of rock mass. The physical
models were composed of three continuous orthogonal joint sets in which joint set-I was inclined at angle θ=0°, 20°, 40°,
60°, 80° and 90° with x-axis, joint set-II was produced at staggering s=0.5 and joint set-III was kept always vertical. Thus, rock mass models with medium interlocked smooth joints (ϕ
j
=36.8°) were simulated under true triaxial compression (σ1>σ2>σ3). Modulus of rock mass shows anisotropy with joint inclination θ which diminishes with increase in σ2/σ3 ratio. The rock mass at θ=60° shows the highest modulus enhancement (599.9%) whereas it is minimum (32.3%) at θ=90°. Further
two empirical expressions for estimation of deformation modulus were suggested based on experimental results, which were developed
by incorporating two basic concepts, e.g. Janbu’s coefficients and joint factor, J
f. 相似文献
8.
Fissures in natural rocks play an important role in determining the strength, deformability and failure behavior of rock mass. However in the past, triaxial compression experiments have rarely been conducted for rock materials containing three-dimensional (3-D) fissures and the failure mechanical behavior of fissured rocks is not well known due to the difficulty of conducting triaxial experiments on fissured rocks. Therefore in this research, conventional triaxial compression experiments were performed to study the strength, deformability and failure behavior of granite specimens with one preexisting open fissure. Thirty-one specimens were prepared to perform conventional triaxial compression tests for intact and fissured granite. First, based on the experimental results, the effects of the confining pressure and the fissure angle on the elastic modulus and the peak axial strain of granite specimens are analyzed. Second, the influence of the confining pressure on the crack damage threshold and the peak strength of granite with respect to various fissure angles are evaluated. For the same fissure angle, the crack damage threshold and the peak strength of granite both increase with the confining pressure, which is in good agreement with the linear Mohr–Coulomb criterion. With increasing fissure angle, the cohesion of granite first increases and later decreases, but the internal friction angle is not obviously dependent on the fissure angle. Third, nine crack types are identified to analyze the failure characteristics of granite specimens containing a single fissure under conventional triaxial compression. Finally, a series of X-ray microcomputed tomography (CT) observations were conducted to analyze the internal damage mechanism of granite specimens with respect to various fissure angles. Reconstructed 3-D CT images indicate obvious effects of confining pressure and fissure angle on the crack system of granite specimens. The study helps to elucidate the fundamental nature of rock failure under conventional triaxial compression. 相似文献
9.
干湿交替对砂岩力学特性影响的试验研究 总被引：5，自引：0，他引：5
由于地下水位的升降等原因,岩体经常处于干湿交替状态,这对岩体工程的长期稳定性不利。以红砂岩为研究对象,进行了干燥－饱水干湿交替作用后的常规单轴和三轴压缩试验研究,获得了砂岩应力-应变曲线,分析了其变形破坏特征。相对于没有经过干湿交替作用的干燥试件,经过不同次数的干燥－饱水交替作用后,砂岩的弹性模量、单轴和三轴抗压强度、黏聚力、内摩擦角等都有不同程度的降低。各力学指标的总体变化趋势是在第1次饱水之后均有较大幅度的下降,此后,随着干湿交替作用次数增加其降低的幅度逐渐减小,干湿交替作用使岩石的延性增强。在围压作用下,砂岩的峰值强度均随着围压的增大而增大,干燥试件强度的围压效应要比多次干湿交替作用后的试件显著。 相似文献
10.
高温作用后花岗岩三轴压缩试验研究 总被引：2，自引：0，他引：2
为综合考察温度、围压对花岗岩力学性质及破坏方式的影响,在高温（25℃～1 000 ℃）作用后,利用MTS815.02电液伺服材料试验系统对花岗岩岩样进行不同围压作用下的三轴压缩试验。研究结果表明,（1）围压一定时,经历不同高温作用后花岗岩三轴压缩全应力-应变曲线经历了压密、弹性、屈服、破坏、塑性流动5个阶段;（2）经历不同高温作用后岩样三轴抗压强度与围压呈非线性二次多项式增长关系,围压为40 MPa时的抗压强度比单轴抗压强度提高了382.30%;常规三轴压缩条件下,400 ℃是花岗岩力学参数的阀值温度;（3）经历高温作用后,岩样弹性模量随围压升高呈增大趋势,围压为40 MPa时的弹性模量比单轴时提高了90.26%;随温度升高呈二次非线性减小,1 000 ℃时的弹性模量比25℃时降低了57.16%;（4）花岗岩的失稳型式同时取决于围压和温度。单轴压缩状态下,随着温度的升高,岩样变形破坏型式由脆性破裂向塑性变形过渡,失稳型式在低温时为突发失稳、中高温为准突发失稳,温度高于800 ℃为渐进破坏;三轴压缩状态下,随着围压的增大,岩样破裂型式由脆性张拉破裂逐渐向剪切破裂过渡,岩样的失稳型式以突发失稳为主。在试验温压范围内,影响花岗岩力学性质的首要因素是温度,其次是围压。 相似文献
11.
This paper presents an elasto‐plastic model for unsaturated compacted soils and experimental results obtained from a series of suction‐controlled triaxial tests on unsaturated compacted clay with different initial densities. The initial density dependency of the compacted soil behaviour is modelled by establishing experimental relationships between the initial density and the corresponding yield stress and thereby between the initial density and the location and slope of normal compression line. The model is generalized to three‐dimensional stress states by assuming that the shapes of the failure surface and the yield surface in the deviatoric plane are given by the extended SMP criterion. A considerable number of the isotropic compression, triaxial compression and extension tests on unsaturated compacted clay with different initial densities were performed using a suction‐controllable triaxial apparatus, to measure the stress–strain–volume change in different stress paths and wetting paths. The model has well‐predicting capabilities to reproduce the mechanical behaviour of specimens compacted under different conditions not only in isotropic compression but also in triaxial compression and triaxial extension. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
12.
为研究片岩的各向异性特征,采用室内三轴压缩试验,获取α=0°、α=45°、α=90° 3种片理倾角试样的应力-应变曲线及强度和变形数据。进一步构建7组片理倾角下的标准圆柱体模型,以室内试验获取的数据为依据,反演材料介质力学参数,利用FLAC3D模拟、探讨了不同片理倾角的片岩破坏模式及抗压强度的片理倾角效应和围压效应。结果表明,三轴压缩条件下,片岩的破坏模式主要分为斜切片理剪切破坏和顺片理剪切滑移破坏,对应的变形破坏的控制结构亦不同。相同围压下,片岩抗压强度随片理倾角呈非对称的"U"字型变化,抗压强度最大值始终位于α=90°,最小值分布在α=45°或α=60°处。围压增大时,对顺片理倾角破坏的片岩强度的增强效应趋于弱化。此外,分析了各向异性岩石抗压强度最大值分布位置的影响因素,发现岩石均匀性程度对各向异性岩石的抗压强度最大值的分布有重要影响,均匀性较差时,最大值位于α=90°;反之,最大值出现于α=0°。 相似文献
13.
Deformation modulus of fly ash is one of the most important mechanical properties generally used in different design problems
and also as an input parameter to sophisticated numerical techniques employed to assess the response of different structures
resting on fly ash fill or embankment made of fly ash. Deformation modulus is usually expressed in terms of compressive strength.
This paper presents the deformation modulus of fly ash modified with lime alone or in combination with gypsum at different
strain levels. The values of deformation modulus obtained from both unconfined compression test and unconsolidated undrained
triaxial test results are presented herein. The specimens for unconfined compression test and for undrained triaxial tests
were cured up to 90 and 28 days, respectively. The effects of addition of lime (4–10%) and gypsum (0.5 and 1.0%) on the deformation
modulus of class F fly ash are highlighted. With addition of lime and gypsum, the class F fly ash achieved the deformation
modulus in the range of 190 MPa in UCS test and up to 300 MPa in triaxial test specimens tested under all round pressure of
0.4 MPa. Based on the present test results empirical relationships are developed to estimate deformation modulus of modified
fly ash from unconfined compressive strength and relationships between initial tangent modulus and secant modulus at different
strain levels are also developed. 相似文献
14.
This paper aims to assess the characteristics of the deformation and strength behavior of frozen soils at different temperatures under monotonic and cyclic triaxial conditions. The deformation and failure patterns of the specimens change from ductility to brittleness with decreasing temperatures under both monotonic and cyclic loadings. The development of axial strain and stiffness with increasing number of cycles for the soils under cyclic loading is presented and analyzed in detail. A collapse behavior in strength and stiffness is observed in tests of frozen soils at ??5 °C, ??7 °C and ??9 °C. The difference in frictional sliding between the samples with high ductility and those with high brittleness is attributed to the different patterns of deformation and failure. The dynamic modulus is plotted versus axial strain, and the state where the stiffness begins to decrease is employed as the criterion of cyclic failure. The proposed criterion of cyclic failure is verified to be more suitable for frozen soils with high brittleness and seems to be consistent with the peak strength under monotonic loading. Finally, the cyclic stress ratios are plotted against the number of cycles up to this failure criterion, and the effect of temperatures on cyclic strength is evaluated.
相似文献15.
Constitutive models for unsaturated soils are most commonly based on conventional critical state type models for saturated soils. The ellipse of the modified Cam-clay model is usually adopted for the formulation of the yield and the plastic potential surfaces in the mean stress – deviatoric stress plane. Despite the wide use of this ellipse it has long been shown that the peak deviatoric stress observed for highly overconsolidated states may be largely overestimated. For fully saturated conditions, a planar surface, termed the Hvorslev surface, has been employed in the literature in order to overcome this shortcoming on the dry side of the critical state. In addition, by employing a no-tension cut-off, stress states are restricted within the compressive region. In unsaturated conditions and due to the effect of suction the soil may be subjected to tensile total stresses which should not, however, exceed a model dependent limit. Nonetheless, adopting a planar surface and in the absence of any provision, illegal tensile stresses may be obtainable. For this reason, a new expression for the Hvorslev surface, which restricts the stress state within acceptable boundaries, is proposed, based on a small number of model parameters. The new surface is curved rather than planar and can also be used in combination with critical state type constitutive models developed for saturated conditions. The new surface is calibrated based on fully saturated undrained triaxial compression and extension tests and on unsaturated drained triaxial tests. The superiority of the new surface in comparison with commonly adopted shapes for the yield and the plastic potential functions – such as the ellipse and the bullet shape of the modified and the original Cam clay models – is demonstrated through numerical analyses of the unsaturated drained triaxial laboratory tests. 相似文献
16.
为了探究川藏交通廊道沿线典型岩石冻融循环条件下的劣化规律,选取昌都-林芝段的花岗岩、片麻岩和砂岩为试验对象,开展冻融循环条件下岩石加卸荷试验,结果表明:（1）随着冻融循环次数的增加,岩石抗压强度损失率达30%,粘聚力降幅达18.4%,内摩擦角降幅达10.5%,弹性模量逐渐下降,泊松比逐渐增加;（2）三轴压缩试验中,岩样的变形模量呈现与抗压强度类似的劣化趋势,但是变形模量的劣化幅度比抗压强度劣化幅度大;冻融循环作用下岩石抗压强度越大劣化程度越低,对砂岩的劣化最明显,片麻岩次之,花岗岩最小;（3）与三轴压缩试验相比,在卸围压试验中,冻融循环作用对岩石的卸荷量同样有劣化作用,卸荷程度较小时岩石劣化并不明显,随着卸荷量的逐渐增加,卸荷量大于80%时,岩石的变形模量呈指数型下降,泊松比呈指数型增加;（4）随着冻融循环次数的增加,三轴压缩试验中由拉张和剪切破坏造成的裂纹数量增多;卸围压试验中岩石以拉张破坏为主;岩石微裂纹数量增加的同时,不平整度增加,矿物颗粒之间的胶结状态变差;（5）综合试验结果分析,冻融作用对岩石劣化作用最强的为砂岩,其次是片麻岩,最弱为花岗岩. 相似文献
17.
Y. L. Chen J. Ni W. Shao Y. C. Zhou A. Javadi R. Azzam 《Rock Mechanics and Rock Engineering》2012,45(2):241-249
In this paper, white Portland cement was used as an experimental material. Prismatic specimens with pre-existing flaws at
different angles of inclination (α) varying through 0°, 30°, 45°, 60°, 75° to 90° and cylindrical specimens with different numbers of pre-existing flaws (n) varying through 0, 1, 2 to 3 were tested under uni-axial compression tests. Crack initiation, propagation, coalescence,
and failure were observed. The corresponding analytical expression for the stress intensity factor under uni-axial compression
was derived, the coefficient of friction and the stress intensity factor of the specimens on the surfaces of the crack were
analysed, and the corrective coefficient for the stress intensity factor was introduced. Fatigue tests with a loading frequency
of f = 100 Hz were carried out on cylindrical specimens with constant amplitude of the cyclic load which is a proportion of the
compressive load at failure (F
f) obtained from the uni-axial compression tests. The fatigue property of the specimens was analysed and the relationship (S
max − lg N
f) between the maximum stress and the number of loading cycles at failure for specimens with pre-existing flaws was proposed.
The effect of pre-existing flaws on the fatigue life (N
f) and dynamic load (S
D) which can be applied was investigated. 相似文献
18.
The interparticle bonding effect due to water menisci plays an important role in the hydromechanical coupling properties of unsaturated soils. This paper presents an unsaturated hydromechanical coupling model that considers the influence of matric suction, degree of saturation, and microscopic pore structure on the interparticle bonding effect. The enhanced effective stress and bonding variable are selected as constitutive variables. The bonding variable is correlated with the ratio between unsaturated void ratio and saturated void ratio. The deformation characteristics of unsaturated soils are described based on the bounding surface plasticity theory. A soil–water characteristic model that considers deformation and hydraulic hysteresis is integrated into the constitutive model to achieve hydromechanical coupling. The proposed model can effectively describe the hydromechanical coupling characteristics and the meniscus bonding force of unsaturated bimodal structure soils; the model parameters can be easily obtained through routine experiments. The experimental results of unsaturated isotropic compression, the wetting/drying cycle, and unsaturated triaxial shear tests are used to validate the capability of the proposed model.
相似文献19.
Rock Mechanical Characterization of an Argillaceous Host Rock of a Potential Radioactive Waste Repository 总被引：2，自引：0，他引：2
Summary The physical properties of foliated marls and shales from the Swiss Central Alps were investigated in the laboratory as part
of the site characterization of a potential low and intermediate level radioactive waste repository. The rocks were first
characterized by density, porosity and water content, then P-wave velocity measurements and uniaxial compression tests were
conducted on samples oriented parallel, perpendicular and ∼45° inclined to the foliation. Correlations between P-wave velocities,
Young's moduli, and uniaxial strengths and directional dependence of compressibility and permeability (determined at elevated
hydrostatic pressures) revealed that two distinct families of microcracks cause the significant anisotropy. The pressure and
time dependence of strength was then measured in triaxial compression, creep, and relaxation tests. In triaxial compression
at room temperature, confining pressures up to 90 MPa and strain-rates as low as 10−8 s−1 failure occured after small inelastic strains. Failure strength exhibits a strong pressure and a weak strain-rate dependence.
The low friction coefficient of clay minerals appears to dominate the bulk frictional properties. Micromechanical modeling
of triaxial compression, creep, and relaxation tests suggests that inelastic deformation is accommodated by subcritical crack
growth. 相似文献
20.
杭州湾浅层储气砂土应力路径试验研究 总被引：2，自引：0，他引：2
利用GDS非饱和三轴试验系统开展了杭州湾储气砂土主动压缩、被动压缩、主动伸长与被动伸长等4种应力路径试验研究,以论证应力路径对非饱和砂土的变形性状与强度特性影响。结果表明,在卸荷应力路径被动压缩与被动伸长下非饱和砂土的应力-应变曲线呈明显的应变软化性状,而加荷应力路径主动压缩与主动伸长则分别表现为轻度应变软化及显著应变硬化变形特征;非饱和砂土的强度参数在卸荷与加荷应力路径中也存在差异,前者的有效凝聚力高于后者,而内摩擦角则相反;但其表观凝聚力与基质吸力关系在不同应力路径下均可用乘幂函数 有效描述,而试验参数a、b值不同,公式 可合理地用于表述非饱和砂土的强度特性。 相似文献