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《Engineering Geology》2002,63(1-2):83-91
This study deals with a weathering problem of historic arch stone bridges built of welded tuff about 150 years ago in Kagoshima, Japan. Based on a detailed comprehensive weathering evaluation we previously carried out, the way in which the weathering affects the structural stability of the bridges is quantitatively evaluated herein by using a distinct element method (DEM).The suitability of this method of analysis was confirmed through a comparison of the numerical analysis results with the in situ load testing data. The analysis results show that when considering the stability of a stone bridge, the slide safety factor and eccentric safety factor are more important than the compressive safety factor. That is, the types of possible failure include sliding and openings between arch blocks. In 150 years of weathering, the shear stress in the arch ring generally increased about 20%. The eccentric safety factor decreased about 9%, from 4.35 to 3.97, and the slide safety factor decreased about 20%, from 8.02 to 6.46. Deflections at the arch crown increased about two times, from 0.60 to 1.28 mm. Despite these changes, the stone bridges are considered to be still in a good condition after 150 years of weathering. 相似文献
3.
Pooyan Asadollahi Marco C. A. Invernizzi Simone Addotto Fulvio Tonon 《Rock Mechanics and Rock Engineering》2010,43(5):597-613
Among the constitutive models for rock fractures developed over the years, Barton’s empirical model has been widely used.
Although Barton’s failure criterion predicts peak shear strength of rock fractures with acceptable precision, it has some
limitations in estimating the peak shear displacement, post-peak shear strength, dilation, and surface degradation. The first
author modified Barton’s original model in order to address these limitations. In this study, the modified Barton’s model
(the peak shear displacement, the shear stress–displacement curve, and the dilation displacement) is validated by conducting
a series of direct shear tests. 相似文献
4.
This paper covers the blast-resistant analysis for a tunnel passing beneath Taipei Shongsan airport. It briefly discusses
the overall analysis process to obtain the maximum lining thrust caused by a bomb explosion for use in the structural lining
design. Because there have not been any established common standards or practices governing the design of such a structure,
a series of parametric studies have been carried out in order to evaluate the significance and sensitivity of several parameters
on the lining thrust. The parameters evaluated are: intensity of blast loading, size of crater, dynamic undrained shear strength,
dynamic Young’s modulus, and soil-damping ratio. It was concluded that a designer should adopt dynamic soil parameters, obtained
from good ground investigation and soil testing, as favorable dynamic soil properties can result in a more economical analysis.
For parameters (e.g. bomb type) that are beyond the control of the designer, an additional protective layer over the tunnel
structure may be considered in order to minimize the impact of the explosion, instead of designing a more costly rigid structure. 相似文献
5.
A constitutive model for sands in monotonic shear is presented. The model is designed to simulate the behavior of sands in
the whole stress and strain range of engineering interest with enough accuracy for practical usage. Material parameters were
chosen to be state independent and easy to calibrate using conventional testing procedures. The formulation is based on effective
stresses, pressure-dependent hyperelasticity, non-associative elastoplasticity, an isotropic hardening law and Rowe’s stress-dilatancy
theory. The implementation of Rowe’s stress-dilatancy theory within the framework of elastoplasticity theory is discussed.
It is found that Rowe’s theory produces a volumetric plastic strain rate function that has a discontinuity in its first derivative
w.r.t. stress, and a smoothed form is proposed instead. Finally, some experimental tests are simulated and the results are
briefly discussed. 相似文献
6.
The stability of a simple coupled ocean-atmosphere system similar to the one studied by Hirst with general ocean thermodynamics
is investigated in which the atmospheric heating is determined by sea surface temperature anomalies as well as the convergence
feedback (low level moisture convergence by the waves themselves). It is shown that the unstable coupled mode found by Hirst
(UH mode) is profoundly modified by the convergence feedback. The feedback increases the unstable range of the UH mode and
can increase its growth rate several folds. The maximally growing UH mode can become westward propagating for certain strength
of convergence feedback. If the convergence feedback strength exceeds a critical value, several new unstable intraseasonal
modes are also introduced. These modes are basically ‘advective’ modes. For relatively weak strengths of the convergence feedback
the growth rates of these modes are smaller than that of the UH mode. As the atmosphere approaches ‘moist neutral’ state,
the growth rates of these modes could become comparable or even larger than that of the UH mode. It is argued that these results
explain why the El Nino and Southern Oscillation (ENSO) signal is clear in the eastern Pacific but not so in the western Pacific
and they may also explain some of the differences between individual ENSO events. Our results also explain the aperiodic behaviour
of some coupled numerical models. Importance of this process in explaining the observed aperiodicity of the ENSO phenomenon
is indicated. 相似文献
7.
Landfill site selection by decision-making tools based on fuzzy multi-attribute decision-making method 总被引：2，自引：2，他引：0
Abdolhadi Nazari Mohammad Mehdi Salarirad Abbas Aghajani Bazzazi 《Environmental Earth Sciences》2012,65(6):1631-1642
Landfill site selection is a complex and time-consuming process, which requires evaluation of several factors where many different
attributes are taken into account. Decision makers always have some difficulties in making the right decision in the multiple
attribute environments. After identifying candidate sites, these sites should be ranked using decision-making methods. This
study applies Chang’s fuzzy AHP-based multiple attribute decision-making (MADM) method for selection of the best site of landfills
based on a set of decision criteria. The Fuzzy Analytic Hierarchy Process (FAHP) was designed to make pairwise comparisons
of selected criteria by domain experts for assigning weights to the decision criteria. Analytic Hierarchy Process (AHP) is
used to make pairwise comparisons and assign weights to the decision criteria. It is easier for a decision maker to describe
a value for an alternative by using linguistic terms and fuzzy numbers. In the fuzzy-based AHP method, the rating of each
alternative was described using the expression of triangular fuzzy membership functions. Once the global weights of the criteria
is calculated by AHP, they are incorporated into the decision matrices composed by decision maker and passed to fuzzy-AHP
method which is used to determine preference order of siting alternatives. In this study, a computer program based on the
Chang’s fuzzy method was also developed in MATLAB environment for ranking and selecting the landfill site. As an example of
the proposed methodology, four different hypothetical areas were chosen and implemented to demonstrate the effectiveness of
the program. By using this program, the precision was improved in comparison with traditional methods and computational time
required for ranking and selecting the suitable landfill site was significantly reduced. 相似文献
8.
This paper presents a shear load transfer function and an analytical method for estimating the load transfer characteristics
of rock-socketed drilled shafts subjected to axial loads. A shear load transfer (f–w) function of rock-socketed drilled shafts is proposed based on the constant normal stiffness (CNS) direct shear tests. It
is presented in terms of the borehole roughness and the geological strength index (GSI) so that the structural discontinuities
and the surface conditions of the rock mass can be considered. An analytical method that takes into account the coupled soil
resistance effects is proposed using a modified Mindlin’s point load solution. Through comparisons with load test results,
the proposed methodology is in good agreement with the general trend observed in in situ measurements and represents an improvement
in the prediction of the shear behavior of rock-socketed drilled shafts. 相似文献
9.
非贯通节理岩体直剪试验研究进展 总被引：1，自引：0，他引：1
基于典型的直剪试验,国内外学者提出了非贯通节理岩体贯通破坏机理,并建立了相应的强度准则,如Jennings方法,即加权平均强度理论和强度准则、Lajtai岩桥破坏理论和强度准则、断裂力学的II型破坏理论和强度准则,拉剪复合破坏和强度准则。然而,非贯通节理岩体破坏机理目前还没有完全弄清楚,已建立的强度准则所包含的重要参数还需深入研究,如：如节理面的传压系数、传剪系数、弱化了的岩桥内摩擦力和内摩擦角等;非贯通节理岩体节理闭合和剪切的本构关系有待建立;不共面非贯通节理岩体全过程最大抗剪强度需进一步研究。伺服直剪试验机、静态应变测试仪、声发射仪、X射线测量等无损检测技术能够为进一步研究非贯通节理岩体的破坏机理,提出新的理论和建立新的强度准则提供强有力的技术支持。 相似文献
10.
To measure the shear strength and deformability of a sedimentary soft rock, a small down-hole in-situ triaxial testing method
is developed. The apparatus consists of a triaxial cell and an axial loading device which enables testing at any depth. In
this method, a columnar specimen of diameter 90 mm and 285 mm height can be sheared at the bottom of a drill hole. A series
of tests were conducted at a 50 m deep experimental cavern. The test gallery is contained in mudstone with some inter-bedded
thin sand layers. The tests were done in three different depths in a borehole by a multiple-step loading method. The new testing
method was successful to measure stress–strain relation of rock mass. The test results demonstrated that the multiple-step
loading method is acceptable in mudstone formation, if an appropriate criterion for load reversal is selected to recognize
the instant of failure by stress–strain relation during loading. In addition, different results for mechanical properties
of mudstone rock mass were observed in the specimens contained sand layers. It is also concluded that, the same loading method
is not successful if a sand layer is located in the middle of the specimen due to large damage induced in early stages of
loading. 相似文献
11.
Temporal distribution of southwest monsoon (June –September) rainfall is very useful for the country’s agriculture and food
grain production. It contributes more than 75% of India’s annual rainfall. In view of this, an attempt has been made here
to understand the performance of the monthly rainfall for June, July, August and September when the seasonal rainfall is reported
as excess, deficient or normal. To know the dependence of seasonal rainfall on monthly rainfall, the probabilities of occurrence
of excess, deficient and normal monsoon when June, July, August and also June + July and August + September rainfall is reported
to be excess or deficient, are worked out using the long homogenous series of 124 years (1871-–1994) data of monthly and seasonal
rainfall of 29 meteorological sub-divisions of the plain regions of India.
In excess monsoon years, the average percentage contribution of each monsoon month to the long term mean (1871–1994) seasonal
rainfall (June –September) is more than that of the normal while in the deficient years it is less than normal. This is noticed
in all 29 meteorological sub-divisions. From the probability analysis, it is seen that there is a rare possibility of occurrence
of seasonal rainfall to be excess/deficient when the monthly rainfall of any month is deficient/excess. 相似文献
12.
Effects of Rock Properties on Specific Cutting Energy in Linear Cutting of Sandstones by Picks 总被引：4，自引：2，他引：4
Summary. Specific cutting energy (SE) has been widely used to assess the rock cuttability for mechanical excavation purposes. Some
prediction models were developed for SE through correlating rock properties with SE values. However, some of the textural
and compositional rock parameters i.e. texture coefficient and feldspar, mafic, and felsic mineral contents were not considered.
The present study is to investigate the effects of previously ignored rock parameters along with engineering rock properties
on SE. Mineralogical and petrographic analyses, rock mechanics, and linear rock cutting tests were performed on sandstone
samples taken from sites around Ankara, Turkey. Relationships between SE and rock properties were evaluated using bivariate
correlation and linear regression analyses.
The tests and subsequent analyses revealed that the texture coefficient and feldspar content of sandstones affected rock cuttability,
evidenced by significant correlations between these parameters and SE at a 90% confidence level. Felsic and mafic mineral
contents of sandstones did not exhibit any statistically significant correlation against SE. Cementation coefficient, effective
porosity, and pore volume had good correlations against SE. Poisson’s ratio, Brazilian tensile strength, Shore scleroscope
hardness, Schmidt hammer hardness, dry density, and point load strength index showed very strong linear correlations against
SE at confidence levels of 95% and above, all of which were also found suitable to be used in predicting SE individually,
depending on the results of regression analysis, ANOVA, Student’s t-tests, and R2 values. Poisson’s ratio exhibited the highest correlation with SE and seemed to be the most reliable SE prediction tool in
sandstones. 相似文献
13.
Auckpath Sawangsuriya Meissa Fall Dante Fratta 《Geotechnical and Geological Engineering》2008,26(5):567-578
A rapid, low-cost evaluation methodology using the wave-based techniques is proposed in this study in order to determine the
design parameters e.g., elastic modulus and Poisson’s ratio of the laboratory compacted lateritic soils. Knowing the elastic
wave velocities as measured with the wave propagation technique (i.e., a small-strain non-destructive test) and total mass
density of the specimens, the elastic moduli and Poisson’s ratio of the soil specimens can be determined. In addition, the
unconfined compression test (i.e., a large-strain destructive test) is also performed on the same specimens under the same
unconfined testing condition in order to compare the moduli corresponding to different strain levels. The experimental results
showed the potentials and limitations of using impulse signal for the determination of the elastic moduli and Poisson’s ratio
for laboratory compacted soil specimens from elastic wave propagation techniques. 相似文献
14.
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
15.
The current state of art for limit equilibrium analysis of slope stability problems lacks a satisfactory procedure for stability evaluation under general, rapid (undrained) loading conditions. Some procedures are available for the analysis of rapid drawdown, but these suffer from several shortcomings and, furthermore, are not applicable to other types of rapid loading. An approach is presented which overcomes these limitations. The approach integrates four components-establishment of soil behaviour on the basis of laboratory testing, estimation of steady-state conditions in the slope using a boundary value analysis, estimation of distribution of undrained strength in the slope using undrained stress paths, and identification of the critical slip surface followed by calculation of its factor of safety. The approach is illustrated through its application to the stability analysis of an earth dam under rapid drawdown and earthquake conditions. 相似文献
16.
The paper pertains to the analysis of piles embedded in liquefiable soils to predict its’ critical buckling load under partial
to full loss of lateral support over a portion of the pile length. The analysis is based on extension of Mindlin solution
for a point load acting inside a semi infinite elastic half space. Degenerated solutions obtained by using the developed method
compares very well with reported results. Parametric studies showed that the depth of liquefiable soil, degradation of soil
strength on liquefaction, slenderness ratio, pile stiffness factor and end conditions have significant influence on the buckling
behavior of the piles. 相似文献
17.
天津市近几年来新建了多座具有独特风格和景观效果的新型桥梁,本文主要介绍其中的三座斜拉桥、三座拱桥、一座自锚式悬索桥和一座集交通、观光、游览为一体的巨型摩天轮桥梁,以及三座经装修改建、使旧桥换新颜的实例。 相似文献
18.
Elastic modulus and Poisson’s ratio of soils are two important parameters required for safe design of various civil engineering
structures. The elastic modulus and shear modulus of the soils are generally obtained from the resonant column, torsional
shear tests and geophysical methods. Though, from these parameters the Poisson’s ratio can be determined, these tests are
quite elaborate, cumbersome, time consuming and require skilled manpower particularly for data interpretation. Moreover, direct
determination of the Poisson’s ratio by employing micro-strain gauges, which measure axial and lateral strains using Wheatstone
bridge circuits, is difficult for soils due to the problems associated with their fixing on the surface of the sample. Under
these circumstances, application of piezoceramic elements, which can generate shear and compression waves, seems to be an
excellent alternative. Using these wave velocities, the Poisson’s ratio can be computed easily and precisely. However, how
this (computed) value of the Poisson’s ratio compares vis-à-vis that obtained from the conventional triaxial tests (i.e.,
strain controlled uniaxial compression tests), which yield stress–strain relationship, needs to be established. With this
in view, investigations were conducted on soils of different types (clays and sands) in their disturbed and undisturbed forms
by resorting to piezoceramic tests and the triaxial tests. Details of the methodology are presented in this paper and it has
been demonstrated that application of piezoceramic elements yields the Poisson’s ratio and the elastic modulus of the soils
quite easily, particularly for the soft clays and sands. 相似文献
19.
In this paper, an approach is presented to analyze the stability risk of rock slopes based on a new rating system. Three factors are used to estimate the risk level of rock slopes: (1) failure probability, (2) element at risk rating, and (3) vulnerability rating. Element at risk and vulnerability ratings are both given a range from 0 to 10, and the probability of failure is varied between 0 and 1, so the risk rating ranges between 0 and 100. This risk rating can be used to determine both the quantitative and qualitative risk levels of slopes at the same time. The method is tested on the western sector of the slopes facing Songun copper plant phase III, Iran, to clarify its procedures and assess its validity. Deterministic kinematic analyses showed that the slope has a potential for circular failure. Risk assessments revealed that the risk levels of the slope in both static and pseudo-static conditions are “very low” and “high,” respectively.
相似文献20.
块体化程度是评价岩体完整性的一种新指标,能从三维角度表征岩体破碎程度,但目前该方法仍存在未充分考虑岩体切割程度及块体规模、未限定基础应用条件、块体化程度等级划分不合理等缺陷。针对上述缺陷,深入分析了其产生原因,并借鉴岩体切割程度、三维块度模数、体积RQD等计算原理,限定了块体体积百分比相关概念,提出了考虑岩体完整性块度尺寸效应的块体体积综合百分比计算方法,确立了块体化程度等级及分级指标取值依据,建立了修正的块体化程度评价方法。通过对比块体化程度评价修正方法、岩土工程规范对岩体完整性的划分结果,分析了修正方法的合理性。分别以广西铜坑矿锌多金属矿体、乌东德水电工程的块体研究数据为基础,开展了修正块体化程度评价方法的实例验证,结果表明：利用修正块体化程度评价方法计算的铜坑矿+255 m中段4#试验区岩体块体体积百分比为11.18%,属轻度块状化岩体;乌东德水电站PD49-1平硐、PD4支硐块体体积百分比分别为12.847%、10.168%,均属于轻度块状化岩体,岩体完整性程度为较完整级别。与现有块体化程度评价方法比较,修正方法计算的块体体积百分比能够更准确地从三维角度表征真实岩体的完整性。研究成果对精确刻画岩体三维完整性具有重要意义。 相似文献