Rock and Soil Mechanics
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Rock and Soil Mechanics
2012, Vol.33 Num.5
Online: 2012-05-10
Fundamental Theroy and Experimental Research
Numerical Analysis
Geotechnical Engineering
 
Fundamental Theroy and Experimental Research
1281 DU Xiu-li, HOU Shi-wei, LU De-chun, CHENG Xing-lei
Shear band analysis of sand based on digital image processing technique
End friction effect and initial defect of sample both can cause inhomogeneous deformation, then form macroscopic shear band in soil test. The triaxial equipment of GDS is improved based on digital image processing technique, and used to do drained test of sand. The strain nephogram and local stress-strain complete curve at each sampling time point are recorded; then end friction effect is researched. The result shows that the end friction has significant effect on mechanical properties of sand sample. The radial strain error reaches 10%. The macroscopic inhomogeneous sample is got by putting silt clay block into sand sample; and the formation process of shear band is tested. The evolution of shear band during the loading process shows that the discontinuation of stiffness formed at interface of two materials; with inhomogeneous deformation developing, the macroscopic shear band is fully formed, so as to fracture.
2012 Vol. 33 (5): 1281-1285 [Abstract] ( 43 ) [HTML KB] [PDF 1357KB] ( 32 )
1286 ZENG Ling-ling , HONG Zhen-shun , CHEN Fu-quan
A law of change in permeability coefficient during compression of remolded clays
The difficulty in measuring the permeability of clays with enough accuracy enhances the importance of quantitatively predicting the permeability with simple physical parameters. This study collects 23 groups of data of permeability of remolded clays considering the effect of oedometer consolidation pressure. The investigated clays cover a wide range of liquid limits, varying from 40% to 300%. Based on the data of permeability, it is found that the logarithm of permeability coefficient changes with the void ratio in the exponential form, other than in the linear relationship, especially when the volumetric strain reaches the level of 20%. The controlling factors of the permeability coefficient of clays are analysed by multiple regression analysis. A simple method is also proposed for predicting the permeability coefficient, which can be applied to remolded clays with wide ranges of liquid limit and void ratio.
2012 Vol. 33 (5): 1286-1292 [Abstract] ( 37 ) [HTML KB] [PDF 485KB] ( 33 )
1293 JIANG Ming-jing , XIAO Yu , SUN Yu-gang , WU Xiao-feng
Experimental investigation on micromechanical model of cement-bonded particles
Bond between particles has become one of the key factors in establishing the constitutive model of natural sands. In this paper, the bonded granulates are idealized by two aluminum rods glued together by cement with cement water ratio 0.34, and the micromechanical responses of the bonded rods are investigated by performing a series of loading tests, such as tension tests, compression tests, shear tests, rotation tests and complex stress path tests. Then the comparison between the present results and the experimental data acquired on the epoxy resin adhesive by Jiang et al., is carried out to analyze the effect of bonding materials. The results show that the mechanical behaviors of cement and epoxy resin bonded rods both satisfy the same micro-contact laws proposed by Jiang et al. in spite of some distinct differences between the two kinds of bond materials. The tension and compression strengths of cement are lower while the ductility is better than those of epoxy resin. Both cement and epoxy resin bonded rods present plastic-softening property in compression tests. In the shear and torsion tests, shearing force and torque initially increase with the normal force until a critical normal force is reached, and then gradually decrease. The strength envelope in the normal-torsion-shear space is a rugby and water-drop shell for the cement and epoxy resin adhesive, respectively.
2012 Vol. 33 (5): 1293-1300 [Abstract] ( 32 ) [HTML KB] [PDF 5064KB] ( 24 )
1300 LI Long-qi, LUO Shu-xue
A simulation test study of vertical bearing capacity of inclined pile foundation in inhomogeneous strata
Inclined pile foundation has been more widely used in the ports, docks and bridge engineering for its superior resistive capability of lateral load. With the construction of highways and other infrastructure in mountains and uneven ground areas, the bridge pile foundation will be more and more adopted in the landslide and similar area. Due to the complex stress state of the inclined pile foundation, its current design theory still refers to the theory of vertical pile foundation and is designed according to the practical experience. Although a lot of exploratory researches have been done, practical calculations theory and design criteria have not yet been formed. Based on that, this paper has conducted physical model test combined with some bridge foundation selection research project in Xiamen-Shenzhen Passenger Dedicated Railway Line. The vertical bearing capacity of pile foundation with inclination of 0°-12 ° has been researched. The results show that load-settlement curve of the vertical pile foundation is slow variant, while that of the inclined pile foundation is steep variant. There is a reasonable pile angle of 8° more or less to exert the vertical bearing capacity of inclined pile foundation. In vertical pile foundation, the largest axial force lies in the corner pile, next in the side pile, then in the middle pile. While in the inclined pile foundation, the largest axial force lies in the middle pile, next in the corner pile, then in the side pile respectively. The pile moment distribution of inclined pile foundation is associated with its pile angle, and the pile moment presents a reverse bending section when the angle reaches 12°. The pile angle difference is the main reason of significantly in different axial bearing properties between inclined pile foundation and vertical pile foundation.
2012 Vol. 33 (5): 1300-1305 [Abstract] ( 23 ) [HTML KB] [PDF 623KB] ( 18 )
1306 DONG Zhi-liang, ZHOU Qi, ZHANG Gong-xin, QIU Qing-chang, LUO Yan, LI Yan
Field comparison test of reinforcement technology of shallow ultra-soft soil in Tianjin Binhai New Area
Some problems of reinforcement of shallow ultra-soft soil in Tianjin Binhai New Area are analysed. Three reinforcement schemes of shallow ultra-soft soil are proposed, including conventional scheme, single-row to single-tube scheme and small spacing scheme. Relying on a project in Tianjin Binhai New Area, field comparison test is carried out. A comparative analysis of the reinforcement effect of three schemes is done with monitoring test results and some further recommendations for reinforcement are provided. Engineering practice shows that, a hard crust with a certain strength and thickness forms after treated by three reinforcement schemes and the physico-mechanical properties of soil are significantly improved, which fully meet the construction requirements of hydraulic fill sand cushion and prefabricated vertical drains. In addition, the reinforcement effects of single-row to single-tube scheme and small spacing scheme are significantly better than that of conventional reinforcement scheme. The first two schemes are beneficial to the formation of hard crust thickness, which are preferable from the point of view of long-term perspective.
2012 Vol. 33 (5): 1306-1312 [Abstract] ( 30 ) [HTML KB] [PDF 1134KB] ( 14 )
1313 LIANG Yan , XING Xian-li , LI Tong-lu , XU Ping , LIU Shu-lin
Study of the anisotropic permeability and mechanism of Q3 loess
The permeability of unsaturated loess is an important part of its properties. The research on loess permeability in different directions is particularly important to determine the range of loess collapse and the study of loess landslides caused by the infiltration of water in the loess. So, the anisotropic permeability and mechanism of Q3 loess are studied. The test samples are the undisturbed Q3 loess with obvious anisotropy from a building site in Xi’an city. The matrix suctions at different volumetric water contents and in different directions are measured with tensiometer. The saturated hydraulic conductivity is measured by falling head permeability test. The results show, while tensiometer is inserted vertically and paralleling with soil layer into samples, that the suctions are very close as the volumetric water content is between 0.23 and 0.41; and the saturated hydraulic conductivity in vertical direction is 4.02 times as that in horizontal direction. Further, the correlation function between the hydraulic conductivity and suction for unsaturated loess in vertical and horizontal directions is obtained by the soil-water characteristic curve based on the measured suctions. It can be obtained that the hydraulic conductivity reduces/increases with the matrix suction increases/reduces in both directions of the loess. The hydraulic conductivity in vertical is generally higher than that in horizontal. The difference of hydraulic conductivity between vertical and horizontal directions reduces with the matrix suction increases when matrix suction is less than 57 kPa. Structure observation shows that the anisotropy of loess structure has a significant effect on the anisotropic permeability.
2012 Vol. 33 (5): 1313-1318 [Abstract] ( 22 ) [HTML KB] [PDF 1330KB] ( 23 )
1319 WANG Yao , WU Sheng-xing , SHEN De-jian , ZHOU Ji-kai
Experimental study of dynamic axial tensile mechanical properties of mortar-granite interface
The mechanical behavior of mortar-aggregate interface transition zone is critical to the macro mechanical properties of concrete. A series of dynamic axial tensile tests on 40 mortar-granite interfaces specimens are carried out on MTS. Effects of different strain rates (10-6～10-2 s-1), different initial static loads (30%、50%、70%) and the cyclic load (frequency of 1、5 Hz) on the dynamic axial tensile mechanical properties are analyzed . The fracture mechanism is explored based on the experiment results. The results indicate that: ① the dynamic tensile strength of the interface is increased obviously with the increasing of the strain rate; ② the initial static load about less than 50 percent of the strength will not influence the dynamic tensile strength but maybe beneficial for it; more initial static load will be harmful to the dynamic strength because of the damage effect; ③ the fatigue damage by cyclic variable amplitude load leads to the descending of strength because of the cumulative damage. Residual strain decreases with the increasing of cycle frequency; ④ the ascending branch of the stress-strain curve before 50% tensile strength can be looked as straight line and then it goes into nonlinear stage which will trend toward linear with the increasing of strain rate. In addition, the complete stress-strain curve of interface is achieved on the condition of stable fracture.
2012 Vol. 33 (5): 1319-1326 [Abstract] ( 19 ) [HTML KB] [PDF 1194KB] ( 15 )
1327 NIE Yu-dong , ZHOU Ru-xia
Static loading comparative test for pile foundation of Fujin-Suibin Songhua River Bridge
The bored piles 2.0 m in diameter is adopted in the foundation under Fujin-Suibin Songhua River Bridge. The in-situ static loading tests using conventional testing method and self-balanced method have been carried out on the test piles which are 45 m long and 70 m long for the latter one with upper shaft upon the load cell. By comparing the data of the testing piles from such two methods, the load-pile head settlement relationship and the vertical load-transfer behavior have been studied as well as the shaft friction resistance. It is indicated that, in the limit state, the displacement difference between the two is 14.97 mm; the side resistances difference is 7.30%; the side frictions of the two test pile meet the requirements. In the pile-soil system before destruction, under the same load conditions, the difference between the displacements gradually becomes larger. The pile skin friction in the same soil layer is consistent each other.
2012 Vol. 33 (5): 1327-1332 [Abstract] ( 21 ) [HTML KB] [PDF 485KB] ( 15 )
1333 MO Zhen-ze , LI Hai-bo , ZHOU Qing-chun , ZOU Fei ,
Experimental study of rock microscopic deterioration under wedge cutter
Penetrating granite specimens with different wedge cutters by changed RMT-150C system which is specially produced for indentation, and using DISP acoustic emission location system to research rock damage and physical deterioration. Acoustic emission test is an effective method to study the microscopic mechanism of rock fragmentation by tunnel boring machine (TBM) cutters. Testing results show that: rock breaking is the macro-phenomenon of internal microcrack’s initiation and development. There is a realistic corresponding trend of load value and AE signals when wedge cutters penetrate specimens at a uniform velocity. Load-penetration curve could demonstrate the process of specimen damage. Acoustic emission plane location results show that: there is a damage core under the dense broken core, which is clustered by micro-seismic locations and is seriously deteriorated. Damage core plays a significant role to produce the next dense broken core. Experimental results provide an explanation for the macro- phenomenon of rock breaking under TBM cutter. Blunt cutter’s indentation produces a damage core of spherical shape while sharp cutter’s water-drop shape. Blunt cutters are better than sharp cutters to break rock specimens because of deeper penetration and wider width of damage core.
2012 Vol. 33 (5): 1333-1340 [Abstract] ( 26 ) [HTML KB] [PDF 888KB] ( 18 )
1341 ZHANG Dan , CHEN An-qiang , LIU Gang-cai
Disintegration characteristics of purple mudstone based on fractal dimension under hydrothermal condition
This study focuses on the disintegration characteristics of sampled mudstone from the Matoushan group (K2m), the Tuodian group (J3t) and the Lufeng group (J1l), Yunnan province of Southern China. These sampled rocks are subjected to the treatments of wetting-drying (WD), wetting-drying + refrigerating-heating (WDRH) and refrigerating-heating (RH) under laboratory condition, respectively. The fractal dimension method is applied to analyze the disintegration characteristics of the sampled mudstone. The results show that the fractal dimension exactly described the disintegration characteristics of purple mudstone. The larger fractal dimension value is, the higher the degree of rock fragmentation is. The rank order of the fractal dimension of the three treatments is WDRH WD RH, and is significantly different between the treatments, indicating the effect of hydrothermal on mudstone is greater than the influence of just water or heat. The rank order of the fractal dimension of three purple mudstones is J3t J1l K2ms, and significantly different between the J3t, J1l and K2m under WD and WDRH, resulting from physical characteristics, chemical elements composition and weathering maturity.
2012 Vol. 33 (5): 1341-1346 [Abstract] ( 16 ) [HTML KB] [PDF 446KB] ( 16 )
1347 ZHAO Hong-bao , WANG Xin , ZHANG Peng
Experimental study of gas flow characteristics of coal sample under unloading axial stress in linear elastic stage
Taking briquette as studied objects, taking gas flow speed of briquette as studied parameters, the gas flow characteristics of coal sample is studied under the complete stress-strain and unloading axial stress in linear elastic stage; the comparative analysis is done by comparing the gas flow characteristics of loading stage and unloading stage. The results show: the special stress point which makes the gas flow speed minimum appeared in gas flow curve of loading stage, and it belongs to the late of linear elastic stage. In the process of unloading axial stress in linear elastic stage, the reverse trend is shown between stress-stain curve and gas flow characteristical curve; the positive trend is shown between gas flow speed and initial gas flow speed of coal sample; the variation law of gas flow speed is more complex as the addition of strength, only the part of gas flow law is reproduction in the process of unloading axial stress. The laws of gas flow are different in the process of loading stage and unloading stage; the former is uniform change of two stages, the latter is hyperbolic. The influence caused by stress change on gas flow law is more sensitive; it is more obvious in local part of unloading stage.
2012 Vol. 33 (5): 1347-1351 [Abstract] ( 21 ) [HTML KB] [PDF 601KB] ( 22 )
1352 SONG Yi-min , JIANG Yao-dong , MA Shao-peng , YANG Xiao-bin , ZHAO Tong-bin
Evolution of deformation fields and energy in whole process of rock failure
The energy evolution characteristics on the whole process of deformation and damage of rock is inspected and analyzed by using the digital speckle correlation method. The specimen surface speckles images are recorded by CCD camera. The deformation evolution process, the displacement evolution of deformation localization region and the surface deformation energy of rock loaded are analyzed. The results show that: for the displacement evolution of deformation band, the displacement evolution is basically linear before the loading peak, the loading peak of rock specimen and the accelerating stage of displacement evolution is corresponding. Displacement evolution of deformation localization band influences the bearing capacity of rock specimens after loading peak. For the surface energy evolution of rock specimen, the energy release and energy accumulation pattern are controlled by the deformation evolution of localization band in the process of loading. The energy evolution reflects the local energy release and overall energy release characteristics.
2012 Vol. 33 (5): 1352-1356 [Abstract] ( 34 ) [HTML KB] [PDF 932KB] ( 30 )
1357 LIU Han-xiang , XU Qiang , FAN Xuan-mei , XU Hong-biao
Influence of ground motion intensity on dynamic response laws of slope accelerations
Based on large-scale shaking table tests, using the pre-processed peak ground acceleration(PGA) and its amplification factor, taking slopes with two types of lithology variations including high strength materials overlying low strength materials and low strength materials overlying high strength materials as the research objects, this paper investigates systematically the change laws of the horizontal and vertical accelerations in different slope levels with the gradual increasing intensity, under sine waves and crude seismic waves. Analysis shows that: ① When crude seismic waves are loaded, the PGAs in two directions both increased as input waves strengthened, while their corresponding amplification factors increased first, then gradually decreased into stability change. ② When sine waves are loaded, the PGAs in two directions also increased as input waves strengthened, however, their corresponding amplification factors still increased slowly all the time, which indicates the weaker nonlinearity. ③ Under the horizontal and vertical seismic action of the same magnitude, the acceleration amplification appears respectively in the upper part and in the lower part of the two slope models. In addition, several extremum zones of accelerations appear at the bottom, middle and top of slope models. ④ Under the horizontal seismic action, the effect of low frequency is stronger than that of high frequency, furthermore, with the same seismic wave, the acceleration responses in slope with high strength materials overlying low strength materials are stronger than those in the other slope; while under the vertical seismic action of the same magnitude, the results are contrary. The research provides a guidance and reference to quakeproof and post-disaster reconstruction in the high seismic hazard zones.
2012 Vol. 33 (5): 1357-1365 [Abstract] ( 21 ) [HTML KB] [PDF 658KB] ( 20 )
 
Numerical Analysis
1366 GENG Xue-yu , YU Jie
Biot consolidation of a transversely isotropic soil layer under traffic loading
This paper gives the solutions of the transversely isotropic consolidation under both vertical and tangential traffic loadings. Based on Biot’s theory for transversely isotropic clay, the general solutions have been previously derived by applying the Laplace-Hankel transform. By using the inverse Laplace-Hankel transform, pore water pressure and settlement are obtained. The obtained numerical results demonstrate that at the early stage of the consolidation, the tangential loading will have the non- neglectable influence on the settlement. Moreover, the surface settlement under the time-dependent cyclic loading, which is used here to simulate the traffic loadings, always lags behind the loading period.
2012 Vol. 33 (5): 1366-1374 [Abstract] ( 21 ) [HTML KB] [PDF 628KB] ( 20 )
1389 TANG Ren-hua, CHEN Chang-fu
Analysis and calculation method of reliability of anchored retaining wall
A series-parallel model of rib beam-anchor system in reliability analyses of anchored retaining wall is presented. Regarding the rib beam as a continuous beam and the anchors as an elastic support, introducing a composite stiffness coefficient of anchor and the soil around anchorage section, the application loads acting on each anchor are obtained by displacement method. Considering the correlation of performance functions, based on the system reliability theory, a series system of three failure models for single anchor and a parallel system for multiple anchors are developed, while the calculation method of system reliability for the two systems is derived. The corresponding program of new method herein is used to compute the reliability in an engineering example. The calculation results show that the three failure models for single anchor are related and they have different effects on anchor’s reliability, yet the parallel system failure probability of three anchors is approximately equal to sum of the three single anchor’s failure probability at the condition of other anchors is not failure.
2012 Vol. 33 (5): 1389-1394 [Abstract] ( 20 ) [HTML KB] [PDF 561KB] ( 17 )
1497 LI Shu-cai , ZHAO Yan , XU Bang-shu , LI Li-ping , LIU Qin , WANG Yu-kui
Study of determining permeability coefficient in water inrush numerical calculation of subsea tunnel
The construction of subsea tunnel is high risky and water inrush is one of the main risk sources. If water inrush into the tunnel, it will have an important influence on the safety of construction as well as the control of operation cost after the subsea tunnel is completed. So making water inrush forecast is very important in the construction phase. Numerical analysis is the most popular method used in the prediction of water inrush at present, of which ascertaining the permeability coefficient is one key problem. Taking Qingdao Jiaozhouwan Subsea Tunnel as the project background, this paper deals with water inrush forecast during the subsea tunnel construction period by comprehensive usage of numerical computation, model test and local monitoring data analysis. Firstly, variation curves of the water inrush are got by monitoring the water inrush after tunnel excavation. Then numerical method is used to calculate the water inrush. During the process of calculating, parameters are adjusted constantly to fit the curve successfully. The permeability coefficient obtained is reasonable; it should be used in the numerical computation. Combined with the model geology, the relationship between the reasonable permeability coefficient and the permeability coefficient which is got from geological packer test in the early stage is obtained by comparison. Then model test is used to verify above conclusions. Finally, the conclusions can be used to other sections of subsea tunnel to make water inrush forecast. The result has significance for practice reference.
2012 Vol. 33 (5): 1497-1504 [Abstract] ( 25 ) [HTML KB] [PDF 949KB] ( 20 )
1505 MA Gang , CHANG Xiao-lin , ZHOU Wei , ZHOU Chuang-bing
Deep anti-sliding stability analysis of gravity dam based on Cosserat continuum theory
The deep slide of gravity dam is mainly reflected in the appearance of sliding channel along the slow-inclination of weak structure plane. The strain accumulates in sliding channel with very sharp discontinuous strain gradient is a typical strain localization phenomenon. The classic continuum theory suffers from the pathological mesh-dependence in strain localization problem of strain softening material in failure analysis. In this contribution, the governing field equations are regularized by adding rotational degrees-of-freedom to the conventional translational degrees-of-freedom and an elastoplastic Mohr-Coulomb model is presented based on the Cosserat continuum theory, in addition, non-associated flow rule is adopted. In the framework of classic plastic theory, the backward Euler algorithm is used to update plastic stress. A uniaxial compression is performed; the numerical results show that the load-displacement curves are uniformly converged upon different mesh sizes and mesh-independence solutions can be obtained. Finally, the overloading method is adopted in the gradually destruction process simulation analysis. The simulation results show that the classical continuum theory has salient mesh-dependence and are inclined to risk; otherwise the Cosserat theory is more reasonable.
2012 Vol. 33 (5): 1505-1512 [Abstract] ( 20 ) [HTML KB] [PDF 913KB] ( 17 )
1513 MIAO Yu , Lü Jia-he , ZHANG Qing-jun , JIN Xiang-yue , LUO Hui
Cracking mechanism and propagation analysis of asphalt pavement with multi-crack
Based on the theory of fracture mechanics, the cracking mechanism and propagation analysis of asphalt pavement with top-down and reflect crack under vertical loads are studied by FEM numerical simulation. The effects of pavement material and structure are further discussed. The influence of the position of top-down crack to the propagation path of reflects crack is analyzed. The propagation behaviors are verified through beam bending test with multi-crack. The numerical results show that under the vertical loads the propagation path of the top-down crack is almost a straight line, which is departed from the load, while the reflect crack is propagated up-toward along a Z-shaped path. The propagation path of crack is influenced by the module and thickness of the pavement components; and the reflect crack is always propagated toward the sides where the top-down crack exists. The experimental results are consistent with the numerical results.
2012 Vol. 33 (5): 1513-1518 [Abstract] ( 23 ) [HTML KB] [PDF 1065KB] ( 10 )
1519 SHI Lu, LI Xiao-chun, BAI Bing, CUI Yin-xiang
Research on open-pit platform slope stability under rainfall condition
The mechanical strength and water conduction characteristic of rock mass near the surface are mainly controlled by joints and fractures. The ubiquitous joint mechanical model and saturated-unsaturated equivalent continuum media seepage model are coupled by joint connectivity rate to simulate the leading role of the joints. Based on FLAC3D, the mechanism of seepage-mechanics coupling，treatment of rainfall boundary condition and connectivity rate evolution are elaborated, as well as new multi-group ubiquitous joint model is developed. Through analysis of seepage and mechanics fields in a platform slope of Hainan iron ore under rainfall, it is shown that rock near the surface is saturated rapidly with the formation of transient saturated zone due to the rainfall. As the rain continues, the negative water pressure region has further shrunk while the transient saturated zone is just on the contrary. After the rain, the transient saturated zone begins to decrease due to rapid water pressure dissipation. The simulation also indicates that the layer is fractured and its connectivity rate is changed as well because of the seepage in rainfall process. Therefore, the coupled model above is reasonable to analyze the influence of slope stability under rainfall condition.
2012 Vol. 33 (5): 1519-1526 [Abstract] ( 35 ) [HTML KB] [PDF 1209KB] ( 24 )
1527 LI Xiang-long , TANG Hui-ming , XIONG Cheng-ren , LUO Hong-ming
Influence of substrate ploughing and erosion effect on process of rock avalanche
The substrate of rock avalanche bears severe ploughing and erosion effect during the depositing process of rock avalanche. Firstly, characteristics of the substrate-ploughing and esrosion are described and compared with each other. Then the calibration and verification of particle flow method are carried out, and multiple numerical rock avalanche depositing tests based on this method are done. Test results reveal that both the substrate ploughing and esrosion effect can enhance the runout ability of rock avalanche moving on a horizontal substrate. The influence of substrate materials are also studied by doing numerical tests. The results indicate that smaller strength of the substrate materials leads to more intensive ploughing and erosion effect, however, it seems that, the characterstic of lower strength and lower density of the substrate’s surface material is the key factor of enlarging the runout ability of rock avalanche, this fragile layer serves as lubricant in the base; in contrast, the strength of the underlying substrate material gives no contribution on the avalanche’s runout ability.
2012 Vol. 33 (5): 1527-1534 [Abstract] ( 22 ) [HTML KB] [PDF 892KB] ( 12 )
1535 HE Ben-guo , ZHANG Zhi-qiang , HE Chuan , WANG Jun-qi
Study of stability of two-lane soft rock tunnel for high-speed passenger railway in tectonic geo-stress
By taking on standard cross section used for two-lane soft rock tunnel on high-speed passenger railway for 250 km/h, Muzhai Mountain soft rock tunnel is cited here. Meanwhile, energy accumulation, deformation, mechanical response and plastic zone are developed to study stability of tunnel in different characteristics of geostress field. When the horizontal maximum principal stress is parallel to the tunnel axis, high energy and plastic zones occur at wall of tunnel mostly. Energy density ahead of working face is smaller; and squeezing deformation of working face is larger. However, when the horizontal maximum principal stress is perpendicular to the axis, high energy and plastic zones distribute at crown and invert of tunnel, ahead of working face. The energy density is larger and the squeezing deformation is smaller ahead of working face. Consequently, the conclusions can be drawn as follows: there is mechanical behavior of deformation-energy orthogonality ahead of working face. Nowadays, squeezing deformation is adopted to evaluate stability ahead of working face simply, which is worth to further study. It is not suitable that tunnel axis should be parallel to horizontal maximum principal stress regulated by means of the relevant codes in different tectonic geostresses. Bolt has effect on formation of arch effect temporarily at initial stage of excavation. It can make the arch effect closer to tunnel and reduce effectively the peak value of tangential stress for surrounding rock at wall. With advance of working face, arch effect moves to deep rock. Therefore, staged arch effect is formed.
2012 Vol. 33 (5): 1535-1541 [Abstract] ( 26 ) [HTML KB] [PDF 1468KB] ( 12 )
1542 XU Wen-qiang , WEN Song-lin
Numerical study of bearing mechanism of geo-reinforcement foundation under vertical load
Geo-reinforcement foundation (GRF) is a new type of reinforcement pile foundation of which the bearing mechanism is not clear at the present time. By building the 3D nonlinear model of geo-reinforcement foundation, considering the contact effects between pile and soil and that between anchors and soil, utilizing geotechnical professional calculating software FLAC3D, the pile and soil displacement of geo-reinforcement foundation is analyzed; and the soil yield characteristics, variation regularity of pile shaft force, side resistance and end resistance are also studied. The numerical calculation results show that geo-reinforcement foundation can arouse the soil around pile to bear load more efficiently; and the side resistance, end resistance, ultimate bearing capacity of geo-reinforcement are larger than that of straight pile with equal diameter; because of the anchor function, the pile shaft force is suddenly decreased, like a “step”, near the anchors; the function of anchors is closely related with the displacement of pile top. Anchors function the bearing capacity only on the condition that the pile top displacement reached a curtain number. Relaxation region appears in the soil up the anchors and compaction zone occurs in the soil down the anchors; anchors move downward together with pile body and they interact with each other, which causes tensile stress in the lower part of the anchors and pile body near the anchors. The study has laid some basis for the extension and application of geo-reinforcement foundation in projects, which is valuable, to some extent, during the process of designing the geo-reinforcement foundation.
2012 Vol. 33 (5): 1542-1548 [Abstract] ( 23 ) [HTML KB] [PDF 1137KB] ( 9 )
1549 HE Li-jun , WU Wen-jun , KONG Ling-wei
Secondary development of viscoelasto-plastic model with SMP strength criterion in FLAC3D
The strength criterion is used to analyse geotechnical engineering. The physical significance of SMP criterion is most explicit than other strength criteria, its expression is nonlinear, and its Secondary development has important meaning. The viscoelasto-plastic rheological constitutive model with SMP strength criterion is developed according to the further developing platform in FLAC3D with VC++; and the SMP criterion is deduced to adapt to cohesive soil. At last, its accuracy and reliability are confirmed by a simple engineering calculation. The proposed mode can bring forward references for the secondary development of other rheological models and strength criteria.
2012 Vol. 33 (5): 1549-1556 [Abstract] ( 36 ) [HTML KB] [PDF 654KB] ( 19 )
1557 WANG Yong-zhi , SHENG Ye-hua , ZHOU Liang-chen , CHEN Jian-zhong , LIANG Yan
Generation method of three-dimensional computing model of wall rock of salt caverns supported by 3D GIS
The paper proposes a new three dimensional computational model in creep simulation of wall rock of salt caverns according to the current drawbacks that the computational grid is too idealized and unaware to adopt advantage of the real detection data. The three dimensional strata model is constructed by a well organized HalfEdge data structure, which integrates the study area boundaries, DEM (digital element model) and drilling data. Based on the sonar detection data of salt caverns, the three dimensional surface model of the salt caverns is constructed; and the topological inspection and correction operations to the model are carried out. To obtain three dimensional surface model of wall rock of salt caverns, Boolean operations between the three dimensional strata model and the three dimensional surface model of salt caverns are executed. The computational model of numerical simulation is generated by executing the mesh generation operation to the three dimensional surface model of wall rock of salt caverns. The three dimensional computational model obtained by this method advantages in providing effective computational mesh for post creep numerical simulation process of wall rock of salt caverns; and it is a scientific basis and technological support for the construction and reasonable utilization of the salt caverns particularly.
2012 Vol. 33 (5): 1557-1564 [Abstract] ( 19 ) [HTML KB] [PDF 833KB] ( 6 )
1565 LI Chuan-xun , XIE Kang-he , LU Meng-meng , MIAO Yong-hong , XIE Gui-hua
Analysis of one-dimensional consolidation of double-layered soil with exponential flow considering time-dependent loading
Based on exponential flow law in soil, the governing equation of one-dimensional consolidation of double-layered soil considering time-dependent external loading is obtained. The finite difference method is adopted to obtain the numerical solution of excess pore water pressure; and then the reliability of numerical solution is verified by comparing numerical results with analytical results. Finally, consolidation behavior of double-layered soil with exponential flow law under various parameters is analyzed. The results show that the value of exponent in the upper layer largely determines the rate of consolidation, and that in the lower soil layer hardly influences the rate of consolidation in the case of single surface drainage. When compressibility of the upper soil layer is not equal to that of the lower soil layer, the average degree in terms of deformation can be not same as that in terms of pore pressure. The lower the relative compressibility, and the larger the relative permeability between the lower soil layer and the upper soil layer, the faster the rate of consolidation of double-layered soil. The rate of consolidation increases with increasing the relative thickness of soil layer with low-compressibility and high-permeability.
2012 Vol. 33 (5): 1565-1571 [Abstract] ( 25 ) [HTML KB] [PDF 559KB] ( 7 )
1572 ZHOU Guo-liang , LI Xiao-jun , LI Tie-ping , HOU Chun-lin
Canyon topography effects on seismic responses of multi-support bridge under incident SV seismic waves
The seismic response of a reinforced concrete continuous rigid frame bridge is analyzed considering the scattering of SV seismic waves by canyon topography. The differences of structural responses between uniform and nonuniform seismic excitation cases are revealed. The results indicate that the canyon topography has significant and complex effects on the seismic response of the bridge. Different structural members suffer critical responses in different analysis cases. The low piers and rigid frames are more sensitive to the nonuniform ground motions obtained from the seismic response analysis of canyon topography in the case of oblique incidence of SV waves; otherwise the flexible high piers are insensitive. Canyon topography effects as well as the incidence angle of the waves should be regarded as important factors taken into account in aseismic design.
2012 Vol. 33 (5): 1572-1578 [Abstract] ( 23 ) [HTML KB] [PDF 4429KB] ( 6 )
1579 CHEN Yi-jun , XUE Qiang , SUN Ke-ming , ZHAO Ying , WAN Yong
A mathematical model for rainfall erosion of steep soil slope and its solution
A mathematical models for rainfall erosion of the soil steep slope is established, which consists of the control equation of overland flow in inter-rill of soil steep slope, the control equation of water flow in rills of variable groove width of soil steep slope, the continuation equation of sediment in inter-rill of soil steep slope, and the continuity equation of sediment in rills of variable groove width of soil steep slope. Through the probability distribution of turbulent flow, the soil erosion equation is determined. The expressions of sediment source/sink terms and rill height and width are determined. To solve the model, two methods are used in combination. The finite element method is applied to discretize the mathematical model that consist of hydrodynamic equation, the motion equation, and the sediment continuity equation in space; and the finite difference method solves the problem in time domain. In this way, we could obtain the numerical calculation formula and the specific solution to the model.
2012 Vol. 33 (5): 1579-1584 [Abstract] ( 30 ) [HTML KB] [PDF 411KB] ( 12 )
1585 ZHANG Chang-liang, WANG A-dan, XING Xian-li, WANG Chang-ye, LI Tong-lu, LI Ping
Research on mechanism of loess landslides caused by erosion
The erosion-induced loess landslide is a typical landslide in the Loess Plateau. It has important practical significance to do some research on its mechanism. Taking Anli landslide in Yaozhou district, Shaanxi province as example, this paper discusses its initiation mechanism, establishes finite element models at different stage caused by headward erosion before sliding through finite element method, and calculates the stress and strain fields in each stage. On this basis, the shear stress, normal stress and shear strength on the final sliding surface in every model are obtained. The stability factors are also acquired by limit equilibrium method. The result shows that, with the deepening headword erosion, the shear stress on sliding surface increases constantly; but the shear strength decreases conversely. The stability of the whole landslide never reduced until failure. The experimental result shows that, the low-strain can produce a significant excess pore water pressure in saturated loess. Therefore, the excess pore water pressure in saturated sliding zone fosters the failure of this landslide. Comparing the shear stress and the shear strength, the erosion-induced landslide has a failure from the foot to the back part gradually. Therefore, this kind of landslides has characteristics of traction damage.
2012 Vol. 33 (5): 1585-1592 [Abstract] ( 23 ) [HTML KB] [PDF 883KB] ( 6 )
1593 LI Hui , YAN E-chuan , YANG Jian-guo , Lü Kun
Study of interaction of landslide mass and retaining wall under condition of reservoir water
Basing on geological model of Hefeng landslide and using finite difference method to analyze the interaction of landside mass and retaining wall under condition of reservoir water, we can get satisfying results. Under the condition of reservoir water, the results show: ①Local tensile stress appears in the wall heel of retaining wall; ②The increment of shearing strain process developed (">"development mode) from backwall to metope along retaining wall and "weak contact face" in stone head; ③The landside mass and retaining wall have same deformation tendency, and the upper deformation is larger than the under-part; The isolines of displacement are parallel to each other, and the retaining wall is bedded destroyed because of shallow landslide; ④The landslide is shallow slippage, and the stability of landside and retaining wall go down. In the end, the paper points out that drift index can be used to evaluate anti-slide stability and anti-tipping stability and determine critical width of retaining wall under the conditions of reservoir water; and then the stability of landslide and retaining wall can be improved for the optimization design of retaining wall. All of these will provide theoretical guiding for geologic hazard control and engineering design.
2012 Vol. 33 (5): 1593-1600 [Abstract] ( 31 ) [HTML KB] [PDF 1321KB] ( 8 )
 
Geotechnical Engineering
1375 LIU Shi-peng , SHI Jian-yong , LEI Guo-hui
Similarity solutions of cylindrical cavity expansion based on SMP criterion
On the basis of the cylindrical cavity expansion theory, the concept of expansion velocity is introduced into the theory. The movement of the plastic boundary b is taken as the scale of “time” and the stress/strain of any point in the expansion body are described as the functions of the plastic boundary b and the current radius r. By using the spatially mobilized plane (SMP) theory of cohesionless soils in the plane strain condition, non-associated flow rule and considering cohesionless soils, shear dilation, the similarity solution of limit pressure is obtained. Meanwhile, the parametric study indicates that the influence of strength and shear dilation on the limit pressure and plastic zone radius is remarkable. With the increase of strength and shear dilation the limit pressure increases greatly while the plastic zone radius decreases. A comparative analysis shows that the limit pressure calculated from the SMP criterion which includes the effect of intermediate principal stress is obviously greater than that from the solutions based on Mohr-Coulomb criterion. The proposed solutions provide some theoretical bases for geotechnical engineering practices in cohesionless soils, such as cone penetration tests (CPT), jacked piles, and so on.
2012 Vol. 33 (5): 1375-1380 [Abstract] ( 21 ) [HTML KB] [PDF 425KB] ( 19 )
1381 YANG Zhi-yong , HUANG Hong-wei , ZHANG Dong-mei , ZHANG Jie
Pushover method for seismic analysis of shield tunnel
The dynamic time-history analysis of shield tunnel seismic design needs long computed time and massive work. The dynamic constitutive model and damp for soils are difficult to determine. Its wide application in practical project is hindered by these problems. In order to solve these difficulties, a modified pushover method for shield tunnel which is developed from pushover method of structure on the ground is put forward; and inclination of shield tunnel is introduced to assess its seismic performance. Since the seismic responses of shield tunnel are determined by the surrounding soils; the horizontal loading model is improved. In this method, the seismic action on shield tunnel is simulated by applying the inverted-triangular lateral horizontal displacement on the model along the depth. The complex problems existed in the dynamic time-history analysis, such as the dynamic constitutive model and damp of soil, the boundary condition, are avoided; and the interaction between tunnel and soil is able to consider in this method. The seismic performance capacity curve also could be obtained by this method. The comparison results with dynamic time-history analysis show that the calculation result of the modified pushover method is reasonable and accurate in the elastic stage. It is an appropriate method for seismic design of shield tunnel.
2012 Vol. 33 (5): 1381-1388 [Abstract] ( 25 ) [HTML KB] [PDF 529KB] ( 15 )
1395 LU Yin-long , WANG Lian-guo , ZHANG Bei , LI Yu-jie
Optimization of bolt-grouting time for soft rock roadway
Bolt-grouting technology is an effective way to maintain the stability of soft rock roadway, and its effects rely heavily on the grouting time. The mechanical characteristics of ruptured soft rock reinforced by grouting are analyzed, and the rational grouting time for soft rock roadway is optimized by numerical simulation using the strain softening constitutive law in FLAC2D. The results show that as the grouting time lags, the infiltration scope of the grout in rock increases gradually but the strength of rock reinforced by grouting decreases dramatically, and the deformation of roadway decreases first and then increases. On the basis of this, a method integrating numerical simulation and monitoring for determining the rational bolt-grouting time is proposed and better results have been achieved in engineering practice. This method provides a favorable guidance for the construction and design of bolt-grouting support in soft rock roadway.
2012 Vol. 33 (5): 1395-1401 [Abstract] ( 24 ) [HTML KB] [PDF 695KB] ( 19 )
1402 HUANG Da-wei , YANG You-hai , LAI Guo-quan , YUE Peng-fei
Analysis of dynamic deformation modulus for high-speed railway subgrade
Through the on-site filling test in the subgrade test section of Lanzhou-Xinjiang Railway two-line in desert area, the relationship between dynamic deformation modulus Evd and subgrade filler as well as the compaction quality of the filler is analyzed, which shows a lack of correlation between Evd and K30 (ground coefficient), while Evd is well correlated to Ev2 (static modulus of deformation). After analyzing the influence factors of Evd by combining the numerical calculation of ADINA (three-dimensional dynamic finite element software) with field test, the findings indicate the following conclusions. Complete linear correlation exists between Evd and Ed (dynamic modulus) in theory, their correlation formula has something to do with dynamic angle of internal friction and dynamic cohesion. When the filler dynamic cohesion keeps low, Evd increases with the dynamic cohesion and dynamic angle of internal friction; while Evd will not change with them when the filler dynamic cohesion is large enough. Also, Evd relates to the shearing strength of soil under the impact load. With Ed stays established, Evd increases with the shearing strength which is relatively low, but when the shearing strength reaches a certain value, Evd will no longer change.
2012 Vol. 33 (5): 1402-1408 [Abstract] ( 24 ) [HTML KB] [PDF 504KB] ( 16 )
1409 CHEN Xu-guang , ZHANG Qiang-yong , DUAN Kang , LIU De-jun , ZHANG Ning
Research on application of optical sensor-based measuring method to model test
Model test has been more and more important as an effective method in solving the complex and special engineering problems. However, comparing with the developed model test system and the well proven similar principle, the measure technology is yet lags behind and can’t fulfill the requirement of the model test. Based on the high precision and stability of the optical grating and the optical fiber, considering the special demands of the model test, an optical sensor technology based displacement/strain model measuring system is developed and the algorithm of the data receive is improved. The system consists of the optical grating displacement measuring system and the optical fiber strain measuring system. The system has the advantage of high precision and stability and measuring discontinuous deformation. Applying the system to the model test of deformation characteristic of the salt rock underground cavern in the condition of changing of the gas injection/production, the displacement convergence and strain creep laws of the cavern are obtained; the different deformation characteristics of the surrounding rock mass in the different air pressure and velocity of the gas injection/production are got. The test is helpful for determining the proper air pressure and velocity of the gas injection/ production and is important to the safe and stable operation of the salt rock underground cavern.
2012 Vol. 33 (5): 1409-1415 [Abstract] ( 21 ) [HTML KB] [PDF 917KB] ( 15 )
1416 XIAO Qi-hang , XIE Chao-juan
Application of tunnel seismic tomography to tunnel prediction in karst area
Dingxiao Tunnel is located at the karsts area in Guizhou province; in which the geological structure is very complicated and full of crushing rocks. All these bring high risk in tunnel excavation; and its tunnel geological prediction work faces great difficulty. Currently there are several tunnel geological prediction techniques, but most of them have three major issues. First, they did not differentiate the echo seismic waves from individual directions; it assumes all the seismic waves come from the front tunnel face. Second, they can not calculate the rock velocity in the front tunnel face. Third, they cannot separate p wave and s wave correctly. So the result cannot be accurate and reliability. For safety and efficiency, a new tunnel geological prediction technique, the tunnel seismic tomography(TST) is adopted in Dingxiao tunnel. TST utilizes spatial observation, F-K filtering and velocity scan techniques which solved all the issues indicated above. The function of spatial observation and velocity scan in TST gives precise velocity analyzing and enabled accurate geological structure locating. The F-K filtering function of TST gets rid of the surface wave and sidewise echo wave, only uses the wave coming back from front.
2012 Vol. 33 (5): 1416-1420 [Abstract] ( 20 ) [HTML KB] [PDF 618KB] ( 14 )
1421 ZHENG Zhi-cheng , XU Wei-ya , XU Fei , LIU Zao-bao
Forecasting of slope displacement based on PSO-LSSVM with mixed kernel
The kernel and the parameters of support vector machine (SVM) have a significant impact on precision of the time series prediction to slope displacement. In view of better learning capability of local kernels and better generalization capability of global kernels, the mixed kernel is constructed by a typical local kernel-radial basis function (RBF) and a typical global kernel-polynomial kernel. By use of particle swarm optimization (PSO), a new PSO-LSSVM model regression with mixed kernels is set up in this paper and applied to the left bank slope in Jinping Ⅰ Hydropower Station. Through comparing with the forecasting results of the existing SVM based on RBF, results demonstrate that the new model has great accuracy than the existing SVM with RBF only and has real application value in predicting deformations of slope.
2012 Vol. 33 (5): 1421-1426 [Abstract] ( 21 ) [HTML KB] [PDF 579KB] ( 12 )
1427 CHEN Yong , BAI Jian-biao , ZHU Tao-lei , YAN Shuai , ZHAO She-hui , LI Xue-chen
Mechanisms of roadside support in gob-side entry retaining and its application
The stability control of roadside support body is the key to keep gob-side entry retaining stable. According to the structural mechanics model of gob-side entry retaining overlying strata, the paper analyzes the load and deformation characteristics of roadside support in the three stages and obtains supporting mechanism of roadside support as follows. Roadside support body could support the roof instantly by increasing support resistance in the setting stage, meets the requirement of cutting off a certain height of the roof before a periodic abutment loading at the back of working face, and has a large deformation capacity during overlying strata movement and a high post-strength after stability of overlying strata movement. Based on the above investigations and the geological conditions of panel 24021 in Jiulishan colliery, we analyze the effect of support body width on the performance of a gob-side entry retaining, and determine a rational width of support body in the condition of support parameters and filling materials. Research results are successfully applied to a field practice.
2012 Vol. 33 (5): 1427-1432 [Abstract] ( 25 ) [HTML KB] [PDF 460KB] ( 15 )
1433 HE Si-ming , ZHANG Xiao-xi , WANG Dong-po
Study of computation methods of ultimate uplift capacity and determining position of failure surface of uplift piles in layered soil
The horizontal slice method is used to study the relation among the uplift capacity, the failure surface and soil parameters with Mohr-Coulomb failure criterion. According to the limit equilibrium approach, the uplift capacity is calculated by dividing soil around the pile into slices with regarding the potential failure surface as a group of several sectional planes. Then the multivariate function used to calculate uplift capacity is established and optimized by the sequential quadratic programming. Through the numerical calculation and comparison with the previous research, the results show that the method is reasonable and effective, and can be used to determine the failure surface shape and the magnitude of the uplift capacity of uplift piles.
2012 Vol. 33 (5): 1433-1437 [Abstract] ( 22 ) [HTML KB] [PDF 460KB] ( 14 )
1438 HU Yun-shi , SUN Qing , HAN Jin-bao
Linear elastic-perfectly plastic solution for cylindrical cavity contraction and its application
Tunnel excavation can be simulated by cylindrical cavity contraction due to the comparability between tunnelling and cavity contraction. The linear elastic-perfectly plastic analytical solution is obtained based on the theory of critical state soil mechanics proposed by Yu[1]. The relationship between the support pressure and ground loss and the maximum surface settlement is given based on the theory of tunnelling. Comparisons have been made between the computed results of the analytical solution and centrifuge tests results conducted by Grant and observed values in some case histories at home and abroad. The results show that: this study is correct and rational; and the analytical solution can be used for predicting the soil deformation due to tunneling.
2012 Vol. 33 (5): 1438-1444 [Abstract] ( 24 ) [HTML KB] [PDF 426KB] ( 16 )
1445 XIA Yan-hua , BAI Shi-wei
Study of building 3D complex strata model based on level set methods and application to underground engineering
In order to represent three dimension complex stratigraphic objects including faults, disappearances , outcrops and other phenomena, we have to face the difficult problems in the process of spatial partition or calculating intersection lines of curved surfaces in building 3D strata model, either based on surface elements , or based on volume elements, or based on hybrid elements. But these methods in building 3D complex strata models usually failed, because of complex topological relationships of the strata, source data error and computer accuracy etc. It is a good idea to resolve these problems by using level set methods. Level sets are implicit functions of surfaces or hypersurfaces, which can represent complex geological bodies and implement a series of topological operations such as union, intersection, difference etc. In building 3D strata model, after interpolating geological interfaces, these interfaces are transformed into level sets, and the complex topological operations based on level sets are applied to building the 3D strata model. After building the 3D strata model, the interfaces of engineering activities represented by level sets, are inserted into the 3D strata model; and the 3D engineering activities strata model is built by the complex topological operations based on level sets. Then the geological interfaces or the interfaces of engineering activities are extracted by marching cube algorithm to constructing a NMTINF-BR 3D strata model or a NMTINF-BR 3D engineering activities strata model which is suitable for real-time visualization and numerical simulation (such as finite elements).
2012 Vol. 33 (5): 1445-1450 [Abstract] ( 28 ) [HTML KB] [PDF 1120KB] ( 15 )
1451 QU Chang-zi , WANG Yong-he , WEI Li-min , GUO Zhi-guang
In-situ test and analysis of vibration of subgrade for Wuhan-Guangzhou high-speed railway
In order to study the vibration characteristics of ballastless-track subgrade for Wuhan-Guangzhou high-speed railway, in-situ train-induced vibration tests are performed in the Huchang-Xianning test section. Magnitudes of vertical vibration acceleration and dynamic stress of all the measuring points are obtained when bullet trains units and track inspection trains run in the test section respectively. Distribution laws of dynamic response in the tested subgrade are summarized. Natural frequencies of the tested subgrade are obtained. Furthermore, incorporating wavelet analysis method, vibration characteristics of the tested subgrade are analyzed in the frequency domain. The results show that the increase in train speed enhances the vibration at the top surface of the tested subgrade, especially at 260-320 km/h. After attenuating over 2.7 m high embankment, magnitudes of dynamic response and vibration energies of the tested subgrade are very little, and the influence of train speeds is not obvious to them. The graded broken stone layer can effectively inhibit the propagation of vibration with depth in subgrade. With the increase in train speed, vibration of subgrade is mainly controlled by wheelbase and track smoothness. Axle loads effect magnitudes of dynamic response and vibration energies more significantly than train speeds. Increase in axle loads concentrates vibration energies in a more narrow frequency band.
2012 Vol. 33 (5): 1451-1456 [Abstract] ( 26 ) [HTML KB] [PDF 512KB] ( 16 )
1457 WEN Jian-hua, ZHOU Cui-ying, HUANG Lin-chong, CHENG Ye
Study of classified evaluation of slope stability based on homotopy fuzzy C-mean clustering algorithm
In order to overcome the shortcoming of sensitivity to the original clustering center in ordinary fuzzy C-mean clustering algorithm, the homotopy theory is introduced to combine with this algorithm to establish a new method of homotopy fuzzy C-mean Clustering algorithm for evaluation of slope stability. Then the method is applied to studying stability of 36 slopes at banks of the Three Gorges Reservoir; and then some characteristics such as the best sample classification and convergence effect of homotopy fuzzy C-mean clustering algorithm are discussed. Clustering results show that the proposed method is a reasonable classification algorithm with global optimization and superior to the ordinary fuzzy C-mean clustering algorithm.
2012 Vol. 33 (5): 1457-1461 [Abstract] ( 29 ) [HTML KB] [PDF 414KB] ( 14 )
1462 ZHANG Hua-lei , WANG Lian-guo , QIN Hao
Study of spalling mechanism and control techniques of mining roadway
According to the sides’ surrounding rocks characteristics of the mining roadway on the work-face with large mining height, a mechanics model about crack board structure of the sides surrounding rocks is established based on the fracture damage theory and plasticity theory, and the instability mechanism of the surrounding rocks of the mining roadway in the Xinzhi Mine, Houzhou Coal is analyzed, and the grouting-cable method is first used in supporting the surrounding rocks of the sides to limit it to be cut down.The results show that there are a lot of rock fissures in the sides of the back-extraction roadway, and the rock fissures develop under high stress, it makes the surrounding rocks of the sides evolve into the spallation board structure. When the multiple bearing pressure on the sides is greater than the smallest bucking critical load, the parts of sides will be cut down. With the increasing of the elastic modulus and spallation board thickness of coal rockmass, the failure scale of the spallation plate expands when instability occurs. Grouting-cable can be used to fill the deep fractures of the surrounding rocks, makes surrounding rocks as a whole, and improves the bearing capacity of supporting structure around the surrounding rocks of the roadway.
2012 Vol. 33 (5): 1462-1472 [Abstract] ( 25 ) [HTML KB] [PDF 615KB] ( 15 )
1467 ZHANG Ding-wen, HAN Wen-jun, LIU Song-yu, DU Guang-yin
Effect analysis of a soft ground reinforced by a combined vacuum preloading and pneumatic fracturing method
To overcome the problems of traditional vacuum preloading method, vacuum preloading and pneumatic fracturing are combined to reinforce the performance of ground improvement. The mechanism and construction procedures of the combined method are introduced firstly. The reinforcement effect of the combined method is validated through a pilot highway embankment on soft clay in Jiangsu, China. Comparing to the traditional vacuum preloading method, the combined vacuum preloading and pneumatic fracturing method would enhance the transfer efficiency of vacuum into deep soil layers and accelerate the dissipation of excess pore water pressure. Therefore, the strength increase of soft soil layers improved by the combined method is much larger than that of ground reinforced by the traditional vacuum preloading method. The combined method also can reduce the construction period than the traditional vacuum preloading method. The test results of cone penetration tests and engineering properties tests of soft soils also indicate the superior of the combined vacuum preloading and pneumatic fracturing method.
2012 Vol. 33 (5): 1467-1472 [Abstract] ( 21 ) [HTML KB] [PDF 519KB] ( 13 )
1473 LIU Zhen , ZHOU Cui-ying , FANG Ming
Research on consistency of nonlinear evolution models and unity of failure criteria for tunnel
Nonlinear dynamics evolution model & criterion of tunnel and energy evolution model & criterion of tunnel are to describe and judge for the same system from dynamic process and energy state. From the description of two models to the zonal disintegration in surrounding rocks, the consistency of two models in space is proved by the relation between thermodynamic entropy S, Kolmogorov entropy and correlation dimension of nonlinear dynamics. The consistency of two models in time by the relation between evolution time of two models. According to the description of two failure criteria to stability state of different evolution stages, from division of system evolution stages by them, the unity of two failure criteria under the conditions of regular development and salutatory development is analyzed. This research more explained nonlinear mechanism of tunnel unstable failure while two models and criteria are validated each other. This research has a great significance for the stability judgment of surrounding rocks of tunnels.
2012 Vol. 33 (5): 1473-1478 [Abstract] ( 27 ) [HTML KB] [PDF 582KB] ( 14 )
1479 WANG Du-bo , LIU Han-long , YU Tao
Seismic risk analysis of earth-rock dam based on deformation
The seismic safety design of an earth-rock dam usually focuses on how to prevent its structure from collapsing, which makes the issue about how to control the structural damage of an earth-rock dam within an acceptable risk level, an important topic worth researching in the field of geotechnical engineering. By applying the theory of seismic risk analysis to practice, this paper witnesses the establishment of a method of seismic risk analysis particularly designed for earth-rock dams. The method explores the seismic risk from three aspects: the seismic hazard analysis, the seismic fragility analysis and the seismic loss assessment. On the basis of the site seismic risk analysis, the ideology of performance-based seismic design is successfully realized in the seismic fragility analysis of an earth-rock dam. The seismic damage level for an earth-rock dam is classified according to the specific condition of the relative settlement of the dam crest which serves as an evaluation index. Finally, with the help of seismic economic losses analysis, a seismic risk model for earth-rock dams is established, which can be used for evaluating the seismic damage risk of an earth-rock dam in terms of technology and economy. This paper also takes a high earth-rock dam for example to analyze and predict its seismic damages and economic losses in an earthquake, using the proposed model. The conclusion of such analysis and prediction can provide a valuable reference for safety evaluations of earth-rock dams and investment decisions, especially when an earth-rock dam is located in an area endangered by possible earthquakes.
2012 Vol. 33 (5): 1479-1484 [Abstract] ( 24 ) [HTML KB] [PDF 475KB] ( 16 )
1485 LI Ning , XU Jian-cong , QIN Ya-zhou
Research on calculation model for stability evaluation of rainfall-induced shallow landslides
Landslides are common geological hazard problems in China; many facts indicate that the rainfall is the main and common environmental factor controlling the instability of slope and triggering shallow landslides. In order to do better research on rainfall-induced shallow landslides, Mein-Larson model is developed based on VG model and modified Green-Ampt infiltration model; then combined with infinite slope stability model, a simplified calculation model is proposed for analyzing rainfall-induced shallow landslides. Compared with the simplified calculation model proposed before, the effect of slope and the characteristics of unsaturated soil are taken into account in this model; it can be used for analyzing rainfall-induced shallow landslides under two different rainfall patterns; and it has a wider range of applications. Compared with the results of FEM, conclusions can be drawn as follows: the results of the calculation model agree with that of FEM; and the safety factor is somewhat safe; so it can be used for analyzing rainfall-induced shallow landslides; the calculation model has simple formula, higher computational efficiency.
2012 Vol. 33 (5): 1485-1490 [Abstract] ( 31 ) [HTML KB] [PDF 426KB] ( 25 )
1491 CHEN Yang, QIAO Zhong-fa
Calculation of ground settlement of sparse pile foundations using united solutions
The composite foundation with sparse piles is widely used in practice as a time-saving and effective way to treat soft soil. Considering the distribution law of skin frictions on capped PTC (prestressed thin-wall concrete pile) rigid piles, this study assumes that the distribution of skin frictions can be simplified as two triangles. Combining Mindlin-Geddes’ solution with Boussinesq’s solution, the formula of additional stresses of the sparse pile foundation can be derived under the full consideration of the radius of influence. In numerical cases, the ground settlement can be determined using the layerwise summation method. The authors compared the results from the traditional calculation method and the united solutions and analyzed the variation of calculated ground settlement using united solutions while the pile spacing varies. The proposed combined method is used to analyze the settlement of the sparse pile foundation for ground treatment. The results show that the calculated settlement is smaller than that from the traditional method and fits well with the monitoring results. When the pile spacing is eight times larger than pile diameter, as the pile spacing increases, the additional stress field shows no significant variation but the settlement increases accordingly. For foundations with a large pile spacing, the utilization of the long-short-pile composite foundation is preferable. With the installation of deep cement mixing piles, the soft embankment can be reinforced and the ground settlement can be effectively reduced.
2012 Vol. 33 (5): 1491-1496 [Abstract] ( 21 ) [HTML KB] [PDF 649KB] ( 12 )
Rock and Soil Mechanics
 
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· The 4th International Conference on Problematic Soils 21-23 September 2012 Wuhan,China
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Address:Institute of Rock and Soil Mechanics Chinese Academy of Sciences Tel:027-87199252,87198484 Email:ytlx@whrsm.ac.cn