Select

null

2004, 23 (10): -0 doi:
Full Text:

[PDF 114 KB] (553)

+

Show Abstract

Select

SEVERAL GEOMECHANICS PROBLEMS IN CONSTRUCTION PROCESS OF THREE GORGES PROJECT

null

2004, 23 (10): -1591 doi:
Full Text:

[PDF 238 KB] (1031)

+

Show Abstract

The Yangtze Three Gorges Project (TGP) is the key backbone project to develop and harness the Yangtze River in China. As the largest water conservancy project in the world with the earth and rock excavation amounting up to 102.83 million m3，it is，therefore，the largest project in scale of geoengineering. The involvement of numerous domestic and foreign research institutions in the scientific research for TGP construction has promoted the development of geo-mechanics. Some geomechanics problems arising during construction of TGP are discussed in this article.

Select

CHARACTERISTICS OF DAMAGE EVOLUTION OF MICROPORE
AND MICROCRACK IN ROCK

null

2004, 23 (10): -1599 doi:
Full Text:

[PDF 382 KB] (1111)

+

Show Abstract

Microstructure and cell of rock are researched by means of SEM. The propagation of rock microcrack is analyzed. The fractal characteristics are analyzed by dissipated energy consumed by microstructure fracture. The form and direction of crack propagation in rock are obtained according to given loading，by use of fractal geometry method and micro-thought method. The regularity of damage evolution of rock is explained. It is shown that the speed，direction and quantity of microcrack propagation depend mainly on the component，combination of mineral，combinatorial density，quantity and direction of load，state of stress，and ratio of stress components.

Select

MODELING OF INHERENT ANISOTROPY FOR GEOTECHNICAL MATERIAL

null

2004, 23 (10): -1604 doi:
Full Text:

[PDF 176 KB] (1110)

+

Show Abstract

A model of anisotropy for geotechnical material is presented. The inherent anisotropy of this kind of material is described with an anisotropy parameter. A microstructure tensor and loading direction are incorporated in the distribution functions of anisotropy parameter，uniaxial compressive strength and uniaxial tensile strength. A failure criterion describing the fracture and yielding for geotechnical material is set up. Numerical simulation results show that the inherent anisotropy of geotechnical material can be efficiently described with the model.

Select

TESTING STUDY ON CRACK DEVELOPMENT IN LIMESTONE PLATE SPECIMEN UNDER UNIAXIAL COMPRESSION

null

2004, 23 (10): -1608 doi:
Full Text:

[PDF 734 KB] (1065)

+

Show Abstract

Testing study is made on the mini-crack development around a prefabricated fracture in a limestone plate specimen subject to uniaxial compression. The rock used for test is limestone，and direct SEM observation is used for testing. The elastic modulus of rock specimen is about 93.7 GPa，Poisson′s ratio 0.25 and uniaxial compressive strength 201 MPa. The specimen is a plate of 25 mm×13 mm×1.1 mm in size with a prefabricated central circular or a slot about 0.6 mm wide and 6.0 mm long. The major axis of the prefabricated slot is inclined to the loading direction at 30°，45°，60°，respectively. The tests are carried out in the vacuum chamber of a SEM using a vise-type loading frame. Its loading capacity is 2 000 N and the load on the specimen is measured by the piezoelectric transducer with an accuracy of ±0.5 N. The development of mini-cracks in limestone specimen under uniaxial loading is photographed and analyzed. The test results are compared with those in marble and sandstone specimens from the previous study. It is shown from the comparison that the initiation points of cracks are similar in all three rock specimens，but there are less multiple mini-cracks development in limestone specimen. Finite element computation of the mini-crack process is performed using NOLM program with a strain-softening constitutive model of low tensile resistance. The computation result represents the experimental observation fairly well. The calculated results are compared with testing data，and they are agreed well with each other.

Select

REAL-TIME TESTING STUDY OF ROCK FRACTURE
UNDER COUPLED COMPRESSION AND SHEAR

null

2004, 23 (10): -1616 doi:
Full Text:

[PDF 465 KB] (1090)

+

Show Abstract

The optimal match system of optical layout for real-time laser holographic interferometry and the loading apparatus of rock under coupled compression and shear is developed. Using the digital image instrument，the real-time holographic interferograms for the wholly failure process of rock under compressive-shearing stress is continuously captured. As the loading increased，on the surface of granite samples several types of the dynamic interference fringes i.e. active fringe with the different forms of distribution appear. Based on the principles of the fringe’s interpretation at the same time by use of the image process methods，the developing rates of microcracks within granite samples are calculated and its growth models are described in details. The results expose the distribution of the local defatormion field，the growing path of microcracks and its rate in the whole process of rock failure under compressive-shearing loading，as well as the mechanical property of rock failure. Under the condition of compressive loading with shearing loading together，the local deformation and the deforming grades of samples are of obvious differences which mostly control non-linear macro deformation of granite samples. The sample’s final failure results from the coupled shear fracture and extensive fracture，and its failure shapes are related to the stress states，the growth path and developing rate of microcracks，and also the mechanical types of microcracks. It is proved that the real-time laser holographic interferometry testing can provide the research of rock damage and fracture with an effective experimental support.

Select

REMOTE SENSING-ROCK MECHANICS (VIII)——TIR OMENS OF ROCK FRACTURING

null

2004, 23 (10): -1621 doi:
Full Text:

[PDF 482 KB] (1130)

+

Show Abstract

There are many omens existing before rock fracturing，which is an important research issue of rock mechanics and rock engineering. Based on the fundamental experiments on remote sensing-rock mechanics，the thermal infrared radiation (TIR) omens of rock fracturing are systematically analyzed and studied. The research contents of this paper include the types and features of TIR omens，the occurring time of TIR omens，the spatio-temporal features of TIR omens，and its mechanism. It is concluded that (1) there are two kinds of TIR omens for rock fracturing，i.e.，TIR image anomaly and curve of average TIR temperature and time anomaly，which reflect the spatial and temporal features of TIR omens respectively，(2) the TIR image anomaly is classified as high-temperature strip and low-temperature strip，and the curve of average TIR temperature and time anomaly is classified as temperature drop，rapid rise of temperature and rise-from-drop of temperature，(3) the omens occur before peak load at the moment when load is 77%～87% of the peak load，and they are tightly related to the formation of micro-cracks，(4) the possibility of omens of shearing fracturing with high confining pressure or high compressive stress is higher than that with low confining pressure or low compressive stress，and the possibility of omens for pure-shear will be less and its occurring time is close to the fracturing moment，and (5) the mechanism for the TIR omens of rock fracturing is the comprehensive effect of rock thermo-elasticity and rock friction.

Select

ANALYSIS ON POST-FAILURE BEHAVIORS OF ROCK IN UNIAXIAL COMPRESSION USING DISTURBED STATE CONCEPT THEORY

null

2004, 23 (10): -1628 doi:
Full Text:

[PDF 308 KB] (1173)

+

Show Abstract

The complete stress-strain curve of rock could be divided into pre-failure and post-failure regions according to the peak stress. In general，the pre-failure region of rock shows stability in the mechanical response，which may be described by the classic strength theories，and the post-failure region of rock shows instability，which is difficult to be described by the classic strength theories. The post-failure mechanical characteristics of rock are corresponding to a good many rock engineering，such as underground excavation，pillar，rock burst and so on. Therefore，the research on the post-failure characteristics of rock is of important significance both in theory and in practice. Based on the disturbed state concept theory (Desai，2001)，it is assumed that the relative intact state of rock is of hyperbolic form and the fully adjusted state of rock is the critical state of rock failure. A new constitutive model reflecting the post-failure behaviors of rock material is established through defining the expression of disturbance function. A series of uniaxial compressive failure tests about five kinds of rock specimens were performed by RMT-150B rock mechanics test system. The complete stress-strain curves of the five kinds of rock specimens were obtained. The mechanical mechanism of the deformation and failure in rocks is studied using the disturbed state concept. The proposed constitutive model is applied to simulate the post-failure behaviors of rock specimens. From correlative study and analysis，it is shown that the proposed constitutive model can predict，in a certain extent，the mechanical characteristics of rock in post-failure region.

Select

CREEP THEORY OF SOFT ROCK AND ITS ENGINEERING
APPLICATION

null

2004, 23 (10): -1635 doi:
Full Text:

[PDF 212 KB] (1368)

+

Show Abstract

The construction of underground engineering often encounters soft rocks，whose compressive strength is lower，with obvious characteristics of rheology. The amount of creep deformation is big enough to cause failure of support. The characteristics of rheology should be taken into consideration for analysis of stability or design of underground engineering. Triaxial creep test is made for mudstone with the authors-developed gravitation lever style rock creep test machine and triaxial pressure cell. Testing results show that the creep of mudstone is of nonlinearity. On the basis of testing results，nonlinear creep equation is established. According to the equation，the stress and displacement field of surrounding rocks may be analyzed. Theory research result shows that the basic way to control excessive creep deformation is to improve the stress state of surrounding rocks，and properly increase prestress of bolt or cable，so that the theory basis is provided for effective control of the harmful deformation of surrounding rocks in deep mining.

Select

NON-LINEAR CREEP MODEL AND STABILITY ANALYSIS OF ROCK

null

2004, 23 (10): -1640 doi:
Full Text:

[PDF 147 KB] (2377)

+

Show Abstract

Based on the modified elastic and visco-elasto-plastic model，the corresponding relationship of complete rock stress-strain curve and creep equation parameters is utilized，and a creep model with non-linear parameters is set up. By analyzing non-linear creep model and the creep curve，in the local scope，non-linear creep question is transfered into linear one，and the stability condition of the modified model is obtained，with which the three stages of rock sample creep，especially the non-linear accelerating creep stage can be described clearly. Meantime，the creep stability criteria of rock sample，analytic expressions of the creep deformation，the creep speed and the creep acceleration are given.

Select

COMPARISON STUDY ON TWO KINDS OF INDIRECT MEASUREMENT METHODS OF TENSILE STRENGTH OF COAL IN LAB

null

2004, 23 (10): -1643 doi:
Full Text:

[PDF 187 KB] (1210)

+

Show Abstract

The basic principle，experiment device and testing method of Brazil test method and sleeve fracturing method are introduced to determine the tensile strength of coal in lab. The distribution characteristics of tensile strength of coal is systematically analyzed. The differences of tensile strength of coal and its formation with the two methods are evaluated.

Select

FINITE ELEMENT ANALYSIS ON LANDSLIDE MECHANISM
AT SHILIUSHUBAO

null

2004, 23 (10): -1648 doi:
Full Text:

[PDF 682 KB] (1123)

+

Show Abstract

The landslide at Shiliushubao is a part of the Huanglashi landslide，a very important ancient landslide in Three Gorges Dam¢s headpond. Analyses are conducted on the mechanism of landslide by means of FEA based on the displacement-controlled method. In case that the slide surface is known，the study illustrates the application of the Katona contact element to modeling sliding surface. As comparison，another computation scheme is set， in which the sliding body is of the property of soil in the sliding band and there is no contact interface between the rock bed and the sliding body. In two manners，the safety factors are approximate but the failure mechanisms are quite different. This states that the property of soil in the sliding band controls the stability of landslide. The study also explains the reason why the safety factors obtained by conventional FEM are different from those by limit equilibrium methods.

Select

ANALYSIS ON MECHANICAL PROPERTIES OF ROCK AND PREDICTION OF MUZZLE VELOCITY OF HIGH-SPEED LANDSLIDE

null

2004, 23 (10): -1654 doi:
Full Text:

[PDF 269 KB] (1158)

+

Show Abstract

Before slope slides at a high velocity，the sliding resistance is corresponded to the shear strength in limit equilibrium state. Once the locked segment is suddenly snipped，half of the original sliding resistance is released owing to peak-residual strength drop，and the elastic strain energy accumulated in the locked segment would be converted into the kinetic energy of the sliding mass. Thus the sliding mass has a high velocity in biginning. After that，as potential energy is convetted into the kinetic energy，the sliding mass would slide still with a higher velocity. Based on triaxial tests，a study is performed on strength and deformation characteristics of the basaltic rock mass from the Touzhai high-speed landslide. The results show that there is remarkable difference between peak shear strength and residual shear strength，and the drop rate of the shear strength is about 50%. The muzzle velocity of the Touzhai landslide is predicted on the basis of the tests.

Select

STABILITY PREDICTION，MONITORING AND CONTROL OF KEY BLOCK SYSTEM IN ROCK SLOPE ENGINEERING

null

2004, 23 (10): -1658 doi:
Full Text:

[PDF 260 KB] (969)

+

Show Abstract

According to the viewpoint of discontinuity control and structure breakthrough of rockmass stability，the stability of rock slope engineering is greatly controlled by the distribution and stability state of key block system which is formed by the combination of rock discontinuities with excavation plane，so it is very important to determine and control the stability of key block system. For a complex high rock slope engineering as example，based on the analysis of geological conditions for the slope，especially the distribution of rock discontinuities，the distribution laws of block system for the complex rock slope engineering are analyzed by key block body theory firstly. Then the location，scale and stability coefficient of key block system of the complex slope are found out and calculated，and above results are used to instruct and optimize the monitoring layout in field，so that the correct bolt support is made effectively according to the monitoring information of key block system.

Select

APPLICATION OF MULTI-ELECTRODES ELECTRICAL METHOD TO DETECTION OF SLIDE-FACE POSITION

null

2004, 23 (10): -1662 doi:
Full Text:

[PDF 1669 KB] (1387)

+

Show Abstract

Multi-electrodes electrical method(MEM) is an effective tool for landslide survey，and the suitable in-situ working scheme and its data analyzing model are the base to obtain believable results. The ideal electrical models are given to figure slide-face in homogeneous soil slope，soft interlayer，and geological structure. Two dimensional apparent resistivity sections are formed with finite element method corresponding to four kinds of routine in-situ data collecting arrays，which are Wenner array，Schlumberger array，dipole-dipole array and pole-pole array. The ideal electric array and abnormal resistivity pattern are determined by analyzing the sections. An innovative data interpretation procedure for locating slide-face position in complex geological conditions is propoped，and a series of case study for slope survey with MEM are made. By analyzing the study result，it is shown that dipole-dipole array and Schlumberger array have the stronger exploration capabilities，and pole-pole array can explore the object inside wider area than other arrays with the same electrode. The apparent resistivity patterns of different types of landslide are different even if the landslide is investigated with the same electrical array. The ration parameter method can improve the capability of two dimensional apparent resistivity section to reflect the distribution of object inside landslide.

Select

GEOMECHANICAL MODELING STUDY ON STABILITY
OF ARCH DAM SHOULDER

null

2004, 23 (10): -1670 doi:
Full Text:

[PDF 335 KB] (728)

+

Show Abstract

In order to demonstrate and evaluate the stability of rock masses for the arch dam shoulders of Xiaowan power station on Langcang River in China，a three-dimensional geomechanical model test was conducted to study the features and mechanism of deformation-failure of the rock masses of right dam shoulder under the condition of excavation，designed load and overload，and to evaluate its stability and overloading capacity. The test result proves that attentions should be paid to the partial stability of the slope at the upper reaches with excavation. Under designed load，there isn’t any cracking in the rock masses and the compressed deformation of the weak zones is restricted in the distribution range of accessional stress caused by designed load. When the load is exceeded up to three times，the minute fissures begin to appear at the upper reaches of the dam foundation. The stability of the dam shoulder is mainly controlled by the deformation of weak zones and the deformation-failure process of the dam shoulder can be described by 3 stages，namely，beginning crack of dam foundation，compressed crack of dam shoulder and large deformation of dam shoulder. There is sufficient safety storage in the dam shoulder’s rock masses because its safety degrees under the normal case and the instable deformation are 3.0 and 7.0，respectively.

Select

HYDRAULIC PROPERTIES OF DYNAMO-RELAXED
ROCK MASS AT SITE OF DALIUSHU DAM

null

2004, 23 (10): -1677 doi:
Full Text:

[PDF 343 KB] (1004)

+

Show Abstract

It is of practical value to determine the hydraulic conductivity tensors of large-scale dynamo-relaxed rock masses at site of Daliushu dam on the Yellow River and to analyze the seepage field. The dominant sets of joints or fractures and their distribution parameters in rock masses of abutments and foundation are obtained by statistics from many prospecting tunnels. Then the hydraulic conductivity tensors are calculated by means of seepage theory through equivalent continuum，and modified by the data of consolidation grouting test，including water pressure test result in the left abutment and the data of seepage discharge measured in the prospecting tunnel under the river. The analyses of seepage through three main sections are also carried out. It can be concluded that the rock mass at site of the dam has great permeability with the magnitude of 10－5～10－4m/s，and that the quantities of seepage discharge and curtain grouting engineering should be large enough.

Select

ENGINEERING PROPERTIES AND AFFECTING FACTORS OF WEATHERED GRANITE IN FOUNDATIONS OF RUNYANG BRIDGE

null

2004, 23 (10): -1681 doi:
Full Text:

[PDF 409 KB] (1184)

+

Show Abstract

Weathering，being a natural process that decreases rock strength，stiffness and durability，is specially concerned in investigation and design of rock engineering. Runyang Bridge is the longest suspension bridge in China and the third longest one in the world by now. Weathering strongly affects the quality of the bedrock of granite and therefore controls the siting and designing of the bridge foundations. Systematical geological analyses and a set of field and laboratory tests were carried out. It is found that the lithology and the geological agents，including vertical tectonic moving，fracturing，unloading，river eroding and infiltration，are the main factors affecting the granite weathering and the various distribution of weathered rockmass at the bridge site. The study indicates that the granite is susceptible to weathering and unloading，and in early chemical weathering stage. The main geotechnical issues due to weathering and correlated countermeasures about selection of bridge type，site and design of the tower foundations，determination of bedrock parameters and control of further weathering of bedrocks are further discussed.

Select

SYSTEMATICAL STUDY ON STABILITY OF LARGE
UNDERGROUND HOUSES

null

2004, 23 (10): -1689 doi:
Full Text:

[PDF 219 KB] (1217)

+

Show Abstract

Based on the underground structure scheme of large houses of a hydro-electrical project，over hundred working conditions are numerically simulated. The variation law of displacement of house periphery is studied with considering four basic classes of rock masses，four different depths and different lateral initial stresses. As a stability criterion，the specific value of displacement of rock masses is presented to judge whether the long prestressed cables are needed to reinforce the rock masses. It is mentioned that a loosen-cracking zone of the side wall should be considered in many conditions，so that the numerical analysis result will be more closed to the reality. Finally，a simulating computation is made for a project. The computed displacement shows a good agreement to the monitoring result.

Select

GENERALIZED FINITE ELEMENT OF EXCAVATION COMPUTATION
FOR UNDERGROUND ENGINEERING

null

2004, 23 (10): -1694 doi:
Full Text:

[PDF 274 KB] (859)

+

Show Abstract

Based on the conventional finite element，Lagrange type interpolation space of displacements on each node is extended to an arbitrary function expansion with any variable number of generalized displacements. The accuracy of the numerical computations is improved only through increasing the order of interpolation functions without increasing the number of nodes. Three-dimensional generalized isoparameteric element of eight nodes and one-dimensional generalized bar element are established. The formulae of generalized shape function and the element displacement formulation are given. The strain matrix，stiffness matrix and load vector of element are formulated. In response to the excavation problem of underground engineering，the combined usage of conventional finite element with generalized finite element is suggested. The generalized finite element is applied to the surrounding rock mass of excavation boundary and the anchored rock mass. The conventional finite element is applied to the rock mass far from excavation boundary. Not only the computation precision，but also the computation efficiency is improved. The numerical implement programs of generalized finite element are discussed. From the computational examination questions as well as the engineering example，the numerical results indicate the advantage of generalized finite element. The proposed method is rational for analysis and computations of underground engineering.

Select

INTELLIGENT OPTIMIZATION OF ANCHORING PARAMETERS FOR LARGE UNDERGROUND HOUSES BASED ON THREE DIMENSIONAL NUMERICAL SIMULATION

null

2004, 23 (10): -1700 doi:
Full Text:

[PDF 420 KB] (913)

+

Show Abstract

The optimization of anchoring parameters for large underground houses is of some characteristics. For example，the object of stability is incompatible with the object of economics，so that the stability analysis of large underground houses is very complicated，and the assessment indexes are required to denote anchoring effect roundly. Further more a lot of schemes with different anchoring parameters will occur and a great deal of calculation is needed. Aiming at these characteristics，large scale numerical simulation is made with FLAC3D，combined with genetic algorithm and NN，and a new evolutionary NN limited difference method is proposed to optimize the anchoring parameters for large underground houses. Constrained conditions and optimization goals are constituted，and the optimization process is proposed. Using above method，the anchoring parameters of Shuibuya underground houses between the third and sixth construction step are optimized for the underground houses of Shuibuya Hydro-Power Station，which proves that the proposed method is feasible.

Select

ROCK MASS CLASSIFICATION FOR UNDERGROUND POWER
HOUSES OF SHUIBUYA PROJECT

null

2004, 23 (10): -1706 doi:
Full Text:

[PDF 190 KB] (1075)

+

Show Abstract

Taking the national standard for engineering classification of rock masses (GB50218-94) as a main method，with Q-system and RMR-system as an assistance，rock mass classification is made for the underground power houses of Shuibuya Project which is located on Qingjiang River in Hubei Province，China. The relationship between national code and support design is also built up.

Select

ANALYSIS AND FORECAST ON DIVISION PIER STABILITY OF PERMANENT SHIPLOCK OF THREE GORGES PROJECT
WITH WAVELET NETWORK

null

2004, 23 (10): -1710 doi:
Full Text:

[PDF 249 KB] (812)

+

Show Abstract

The stability of division pier influences the safety of the permanent shiplock of Three Gorges project. The safety coefficient is usually used to evaluate the stability of division pier. Wavelet network combines the time-frequency domain localization properties of wavelet transform and self-learning ability of traditional feed-forward neural network. Wavelet network was used to approximate the nonlinear relation between safety coefficient and control factors of the division pier stability of the permanent shiplock. The stability of division pier can be analyzed and forecasted with wavelet network trained by engineering case as learning samples. The numerical example shows that the precision of approximation and prediction of the proposed model can satisfy the quantitative evaluation for the stability of division pier of the permanent shiplock. The model is of good capability of noise-resistance. The wavelet net work is trained by the hydrid learning algorithm of Levenbery-Marquardt algorithm and Least-Squares algorithm. Levenbery-Marquardt algorithm can train the nonlinear parameters. Least-Squares algorithm can train the linear parameters. Error objective function is minimized in subspace of whole parameter space of wavelet network with the presented algorithm. Wavelet network is obviously superior to conventional algorithms.

Select

MODELING TEST STUDY ON DEFORMATION AND SUBSIDENCE OF GROUND SURFACE INDUCED BY UNDERGROUND MINING WITH THICK OVERBURDEN

null

2004, 23 (10): -1715 doi:
Full Text:

[PDF 345 KB] (1180)

+

Show Abstract

Based on the prototype of metal mine，the geological mechanics modeling test is made to deeply analyze the variation rules of deformation and subsidence of ground surface induced by excavation with thick overburden. With the modeling test，not only the complex geological condition of the selected sections，but also the excavating process of natural mining is realistically simulated. The roof of stope is of obvious creep property，but it behaves convergently according to the test. The location of the biggest subsidence of ground surface is also found for given case. Based on the testing results，the optimized initial-mining altitude is adopted by mining company.

Select

PHYSICAL SIMULATION ON BOLTED EFFECT OF LAYERED AND JOINTED ROCK MASSES UNDER CYCLIC LOAD

null

2004, 23 (10): -1724 doi:
Full Text:

[PDF 335 KB] (968)

+

Show Abstract

Using physical simulation method，the variety laws of elastic modulus E with the rock-layer thickness h and the fragmentation degree ，the cube root of rock block volume，of the layered and jointed rock masses under cyclic load with and without bolt support are studied in detail. The four non-bolted models and four bolted models of layered rock masses，and four non-bolted models and four bolted models of layered and jointed rock masses are adopted for testing. The thicknesses of layered rock masses are 540，270，135 and 67.5 mm, respectively. The corresponding joint intervals are 540，450，385.7 and 337.5 mm, respectively，in the layered and jointed rock masses. The fragmentation degrees of the layered and jointed rock masses are 540，380，272 and 197 mm, respectively. It is shown from the test that (1) the variety law of E with h or of non-bolted models in layered and jointed rock masses is of exponential regularity，(2) the variety law of E with h or of bolted models in layered and jointed rock masses is of logarithm regularity under the first loading, and linear one under cyclic loadings，(3) under non-bolted condition，the layered failure takes place in layered and jointed rock masses and (4) under bolted condition，the layered failure is effectively controlled，so that the broken models are still of good loading-bearing capacity.

Select

COMPUTATIONAL SIMULATION AND ANALYSIS ON FRACTURING MECHANISM OF CRANE GIRDER BOLTED TO ROCK WALL OF CHAMBER

null

2004, 23 (10): -1730 doi:
Full Text:

[PDF 370 KB] (1054)

+

Show Abstract

The mechanical behavior of reinforced concrete crane girder bolted to rock wall of chamber is analyzed with nonlinear finite element method. The concrete and rock mass are modeled by Drucker-Prager elasto-perfectly plastic constitutive relation. The Drocker-Prager yield criterion has found wide practical application as a method of defining the stress conditions under which rock mass will deform inelastically and collapse. Combined with the extending project practice of underground powerhouse at hydropower stations，the fracturing mechanism and stability of crane girder are investigated numerically. Computational results show that the cohesion and friction angle between rock mass and concrete have a notable influence on the stability of crane girder bolted to rock wall of chamber. The safety factor of concrete crane girder will be reduced with the decrement of inner cohesion between the rock mass and concrete crane girder. The safety factor of concrete crane girder can exceed 3.7 while the failure of interface between the rock mass and concrete occures. The further excavation of underground powerhouse will affect the stress distribution of system bolts and rock mass near crane girder. It is very important for improving stress states and enhancing stability of concrete crane girder to control effectively rock damages induced by excavation blasting.

Select

IN-SITU TESTING STUDY ON BEARING CAPACITY OF ROCK BOLTS AND CORRESPONDING CALCULATION METHOD

null

2004, 23 (10): -1735 doi:
Full Text:

[PDF 316 KB] (1106)

+

Show Abstract

The research achievements of in-situ tensile test on the bearing capacity of rock bolts for support of large-scale excavation are presented. The different methods of in-situ tensile test for bolts are discussed. Based on the test results，the distribution characteristics of axial strain along the anchored part and the displacements on bolts head and adjacent rock mass surface are given out. The influence of the dip angle of rock bedding planes on the stress of rock bolts and the coherence between grout and bolt are analyzed. At last，a new method is proposed to determine the bearing capacity of rock bolts. This method is far different from conventional methods. This method is derived from the in-situ test data and the uneven distribution characteristics of shear stress along the bolt are considered. The length of bolt is determined by the stressed part and the anchored part. The bearing capacity of rock bolts is calculated by the peak shear stress along bolt. The calculated results by the method are in accordance with the real force condition in bolting engineering.

Select

NONDESTRUCTIVE TESTING OF PARAMETERS OF BOLT
ANCHORING STATE AND ITS APPLICATION

null

2004, 23 (10): -1741 doi:
Full Text:

[PDF 275 KB] (1309)

+

Show Abstract

The fundamental principles of the reflection wave method，and its application to nondestructive testing of parameters of bolt anchoring state are presented. The testing results shows that reflection wave method is available to detect the anchoring state of bolt in ground.

Select

APPLICATION AND DISCUSSION OF THREE DIMENSIONAL NUMERICAL MANIFOLD METHOD BASED ON
HEXAHEDRON ELEMENT

null

2004, 23 (10): -1745 doi:
Full Text:

[PDF 325 KB] (873)

+

Show Abstract

In this paper，three-dimensional numerical manifold method (NMM) based on hexahedron element is proposed and the shape functions of C8 isoparametric element are used as the cover weight functions. All sub-matrices of equilibrium equations are derived according to this cover weight function. In 2D contact，the direction of shear stiffness and friction force is easily defined along the contact edge. For the corresponding 3D contact problem，it is difficult to determine similar relations in simple way. In the present paper，vector theory and iterative method are proposed to overcome this kind of difficulty. An example of underground excavation is also presented.

Select

NUMERICAL MODELING TECHNIQUE OF SINGLE SCAN LINE METHOD TO ASSESS JOINT TRACE LENGTH

null

2004, 23 (10): -1755 doi:
Full Text:

[PDF 212 KB] (1011)

+

Show Abstract

Due to the limitation of field condition，single scan line method has been applied to estimate randomly distributed joint trace length on occasion，namely，sampling bias correction of random joint trace length. In order to obtain more precise joint trace length，it is proposed that (1) the method of probabilistic delineation of orientation data is used to delineate randomly distributed joint trace to obtain the predominant joint clusters，(2) each observed joint trace length and mean value of trace length are obtained for every cluster，(3) a probabilistic numerical method is used to model the probabilistic density function (PDF) of trace length for each clusters，and (4) according to the PDF of trace length for each cluster，semi-trace length scan line method is applied to correct the sampling bias of observed trace length for each cluster and to obtain the corrected mean value of trace length. The presented research results prove reasonable by actual engineering project.

Select

STUDY AND MANUFACTURE OF FLEXIBLE BOUNDARY LOADING TESTING MACHINE

null

2004, 23 (10): -1760 doi:
Full Text:

[PDF 190 KB] (1091)

+

Show Abstract

Existing testing machines for rock and soil mechanics and geo-engineering are all under stiff boundary loading，that is，all the displacements at every point of boundary surface are equal. These kinds of testing machines are aimed at homogeneous materials. The existing testing machines are mainly used to study stress-strain state and strength criterion at a point inside homogeneous materials. This does not correspond with the fracture patterns of rock and soil mixture or fractured rock. The reason is that these materials contain structural faces and joint faces，and they are inhomogeneous and discontinuous. While external forces are applied on them，the stress distribution inside materials is uneven. For these materials，the real state is that stresses acting on every point of boundary surface are equal. In order to study the mechanical behaviour of rock and soil mixture or fractured rock，a new type of triaxial compressive test machine is developed，namely flexible boundary loading testing machine. This testing machine is good at studying the deformation and failure of inhomogeneous and discontinuous media from the angle of loading equability. The working principle and design thought of this machine are illustrated. The correlation among axial pressure，confining pressure and balance pressure is derived. At the same time，the application of ultrasonic displacement measuring system to flexible boundary loading testing machine and the making process of test sample are also presented.

Select

INFLUENCE OF BED ROCK CRACKING ON EARTHQUAKE AFFECTING COEFFICIENT IN TANGSHAN CITY

null

2004, 23 (10): -1765 doi:
Full Text:

[PDF 215 KB] (986)

+

Show Abstract

China is the country with land earthquake taking place frequently. All the two big earthquakes during 20 century in the world，which caused more than 200 000 lives lost，took place in China. Land earthquake is mainly caused by fault activity and quick transmission of earthquake waves in land. Earthquake disaster is controlled by two main factors，site condition and base rock condition. The consideration of site condition is usually made in earthquake disaster prediction，but less attention is paid to base rock condition. As densely populated area with highly developed civilization，city shows obvious fragility to natural disasters. Tangshan，as a heavy industry city with six million populations，is located in the north east of Heibei province，China，and has been frequently suffered from natural disasters such as earthquake，karst collapse and ground collapse. The Big Earthquake in 1976 of Tangshan still remained freshly in people’s memory，which caused 240 000 lives lost，and especial attention has been paid to disaster resistance. Earthquake affecting coefficient is one of the most important factors for earthquake security evaluation，but it is very difficult to determine earthquake affecting coefficient accurately because of the influence of underground rock conditions. Traditional methods couldn’t analyse well earthquake resistance in city and engineering construction. Based on numerical calculating results of energy，and cracking probality in undeground base rock，the influences of these factors on earthquake affecting conefficient are analyzed. According to the base rock condition parameters，neural network method is applied，and the relation among earthquake affecting coefficient，energy，displacement and cracking probablity of undergroud rock is determined. The calculating model of earthquake affecting coefficient is constructed and the distribution of earthquake affecting coefficient in Tangshan city is calculated. From the calculating results，it is found that the earthquake affecting conefficient in southeast of Tangshan city is bigger than 0.48，even more than 0.64 somewhere，which means that the intensity of earthquake disaster is 10 degree. At last，some suggestions for city planning and engineering construction are given.

Select

FIELD TEST AND THEORETICAL ANALYSIS ON FLEXIBLE LARGE-DIAMETER ROCK-SOCKETED STEEL PIPE PILES UNDER LATERAL LOAD

null

2004, 23 (10): -1770 doi:
Full Text:

[PDF 554 KB] (1352)

+

Show Abstract

The flexible large-diameter rock-socketed steel pipe piles in a coal wharf is a new form of structure，which consists of 7 large-diameter rock-socketed steel pipe piles. The steel pipe pile is rare in the domestic and international engineering，with its outside diameter of 1 400 mm，thickness of 16 mm，lengths of 30.74～32.24 m，and 4.94～5.63 m socketed into rock. In order to verify the safety of structures and the quality of construction as well as to improve the design methods，a field test on two piles under lateral load is carried out. This full scale test shows that the design and the construction are excellent，and meet the demand of the original design. However，the improvement of design methods for lateral load piles is a complex problem，as it requires the determination of relevant properties of soil and soil-pile. So a new calculation method for lateral loaded pile，named composite stiffness principle with biparameter method，is presented and verified by comparing its results with available field test data. Thus the regulation of the pile-soil interaction and the range of composite stiffness EI and biparameter 1/n with a is obtained. These parameters can be used in the design of other long piles nearby. At the same time，the pile-soil parameters for the large-diameter rock-socketed steel pipe piles are accumulated for development of this new method.

Select

COMPREHENSIVE TREATMENTS OF ANCIENT LANDSLIDE AT
DIAOZHONGYAN SECTION OF 319 NATIONAL ROAD IN SHANGHANG COUNTY

null

2004, 23 (10): -1778 doi:
Full Text:

[PDF 384 KB] (1035)

+

Show Abstract

The ancient landslide at Diaozhongyan section of 319 national road in Shanghang county，Fujian Province，China，has been activated due to highway rebuilding. By judging the actification with detailed geological prospecting and by summarizing several disease recovering expreiences，the comprehensive treatments are proposed and proved to be successful for the landslide. The treatments include combined measures of anti-slide pile with prestressed cable，prestressed cable frame beside shoulder wall，cut work to lose weight，and drainageway. Now the observation of two years shows that the landslide is stable with the support presented in this paper.