对于地下洞室的稳定性分析,初始地应力的回归分析是十分重要的第一步.现行的初始地应力回归方法如函数法、位移反分析法、边界法等不易操作,且准确度也不高.本文以黄岛地下水封石油洞库为例,根据实测的初始地应力拟合出水平向主应力与竖直向自重应力的关系,在已有自重应力计算结果的基础上,通过坐标变换,将拟合出的水平向主应力转换至模型坐标下的正应力和剪应力,利用FLAC3D的FISH语言,遍历所有单元读入上一步得到的正应力和剪应力,计算至收敛后直接生成初始地应力场.将回归结果与现场实测结果进行对比分析,相对误差在10％以内,取得了较好的效果,此种方法简单且有效.

The underground water-sealed storage technique is critically important and generally accepted for the national energy strategy in China. Although several small underground water-sealed oil storage caverns have been built in China since the 1970s, there is still a lack of experience for large-volume underground storage in complicated geological conditions. The current design concept of water curtain system and the technical instruction for system operation have limitations in maintaining the stability of surrounding rock mass during the construction of the main storage caverns, as well as the long-term stability. Although several large-scale underground oil storage projects are under construction at present in China, the design concepts and construction methods, especially for the water curtain system, are mainly based on the ideal porosity medium flow theory and the experiences gained from the similar projects overseas. The storage projects currently constructed in China have the specific features such as huge scale, large depth, multiple-level arrangement, high seepage pressure, complicated geological conditions, and high in situ stresses, which are the challenging issues for the stability of the storage caverns. Based on years' experiences obtained from the first large-scale (millions of cubic meters) underground water-sealed oil storage project in China, some design and operation problems related to water curtain system during project construction are discussed. The drawbacks and merits of the water curtain system are also presented. As an example, the conventional concept of “filling joints with water” is widely used in many cases, as a basic concept for the design of the water curtain system, but it is immature. In this paper, the advantages and disadvantages of the conventional concept are pointed out, with respect to the long-term stability as well as the safety of construction of storage caverns. Finally, new concepts and principles for design and construction of the underground water-sealed oil storage caverns are proposed.

The effect of groundwater level on mine cavern block stability is analyzed by Unwedge.Two methods are used,one considering the groundwater pressure and the other not.The safety factors of blocks are obtained respec-tively.Besides,the calculation is carried out under different groundwater levels and different water pressure against structure surfaces.The curves are obtained,which show the change trend of the safety factor according to the height change of water level.The data comparison shows that groundwater pressure can greatly reduce the safety factor of blocks,and may also decrease nonlinear with the increase of water level.The results prove that Unwedge is a reasona-ble and necessary tool to analyze the cavern block stability.

文章以某大型地下洞室群工程项目为背景,首次引入标准极差(R/S)分析法处理收敛变形时程数据.首先,根据Hurst指数的基本含义并结合力学原理,指出分形维数代表断面变形的收敛速度,而Hurst指数本身代表监测开挖后围岩的松动程度;然后,计算分析了实际变形数据的Hurst指数及其分形维数,从而判断了变形时程曲线的动力特征,比较了同一断面各测线之间的区别;进一步分别计算了同一轴线上不同断面监测数据的Hurst指数值,推测了本工程区域内围岩变形性能的演变趋势;最后,总结了Hurst指数的影响因素及其算法的改进思路.

The surge tank at tailrace of Jinping I hydropower station is composed of two vertical cylindrical wells of large-diameter at the location of high stress and complex geological configurations with two large scale faults and multiple sets of joints. It was difficult to cavern out the domes and setup supporting structures at the top of cylindrical wells. Engineering practice and theoretical research show that the methods of excavation and the parameters of supporting are the key factors influencing the stress distribution and deformation at the crest of the dome of the tailrace surge tank. Lamprophyre veins and fault f14 were found to exist above the dome of tailrace surge tank #1 through in-situ investigations. The deformation and failure mechanisms of surrounding rock of the tailrace surge tank are studied through mechanical analysis,in-situ monitoring and 3D numerical simulation. The deformational and mechanical characteristics of the dome rocks during excavation process were studied. Some advices on the excavation and support for the tailrace surge tank are thus presented as the technical supports for its excavation and design of the support.

为了研究底板保护层的实际效果,采用数值计算软件FLAC3D对预留和取消底板保护层两种方案进行了对比分析,结果表明:取消底板保护层时,底板的位移和塑性区深度、拱顶和边墙的变形都小于预留底板保护层的开挖方案;对改变洞室第三层和第四层开挖深度的不同方案进行了对比分析,结果表明:第四层的深度越大,开挖完成后底板的位移和洞室边墙的变形越小.通过对比分析可知,取消底板保护层的方案较好,并且底板上部预留的开挖深度越大越好.

Taking an underground oil storage project in Shangdong as study case, the Unwedge procedure is used to find out possible block in rock mass and then the stability coefficient of block is calculated based on investigated parameters in order to evaluate its stability and the effectiveness of supporting programs. According to the tendency of joints on middle level of underground rock carven, the possible block in lower level is forecasted and then the supportings for lower level excavation are proposed.

In underground works ,displacement monitoring has become a key means to grasp rock dynamic chan-ges.Simultaneously ,the arrangement of the measurement points has a significant impact on accuracy and uniqueness of the displacement back analysis .Based on the principle of maximum displacement ,the problem of optimization arrange-ment for measurement points of back analysis in transversely isotropic rock mass is studied .The circular roadway dis-placement variation with angle and radius has been analyzed .Therefore,further analysis of the impact of lateral pres-sure coefficient 'svariation with the displacement has been studied ,and then the rule of optimization arrangement for measurement points has been obtained .The results show that a lager area near the wall in the direction of principal stress is the most suitablearea to arrange measuring points in .

Firstly,the construction technology of the low-temperature liquefied petroleum gas(LPG) and low-temperature liquefied natural gas(LNG) underground storage caverns is introduced. The field experiments and theoretical analysis for low-temperature LPG and LNG underground storage caverns engineering are summarized. And the frozen rock mechanics problems related to these engineering are introduced,from the four following reviewed researches:(1) Rock physical properties under low temperature or freeze-thaw cycle;(2) Effect of low-temperature freezing or freeze-thaw cycle on fractures of rock;(3) Moisture migration;(4) The frozen rock mass coupled thermo-hydro-mechanical model under low-temperature freezing condition. Due to the differences of freezing in the laboratory and field conditions,the mechanism of the frozen action to intact rock and rock mass is explored. Moisture migration and temperature filed of frozen rock mass are also considered. The last,the construction technology and stability of LPG and LNG underground storage caverns are discussed.

During processing of section deformation's convergent data of large underground cavern group engineering, obvious regularity is found at degree of fluctuation of the time history curve. Therefore, one-dimensional box dimension is introduced to quantitative description of this feature; and then relevant mechanical meaning of properties of surrounding rock is discussed based on the testing calculation results. Furthermore, the index is used to compare variation of the results of different monitoring cross-sections; and the corresponding relationship between integrity of rock and box dimension is confirmed. Through analyzing the relationship of various sections' spatial locations and their box dimension values, the evolution tendency of rock's integrity on the whole region is drawn. Finally, validity of the paper's inference is proved by surrounding rock conditions which is revealed by subsequent excavation.

The underground cavern group of Jinping I hydropower station, whose are huge scale and complicated arrangement, is located in geological body whose stress is high. There are three large-scale faults and multiple sets of joints in the rock mass. For the main structural plane or fracture zone, the pattern or time about supporting system, as well as parameters optimization, are the key problems to the stability for cavern group during the multistep excavation in the multi-cavern group. According to the excavation and supporting process for the underground cavern group, the deformation and cracking mechanism of surrounding rock mass and faults in main cavern have been researched, as well as the coupling mechanism and characteristics of mechanics and deformation about multiple supporting have been discussed. Based on numerical simulation and measurement in-situ, studying the strong flexible technology that shotcrete system and steel arch rib. It is showed that the huge deformation of surrounding rock mass reduced greatly; and the instability or collapse that caused by the local instability are avoided by applying the new technology. There are important reference and guide significance to the construction and design of the underground cavern group.

Seepage is one of the key factors which affect the stress and deformation of surrounding rock in excavation process. By combining 3D geo-mechanical model test for the diversion tunnel of Jinping II Hydropower Station, two hydraulic servo-controlled water supply schemes are designed. The discrete holey tube seepage generation system is optimized and selected for solving the percolating water question among the test bench retaining plate system, the mini-type multi-point extensometer transfer rod and the support sleeve. Based on discrete multi-principal stress plane, a new loading technology which has waterproof function is brought forward to make sure to generate the initial stress field while no seepage in assembly airbag steel sleeve and the wire hole of data collection equipment. The high simulation of seepage field is realized.

The visualized model test of gas storage cavities destruction process in salt rock is more difficult than the ordinary geo-mechanical model test, which demands the air tightness of cavities, the visibility of destruction process and the similarity of rheological property and self-healing between model material and as salt rock. The authors have excogitated an air impermeable and transparent material, which imitates the self-healing and rheological property of salt rock after large numbers of tests. In this article, techniques of constructing the physical model by utilizing this model material are introduced, and the load control system is also described in detail. A kind of non-disturbed 3-D deformation measurement method which bases on Digital Speckle Correction Method (DSCM) and pre-embedded displacement sensor method is put forward. Besides these, the system of measuring model internal deformation and monitoring the destruction process are illustrated.

The stability criterion for underground caverns based on the unbalanced force and the minimum plastic complementary energy is introduced into the software fast Lagrangian analysis of continua in three dimensions (FLAC3D),and its equivalent form is deduced. The rationality of using the maximum unbalanced force and the plasticity distribution to determine the stability and using the unbalanced force distribution and adjustment process to indicate the destruction location and evolution path of storage group is demonstrated. The layout of dense storage group is optimized from two aspects of the reasonable space between two caverns and the layout pattern,respectively. The results show that distance 1.5 times of cavern diameter is safe and economic between two caverns;and equilateral triangle layout is the optimal plane layout pattern. Two kinds of destruction sources in the storage group are compared. The results show that the influence of sudden pressure loss starting from internal caverns is more significant and cause more serious damage than that from the outlying caverns. The stability of single internal cavern with sudden pressure loss is analyzed by using equilateral triangle layout. Considering the long-term strength reduction of salt rock,the stability of the same model is carried out. The results are applied to the chain destruction analysis later as an indicator of local failure. The chain destruction process is studied by numerical simulation;and the results show that the sudden pressure loss in single cavern doesn′t tend to cause chain destruction of storage group.

Uniqueness research is one of the basic theories of displacement back analysis. The displacement analytic solution of a deep circular tunnel in transversely isotropic rock mass is deduced firstly; and then the uniqueness of displacement back analysis of a circular tunnel in transversely isotropic rock mass is discussed by means of identifiability conditions. The results indicate: all of 6 parameters can't be determined simultaneously no matter how many the measuring points are set; only when there are at least 3 known parameters, may the other parameters be determined simultaneously; whether the vertical ground stress component is equal to the horizontal one has obvious influence on the results; in the aspect of identifiability, two ground stress components have the best effect, elastic modulus and Poisson ratio on the isotropic plane take the second place, and elastic modulus and Poisson ratio in the direction vertical to the isotropic plane have the worst effect.

Through a single crack,the main cracks appeared in the wall and imbedded near the wall of cavern are simplified as a half infinite plane with a fringe crack and one with a crack near the free edge for chilled liquefied petroleum gas(LPG) storage cavern respectively.To explore the influence mechanism of temperature decreasing on crack propagation,firstly the effect of rock parameters change caused temperature decreasing on the crack propagation is analyzed.Secondly,the effects of temperature boundary type,intensity and velocity of temperature decreasing,and angle between crack and wall on the temperature fields,stress fields and the stress intensity factors(SIF) of cracks with different lengths are researched.Finally,as a tentative research,the inhibition action of the ground stress on crack propagation during the temperature decreasing of crack is taken into consideration through the principle of superposition;and the relationship between the of temperature storage medium and the ground stress of cavern is analyzed under the condition of the existent crack non-propagating.

Sedimentary rock with layered structure accounts for 2/3 of global land area, and lots of metamorphic rock also has significant features of layered structure, so there are many stability problems about layered rock mass in geotechnical engineering. Layered rock mass is generally considered to be transversely isotropic solid. Based on the complex variable expression of stress function, the complex variable expression of displacement components of transversely isotropy is deduced; the displacement analytical solution of a deep tunnel with arbitrary cross section in transversely isotropic rock mass is derived by conformal mapping method. Although the cross section of the tunnel is assumed to be parallel to the isotropic plane, the displacement analytical solution indicates that radial displacement of surrounding rock is related not only to elastic modulus and poisson ratio on the isotropic plane but also to that in the direction normal to the isotropic plane.

The feedback analysis of underground powerhouse caverns excavation of large-scale hydropower stations attracts more and more attention recently.The effective feedback analysis method is very crucial to such problem.A direct solution scheme based on artificial neural network(ANN) is suggested considering that the feedback analysis is virtually a constrained optimization problem.It mainly consists of analyzing the structure numerically to build the constraints and obtaining the input parameters by ANN to fulfill the objective function.The steps of this method are also illustrated in detail,from which can find that the method is simple but universal.The ANN based feedback analysis method can avoid the deficiency of the traditional mathematical programming and improve the effectiveness and the convergence of feedback analysis.Taking the underground powerhouse caverns excavation of Xiluodu hydropower station in China for examplet,he fast Lagrangian analysis of continua,FLAC3D,is used to establish the ANN based feedback analysis system.The feedback analysis with the monitoring deformation data during excavation is conducted.The surrounding rock displacements obtained by feedback analysis agree with the measured displacements.The predicted deformations and stresses of caverns and the loads on the supporting structures in the next excavation are also reasonable.These not only help to evaluate the stability of the powerhouse caverns of Xiluodu hydropower station but also show that the method proposed is valid and applicable for complex monitoring feedback analysis problems;and the method may get extensive application in engineering.

The creep tests on marble specimens from the underground powerhouse of Jinping I hydropower station of China are carried out to meet the demand of long-term stability analysis of the caverns during the construction and the operation periods.Two common rheological models,Hooke-Kelvin model and Burgers model,and their parameters determination are described with comparative discussion for the model selection.The least squares fitting to the testing results with the model curve is recommended to gain the model parameters.The creep testing system and the testing procedure are introduced briefly.It is manifested by the uniaxial creep tests and the biaxial creep tests that the considered marble shows time-dependent behavior to some extent under certain stress states.The deformation gradually approaches to corresponding constant after the early stage of creep attenuation,which accords with the creep characteristic of the Hooke-Kelvin model.The measured strains with respect to the loading time are close to the Hooke-Kelvin model curve.Therefore,the Hooke-Kelvin model is recommended to describe the rheological properties of marble.As for the Burgers model,the analysis shows that it is unsuitable for modeling the viscoelasticity of hard rock like marble.The creep behavior during relatively longer testing time,e.g.150 hours or so,needs to be examined if the Burgers model is adopted.The fact that the deformation of the underground powerhouse caverns of Jinping I hydropower station finally tends to become steady after excavation can be better explained by means of the Hooke-Kelvin rheological model.The Hooke-Kelvin rheological model and the model parameters obtained from creep tests may also be served as the fundamental data in the later long-term stability analysis of the surrounding rocks of the underground powerhouse caverns in the periods of construction and operation.