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云南某矿山年产20万吨镍精矿
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云南某矿山年产20万吨镍精矿 选矿厂设计,云南某矿山年产20万吨镍精矿,选矿厂设计,云南,矿山,年产,20,万吨镍,精矿,选矿厂,设计
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Journal of University of Science and Technology BeijingVolume 11, Number 4, August 2004, Page 289Corresponding author: Yongtao Gao, E-mail: gaoyongtMineralCut slope reinforcement technique in open-pit minesYongtao Gao1), Jianbo Sun2), Shunchuan Wu1), and Aibing Jin1)1) Civil and Environmental Engineering School, University of Science and Technology Beijing, Beijing 100083, China2) Highway Development Limited Company of Henan Province, Zhengzhou 450052, China(Received 2003-09-18)Abstract: The design and practice in supporting the cut slope of an open-pit mine were introduced, in which the high pressuregrouting method was used in reinforcing the weak formation in the slopes. Based on a detailed geological survey of the slope, a theo-retical analysis was carried out, and the design parameters were proposed, where the Tresca or Mohr-Coulomb yield criteria was em-ployed. A patent technology, named “Technology of high pressure and multiple grouting in different levels within a single hole”, wasemployed in the construction. Anchor bars were also installed as grouting proceeds. This method combines anchoring and groutingcomprehensively and was found successful in practice.Key words: mining engineering, open-pit slope; weak formation; supporting; high pressure groutingSlope collapse is common but would be a disasterduring the course of mining and transportation ofopen-pit mines. It often induces a serious accident thatcauses the pause of production and the fatal casualty.Therefore, an effective reinforcement to the unstableslope, particularly that the slope is facing with the un-stable state, is an important and difficult technicalproblem that we often faced with and must be solvedin the construction of open-pit mines, highway, rail-way, irrigation engineering, hydraulic-power engi-neering, and so on. In this paper, a new reinforcementtechnique is described for the excavation of a cut-slope of the transportation line in an open-pit mine. Itis proven a great success in practical engineering 1,2.1 Geology characteristics of the slope and itsinfluenceThe slope body was considerably unstable in thegeological examination. It is formed by quartzite for-mation, in which a weak interlayer is distributed. Thegeologic features can be summarized as followings.Firstly, the body of the slope is made of silicarenite,where joints and crevices reach 20 to 30 per meter.Although the strength of the rock is high, the stabilityof the slope is poor regarding to the rock strength (seefigure 1, tables 1 and 2).Table 1 describes the mechanical properties of thesilicarenite formation and the weak formation. Boththe cohesion (c) and the internal friction angle () inthe silicarenite formation are much higher than thoseat the interface. Generally, both the cohesion and theinternal friction angle of the silicarenite formation arehigher than those of the weak formation. However, theinternal friction angle of the silicarenite at the inter-face is significantly higher than that of the weak for-mation at the same position. This means the sili-carenite is so fractured that the inclusion of the weakformation has been fulfilled the joints and crevices,resulted in the reduction of internal friction factor.Water in the slope body flew through the joints andcrevices, which brought the inclusion in the weaklayer and filled in the joints and crevices of the sili-carenite formation.Figure 1 Rock stratum of the road cut of a section of E-BS(LIGS, 1998).In table 2, it can be found that the rock at the shal-low is less weathered than that in the deep.Secondly, the main angle of rock formation isclosed to the inclination of the right slope of the roadcut, increases the instability of the slope.Thirdly, the potential risk is the weak formation (asshown in figure 1), which is made of a lamprophyre万方数据290J. Univ. Sci. Technol. Beijing, Vol.11, No.4, Aug 2004vein of 7 m in width. The lamprophyre formation wasfound on the slope root, which is located in the sili-carenite formation. The weak formation inclines to theroad, and it brings the stability problem of the rightslope.Table 1 Mechanical properties of the silicarenite formation and the weak formationUnit weightRock stratumInterfaceRock typeNature /(kNm3)Saturated /(kNm3)c/ kPa / ()c / kPa / ()Weak formation25.025.43527526Up and buried silicarenite formations27.027.360312020Table 2 Physical characteristics of the silicarenite rock massRQD / %Density of joints and crevices(joints per meter)Stability evaluation of rock massDeepShallowDeepShallowDeep(NGI)Shallow(NGI)Deep(CSIR)Shallow(CSIR)45402020 to 301.20.814529Notes: 1) Data of deep situation was acquired from the border of the collapsed section; 2) RQDrock quality degree; 3)NGINorwegian Geotechnical Institute, CSIRCouncil for scientific and industrial research. From the geology characteristics of the open-pitmine slope as mentioned above, the weak formationwould directly cause the slope collapse. The reasonsare as follows.(1) Plastic deformation. The water content in theweak formation is high, and the water conductivity ofboth the weak formation and the silicarenite layer arealso comparatively high due to densely developedjoints and crevices (also see table 2). During the exca-vating, water flows out of the slope and brings the siltfilled the formation. The bearing capacity of the layerwould then reduce. The pressure in the upper layercaused the plastic deformation of the weak formation.The integrity of the above silicarenite formation is notso high that the whole slope would hereby collapse. Itis the main reason that a section of the slope has col-lapsed.(2) Supply of the rainfall. Since the high water con-ductivity of the slope, the slope would soon get supplyfrom the rainfall. Hereby, the water in the slope con-tinuously brings the fillings out of the slope and theplastic deformation is then accumulated.(3) Slide component force of gravity. The weakformation inclines to the same direction as the slopedoes. The above silicarenite formation would slidealong the weak formation.(4) Hazardous position of the weak formation. Theweak formation presents at the risk position of theslope, which is located 2 to 3 m above the slope baseand exposes at a range of 140 m.2 Technical optionsIn order to avoid the collapse of the slope, it is ofmost importance to provide reinforcement or supportto the weak formation. The proposed options could beas follows.(1) Reducing the slope angle. If the slope is reducedto 1:1.2, and a shotcrete wall of mortar of 500 mmthick is constructed, the slope would then keep stable.Whereas, this option has disadvantages of enlargingthe right boundary of surface land and increasing theexcavation work.(2) Pre-stress anchoring. In this option, belt beamsmade of reinforced concrete need to be constructed onthe surface of the slope first, because the surface ofthe slope is heavily fractured. One end of anchor bar isthen installed on the belt beam, and also cement is in-jected in the slope. At last, the pre-stress is applied tothe bar to improve the stability of weak formation 3.(3) High-pressure grouting. Instead of applying pre-stress to the anchor bars, high pressure grouting canimprove the physical characteristics of the rock massin the slope. It is a much simple method and has ad-vantages as the following: The cement can spread in the weak formation ef-fectively and become the backbone of the weak for-mation when it hardens. The supporting capacity ofthe hardened grout can reach more than 8 MPa. Under the high pressure, a cement medium is in-jected into the fillers of the formation, through whichthe weak formation is modified. The spreading ofgrout cement also combines the ruptured silicareniteformation with the joints and conceives. It gives riseto the stability of the formation by 50%. In construction, steel bars are installed when thegrout hole is taken the shape. Then the hole is ce-mented. This combines the grouting and anchoring万方数据Y.T. Gao et al., Cut slope reinforcement technique in open-pit mines291comprehensively. Here, steel bars are shorter than tho-se in option (2).3 Mechanism of high-pressure grouting3.1 Mechanism of strength increaseCement grouting is to improve the characteristics ofthe existing soil and rock and to form a new mediumin the grouting area. The chemical mechanism ofgrout includes the following three aspects 4, 5:(1) Chemical cementation. The soil or rock bodystructure is strengthened by the chemical action ofgrout, which brings cementing power through eithergrout or chemical grout.(2) Inert filling action. The grout, which is fulfilledin the void of soil and rock, hardens and improves theload bearing capacity and the rigidity module of theslope. The deformation of the slope is hereby con-strained.(3) Ion exchange action. Some elements of cementgrout have ion-exchange reaction with the elements inthe rock and clay, which the new generated materialshave more ideal mechanical properties.3.2 Split-grouting mechanismThe mechanism of high pressure split grouting iseventually a question of the expanding of a round hole6. As shown in figure 2, the plastic zone is distribut-ed around the hole and the elastic zone is around theplastic zone. For simplicity, some basic hypothesesare given as follows.Figure 2 Expanding diagram of a round hole.The material around the hole is an ideal homogene-ous isotropic elasto-plastic mass, which is accordancewith the Tresca or Mohr-Coulomb yield criteria.In the plastic zone, where r is specified betweena and b, the distribution of expanding compressiveforce is quite different from that in the elastic zone.The expanding compressive force distribution can bederived through Tresca Yielding Criteria:Kr2=(1)where K is the yielding strength of the material, r theradial stress, and the circumferential stress.Accordingly, the critical expanding stress Pc can beobtained by the following equation 6:rrrmKP1c2=+=(2)where 011=+E, 01=+Er,0)(4)(21+=+, +=EE;E+ and E are the compressive and tensile modulus re-spectively; + and the compressive and tensilePoisson ratio respectively; Pc is the critical expandingstress.If the grouting compressive force p is less than Pc,the border of the grouting hole would not yield, so thatthe material is in elastic state. However, if p is greaterthan Pc, then the plastic zone begins to expand gradu-ally. Moreover, if p is enlarged to a certain number, Pu,the radium of the plastic zone would then reach b. ThePu and b can be derived as follows 6:ru1ln2mabKP+=(3)121mab = (4)From the derivation given above, it is seen that Pc,Pu and b can be determined by the physical character-istics of the material. Theoretically, the criticalgrouting compressive force Pc is defined by the ten-sion modules of the material, and the radium of theplastic zone b is determined by the characteristic ofthe surrounding rock 6, 7. Under the high pressure,the weak stratum is compacted. When the groutingcompressive force exceeds Pc, the grouting cement isinjected in the weak stratum. This improves themechanical characteristics of the weak stratum, whichsurrounds the grouting hole (as shown in figure 3).The grouting compressive force p can be calculatedthrough equation (3) and table 1. In this case, thegrouting compressive force was calculated greaterthan 3 MPa. Another important grouting parameter bwas also calculated less than 3 m. Hereby, the distancebetween adjacent grouting holes can not exceed 3 m.万方数据292J. Univ. Sci. Technol. Beijing, Vol.11, No.4, Aug 2004Figure 3 Grout splitting diagram in soil.4 ConstructionFollowing the analysis of geological characteristicsof the slope given in section 1, the collapse of the slo-pe comes from three aspects: (1) the plastic deforma-tion of the weak formation, (2) water in the stratum,and (3) the slide force of the gravity on the inclinedlayer. The construction methodology is to cope withthree aspects: Firstly, cement was grouted in the weakformation to enhance its geological characteristics (asshown in figure 4); Secondly, anchored rods were in-stalled to improve the monolithic of the slope; Thirdly,water outlets was made on the slope to allow the waterin the slope flowing out.Figure 4 Diagram of slope support design.The procedure of high pressure grouting in differ-ential level in a single hole was carried out success-fully through the core sample of the rock stratum. Theresults are given in table 3. A comparison of physicaland dynamic characteristics is before and after thecement grouting in the weak formation. It shows thatthe unit weight does not change so significantly beforeand after grouting; whereas, the shear yield capacitiesof both the weak formation and the interfaces are im-proved considerable, especially their cohesion im-proved greatly.Table 3 Mechanical characteristics improvement of the weak formationUnit weight / (kNm3)Shearing capability of the formationShearing capability at the interfaceWeak formationNatureSaturatedc / kPa / ()c / kPa / ()25.025.43527526OriginalAfter grouting25.926.042281928On the other hand, water was found to flow out ofthe embedded outlets in the slope surface. Moreover,cracks on the hip of the slope measured did not de-velop, which eventually demonstrated the success ofthe supporting options.5 Conclusions(1) An ideal option, the high pressure grouting, isobtained by comparing different options.(2) Based on the theoretical model, the groutingparameters were determined.(3) An important technique, named high pressuregrouting in different level in a single hole, was intro-duced to solve the problems faced in practice, and wasfound successfully.(4) It should be pointed out that some mechanismsstill remain uncertain. For instance, after the groutingcement is injected into the slope, a kind of retainingwall formed the superficial stratum of the road cut,which keeps the slope more stable. This study doesnot take the effect of the retaining wall into account.The question if the thickness of the retaining wall canbe reduced, or, if less cement can be injected, will bediscussed in a separated paper.References1 Y.P. Zhang, Y.T. Gao, and S.C. Wu, Unstable analysis ofslope under dynamic loading condition J, J. Univ. Sci.Technol. Beijing (in Chinese), 25(2003), No.2, p.110.2 Y.T. Gao, Y.P. Zhang, and S.C. Wu, Stability analysis ofreinforcement for landslide rock mass slope J, Chin. J.Rock Mech. Eng., 21(2002), Suppl., p.2562.3 Y.T. Gao, S.C. Wu, and J.H. Shun, Application of the pre-stress bolt stress distributing principle J, J. Univ. Sci.Technol. Beijing (in Chinese), 24(2002), No.4, p.387.4 E. Hoek and J.W. Bray, Rock Slope Engineering M (inChinese), Metallurgical Industry Press, Beijing, 1983.5 J.Y. Luo, Geotechnical Engineering and Road Bed M (inChinese), China Railway Press, p.187, 1997.6 Q.T. Wang and X.F. Cao, Solution for the hole expandingproblem of the materials with different module of tensionand compress, in Proceedings of the First Symposium onAnchoring and Grouting Techniques C, Beijing, 1995,p.46,7 Y.T. Gao, Y.P. Zhang, and S.C. Wu, Mechanism analysisof anti-sliding piles in soil slope J, J. Univ. Sci. Technol.Beijing (in Chinese), 25(2003), No.2, p.117.万方数据Cut slope reinforcement technique in open-pit minesCut slope reinforcement technique in open-pit mines作者：Yongtao Gao， Jianbo Sun， Shunchuan Wu， Aibing Jin作者单位：Yongtao Gao,Shunchuan Wu,Aibing Jin(Civil and Environmental Engineering School, University ofScience and Technology Beijing, Beijing 100083, China)， Jianbo Sun(Highway Development LimitedCompany of Henan Province, Zhengzhou 450052, China)刊名：北京科技大学学报(英文版)英文刊名：JOURNAL OF UNIVERSITY OF SCIENCE AND TECHNOLOGY BEIJING年，卷(期)：2004,11(4)被引用次数：1次 参考文献(7条)参考文献(7条)1.Y P Zhang;Y.T. Gao;S.C. Wu Unstable analysis of slope under dynamic loading condition期刊论文-Journal of Universityof Science and Technology Beijing(English Edition) 2003(02)2.Y T Gao;Y.P. Zhang;S.C. Wu Stability analysis of reinforcement for landslide rock mass slope 2002(zk)3.Y T Gao;S.C. Wu;J.H. Shun Application of the prestress bolt stress distributing principle 2002(04)4.E Hoek;J W Bray Rock Slope Engineering 19835.J Y Luo Geotechnical Engineering and Road Bed 19976.Q.T.Wang;X.F.Cao Solution for the hole expanding problem of the materials with different module of tension andcompress 19957.Y T Gao;Y.P. Zhang;S.C. Wu Mechanism analysis of anti-sliding piles in soil slope期刊论文-Journal of Universit
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