E24 profile slope stability analysis in Haizhou Opencast Coal Mine of Fuxin

Global Geology,10(2):171-184(2007)Article Im:l6739736(2007)020171-4E24 profile slope stability analysisin Haizhou Opencast Coal Mine of FuxinSimplice F. BOBY and Jianping CHENollege of Construction Engineering, Jilin University, Changchun 130026, ChinaAbstract: The E24 profile slope analyzed belongs to a series of excavated slopes of the haizhou Opencast CoalMine. It seems to be divided into Downslope Part and Upslope Part. Its profile comprises two noticeable coalseams, called the 8# and 9# weak layers, considered as the potential failure surfaces. In consideration of theactual configuration as in the perspective of any modification, assessing the stability of this slope with variousprofile forms under given conditions, and assessingof instability and quantifying the influence of earthworks or other modifications to the stability of this slope, have constituted the primordial objectives carried out.From assumed potential failure surfaces, any specific profiles and specified slip surfaces are defined. A factor ofsafety( Fos)is computed for each specified slip surface; the smallest Fos found corresponds to the least favoraethods of vertical slices implemented in Slope/W, computer program for slope stability analyses, have been a-dopted to perform the E24 slope stability analysis. The safety factor values computed with 9# weak layer anlower than for 8#; the factors of safety obtained with Sarma's method are the smallest; more, without groundwa-ter(long term) overall values are greater than those determined under groundwater condition( short term).Thelowest safety factor value is found for a profile depending on an adopted earthwork sequence. The E24 profileslope stability analysis shows the instability risk for the deepest weak layer, and also shows the short and longterm stability of this slope for the envisaged earth movements. However it demonstrates the existence of instabili-ty risk for any earthwork firstly affecting the downslope part.Key words: limit equlibrium; opencast Coal mine; slope stability safety factor; weak layerIntroductionprise any weak layers less favorable to their stabilityseeing that they generally constitute potential failureAfter the closure of the Haizhou Opencast Coal surfaces. Consequently, assessing the risk of theirMine, the spectacular slopes formed by deep excava- stability and quantifying the influence of any modifications resulting of its long mining, have always raised tion to their stability have to be necessarily analysedthe unavoidable question of short term or long term The E24 profile slope, in its actual configurationstability analysis of slopes; these slopes mostly com- veals two weak layers considered as potential faiYH中国煤化工Received 8 July, 2007; accepted 10 September, 2007ported by Project o NSFC(No. 40472136): Scientific Research Foundation for theCNMHNo.120413133);985 Project of Jilin University(No.1052132000007172S. F. Boby and J. P. Chensurfaces; thus the analysis of its stability under parti- weak layer, and the last(+ UP-DP)a combination nfcular conditions is carried out to determine the factor the capital letters UP ( for Upslope removable Part)of safety for specified slip surfaces passing through and DP( for Downslope removable Part)both bearingconsidered weak layerseither the plus sign or the minus sign; the minus andAnalysing the stability of slopes, one of the two plus signs respectively mean that the concerned part isslope analysis categories, is the most commonlyremoved and non-removed from the original slope informed in geotechnical engineering; in this paper only study; a removable part stands for a soil massthe calculation of the factor of safety for a specifiedd above a fixed slope profile, susceptible toslip surfaces has been carried out. The strength infor- fected by an earthwork projectmation of the soils and possible failure surfaces beingknown, the methods of vertical slices using limit equi-1 General situation of study arealibrium analysis have been chosen. The idea of disHaizhou Opencast Coal Mine, the study area incretizing a potential sliding mass into slices was intro-tion and one of the China s larduced early in the 20 th century. In 1916, Petterson open-pit coal mine, was built during 1953-1957 pe-(1955)presented the stability analysis of the Stigberg riod. It is located in Fuxin, a city in northeast China'sQuay in Gothenberg, Sweden where the slip surface Liaoning Province. It is closed down in 2005 and left awas taken to be circular and the sliding mass was dihuge pit behind in the middle part of Fuxin coal fieldvided into slices fellenius(1936)introduced the Or- The open-pit has an east-west length of 4 kilometersdinary or Swedish method of slices. In the mid 1950and a south-north width of 2 kilometers with an explJanbu(1954 )and Bishop(1955)developed ad- tation depth of 350 meters. The E24 profile slope exvances in the method The advent of electronic com-amined in the present stability analysis belongs to aputers in 1960, s made it possible to more readily han- series of excavated slopes within the pit afore-mensuch as those developed by Morgenstern and Pricefaults, anticlines and synclines(1965 )and by Spencer(1967). Nowadays, slope is presented in Fig. 1s areformed by2 General considerations and meth-longer by hand calculation. For the analysis of thenentod of slope stability analysiscomplete suite of geotechnical products called Geo2.1 General considerationsStudio has been used; it has been designed and develThe E24 profile slope selected for the stability a-nalysis is located in the Haizhou Opencast Coal Minestructures( Geo-Slope International Ltd. 2001c)its crest and its toe are respectively oriented in northHere it would be well to specify the adopted des- east and southeast of the haizhou coal mine that by itsignation for identifying the specific profiles; for exam- nature has any instability problems; some hydro-geople the E24 slope_9#_UP-DP designation, it presentlogical boring-holes almost carried out in its axis havethree parts; respectively the first part( E24 slope) revealed the nature of soil layers in depth as well aswill indicate the profile number of the original slopethe中国煤化工 called F( easterstudy, the second(9# )the number of the consideredNoCNMHOpe(Fig. 2)E24 profile slope stability analysis in Haizhou Opencast Coal Mine of Fuxin173EwOE10E30per coal seNl000SNO400800mAweak laver/No Fcoal seam F Fault E+Anticline E+SynclineFig. 1 Haizhou Opencast Coal Mine schematic geological mapfaceNIOicdFig 2 E24 profile slope geological cross-section中国煤化工CNMHG174S. F. Boby and J.P. ChenThe stability analysis of the proposed E24 profile under assumption of an particular earthwork methodology, four specific profiles of slopes for each weak lay-from Geo-Slope Intermational, Ltd, with the main er have been fixed; therefore two main cases haveaim to determine the factor of safety for fully specified been assumed and examined according to the specificslip surfaces going through the 8# and 9# materials, profile slopes. In first case 8# weak layer is consid-two weak layers, distinguishable in upper part of the ered as potential slip surface and in the second it isE24 profile( Fig 2), with known mechanical charac- the 9# weak layer( Fig 3. la, Fig, 3. 2a, Fig, 3. 3ateristics; and this depending on the shapes of theand Fig. 3. 4a)slope before and after profile changes. For this analyFor 8# weak layer failure surface, four followingsis a piezometric line has been applied to the soils for slope profiles have been investigated in order to verifytaking into account the pore-water conditions; neitherwhich of them is the least stable: in other terms toextermal loads nor seismic effects have been consid- find which profile has the lowest factor of safetyered; the parameters of total strength have been fixed(1) The first profile is the E24 profile slope inThe soil model used in this analysis is the Mohr-Cou. the conditions of the absence of any earthwork on itslomb modeloverall surface; this profile is the initial E24 profileThe input data, used for this slope stability anal- slope; it includes both the DP Downslope removableysis, are selected from the complete Study Report of Part)and the UP Upslope removable Part): it isTreatment Measures and Slope Stability Evaluation; designated by E24 slope_8#_DP + UP;this report, established after prior site investigatic(2) The second specific profile, called the finaland other desk studies carried out during 1991-1993 E24 profile slope, is the profile envisaged or fixed byis also available in the Department of Fuxin the earthwork project; it corresponds to the situationCoal Mining group.wherein the dP and the up are both removed at theFor graphically defining the E24 slope stability end of the earth movements; it is indicated by E24problem, separate properties for four soil types have slope_8#_DP-UP.been defined and considered, namely upper soil ( soil3)The third specific1), 8# weak layer(Soil 2), 9# weak layer(Soil 3) wherein only the DP is entirely removed; the UP isand impenetrable soil layer or bedrock( Soil 4not yet affected by any earthwork this profile is notedThese weak layers are considered as potential slip sur-24 slope_8#_ UP-DPfaces and both of them are analysed with different ca-(4)The last specific profile corresponds to theses of potential sliding masses; note that here a potersituation where only the UP is entirely removed; theal sliding mass is demarcated by a fully specified slip DP is not influenced by any earthwork this profile issurface going throughout a considereI weak layerindicated by E24 slope_8#_DP-UPFig. 3. 1a b, Fig, 3. 2a& b, Fig, 3. 3a& bFor 9# weak layer slip surface, the assumptionFig. 3. 4a& b).and descriptions relating to the above specific pro-The shape of the E24 profile slope before any files, made for the 8# weak layer slip surface, are al-artwork, called the initial E24 profile slope, presso applied to the 9# weak layer slip surface. Conse-ents an intermediary platform dividing the slope into quently 4 profiles are also determined for the stabilitytwo parts practically: the downslope and upslope中国煤化工8# weak layer sliparts;each part comprises a removable soil mass loca- surfCNMHGed above the profile aimed by the next earthworks(1)E24 slope_9#_DP +UP( Fig 3. 1a)E24 profile slope stability analysis in Haizhou Opencast Coal Mine of Fuxin(2)E24 slope_9#_DP-UP( Fig 3. 2a)lems, seems also be turmed into an industrial heritage(3)E24 slope_9*#_UP-DP( Fig 3. 3a)site; it could probably attract tourists for its display of(4)E24 slope_9_DP-UP( Fig 3. 4a)interactive machinery; moreover in the perspective ofSo according to these geometric and stratigraphic any modification of its actual configuration due to anyand from the E24 profile slope in total earthwork project particularly affecting the E24 profile8 profiles have been fixed for a verification of the E24 slope; this slope has been an excavated slope Let usslope stability. These input data including properties recall that before or after any excavation some changesof the aforementioned soils are tabulated in Table 1can take place(excess pore pressures, existence of ahydraulic gradient, water flows, water table levelsTable 1 Soil properties and computation parameters forat the various rates depending on the perE24 profile slopemeability of the soil and the construction nature; forPhi Cohesion Unit WeightSoil odelthis analysis the long term has been considered(°)(kPa)(kNm3)ing the period where the most critical state of the slopeUpper Soil 33. 07 115Mohr-Coulomb19. 71 45 17. 99 Mohr-Coulomboccurs:9# weak layer 15.5 17. 5 20. 1 Mohr-CoulombThe earth movements envisaged on the E24 proBedrockfile slope will be due to the excavation; the soils inthis profile not being free draining materials as sandsor gravels, their more and less low permeability at theing that the E24 profile slope is an excavatend of the earthworks might influencede decreasesslope on the one hand having some consequences a-or increases in total stress which result in changes inbout human life, adjacent structures, services inter-pore water pressure in the vicinity of the slope and, inruption and so on, and so forth in the case of a failparticular, along a potential failure surface; this is theure,and on the other hand the 8# and 9# weak layerscase where with time an excavated slope meet the mostdoubtful conditions for its stability. Hence the analysisted factor of safety to keep the slope stable is Foscan be done under total stress, with the use of the un-1. 2. To make an idea on factor of safety values re-drained shear strength( that is under groundwater con-quired for the slope stability, see the guidelines in Ta- ditions), and also without take into account groundwole 2 beater for simulating the effective stress analysis; so theslope stability analysis is performed for long-term asTable 2 Guldelines for lmt equilbrium of a slopewell as for the short-term for each specific profileDetails of Slopeslope Let us note that Slope/W with only the known<10total stress parameters can perform this latter by neg-1.0-1.25Questionable safetylectingre-water conditions1.251,4Satisfactory for routine cuts and fillsQuestionable for dams, or where failurerameters used for the stability analysis are tabulated inwould be catastrophicTable 1SatisfactorSeeing that the site investigations in the study arntion of tension cracks on the crestThe Fuxin Haizhou Opencast Coal Mine, closed中国煤化工 those are notdown in 2005 and left a huge pit behind with excava-allCNMHGsis(Bromheadted slopes having any unavoidable instability prob.1992), they are not used in this slope stability calcu176S.F. Boby and J. P. Chentropic shear strength and the presence of adjacent stra-the limit equilibrium methods have been used under suppose that in this slope instabilities can take the(1) The factors of safety of the cohesive compo- lop, 1969; Wright and Duncan, 1972); this leads tonent of the strength and the frictional component of the abandon the circular arc slip assumption for consider-strength are equal for the soils 1, 2, 3 and 4,ing the non- circular are slip assumption; according to2) The computed factor of safety is the same for the latter the 8# and 9# weak layers seem to be poten-al failure surfaces; the strength information aboutIt should be convenient to recall that the strati-soils being available( Table 1)and two failure sur-hic cross-section of the E24 slope revealed the ex-faces are identified, the limit equilibrium analysisstence of two weak layers along which shear couldnethods are indicated. For the E24 profile slope themore easily take place; these two layers, called the 8 stability analysis is done with the Slope/W computerand 9# weak layers, are coal layers or coal seams; program based on the limit equilibrium theory. Thethey are considered as potential failure surfaces; howSlope/w, geotechnical software for slope stability a-ever the critical failure surface or critical slip surface nalysis from Geo-Slope/W Intemational Ltdis this for which the lowest factor of safety is foundcompute the factors of safety for specified slip surfacesFor the E24 profile slope analysis the critical slip sur- and also compute the detailed forces acting on eachfaces have been defined as follows: each assumed slice for the slip surface with the minimum factor ofcritical slip surface passes through the considered po- safety. Spencer(1967), Sarma(1973)and Morgentential slip surface or weak layer before to come-out a- stem- Price(1965)methods, some of the limit equgain at the toe and the top of the slope surface going librium methods of vertical slices implemented inthrough removable soil mass or potential sliding mass; Slope/W, are used to compute the factor of safetyso forming a series of straight line segments called a they have been selected because, unlike Felleniusfully specified slip surface; moreover, each time a ( 1936)or Bishop(1955)or Janbu (1954)methweak layer is considered as failure surface, the overlyods, they satisfy both the force and moment equilibing soil mass bocomes the upper soil and the soil mass um conditions in other terms all equations of staticsimmediately located beneath it as the Bedrock See and consider both the shear and normal interslice2.2 Method of slope stability analysislized in the soil, to compare this strength with the a-It should be primordial to note that in practiceilable shear strength of the soillimit equilibrium methods are generally adopted, in3 Resultswhich it is considered that failure is on the point ofoccurring along an assumed or a known failure surThe overall results of minimum computed factorsface. For the stability analysis of the E24 profile slope of safety, for all fully specified slip surfaces goingit is reasonable to assume that the 8# weak layerthrough the 8# and 9# weak layers, are respectivelywell as the 9# weak layer both are failure surfacetabulated in the tables 3 and 4. Let us recall thatlong which failure is on the point of occurring;中国煤化工 by the limit equi-deed, the non-homogeneity of the ground, the exist-libriC MH Ghich consider bothence of 8# and 9# weak layers and their highly aniso- normal and shear interslice forces and satisfy bothE24 profile slope stability analysis in Haizhou Opencast Coal Mine of Fuxin177force and moment equilibrium; especially the Sarmasistance graphics where the ascendance of mobilizedSpencer and Morgenstern-Price methods. With Slopeshear strength and forces against shear strength andW each of these methods simultaneously gives for any forces are always observable.computed factor of safety, the corresponding(3) The lowest factor of safety 1. 254 is obtainedthe Ordinary, Bishop and Janbu methods. The safety for the E24 slope_9#_UP-DP; this factor of safety isfactor values for these last quoted methods are not giv- practically equal to that suggested; this can bring theen in the Tables 3 and 4. The factor of safety compu- E24 slope near the stability failure; this situationtations are firstly performed with the totalvoluntarily fixed by an excavation procedure, revealsrameters as input data and on the other hand without that the earthworks concerming only the down-slope af-groundwater conditions for simulating the effective fects the stability of the E24 profile slopstress parameters. The situation of the noticeable nor-(4) The E24 Slope_9#_ DP-UP has a factor ofmal and shear interslice forces are graphically presesafety equal to 7. 962; comparatively to the suggestedted; this can indicate the location where these forces factor of safety, this value indicates that in this stageare more important; the Figs. 3. lc d andof excavation procedure the adopted slopeFigs. 3. 2c d, show the graphs relating to these safe.es for respectively the E24 slope_9#_DP + UPIn all cases of the E24 profile slopes, the factorE24 slope_9#_DP-UP particular profiles. For of safety values computed without groundwater condithis slope analysis 8 particular E24 profile slopes have tion are superior to these obtained under groundwaterbeen analysed. From these results, it should be rele- condition; this means the factor of safety increasesvant to point out the following observationswhen the site conditions are favorable to increase the(A)With fully specified slip surface going effective stress(local lowering of the water table, dis-through 9# weak layer and under groundwater condisipation of excess pore pressures, existence of hydrationslic gradient, and so on)(1)The E24 slope_9#_DP UP has a factor of(B)With fully specified slip surface goingty equal to 4. 668 greater than 1 2 the suggested through 8# weak layer and under groundwater condifactor of safety; so this slope is stable in its actualtonsconfiguration; this stability can be observed from the(1)The lowest minimum factor of safety amonginterslice forces and shear resistance graphics the four proposed slopes for the stability analysis withFig 3. lc& d). It points out that in the slope parts the 8# weak layer is 2. 019 and is obtained for thewhere the potential sliding mass is considerable the E24 slope_8#_ UP-DP; this slope is defined in thecomputed normal forces are superior to the shear same particular conditions of excavation procedure asforces; it goes the same for the computed shear for the E24 slope_9#_ UP-DP; one can observe thatstrength which overpasses the shear mobilized atthe computed factor of safety is superior to the sugges-iven point of the fully specified slip surface.es not(2)The E24 slope_9#_DP-UP profile slope, constitute a potential failure surface for the E24 profilegives a factor of safety of 1.478 superior to 1. 2 the slopesuggested factor of safety; thus with this new slope.Le faata- ofprofile obtained after the DP and UP parts be entirely comprYHC中国煤化工tions are smallerremoved, the slope keeps a relative stability. TheN MH Water conditionsfig 3. 2. c& d show the interslice forces and shear re- they are obtained by the Sarma's method with the fully178S F. Boby and J. P. ChenE24 sope 9 DPUP (DownsSlap Surface Option FullyS pecifiedSog: 9a WeasSoill: Uppersoi: BedocFig, 3. la E24 Slope_9#_ DP +UP, fully specified slip surface, piezometric line, upper soil, 9# weak layer and bedrockSlope stability analysis650 Slip SurfFactor of Safety: 4.668Soil4: Bedrock08ig 3. Ib Cross section showing E24 Slope_9#_DP + UP, sliding mass shape(Sarma's FoS=4. 668)E24 Slope 9# DP+UPIntcrsliee Forccs Shear Resistance vs. Distance90.090Shear force100,200300400500600700800900Distance(m)Fig 3. 1e Graph of interslice shear and normal forces along slip surfYH中国煤化工 Sarma's method)CNMHGE24 profile slope stability analysis in Haizhou Opencast Coal Mine of FuxinE24 Slope 9#f DP+UPShear resistance vs DistanceShear mobilize0100200m400500600700800900StancFig 3. 1d Graph of shear strength available and shear strength mobilized along slip surface for E24 Slope_9#_DP + UPSlope stability analysIswithout DPhout UlCT(Downmovable Part)(upsonable PartSlip Surface Option: Fully specifiedSoil 3: gu weak layer450 Soil 1: UpperI# East FaultSoil 4: BedrockFig, 3. 2a E24 Slope_9#_DP-UP, fully specified slip surface, piezometric line, upper soil, 9# weak layer and bedrockcross sectionSlope stability analysis650. Slip Surface Option: Fully specifiedFactor of Safety: 1. 47Koil 3: 9s weak layeSoil 4 Bedrock中国煤化工Fig 3. 2b Cross section showing E24 Slope_9# DP-UP, slidinYHCNMHG=1.478)180S. F. Boby and J. P. ChenE24 Slope_9#-DP-UPInterslice Forces vs DistanceNornal Force20,00010000010,0000100200300400500600Distance(m)Fig. 3. 2e Graph of interslice shear and normal forces along slip surface for E24 Slope_9#_-DP-UP(Sarma' s methodE24 Slope 9#-DP-UPShear strength00200300Distance(m)Fig, 3. 2d Graph of shear strength available and shear strength mobilized along slip surface for E24 Slope_9#.DP-UPSarma s method)E24 slope 9# UP-DP Down-slon650 Method:Sarmalip Surface Option: Fully Specified400 Soil 4. BedrockDistance (I0 m)Fig, 3. 3a E24 Slope_9#_UP-DP, fully specified slip surfaceross sectonYH中国煤化工 erCNMHGE24 profile slope stability analysis in Haizhou Opencast Coal Mine of Fuxinl81lope stability Analsof Slip Surface Option. FullySpecifiedFactor of Safety: 1254asol Soil l: Upper#上 ast FaultDitance ( mlFig 3. 3b Cross section showing the E24 Slope_9#_ UP-DP sliding mass shape(Sarma's method FoS=1.254lope stability analysisE24 slope 9a DP- LP"(Town-stope removable TaSol 3: 9 WeakSoil 1: UpperSoil 4: Bedrock0.8Distance(I0 m)Fig 3. 4a E24 Slope9# DP-UP, fully specified slip surface, piezometric line, upper soil, 9# weak layer and bedrockcross section)PUPMethod: SarSlip Surface Option, Fully SpecifiedFactor of saferySoiloil 3: 9* Weak IaSoil 4 Bedrock中国煤化工Fig, 3. 4b Cross section showing the E24 Slope_9# DP-UP sliqYHCNMHGS. F. Boby and J. P. Chenspecified slip surfaces going through the 9# weak layer tirely removed; because the value of the safety factoras well as 8# weak layer; however the lowest factors of computed with the 9# critical slip surface(1. 478 )issuperior to the suggested factor of safety(1. 2).Howspecified slip surfaces passing through the 9# weal ever one situation could bring the E24 profile slope tolayer;consequently this weak layer is the least favora- the instability this is the situation in which only theble failure surfacedown-slope part is removed; it corresponds to the E244 Discussionslope_9#_UP-DP for which the minimum computedfactor of safety 1. 254 is practically equal to 1. 2 theIn the actual configuration of the E24 Profile suggested factor of safety.slope, it should be useful to know its stability degreebefore, during and after any envisaged earthwork. LetTable 3 General results of Fos computed for 8# weak layerrecall that an excavationope leadweak layer numberSoftwareFactors of safechanges of gravitational and seepage forces which tendrofile slope designation Meto cause instability in natural slopes and in slopes6.8486.918formed by excavations. So it is obviously necessary to8# DP+UPMP(3)quantitatively evaluate the stability of a slope or hill- (with DPO and UP2)6.8506.926side and find a factor of safety for one particular workBsam29003.128# DP-UP29503.163Therefore the minimum value of the safety factors for(without DP and UP)3.163ch fully specified slip surfaces of17.139slope, according to the previously evoked cases and8# DP-UP16.94917.187(with DP, Without UP)Spencer16.94917.187assumptions, has been computed using the limit equilibrium methods of vertical slices implemented in8# UP-DP20432.113Slope/W computer program. The analysis of the dif-(with UP, Without DP)ence2.0432113ferent computation results and the examination of some1): Down-slope removable Part (2): Up-slope removable Part(3): Morgenstem prices Methodgraphics relating to the shear strength as well as interlice forces within the slip surface can lead to the fol- Table 4 General results of Fos computed for g weak layerweak layer numbeThe E24 profile slope appears like a slope withprofile slope designationMethodgroundwater groundwaterdeep-seated instability since its 9# critical slip surfaceis located in depth9#DP+Mp()4677494The E24 profile slope in its actual state designat-(with DP() and UP(2))Spencer 4. 677 4.94Sarma 1. 478ed by E24 slope_9#_DP + UP, in despite of the two9# DP-UPMP1.494potential failure surfaces 8# and 9# weak layers(without DP and UP) 4 Spencer 1. 494 1.809keeps its stability; seeing that the factor of the safetySam7.9628.484computed with the least favorable slip surface(the 9# (with DP, Without UP) Spencer 7.9718.494eak layer)gives a value of 4. 668 greater than 1.2Sarma1.2541.458the suggested factor of safety for this type of slop9# UP-DPMP1.2721.474(withYH中国煤化工L.272he E24 profile slope stays stable even if the soil(1)slope removable Partmasses in the down-slope and up-slope parts are en(3)CNMHGE24 profile slope stability analysis in Haizhou Opencast Coal Mine of Fuxin183It is useful to note that by removing soil mass in surfaces. The Sarma s method implemented in thethe downslope partfactor of safety has criticallputer program has given the critical fac-been decreased; that shows if necessary the impor- tors of safety for each of the 8 specific profile slopestance of loading a slope toe as one of the remedial proposed in this slope analysismeasures increasing the slope stability; consequentlyThe different results obtained from factors of safethis specific profile have to be avoided when some ty computations with 8# and 9# weak layers as poterearthworks are envisaged on it and particularly in its tial failure surfaces lead to the following findings:downslope part(1) The 9# weak layer deeper than 8#It also appears that the adopted earthwork se- er constitutes the layer the least favorable toquences can dangerously affect the slope stability ity of the E24 profile slope.making it the least safe in the case where any ground(2)The safety factors values obtained withmovement is only executed at the slope toegroundwater condition indicate that by performing theThis slope stability analysis did not take into ac- stability analysis, the short term stays the critical peri-count the seismic effects from neither any earthquakeod for a potential failure surface(Tables 3 and 4)nor blasting within in the mine for an eventual change(3)In its actual configuration the E24 profilein the exploitation system of the Haizhou coal mineslope, analysed with any potential failure surface, isbeing given that they might be sufficient to trigger a stable at short term as well at long term; however itwith the limit equilibrium methods of the vertical ing mass located in its downslope part is removedlandslide. The E24 profile slope has been analysed can become unstable when only the potential soil-slicthese mThese results also shows that in the E24 profilepermitted to compute the factors of safety seeing theslope the 9# weak layer, deeper than 8# weak layerSlope/w can also compute both the total shear resistconstitutes the potential failure surface; in the actualance and mobilized shear stress along the entire slipsituation as at the end of the earth movements envis-urface, it should be interesting to calculate a stabilityged on its surface, the E24 profile slope remains sta-factor based on finite element computed stresses; this ble as well at short term as at long-term. However thiscan advantageously enlarge the means of verification slope, under a particular condition in a perspective offor the E24 slope stability analysis. In this paper thethe earthworks, presents a risk of the instability. FiE24 profile slope has exclusively been proposed for a nally the stability analysis of the E24 profile slopeslope stability analysis: one of the two categories of leads to observe that the excavated slopes of Haizhouthe slope analysis methods it should be useful toer- Opencast Coal Mine comprising at least one weak lay-form a slope movement analysis by using finite ele- er become instable with the deepest weak layer; andment solutions in order to get some information about in the case of the modification of their surface, anye magnitude movements susceptible to take place earthwork firstly carried out at their toe could endanurng any slop5 ConclusionAcknowledgementsThe E24 profile slope of the Haizhou Opeial thanks go to jing ZHANG, yang LI andal mine has been analysed using the limit equilibr中国煤化工$ hengwu QIN andum methods of vertical slices with 8# and 9# weakCN MHGfor their collabora-layers in this slotduring this study184S. F. Boby and J. P. ChenVersion 4.0. Calgary: Geo-Slope IntHuang Y H. 1983. Stability of earth slopes. New York: VanBishop A W. 1955. The use of the slip circle in the stability a-Nostrand Reinhold Co., 200, 215-218, 249-254.alysis of earth slopes. Geotechnique, 5: 7-17.Janbu, N. 1954. Application of composite slip surfaces forBromhead E N. 1992. The stability of slopes. 2nd Editionbility analysis //Proceedings of the European Confer-London: Blackie Academic Professional, 141ence on Stability of Earth Slopes. Stockholm, 3: 4349.Chen W F, Snitbahn N, Fang H Y. 1975. Stability of slopesLambe T W, Whitman. R v. 1979. Soil mechanics, Newin anisotropic, non-homogeneous soils. Technical Note,York: John Wiley Son, 333-340, 366-369Canadian Geotechnical Journal, 12: 146-152Morgenstem R, Price V E. 1965. The analysis of the stabiliDuncan JM. 1996. soil slope stability analysis in landslidesty of general slip surfaces. Geotechnique, 15: 79-93investigation and mitigation// Tumer A K, Schuster R LPetterson K E. 1955. The early history of circular sliding sur-(eds). Special Report 247. Washington: Transportationfaces. Geotechnique, 5: 275-296Research board 337-371Peterson R. Iverson N L, Rivard P]. 1957. Studies of severalDuncan J M, Dunlop P. 1969. Slopes in stiff-fissured claysdam failures on clay foundations/Proceedings of Fourthd shales. Jounal of the Soil Mechanics and FoundationsIntemational Conference on Soil Mechanics and Founda-Din,95(2):467492tion Engineering, London: [s.n. ] 348-352.Duncan JM, Wright S G. 1980. The accuracy of equilibriumSarma S K. 1973. Stability analysis of embankments andmethods of slope stability analysis. Engineering Geology16(1/2):517Fellenius W. 1936. Calculation of the stability of earthslopes. Journal of the Geotechnical Engineering Divisiondams/Transactions of Second Congress on Large Dams105(12):1511-1524.Washington: Intemational Commission on Large Dams ofthe World Power Conference, 4: 4454bankments assuming parallel inter-slice forces. Geotecheo-Slope Intemational Ltd. 2001c. SLOPE/W user's manualngue,17(1):1126中国煤化工CNMHG