A Test Model of Water Pressures within a Fault in Rock Slope

Journal of China Unrversily of Geosciences, Vol. 12. No, 1, p. 309 - 311, Decemnber 2001ISSN 1002 - 0705Printed in ChinaA Test Model of Water Pressures withina Fault in Rock Slope *P5 AYang Tong Wang Baoxue Hu HengCivil and Environmental Engineering School，Beijing Institute of Technology，Beijing 100083ABSTRACTThis paper introduces model test rsls of water pressure in a fault, which is located in a slopeand 16 dffereat conditions. The resuts show that the water pressures in fault can be expressed by a linr-ar function, which is similar to the theoretical model suggested by Hoek. Factors affecting water pres-sures are water level in temsion crack. dip angle of fault, the height of filing materials and thickness offault zone in sequence,KEY WORDS rock slope. water pressure, model test.INTRODUCTIONtension crack in upper! surfact of slopeAnalysis of stability stalus is necessary for slopes of openpir, slope dam. road and the building of basement. Among fac1ors affecting slope stability, water is the most scnsitive andcommon factor. Hoek and Bray (1977) gave the calculatingformula of plane failure in their book,“Rock Slope Engineer~ failut surfactwing”. For a single fault which is connected with open fracturesa1 ibe lopof the slope, its dip angleis less lban the sope angle Figur 1. Geometry of slope wih tensio crack in uper slopeand the distribution of water pressures is shownin Fig.1. In surface.this case. the factor of safety of the slope (F) can be estimatedby the ratio of the resising force and the disturbing fores.0. I3F= c●A+ (W :cosy,-U-V .sin4).84(1)W●sinψ+v●cos ψThis formula is commonly used to estimate the fator oftubetensioncncksafety of a slope at present. It is clear that F is related to山(slope angle), ψ(dip angle of the fault), W (weight of slidingblock). U (uplift force due to water pressure in the sliding sur.。faultface), V (force caused by water pressure in tension crack), cand P (cohesion and friction angle on sliding surface), Z.(wa-ter level in tension crack). Among these factors, U and V arerelative to water pressure, and V is easy to be determined by2 J0cmwater level in the tension crack. Distribution of U is not clear,Hoek and Bray (1977) suggested a linear distribution, but itFigure 2. A simplified diagram of test model.has not been verified, This paper verify the suggestion by mod-el test.INSTALLING OF TESTING MODELTwo parallel organic glass plates are used as hanging wall，This paper is supported by the Research Fund for the Doctoral Proand footwall of a fault, Al the 1op of the fault. there is a ten-gram of Higher Fducation of China.sion fract中国煤化工"inic glass plates.Sand andglass plates. Water is pouMHC N M H Gacure. uand leaksout through flling materials.Manuscript accepted September 20. 2001.Yang Tong. Wang IBaoxue and Hu HengThe frame of the model is made of wood and angle steel. netic boundary conditions and fllig materials ure sutistied inThe glass plates are sealed with rubber spacers. Nine glass this model.tubes are istalld along the central line of hanging wall of thefault (Fig. 2). and the other 4 glass tubes are intelled in the TEST RESULTtop tension crack. They are used to measure the water level inFigure 2 is the simple diagram of the test model. In modelthe fault. Red ink is added into water so that it is easier loob- 1# . the length of the fault along dip is 85 cm. with a dip angleserve and uake a picture.of 40. 3° and a fault thicknessof 1.1 cm. The height of fllingThe model is made of similar materials as natural or man: materials in tension fracture is I cm with a water head of 28made slopes of open pit. dam and other structures ( Mao,cm. The water pressure in glass tubes (p.) is listed in Table1991; Lin, 1984). It is 54- 93 cm high. which simulates a 1. Parameters for other 15 models (2# - 16# model) are lis-slope of 54 - 93 m high. Simiariries of geometry. dynamic, ki- ted in Table I.TABLE1 WATER PRESSURE (p.) IN GLASS TUBES ()F 1# MOIDELnumber of tubule59 10-13water head/em3.8,813.517.819.522.323.9228. 0TABLE2 WATER PRESSURE DISTRIBUTION EQUATION IN VARIOUS TEST CONDITIONSlinear regressin equationsimplified equation.!T91lo.Mp:/(°)p=a+brp=brcmcn井1.1.02.070.970. 335#1.1 040.30.410. 2520. 990. 255 33#40. 3.00.170.139.0. 9700. 1409280.32.370. 2880.9790. 325 01.6 040.3 1,00. 2240.9840.245 75#1.6 a1.09.0.1170. 9770.133 67#0.780.264 .0. 9940.275 81.1 a40.3 10.50.340. 1940. 9890. 19820.060.0740. 9920.073010#1,880.309.0.9740.337 811#40.3 1.00. 700.2450.9920.254 8110.1190. 9540.145 6a35.62.060.2980. 9880. 329 114#2.180.0980. 9300.132745.1.1.810.2690. 9800.298016#_21.6①_ 45.10.95.0. 2090.223」Note: 2. waler level in tension crack; T. thickness of flingi M. flig materials; 中。dip angle of feult; H. heisht of flling; R. crtelation cficiet;①. silty sand, k-2. 10X10-。cm/st 2. slty sand, k=1.02X10 s cm/s: k. coffcicnt ofpermeabiliy. .Coordinate system of the model is shown in Fig. 3, inNOwhich zero point is at foot of the slope; r axis is along dip di-12rection (up is positive) and y axis represents water head, Testresults for 16 model tests are expressed as a linear equationusing linear regression method, p. =a+bxr. or a simple equa-tionp. =br. The values of a and b are listed in Table 2.，H. EFFECTING OF WATER HEAD DISTRIBUTION IN VARIOUS6TEST CONDITIONSWater head distribution along the dip of a fault is observedand recorded in various conditions by changing dip angle of中国煤化工fault. thickness of fault zone. size of fllig tmaterials, heightMYHCNMHG。e diagram.of flling materials and water head of tension crack. 16 tests of5 groups are made. The first group (1工-3#) is basic tes.in which waler head distribution is gained by changing the #) is replaced by changing filing thickness. the 3rd group (7height cf water level in tension ereck. The 2nd group(4# -6 # -9#) by chaning fling height. tbe 41b group(10= - 12A Tcst Model of Water Pressures within a Fault in Rock Slope二) by changing fling materials, and the 5th group (13#- 16 The geomery condions (arcording to Fig. 1). mecbanic prop.=) by changing dip angle of the fault and fling thickness eries of rocks. calculation paraneters and resuts ( based on(Table 2).formula 1) of the slope are listcd in Table 3, in which dried andsaturated rock are considered.TABLE了ANALYSIS OF ROCK SL()PE EXAMPLEIt is due to the flling of water in tensile crack after heavymoisture statetrysaturated rain that the safety coefficient is redured to the critical value.geometryH/m .12and resulting in landslide.4%/(°)的/(*)CONCLUSIONSZ/m(1) The test model is a success. Not only the leakage ofZw/mcrack and measurement technique have been solved, but alsomechanic propertyp/(kN.m-')26.927.0the dip angle and thickness of fault, size and height of fllingP./(kN.m~-4)materias, and water head in tension fssure have been adjus-c/(kN.m-2)25.09/(°)21.0(2) Based on tcst results, the factors afecting water pres-calculation parame1er( slice A/m210. 89sures are identified as the water head in tension fissures, theof unut thickness)W/kN706. 93709. 56.U/kN053. 36dip angle of fault, and the bheight of flling materials, as well asV/kNthe sorts of flling materials in sequence.factor of saietyF1.20I.00(3) Water pressure distibution in fault can be representedby a linear function y= br. which is similar to the model sug*gested by Hoek and Bray (1977). Hence. the test model pro-AN EXAMPLE OF PLANE FAILUREEkou iron deposit, located in Shanxi Province. is a largevides a strong support to the Hoek model.(4) An example from Ekou iron deposit shows that theopen- pit mine. The deposit belongs to pre Cambrian metamor-test model is useful for ilustrating the mechanics of plate land-phic iron deposit , with intense folded strata and various faults.slide. Iandslide is a extremely complex engineering problemThe country rocks are composed of sericite quartz schist andbecause of variety of rock and soil. The further study and tak-sericite chlorite schist. The area bas high and precipitous ter-ing more practical examples should be done in the future.rain. and meteoric water is main source for underground water. The maximum day ranfall rcorded is 65 mm. Plane fail.ACKNOWLEDGEMENTure happened repeatedly since the mine has been exploited.This work is financed by the Rescarch Fund for the Doc-Among them, the landslide on the Jidoushan bill is a typicaltoral Program of Higher Education of China (RFDP).one along the surface of schistosity alfter a bheavy rain.The slide block is located at the southeast part of an uREFERENCES CITEDhill load, with 43 m lengh along the strike of schis strara andHoek E, Bray J w, 1977. Rock Slope Engineering. London: Stephen12 m high. The tensile crack extends 5 m in depth and stops inAustin and Sons Limittedthe impermeable layer because it has lower speitice permeability Liny, 1984. Tesing Rock Mechamies Simuiate Reserch. Bejini;than that in the upper, The slide surface had a 40° dip angleThe Publishing House of Coal Industryand the same direction of the 310° open-pit slope, which hada Mso C.1991. Study on Computation Methods of Seepage Flow in58° slope angle. Based on hydrogeological conditions in theFractured Rock Masses. Chinese Journal of Geotechnical Engr-mine area. Z./Z in tensile crack could be supposed to be 0. 2.nering. 13(6);1-10中国煤化工MYHCNMHG