岩体渗透结构类型及其渗透特征

岩体渗透结构类型及其渗透特征李清波闫长斌（黄河勘测规划设计有限公司，河南郑州450001）摘要分析了控制岩体渗透特征的主要因素，提出了岩体渗透结构类型的划分原则以及不同渗透结构的宏观渗透特征，并给出了工程实例，对水库渗漏问题评价及防渗、排水工程设计具有重要意义。关键词裂隙岩体；渗透结构类型；渗透特征；防渗排水1引言在水利水电工程建设中，经常遇到与岩体渗流相关的水文地质问题。由于岩体中通常发育有裂隙或溶蚀管道，受裂隙、溶蚀管道分布的方向性和不均匀性控制，地下水在岩体中的渗流状态远较在土体中复杂，一般具有明显的各向异性和不均一性。如对其认识不足，则可能导致防渗、排水工程的低效甚至失误。国内外学者在裂隙岩体的渗透特性研究方面取得的成果⑪⑸表明，岩性、断裂构造、风化卸荷作用及岩溶作用是控制岩体渗透结构及其宏观渗透特征的主要因素。谷德振先生⑺以地质体结构为基础，将岩体划分为不透水体、统一含水体、层状含水体、脉状含水体、管道含水体等水文地质结构类型。孙广忠先生⑻提出了以透水体（层）和隔水体（层）为基本单元划分岩体水力学结构的概念，将透水体划分为孔隙透水体（层）、裂隙透水体（层）和管道透水体三种类型，将隔水体划分为块状隔水体、夹层或带状隔水体、层状隔水体三种类型。万力［1］等研究了砂泥岩互层裂隙地层的渗透性特征，指出砂泥岩互层地层具有层状、带状和壳状三种渗透结构。周志芳⑵等则提出了块状岩体的水文地质结构类型划分意见。本文在上述研究的基础上，系统地提出了岩体渗透结构类型的划分原则及各类渗透结构所具有的宏观渗透特征，对水库渗漏问题评价及防渗、排水工程设计具有重要意义。2控制岩体渗透特征的主要因素一般情况下，完整岩块的渗透性很小，多在10-7〜10-6cm/s以下。相比之下，岩体的渗透性比岩块大得多，二者相差可达几个数量级。导致这种差异的主要原因，在于岩体中除包含各种尺度的岩块外，还发育有不同成因类型的裂隙或溶蚀管道（灰岩中）。总体上看，岩体的渗透性大小及宏观渗透特征主要受岩性、断裂构造、风化卸荷作用及岩溶作用等因素控制。岩性对岩体渗透性的影响非常明显。在裂隙岩体中，裂隙是地下水渗流的唯一通道，而裂隙的发育规律则严格受岩性控制。大量调查统计结果表明，脆性岩（如砂岩、石英岩等）中裂隙的发育程度一般远大于塑性岩（如粘土岩、页岩等）中裂隙的发育程度。相应地，脆性岩的渗透性一般也远大于塑性岩，构成透（含）水层（体），塑性岩则多构成相对隔水层（体）。断裂构造是影响裂隙发育的重要因素。一般说来，在断裂两侧常发育有裂隙密集带，从而使断裂影响区内的岩体在平面和剖面上均表现为一个渗透性相对较强的带状区域。另一方面，较大规模的断裂带内多发育有低渗透性的断层泥等物质，从而使断裂带在横向上往往具有一定的阻（隔）水性。风化卸荷作用对岩体渗透性也有比较明显的影响。对花岗岩等侵入岩体而言，其全强风化带通常类似于各向同性的孔隙介质，弱、微风化带岩体的渗透性则有不同程度的增强；对脆性沉积岩及火山岩而言，其风化卸荷带内岩体的渗透性一般会有明显增加。岩溶发育程度对灰岩等可溶岩类的渗透特征具有突出的控制作用。岩溶不发育的灰岩，其渗透特征与一般裂隙岩体相同；仅发育溶蚀裂隙的灰岩，其渗透特征仍与一般裂隙岩体类似，地下水运动以层流为主，但透水性和富水性有所增大；发育有溶蚀管道的灰岩，透水性和富水性强，地下水运动状态复杂。需要指出的是，到目前为止，人们在大多数实际工程中仍习惯于把裂隙岩体视为各向同性的孔隙介质来处理，并通常采用常规的垂直钻孔压水试验获取岩体的透水性指标，进而评价岩体的渗透特性以及库水渗漏问题。事实上，对高倾角裂隙发育的岩体来说，由于垂直钻孔揭露高倾角裂隙的几率较小，岩体透水性试验结果往往比实际情况明显偏低。小浪底工程对比试验表明，采用水平钻孔压水试验获取的高倾角裂隙岩体的透水性指标一般要比垂直钻孔压水试验所得指标高出2〜5倍。工作中如对此认识不足，可能导致较大失误。3岩体渗透结构类型及其渗透特征所谓岩体渗透结构，是指透（含）水层（体）和相对隔水层（体）的空间分布及组合规律。合理划分岩体渗透结构类型，有助于从宏观上把握岩体的渗透特征，为岩体渗流计算及防渗、排水工程设计提供科学依据。岩体渗透结构一般可划分为5类，即散体状渗透结构、层状渗透结构、带状渗透结构、网络状渗透结构、管道状渗透结构。3.1散体状渗透结构散体状渗透结构主要由侵入岩类全强风化带岩体构成。其渗透介质类型以孔隙介质为主，具均质各向同性渗透特征，透水性一般相对较强。3.2层状渗透结构层状渗透结构主要由透水层与相对隔水层互层的缓倾岩层、平缓的多层结构的喷出岩以及平缓的断层破碎岩等构成。其渗透介质类型以裂隙介质为主，地下水主要赋存、运移于各透水层中，其补、径、排严格受透水层上下的相对隔水层控制，常具多层水位。宏观上看，顺层方向渗透性远大于垂层方向渗透性，具有明显的各向异性渗透特征。3.3带状渗透结构带状渗透结构主要由产状较陡的断层破碎带、裂隙密集带、岩脉裂隙带以及透水层与相对隔水层互层的陡倾岩层、河谷岸边强卸荷带等构成。其渗透介质类型以裂隙介质为主，透水性一般较强，多与层状、网络状等渗透结构相通，构成地下水集中渗漏通道，亦可构成不同透水层地下水间的水力联系通道。宏观上看，顺带方向渗透性明显大于垂带方向渗透性，具有明显的各向异性渗透特征。3.4网络状渗透结构网络状渗透结构主要由弱风化〜新鲜的块状岩体及岩性单一、裂隙（包括溶蚀裂隙）较发育的沉积岩等构成。其渗透介质类型为裂隙介质，透水性一般较差，地下水运动主要受裂隙网络发育特征及其渗透性控制，具有明显的非均质各向异性渗透特征。赋存于同一岩层中的裂隙水不一定具有统一的地下水位。3.5管道状渗透结构管道状渗透结构主要由溶蚀洞穴、管道发育的灰岩构成。其渗透介质类型主要为溶穴介质，常形成大水量集中渗漏通道。地下水主要沿岩溶管道流动并以泉的方式排泄，分布不均一，动态变化大，流态较复杂。需要强调的是，多数情况下工程区的岩体渗透结构类型不是单一的，而是多种渗透结构类型的叠加。而不同类型渗透结构交叉叠加的部位，往往形成透水性较强的地下水集中渗漏通道，也是防渗、排水工程需要关注的重点。此外，层状渗透结构中的透水岩层，局部而言亦具有网络状渗透结构的渗透特征。4工程实例4.1实例1小浪底坝址区岩体渗透结构类型划分4.1.1基本地质条件坝址区出露地层主要为二叠系上统及三叠系下统，岩性为硅钙质砂岩、泥质粉砂岩、粉砂质粘土岩互层。砂岩为硬岩，性脆，裂隙发育，属透（含）水层；泥质粉砂岩与粘土岩为软岩，裂隙不发育，属相对隔水层。坝址区岩层产状平缓，倾向北东（下游方向），倾角8°〜12。。出露的断层主要有规模较大的F1、F28、F461以及F236、F238等，均为陡倾角。F1分布在右岸河床部位，走向与黄河近平行；F28沿左岸风雨沟展布，走向为30。〜60。；F461分布在左岸小南庄一带，走向290°〜310°；F236、F238穿过左岸洞群区呈近东西向展布，贯穿水库上下游。坝址区砂岩中发育有3〜4组陡倾角裂隙，泥质粉砂岩与粘土岩中裂隙不发育。风化卸荷带内的裂隙张开宽度相对较大。4.1.2渗透结构类型划分通过对小浪底坝址区基本地质条件的分析，可以确定其渗透结构类型主要表现为层状及带状（图1）。水库蓄水后，库水将主要沿分布于不同高程的透水砂岩层及贯穿水库上下游的断层破碎带向下游渗漏。考虑防渗、排水工程处理措施时，应对主要透水砂岩层以及透水砂岩层与断层破碎带交叉部位岩体予以重点关注。图1小喂底坝址区砂”泥岩地层渗透始辎典型剖面示意图4.2实例2三峡坝址区岩体渗透结构类型4.1.1基本地质条件三峡工程坝址区出露的主要岩石为闪云斜长花岗岩，并有多期酸一基性岩脉侵入。岩体表部存在较厚的风化壳，可划分为全、强、弱、微四个风化带。全风化带以疏松但略具联结力的碎屑状岩石为主，强风化带由疏松、半疏松状岩石夹坚硬、半坚硬状岩石组成，弱风化带为坚硬、半坚硬状岩石为主，微风化带岩石风化轻微。坝址区发育有北北西、北北东向等四组断层，均以陡倾角为主。相对发育的四组裂隙大部分为陡倾角，少部分为中等倾角及缓倾角。岩脉与围岩多呈断层或裂隙接触。4.1.2渗透结构类型划分通过对三峡坝址区基本地质条件的分析，可以确定其渗透结构类型主要表现为散体状（全强风化岩体）、网络状（裂隙岩体）及带状（断层及岩脉）3种（图2）。其中带状渗透结构可构成渗流场的主干网络，对地下水起着类似于集水、输水廊道的作用，在防渗排水工程设计时需予以注意。一弓KN匚-f七IT-I白 ,或0HF!笙写烦此止Ml玉起：吒夫’荏十字*“族*htH；HC1无心：芯X攻（据周志芳修改）5结论（1） 岩性、断裂构造、风化卸荷作用及岩溶作用是控制岩体渗透结构及其宏观渗透特征的主要因素。（2） 岩体渗透结构系指透（含）水层（体）和相对隔水层（体）的空间分布及组合规律。岩体渗透结构类型一般可划分为散体状、层状、带状、网络状以及管道状5类。（3） 工程区的岩体渗透结构类型一般不是单一的，而是多种渗透结构类型的叠加。不同类型渗透结构交叉叠加的部位，往往形成透水性较强的地下水集中渗漏通道，也是防渗、排水工程需要关注的重点。（4） 合理划分岩体渗透结构类型，有助于从宏观上把握岩体的渗透特征，为岩体渗流计算及防渗、排水工程设计提供科学依据。参考文献：万力，李清波等.砂泥岩互层裂隙地层的渗透性特征[J].水利学报，1993,（9）.刘光尧.砂岩业页岩和泥岩的含水条件及含水层分类[J].水文地质工程地质，1990，（5）.周志芳，王锦国.裂隙介质水动力学[M].北京：中国水利水电出版社，2004.Snow，D.T.Anisotropicpermeabilityoffracturedmedia[J].Waterresourcesresearch,Vol.5,No6,1969.Withspoon,P.A.Newapproachesofproblemsoffluidflowinfracturedrockmass[J].Proc.22ndU.S.Symp.RockMech.,1981.BearJ，Tsangchin-FuandGhislaindeMarsily.Flowandcontaminanttransportinfracturedrock[M].AcademicPress,Inc.California,1993.谷德振.工程地质力学基础[M].北京：科学出版社，1978.孙广忠.地质工程理论与实践[M].北京：地震出版社，1996.PermeabilityCharacteristicsLIQing-boYanChang-bin(YellowRiverEngineeringConsultingCo.,Ltd,HenanZhengzhou450001)Abstract：Keyfactorsthatcontrolpermeabilitycharacteristicsofrockmassareanalyzed.Dividedprinciplesofrockmasspermeabilitystructuretypesandmacroscopicpermeabilitycharacteristicsofdifferentpermeabilitystructuresareputforward.Andengineeringexamplesarepresent.Itismostsignificantforseepagecontrolanddrainagedesignofwaterconservancyandhydropowerengineering.Keywords：fracturedrockmasses；permeabilitystructuretypes；permeabilitycharacteristic；seepagecontrolanddrainageIntroductionProblemsofhydrogeologicrelatedwithrockmassseepagearemetfrequentlyinwaterconservancyandhydropowerengineeringconstruction.Cranniesandkarstpassagesaredevelopedinrockmasscommonly.Controlledbyorientationandnon-uniformityofcranniesandkarstpassagesdistribution,seepagestateofgroundwaterinrockmassisfarmorecomplexthanthatinsoilandtakesonobviousanisotropyandnon-uniformitygenerally.Theseepagecontrolanddrainageengineeringmaybelowefficiency,evenbemistaken,withoutenoughcognition,Researchachievements[1]~[5]forpermeabilitycharacteroffracturedrockmassesobtainedbyscholarsathomeandabroadshowthatlithology,faultedstructure,weatheringandunloadingandkarsteffectarekeyfactorsthatcontrolpermeabilitystructuresanditsmacroscopicpermeabilitycharacteristicsofrockmass.RockmassisdividedintohydrogeologicstructuretypesbyMr.GUDezhen[7],suchasimperviousmass,uniformaquifer,layeredaquiferandveinaquifer,basedonstructureofgeologicbody.TheconceptionofrockmasshydraulicsstructureisputforwardbyMr.SUNGuangzhong[8],inwhichpermeablemass(layer)andimperviousmass(layer)areconsideredasbasicunit.Itdividespermeablemassintothreetypes,whichareholepermeablemass(layer),fracturepermeablemass(layer)andpipepermeablemass(layer),andalsodividesimperviousmassintothreetypes,whichareblockyimperviousmass,interlayerorzonalimperviousmass,layeredimperviousmass.WANLi[1]studiedthepermeabilitycharacteristicsofinterbeddedandfracturedsandstoneandmudstonestrata,andpointedoutthattherewerethreepermeabilitystructures,whichwerelayered,zonalandshell-perm,ininterbeddedandfracturedsandstoneandmudstonestrata.ZHOUZhifang⑵putsforwardtheideastodividethehydrogeologicstructureofblockyrockmass.Onthegroundofaboveresearches,dividedprinciplesofrockmasspermeabilitystructuretypesanditsmacroscopicpermeabilitycharacteristicsofallkindsofpermeabilitystructuresaresystematicallyputforwardinthepaper.Itismostsignificantforseepagecontrolanddrainagedesignofwaterconservancyandhydropowerengineering.KeyfactorsofcontrollingrockmasspermeabilitycharacteristicsInageneralway,thepermeabilityofintactrockisverylow,mostlylowerthan10-710-6cm/s.Comparedwiththeintactrock,thepermeabilityofrockmassisfarhigher.Thediscrepancybetweenthemcanbeseveralmagnitudes.Themainreasonswhichinducethisdiscrepancyarethattherearemanyfracturesandkarstpassages(inlimestone)ofdifferentcausesinrockmass,inadditiontoblockyrockofallkindsofscale.Asawhole,thepermeabilityandmacroscopicpermeabilitycharacteristicsofrockmassismostlycontrolledbylithology,faultedstructure,weatheringandunloadingandkarsteffect,etc.Theinfluenceoflithologyonrockmasspermeabilityisveryobvious.Thefractureistheuniquechannelforseepageofgroundwaterinfracturedrockmass,whilethedevelopmentruleoffracturesiscontrolledbylithologystrictly.Resultsfromaboundofinvestigationandstatisticshowthatthedevelopmentdegreeoffracturesinbrittlerock,suchassandstoneandquartzite,isfarbetterthanthatinplasticrock,forexampleclaystoneandshale.Thepermeabilityofbrittlerockiscommonlyfarhigherthanthatofplasticrockaccordingly.Thebrittlerockmakesupofpermeablemass(layer)oraquifer,whiletheplasticrockmakesupofrelativeimperviouslayer(mass)mostly.Faultsareimportantfactorsthatinfluencethedevelopmentoffractures.Fracturesconcentrationzonesexistonthebothsidesoffaultscommonly.Therebytherockmassinfaultsinfluencedzonesbehavesfromplaneandsectionasthezonalareawhosepermeabilityisrelativehigher.Ontheotherhand,lowpermeabilitysubstancesuchasgougedevelopsinrelativelarge-scalefaultzonesfrequently,andthenthefaultzoneswillformtransversewater-resistingpropertytosomeextent.Theinfluenceofweatheringandunloadingonrockmasspermeabilityisalsorelativeobvious.Forintrusiverocksuchasgranite,itsfullandhighlyweatheredzoneisgenerallysimilarwithisotropicporousmedia,whileitspermeabilityofweaklyandslightlyweatheredzoneincreasesinvariousdegrees.Forbrittlesedimentaryrockandvolcanicrock,theirrockmasspermeabilityinweatheringandunloadingzonewillincreaseobviouslyinageneralway.Karstdevelopmentdegreecanobservablycontrolthepermeabilitycharacteristicsofsolublerocksuchaslimestone.Thepermeabilitycharacteristicsoflimestonewherekarstdoesnotdeveloparethesameasthoseofcommonfracturedrockmass.Thepermeabilitycharacteristicsoflimestonewhereonlycorrodedfracturesdeveloparesimilarwiththoseofcommonfracturedrockmass.Inthecircumstances,stratifiedflowismainmovementstateofgroundwater,whilepermeabilityandyieldingpropertywillincrease.Forthelimestonewherecorrodedpassagesdevelop,itspermeabilityandyieldingpropertyarestrong,andmovementstateofgroundwateriscomplex.Itisnecessarytopointoutthatpeopleareusedtotakefracturedrockmassforisotropicporousmediamostlyinpracticebyfar,andgetpermeabilityindexesofrockmasswithgeneralverticalwaterpressuretestinborehole,thenevaluatethepermeabilitycharacteristicsofrockmassandseepageofreservoir.Infact,asfarastherockmasswherehighdipangledfracturesdevelop,theresultsobtainedbythepermeabilitytestofrockmassareusuallylowerthanthoseinengineeringpractice,becauseoflessprobabilitywithverticalboreholediscoveringhighdipangledfractures.ContrasttestofXiaolangdiprojectshowsthatpermeabilityindexesofhighdipangledfracturesrockmassobtainedbyhorizontalwaterpressuretestinboreholearethreetosixtimeshigherthanthoseobtainedbyverticalwaterpressuretestinboreholecommonly.Itwillinducerelativebigmistakesinwork,withoutenoughrecognition.PermeabilitystructuretypesofrockmassanditspermeabilitycharacteristicsSo-calledpermeabilitystructuresofrockmassarespatialdistributionandcombinationlawofpermeablemass(layer)oraquifer,andrelativeimperviouslayer(mass).Todividepermeabilitystructurestypesofrockmassinreasonishelpfulforgraspingpermeabilitycharacteristicsofrockmassfrommacro-scale,andcanprovidebasicreferenceforseepagecalculationandseepagecontrolanddrainageengineeringdesign.Thepermeabilitystructuresofrockmasscanbedividedintofiveclasses,whicharediscretemasspermeabilitystructure,layeredpermeabilitystructure,zonalpermeabilitystructure,netlikepermeabilitystructureandduct-likepermeabilitystructure.DiscretemasspermeabilitystructureDiscretemasspermeabilitystructureismainlymadeupoffullandhighlyweatheredzoneofintrusiverock.Itspermeabilitymediatypeisporousmediabasically,andtakesonhomogeneousisotropicpermeabilitycharacteristics.Itspermeabilityisrelativestrongcommonly.LayeredpermeabilitystructureLayeredpermeabilitystructureismainlyformedbygentlydippingstrataofinter-layersbetweenpermeablelayersandrelativeimperviouslayers,gentlyeruptiverockwithmultilayerstructureandgentlyfaultfragmentizedzone,etc.Itspermeabilitymediatypeiscrannymediabasically.Groundwatergenerallyhosts,transportsineachpermeablelayer.Itsrecharge,runoffanddrainagearecontrolledbytherelativeimperviouslayersaboveandunderpermeablelayers,andtakesonmultilayerwaterlevelfrequently.Itcanfoundfrommacro-scalethatthepermeabilityincataclinallayerdirectionisfarhigherthanthatinverticallayerdirection,andtakesonobviousanisotropicpermeabilitycharacteristic.ZonalpermeabilitystructureZonalpermeabilitystructureismainlymadeupofthefaultfragmentizedzonewithhighdiporientation,fracturesconcentrationzone,dikefracturedzone,highlydippingstrataofinter-layersbetweenpermeablelayersandrelativeimperviouslayers,strongunloadingzonebesiderivervales,etc.Itspermeabilitymediatypeiscrannymediabasicallyanditspermeabilityisrelativestrongcommonly.Itoftenconnectswithlayeredandnetlikepermeabilitystructures,andformsconcentrativeseepagepassagesofgroundwater,andalsocanformhydraulicrelationchannelsofgroundwaterbetweenvariouspermeablelayers.Itcanfoundfrommacro-scalethatthepermeabilityincataclinalzonedirectionisfarhigherthanthatinverticalzonedirection,andtakesonobviousanisotropicpermeabilitycharacteristic.NetlikepermeabilitystructureNetlikepermeabilitystructureismainlymadeupofslightlyweatheredtofreshblockyrockandsedimentaryrockwhoselithologyissingleandfracturesincludingkarstcranniesrelativedevelop,etc.Itspermeabilitymediatypeiscrannymediaanditspermeabilityisrelativeweak.Themovementofgroundwaterismainlycontrolledbydevelopmentcharacteristicsoffracturenetworkanditspermeability,andtakesonobviousinhomogeneousandanisotropicpermeabilitycharacteristic.Fracturedgroundwaterhostinginthesamestratadoesnotalwayshaveuniformgroundwaterlevel.Duct-likepermeabilitystructureDuct-likepermeabilitystructureismainlymadeupofkarstcavesandlimestonewherepipelinesdevelop.Itspermeabilitymediatypeiskarstcavemediaandoftenformsconcentrativeseepagepassagesoflargewaterquality.Groundwatergenerallyflowsalongkarstpassagesanddrainagesbywayofspring.Thedistributionofgroundwaterisinhomogeneous,andgroundwaterdynamicschangegreatly.Itsflowingstateisrelativecomplex.Itisnecessarytoemphasizethatpermeabilitystructureofrockmassisnotsingletypeundermostconditions,butthesuperpositionofmanypermeabilitystructuretypes.Thepositionwherevariouspermeabilitystructurescrossandfoldwillformconcentrativeseepagepassagesofgroundwater.Soitistheemphasesthatneedpaymoreattentiontoforseepagecontrolanddrainageprojects.Inaddition,layeredpermeabilitystructurealsohasthepermeabilitycharacteristicsofnetlikepermeabilitystructure,intermsoflocalscope.EngineeringcasesCase1divisionofrockmasspermeabilitystructuretypesforXiaolangdidamsiteBasicgeologicconditionsOutcroppingstrataatdamsitearemainlyupperPermiansystemandlowerTriassic,itslithologyissiliceousandcalcareoussandstone,muddysiltstone,andinterlayerofsiltyclayrock.Thesandstoneishardandbrittlerock,wherefracturesdevelop.Itbelongstopermeablelayeroraquifer.Muddysiltstoneandclayrockwherefracturesdonotdevelopbelongtoimperviouslayer.Theorientationofstrataatdamsiteisgently,thedipdirectionisNE(downstreamdirection),andthedipangelis8°〜12°.Theoutcroppingfaultsaremainlyrelativelarge-scale,whichareF1、F28、F461andF236、F238,etc.Theyareallhighdipangel.F1faultdistributesatriverbedofrightbank,whosestrikeisclosetotheparallelofYellowRiver.F28faultdistributesalongwindandrainravineofleftbank,whosestrikeis30°〜60°.F461faultdistributesatXiaonanvillageofleftbank,whosestrikeis290°〜310°.F236andF238faultstraversetheareaofchambersgroupatleftbank,andwhosedistributionisclosetoeastandwestdirection,andpasstroughupstreamanddownstreamofreservoir.Thereare3〜4grouphighdipfracturesdevelopedatdamsitesandstone.Thefracturesdonotdevelopatmuddysiltstoneandclayrock.Thepatulouswidthoffracturesatweatheringandunloadingzoneisrelativelarge.DivisionofpermeabilitystructuretypesThepermeabilitystructuretypescanbeconfirmedtobelayeredandzonal(Fig1.),byanalyzingbasicgeologicconditionsofXiaolangdidamsite.Thereservoirwaterseepstodownstreamalongpermeablesandstonedistributingatvariousheightandfaultfragmentizedzonewhichpassesthroughupstreamanddownstreamofreservoir.Theemphaticattentionshouldbetakentothepermeablesandstoneandtherockmasswherepermeablesandstoneandfaultfragmentizedzonecross,whentreatmentsofseepagecontrolanddrainageengineeringareconsidered.l Z.O1inipeiiiiien iy^rniciuieF236Fig.1ThetypicalpermeabilitystructuresectionofsandstoneandclayrockstrataatXiaolangdidamsiteCase2thepermeabilitystructuretypesofrockmassattheThreeGorgesdamsiteBasicgeologicconditionsOutcroppingrockattheThreeGorgesengineeringdamsitearemainlyporphyriticgranite,andintrusiveacid-maficdikesofmorethanoneperiod.Thereisrelativethickweatheredshellatsurfacelayerofrockmass.Itcanbedividedintofourweatheredzones,whicharefull,highly,weaklyandslightlyweatheredzonesrespectively.Thefullweatheredzoneconsistsofloosenclasticrockwhichhassomejointedforce.Thehighlyweatheredzoneismadeupofinterlayerbetweenloosen,halfloosenrockandhard,halfhardrock.Theweaklyweatheredzoneishardandhalfhardrockmainly.TheweathereddegreeofslightlyweatheredzonerockisslightTherearefourgroupsoffaultsdevelopingatdamsite,whosestrikesareNNWandNNE,etc.Theirdipangelsarehighgenerally.Thefourgroupsoffractureswhichdevelopwellrelativelyhavehighdipangelmostly,andfewofmiddleandgentledipangel.Thedikecontactswithsurroundingrockthroughfaultsorfracturesfrequently.DivisionofpermeabilitystructuretypesThepermeabilitystructurecanbeconfirmedtothreetypes,whicharediscretemass(fullweatheredrockmass),netlike(fracturedrockmass)andzonal(faultsanddikes)byanalyzing

basicgeologicconditionsoftheThreeGorgesdamsite.ItcanbeseeninFig.2.Thezonalpermeabilitystructurecanformthechiefnetworkofseepagefield,anditseffectsareclosetocatchmentsandfilling&emptyingculvert.Itisnecessarytopayattentiontowhenthedesignofseepagecontrolanddrainageengineeringiscarriedout.Fig.2ThetypicalpermeabilitystructuresectionofblockyrockmassattheThreeGorgesengineeringdamsite(accordingtorevisionbyZHOUZhifang)霎一切履辛一-fiussFig.2ThetypicalpermeabilitystructuresectionofblockyrockmassattheThreeGorgesengineeringdamsite