摘要
目前,地裂缝的发育分布特征和活动特点等已经被人们基本掌握,但在成因机理方面的研究还不够成熟,仍存在不同观点和争议,另外已有裂缝再次开裂扩展的机理尚需深入研究。本文以汾渭盆地地裂缝为研究背景,以西安市f14地裂缝探槽和泾阳地震台地裂缝探槽为试验场地,通过对地裂缝发育的介质环境—黄土(包括原状黄土、裂隙性黄土、重塑黄土)进行三轴拉伸特性试验研究,分析了与地裂缝有关的黄土破裂特性及破裂行为,并在此基础上讨论了黄土地区地裂缝的成因机制与扩展机理。
原状黄土的三轴拉伸试验表明,黄土的抗拉强度及极限拉应变均很小,且随着围压的增大,其断裂时的轴向应力由拉应力向压应力转变。当黄土体内应力储备大于其极限强度时,内部应力便会寻找一种可以释放能量的通道,很容易在地表土体中产生拉张裂缝,且随着深度的增加,逐渐呈闭合的趋势。裂隙性黄土的三轴拉伸破裂特性试验表明,其破裂主要受控于所处的应力状态及土体中原有的宏观结构面,在低围压情况下,裂隙性黄土更容易沿原有裂隙结构面产生裂缝而破坏,黄土体中多数地裂缝是在土体中原有的结构面上发育起来的。重塑黄土的三轴拉伸试验表明,土体的抗拉强度与围压和含水率关系密切。单轴拉伸情况下,抗拉强度随着含水率的增大呈先增大后减小的趋势,三轴拉伸情况下,抗拉强度随着含水率的增大而减小。与此同时,笔者从微观角度对重塑土单轴抗拉强度进行了理论预测,含水量为10%时预测值为7.4kPa,实测值为7.9kPa；含水量为15%时,预测值为10.25kPa,实测值为12.1kPa,预测值与试验结果吻合较好。
黄土在各种作用下的破裂特性试验研究表明,汾渭盆地的构造应力场是引发地裂缝的主控因素,其他一些作用则为附加因素。
Recently, the distribution and activity character of ground fissure have been mastered basically, but its genetic mechanism is immature being many different points of view and disputes on it because there are some key basic problems being unresolved. This paper researched the mechanism of ground fissures in Fen-Wei basin by experiment studying loess samples with fracture fillings and without fracture fillings excavated from the trench in Xi'an and Jing-yang ground fissures field. Based on a series of triaxial tensile test of loess, the rupture characteristics and behavior related to loess ground fissures were analyzed and the genesis and expansion mechanism of ground fissures developed in loess were discussed.
The triaxial tensile test of intact loess indicates that the tensile strength and strain of loess are very small. And with the increase of confining pressure, the tensile stress would become compressive stress. When the tensile stress in loess is bigger than tensile strength, the tensile cracks would come into being to release the tensile stress, with the buried depth increases, the crack would become closed. The triaxial tensile test of loess with fracture fillings indicates that the stress state and the initial structural plane controlled the rupture development and cracks are easier to be formed near initial cracks under low confining pressure. The triaxial tensile test of remolded loess indicates that the tensile strength of loess is related to the confining pressure and water content. Under uniaxial tension, with increasing of water content, the tensile strength increases firstly and then decreases, Under triaxial tension, with increasing of water content, tensile strength decreases At the same time, the author carried out theoretical analysis from microscopic view to predict the uniaxial tensile strength of remolded loess. The predicted value is 7.4kPa and the measured value is 7.9kPa when w=10%; The predicted value is 10.25kPa and the measured value is 12.1kPa when w=15%;which indicates theoretical analysis agree with the test result well。
The broken test of loess showed that the tectonic stress field of Fen-Wei basin was the controlling factor to ground fissures, and other factors were additional factors.
引文
[1]王景明等.地裂缝及其灾害的理论与应用[M].西安：陕西科学技术出版社,2000
[2]彭建兵等.汾渭盆地地裂缝成因研究中的若干关键问题[J].工程地质学报,2007,15(4)：433-440
[3]张家明.西安地裂缝研究[M].西安：西北大学出版社,1990
[4]李永善等.西安地裂及渭河盆地活断层研究[M].北京：地震出版社,1992
[5]彭建兵等.渭河盆地活动断裂与地质灾害[M].西安：西北大学出版社,1992
[6]姜振泉等.临汾地裂缝的成因及发育环境研究[M].徐州：中国矿业大学出版社,1999
[7]冯希杰.西安地裂缝活动成灾评估[J].西安地质学院学报,1990,12(4)：44-48
[8]李新生.西安地面沉裂环境问题研究[D].西安：西安地质学院,1994
[9]陈志新等.渭河盆地地裂缝发育基本特征[J].工程地质学报,2007,15(4)：441-447
[10]宋彦辉等.山西地堑系一类特殊的剪切—挤压型地裂缝[J].工程地质学报,2007,15(4)：448-452
[11]黄强兵等.西安地铁二号线沿线地裂缝未来位错量估算及工程分级[J].工程地质学报,2007,15(4)：469-474
[12]党进谦,张伯平,熊永.单轴土工拉伸仪的研制[J].水利水电科技进展,2001,21(5)：31-32
[13]党进谦,郝月清,李靖.非饱和黄土抗拉强度的研究[J].河海大学学报,2001,29(6)：106-108
[14]周鸿逵.三轴拉伸试验中试样的断裂机理[J].岩土工程学报,1984,6(3)：11-23
[15]张少宏,郭敏霞,邢义川.三轴拉伸试验技术研究[J].西北水资源与水工程,2001,12(2)：24-27
[16]朱崇辉,刘俊民,严宝文,巨娟丽.非饱和黏性土的抗拉强度与抗剪强度关系试验研究[J].岩石力学与工程学报,2008,27(增2)：3453-3458
[17]贾坚.室内水泥土抗拉强度的测试方法及若干探讨[J].上海地质,1999,70：48-55,59
[18]Rumpf H. The strength of granules and agglomerates.Knepper,W.A, Agglomeration.Knepper,Interscience, New York:379-418
[19]Schubert H. Cappillary forces-modeling and application in particulate technology[J].Powder Technology,1984,37:105-116
[20]Molenkamp F, Nazemi A H. Interactions between two rough spheres, water bridge and water vapour [J].Geotechnique,2003,53(2):255-264
[21]Pierrat P, Caram H S.Tensile strength of wet granula materials[J].Powder Technology,1997,91:83-93
[22]Kim T H, Hwang changsoo.Modeling of tensile strength on moist granular earth material at low water content[J].Engineering Geology,2003,69:233-244
[23]Lu Ning, Wu Bailin, Tan C P.Tensile Strength Characteristics of Unsaturated Sands[J].Journal of Geotechnical and Geoenvironmental Engineering,2007,133(2):144-154
[24]孙萍.黄土破裂特性试验研究[博士论文D].西安：长安大学,2007.
[25]刘祖典.黄土力学与工程[M].西安：陕西科学技术出版社,1997
[26]郑建国,张苏民.湿陷性黄土的结构强度特性[J].水文地质工程地质,1990,4：22～25.
[27]邢义川,骆亚生,李振.黄土的断裂破坏强度[J].水力发电学报,1999,No.4.
[28]骆亚生,邢义川.黄土的抗拉强度[J].陕西水力发电,1998,No.4.
[29]丁维利,王晓州,朱永全,王庆林,赵永明.郑西客运专线黄土隧道施工地表裂缝调查分析[J].铁道标准设计,2007,增刊(1)：87～89
[30]邢义川.黄土力学性质研究的发展和展望[J].水力发电学报,2000,(71)：54-65
[31]党进谦、郝月清.含水量对黄土结构强度的影响[[J],西北水资源与水工程,19989(2)：15-19
[32]蒋建平,章杨松,罗国煜.基于土体中结构面的岩土程问题探讨[J].工程地质学报,2002,10(02)：160-166.
[33]Tae-Hyung Kim, changsoo Hwang. Modeling of tensile strength on moist granular earth material at low water content[J]. Engineering Geology,2003(69):233-244
[34]S.Y.Ibarra, E.McKyes, R.S.Broughton. Measurement of tensile strength of unsaturated sandy loam soil[J]. Soil & Tillage Research,2005, (81):15-23
[35]李晓军,张登良等.路基填土抗拉强度测定的试验研究[J].西安公路交通大学学报,2000,20(2)：20-22
[36]Skempton, A. W.. Long-term stability of clay slope [J]. Geotechnique, London, England,1964,14(2): 77-101
[37]Skempton, A. W., Schuster, R. L., and Petley, D. J.. Joints and fissures in the London clay at Wraysburg and Edgware [J]. Geotechnique, London, England,1969,19(2):205-217
[38]Skempton, A. W., and Vaughan, P. R.. The failure of Carsington dam [J]. Geotechnique, London, England,1993,43(1):151-173
[39]Simons, N. E.. Field studies of the stability of embankments on clay foundations [J]. Bjerrum Memorial Voulme, NGI, Oslo, Norway,1976, pp.183-209
[40]Potts, D. M., Dounias, G. T., and Vaughan, P.R.. Finite element analysis of progressive failure of Carsington embankment [J]. Geotechnique, London, England,1990,40(1):79-101
[41]F. Tun(?)demir, and M.U. Ergun. A laboratory study into fracture grouting of fissured Ankara Clay [J]. Innovations in Grouting and Soil Improvement,2005, pp.1-12
[42]J.K.Kodikara, and X.Choi. A simplified analytical model for desiccation cracking of clay layers in laboratory tests [J]. Unsaturated Soils,2006, pp.2558-2569
[43]Abbas Elzein. Contaminant transport in fissured soils by three-dimensional boundary elements [J]. International Journal of Geomechanics,2003,3(1):75-83
[44]孔德坊等.裂隙性粘土[M].北京：地质出版社,1994
[45]胡卸文,李群丰,赵泽三等.裂隙性粘土的力学特性[J].岩土工程学报,1994,16(4)：81-88
[46]邓京萍,张惠英.成都粘土的裂隙性对力学性能的控制作用[J].水文地质工程地质,1988(2)：42-46
[47]张慧英,田金花.成都粘土的胀缩特征[J].成都地质学院学报,1990,17(2)：25-30
[48]田金花,张慧英.成都粘土固结特征的初步研究[J].四川地质学报,1987,7(1)：36-41
[49]施斌,姜洪涛.粘性土的微观结构分析技术研究[J].岩石力学与工程学报,2001,20(6)：864-870
[50]陈铁林,邓刚等.裂隙对非饱和土边坡稳定性的影响[J].岩土工程学报,2006,28(2)：210-215
[5l]袁俊平,殷宗泽.考虑裂隙非饱和膨胀土边坡入渗模型与数值模拟[J].岩土力学,2004,25(10)：1581-1586
[52]袁俊平.非饱和膨胀土的裂隙模型与边坡稳定分析[D].南京：河海大学,2003
[53]赵中秀,王小军.超固结状态下裂隙粘土的强度特性[J].中国铁道科学,1995,16(4)：56-62
[54]黄质宏,朱立军等.裂隙发育红粘土力学特征研究[J].工程勘察,2004,(4)：9-12
[55]韩贝传,曲永新,张永双.裂隙型硬粘土的力学模型及其在边坡工程中的应用素[J].工程地质学报,2001,9(2)：204-208
[56]卢全中,彭建兵等.大尺寸裂隙性黄土的直剪试验[J].公路,2006(5)：184-187
[57]卢全中.裂隙性黄土的力学特性及其工程灾害效应研究[D].西安：长安大学,2007
[58]谢富仁等.中国大陆地壳应力环境研究[M].北京：地质出版社,2003
[59]刘恩龙.岩土结构块破损机理与二元介质模型研究[D].北京：清华大学,2005.
[60]中华人民共和国水利部.土工试验方法标准(GB/T 50123—1999)[S].北京：中国计划出版社,1999.
[61]孟祥跃,丁雁生,朱怀球,等.软煤拉伸应力—应变关系的实验研究[J].力学学报,1997,(5)：139—142.
[62]杨少丽,Rolf Sandven,林霖,等.改进的室内粉土制样技术[J].岩土工程学报,2000,22(3)：379 —380.
[63]赵振勇,周春儿,曹喜仁.重塑土简易制样技术及工程应用[J].广东公路交通,2006,(1)：57—60.
[64]郑剑锋,马巍,赵淑萍,等.重塑土室内制样技术对比研究[J].冰川冻土,2008,30(3)：494—500.
[65]Jiang M J, Konrad J.M, Leroueil S. An efficient technique for generating homogeneous specimens for DEM studies[J]. Computers and Geotechnics,2003,30:579—597.
[66]孙明星,党进谦,康顺祥.重塑黄土抗拉特性研究[J].西安文理学院学报,2006,9(3)：60—61.
[67]朱俊高,梁彬,陈秀鸣,曹荣.击实土单轴抗拉强度试验研究[J].河海大学学报,2007,35(2)：187—190.
[68]钮泽明,陆士强.粘性填土单轴抗拉强度的几个影响因素[J].岩土工程学报,1983,5(2)：36—40.
[69]李广.渭河盆地地裂缝主要特征和分布规律研究[硕士论文D].西安：长安大学,2007
[70]陈立伟.地裂缝扩展机理研究[博士论文D].西安：长安大学,2007.
[71]刘玉海等.大同机车工厂及临区地裂缝研究[M].西安：陕西科技出版社,1990
[72]Wang Qingliang. Wang Wenping et. al.. Horizontal aquifer movement induced by groundwater pumping and its applications to the analysis of some geological disasters[J]. ACTA SEISMILOGICA SINICA,1997,17(4),434掣1
[73]王庆良,刘玉海,陈志新等.抽水引起的含水层水平应变地裂缝活动新机理[J].工程地质学报.2002,10(1)：46—50
[74]董东林,武强,姜振全等.析临汾地裂缝之地质成因[J].中国矿业大学学报,2002,31(1)：34—38
[75]Huckell, Bruce B. The Paleo-Indian and Archaic Occupation of the Tucson Basin:An Overview[J]. Kiva,1984,49(3-4):133-145