After installation, the jacks were initiated to load asmall amount and make the system combine closely.There were four samples for the shear tests on the clay–limestone contact. One day before the tests, the clay was satu-rated; in test processes, the normal loadingwas pided into fourgrades, the next load was loaded after the previous load reachedstable state. The different normal stresses acted on four sampleswere the same as the laboratory clay test. After the last loading,the shear stresses were loaded slowly; in shear processes, theshear stresses and shear displacements were recorded.The stress–strain curves are shown in Fig. 9. At the sametime, it is assumed the shear surfaces are Mohr–Coulombmaterial, when the samples yield, the relationship of the normal and shear stresses is shown in Fig. 7. The best linearfit results indicate that strength parameters are c = 42.2 kPa,/ = 22  (R2= 0.997), thus the factor of stability of crosssection I–I calculated by formula (1) is 1.03. Consideringunder high normal stress, such as 400–600 kPa, c =16.0 kPa,/ = 24.4  (Fig. 7), thus the factor of stability is 1.01; the twocalculated results are very close to the limit equilibrium state.According to the back analysis results (Fig. 5),when the blockis in limit equilibrium state, / = 22 , c = 40.8 kPa. The testresults on the contact are consistent with the back analysisresults. It can be sure that the instable block slides along thecontact of clay–limestone, and the tested strength parameters(c = 42.2 kPa, / = 22 ) of the sliding plane are reasonable.DiscussionFrom the discussed results, the strength parameters of theweak intercalated layer can be decided from Table 1. The laboratory direct shear tests indicate that thecohesion and friction angle of the filling clay arec = 207.6 kPa, / = 17.0 . The factor of stability of thefailure is 1.66, assuming that the failure sliding throughthe clay, which means that the slope must be stable. Forsimilar landslide, which sliding plane is near the relativeweak layers, conventional or intuitive laboratory testmethods pay more attention to the mechanics characteris-tics of the filling clay; this case indicates that the ideas andstudy methods are unconservative and misleading, becausethey ignore the contact of the clay–stone.The in situ direct shear tests indicate the cohesionand friction angle of the weak intercalated layer arec = 42.2 kPa, / = 22.0 , which implies that the calculatedfactor of stability is very close to the limit equilibriumstate. The test results are consistent with the back-analyzedresults. Therefore, it can be sure that the shear of instableblock commences along the clay-stone contact, but notthrough the clay.Earlier workers (Goodman 1976; Ladanyi and Archa-mbault 1970) found that when the infilling thickness isgreater than the roughness amplitude, the shear strength ofthe discontinuity is controlled by the strength of theinfilling. The results of this paper indicate that shearlandslide may be along the contact of the clay–limestone,although the thickness of the infilling was much greaterthan the roughness amplitude of discontinuity. The dis-crepancy can be explained by the engineering properties ofthe stiff clay, which has high cohesion (much greater thanthe cohesion on contact of clay–limestone).The shear strength of the weak plane by artificially saw-cut stone surface filled with remolded clay was testedby Hatzor (1997), whose test results are c = 160 kPa,/ = 18 .
Because of the disturbance to the stone and clay,Hatzor believes that the tested cohesion is negligible. Inthis study, the shear strength parameters of the contact aretested by the in situ direct tests; the samples were disturbedlittle; the tested parameters (c = 42.2 kPa, / = 22 ) areclose to the real situation, which indicate the cohesion isnot ‘0’ or ignorable.ConclusionIn this study, a plane shear failure along a clay-filledbedding plane in limestone is back-analyzed by site measurement and careful geological mapping of theinstable block’s geometry. Then the laboratory and in situdirect shear tests for the clay infilling or the contact surfaceare undertaken, respectively. Thus, the material propertiesof the limit equilibrium are obtained. Some conclusionscould be obtained:1. To the bedding landslide along the weak layer, theearlier study results, such as Goodman (1976),Ladanyi and Archambault (1970, 1977), found thatwhen filling thickness is greater than the roughnessamplitude, the shear strength of the discontinuity isgoverned by the strength of the infilling. In this case,it is shown that the shear strength of the clay–limestone contact dictates the resistance force of thesliding plane rather than the strength of the clay. Thisdiscrepancy could be the result of the stiff clay. Theconventional or intuitive assumption of shear failurethrough the clay may be erroneous or unconservative.2. Hatzor (1997) considered that the cohesion on theclay-stone contact is negligible. However, in thisstudy, the in situ direct shear test results, which areconsistent with the back-analyzed results, indicate thecohesion is not negligible for the original structuralsurface.3. In view of the characteristics of the landslide and itscurrent stability state, it is recommended that monitor-ing should be undertaken to identify any displacement,and the retaining walls or appropriate reinforcementshould be constructed at the front of the landslide tominimize the possibility of a catastrophic event.Acknowledgments This paper is financially supported by NationalBasic Research Program of China (973 Program) (No.2006CB403204). Zheng Quanming of Shandong Zhengyuan Con-struction Co., Ltd. provided great help in the field and assisted withsample preparation and direct shear testing, his careful work isacknowledged. Laiwu Iron & Steel Co., Ltd. provided free access todigitized mapping data and borehole data.ReferencesAlhomoud AS, Tubeileh TK (1998) Analysis and remedies oflandslides of cut slopes due to the presence of weak cohesivelayers within stronger formations. Environ Geol 33(4):299–311Barton NR (1971) Estimation of in situ shear strength from backanalysis of failed rock slopes. In: Proceedings of internationalsymposium on rock mechanics, vol 1.a. Nancy, France, pp 2–27Barton N (1973) Review of a new shear strength criterion for rockjoints. Eng Geol 7:287–332Barton NR, Bandis S (1982) Effects of block size on the shearbehavior of jointed rock. In: Proceedings of the 23rd USsymposium on rock mechanics, Berkeley, California, USAFookes P, Reeves B, Dearman W (1977) The design and constructionof a rock slope in weathered slate at Fowey, South-WestEngland. Geotechnique 27(2):533–556 石灰石夹层顺层滑坡分析英文文献和中文翻译(5):http://www.youerw.com/fanyi/lunwen_54410.html