The extent and an analysis of shallow failures on the slopes of highway earthworks

The reported incidences of shallow failures on the slopes of highway earthworks have increased in recent years. This Thesis includes a study of the extent of this problem, the likely factors contributing to failure, and presents the results of empirical design and the analysis of the likely mechanism of failure. A survey was conducted, covering a total length of 570km of selected lengths of motorway in England and Wales, which included the principal geologies encountered on the British motorway system, in particular, areas where over-consolidated clays predominate. From the survey, the basic factors that have contributed to shallow failures on the side slopes of embankments and cuttings can be deduced, and attempts are made to quantify any long-term problems. The results show a high incidence of failure associated with the major influences of geology, age of earthworks and geometry of slope, with many more failures occurring on embankments than on cuttings. The slope angles recommended are empirically derived and can be used both in the design of new earthwork side slopes and to identify slopes at risk of failure in existing earthworks. An estimate is made of the extent of failures in the future which suggests that three times as many slopes are likely to fail than have failed so far. To study the mechanisms of failure and the behaviour of over- consolidated clays at extremely low effective stresses, an analytical method is developed which includes a detailed study of non-linear failure envelopes and the fitting of the most representative curve to peak strength data. Also a new rigorous slope stability analysis method is developed which incorporates this type of failure envelope. Back-analyses are conducted for several embankment slopes from which samples have been tested in the laboratory. Results indicate that the critical state strength rather than the peak strength governs the formation of shallow failures.

[1]  N. Morgenstern,et al.  Stability Coefficients for Earth Slopes , 1960 .

[2]  James R Blacklock,et al.  INJECTION STABILIZATION OF FAILED HIGHWAY EMBANKMENTS , 1986 .

[3]  D J Ayres.  STABILIZATION OF SLIPS IN COHESIVE SOIL BY GROUTING , 1985 .

[4]  H. Fang,et al.  Stability of Earth Slopes , 1991 .

[5]  W. Fellenius.  Calculation of stability of earth dam , 1936 .

[6]  J Perry.  A SURVEY OF SLOPE CONDITION ON MOTORWAY EARTHWORKS IN ENGLAND AND WALES , 1989 .

[7]  J Wrightman,et al.  USE OF FABRIC REINFORCEMENT FOR REINSTATING UNSTABLE SLOPES , 1982 .

[8]  G C Wilson,et al.  SOIL STABILITY PROBLEMS IN ROAD ENGINEERING. , 1953 .

[9]  Alec Westley Skempton,et al.  First-Time Slides in Over-Consolidated Clays , 1970 .

[10]  D M Farrar,et al.  STRESS PATH TESTS TO MEASURE SOIL STRENGTH PARAMETERS FOR SHALLOW LANDSLIPS. PROCEEDINGS OF THE ELEVENTH INTERNATIONAL CONFERENCE ON SOIL MECHANICS AND FOUNDATION ENGINEERING, SAN FRANCISCO, 12-16 AUGUST 1985 , 1985 .

[11]  I F Symons.  THE MAGNITUDE AND CAST OF MINOR INSTABILITY IN THE SIDE SLOPES OF EARTHWORKS IN MAJOR ROADS , 1970 .

[12]  J Perry.  INCIDENCE OF HIGHWAY SLOPE STABILITY PROBLEMS IN LOWER LIAS AND WEALD CLAY , 1985 .

[13]  Richard John Lisle,et al.  Least-squares fitting of the linear Mohr envelope , 1982, Quarterly Journal of Engineering Geology.

[14]  Eduardo E. Alonso.  PROCEDURE OF SLOPE FAILURE PREDICTION DURING RAINFALL BASED ON THE BACK ANALYSIS OF ACTUAL CASE RECORDS , 1990 .

[15]  Evert Hoek,et al.  Strength of jointed rock masses , 1983 .

[16]  R. Hill.  The mathematical theory of plasticity , 1950 .

[17]  V. V. Sokolovskii,et al.  Statics of Granular Media , 1965 .

[18]  S. Sarma.  STABILITY ANALYSIS OF EMBANKMENTS AND SLOPES , 1973 .

[19]  J Perry,et al.  SLOPE STABILITY PROBLEMS IN AGEING HIGHWAY EARTHWORKS , 1985 .

[20]  James M. Bell,et al.  General Slope Stability Analysis , 1968 .

[21]  D. York.  Least-squares fitting of a straight line. , 1966 .

[22]  Delwyn G. Fredlund,et al.  Stability of swelling clay embankments , 1979 .

[23]  B. Efron,et al.  A Leisurely Look at the Bootstrap, the Jackknife, and , 1983 .

[24]  A. B. Hawkins,et al.  Measurement and use of residual shear strength of cohesive soils , 1985 .

[25]  R. L. Schuster,et al.  Stability of Simple Cuttings in Normally Consolidated Clays , 1968 .

[26]  Donald W. Taylor,et al.  Fundamentals of soil mechanics , 1948 .

[27]  Zhang Xing,et al.  THREE-DIMENSIONAL STABILITY ANALYSIS OF CONCAVE SLOPES IN PLAN VIEW , 1988 .

[28]  Nilmar Janbu,et al.  Stability analysis of slopes with Dimensionless parameters , 1954 .

[29]  Alec Westley Skempton,et al.  STABILITY OF NATURAL SLOPES AND EMBANKMENT FOUNDATIONS , 1969 .

[30]  B F J Bradbeer,et al.  DISCUSSION. SOIL STABILITY PROBLEMS IN ROAD ENGINEERING. , 1953 .

[31]  P. L. Bransby,et al.  THE MECHANICS OF SOILS, AN INTRODUCTION TO CRITICAL STATE SOIL MECHANICS , 1987 .

[32]  A. Skempton.  Slope Stability of Cuttings in Brown London Clay , 1984 .

[33]  Robert W. Day,et al.  Surficial Stability of Compacted Clay Slopes , 1989 .

[34]  E. T. Brown,et al.  EMPIRICAL STRENGTH CRITERION FOR ROCK MASSES , 1980 .

[35]  Robin Chowdhury,et al.  Probabilistic Model of Progressive Failure of Slopes , 1982 .

[36]  Joakim G. Laguros,et al.  FAILURE OF SLOPES IN WEATHERED OVERCONSOLIDATED CLAY , 1982 .

[37]  P. I. Lewin,et al.  UNDISTURBED SAMPLES OF LONDON CLAY FROM THE ASHFORD COMMON SHAFT' STRENGTH-EFFECTIVE STRESS RELATIONSHIPS , 1965 .

[38]  S G Wright,et al.  AN EXAMINATION OF EARTH SLOPE FAILURES IN TEXAS. FINAL REPORT , 1984 .

[39]  E. Bromhead.  STABILITY OF SLOPES , 1986 .

[40]  Leslie L. Karafiath,et al.  General Yield Conditions in a Plasticity Analysis of Soil-Wheel Interaction , 1974 .

[41]  Jr Greenwood.  A SIMPLE APPROACH TO SLOPE STABILITY , 1983 .

[42]  Wang Yan,et al.  Slope stability analyses for materials with a non-linear failure envelope , 1988 .

[43]  O. Hungr.  An extension of Bishop's simplified method of slope stability analysis to three dimensions , 1987 .

[44]  J. A. Charles,et al.  Stability of compacted rockfill slopes , 1984 .

[45]  C Garrett,et al.  PERFORMANCE OF EMBANKMENTS AND CUTTINGS IN GAULT CLAY IN KENT , 1985 .

[46]  A.J.M. Spencer,et al.  General yield conditions in plane deformations of granular media , 1970 .

[47]  R. E. Gibson,et al.  A Note on the Stability of Cuttings in Normally Consolidated Clays , 1962 .

[48]  Dimitri Grivas,et al.  CONVENTIONAL AND PROBABILISTIC EMBANKMENT DESIGN , 1982 .

[49]  A. Bishop.  The use of the Slip Circle in the Stability Analysis of Slopes , 1955 .

[50]  R. J. Chandler.  Recent European experience of landslides in over-consolidated clays and soft rocks , 1984 .

[51]  G West,et al.  MONITORING PORE WATER PRESSURES IN AN EMBANKMENT SLOPE , 1985 .

[52]  F. W. Kellaway,et al.  Advanced Engineering Mathematics , 1969, The Mathematical Gazette.

[53]  Brian Vickers.  Laboratory Work in Soil Mechanics , 1983 .

[54]  N. Coppin,et al.  Use of Vegetation in Civil Engineering , 1990 .

[55]  W. Tang,et al.  Reliability model of progressive slope failure , 1987 .

[56]  P. Lumb,et al.  Probabilistic design of slopes , 1987 .

[57]  Karl Pearson F.R.S..  LIII. On lines and planes of closest fit to systems of points in space , 1901 .

[58]  A. Skempton,et al.  The design of permanent cutting slopes in stiff fissured clays , 1974 .

[59]  A. Schofield,et al.  Critical State Soil Mechanics , 1968 .

[60]  W. F. Chen,et al.  Stability analysis of slopes with general nonlinear failure criterion , 1987 .

[61]  Great Britain. Office for Standards in Education,et al.  Transport statistics, Great Britain , 1976 .

[62]  Yu. K. Zaretskii,et al.  Stability of earth slopes , 1980 .

[63]  A. Bishop.  The stability of earth dams , 1952 .

[64]  J. Haldane,et al.  Organic correlation and allometry. , 1950, Biometrika.

[65]  Donald H. Gray,et al.  FILL SLOPE REPAIR USING SOIL BIOENGINEERING SYSTEMS , 1989 .

[66]  N. Morgenstern,et al.  The analysis of the stability of general slip surfaces , 1965 .

[67]  D A Holt,et al.  SHALLOW SLIPS IN HIGHWAY EMBANKMENTS CONSTRUCTED OF OVERCONSOLIDATED CLAY , 1985 .

[68]  P E Johnson.  Maintenance and repair of highway embankments: studies of seven methods of treatment , 1985 .

[69]  V. D. Mello,et al.  Reflections on design decisions of practical significance to embankment dams , 1977 .

[70]  A. W. Bishop,et al.  A hydraulic triaxial apparatus for controlled stress path testing , 1975 .

[71]  Ja Bland,et al.  TECHNICAL NOTE. DISCUSSION. NUMERICAL DETERMINATION OF THE MOHR ENVELOPE AND CONFIDENCE ANALYSIS. , 1981 .

[72]  D. Fredlund,et al.  Comparison of slope stability methods of analysis , 1977 .

[73]  R D Andrews.  DETERMINING THE AGE OF FAILURE OF MOTORWAY EARTHWORKS FROM AERIAL SURVEY PHOTOGRAPHS , 1990 .

[74]  P. Kneale,et al.  The influence of shrinkage cracks on pore-water pressures within a clay embankment , 1982, Quarterly Journal of Engineering Geology.

[75]  John C. Cripps,et al.  Engineering characteristics of british over-consolidated clays and mudrocks I. Tertiary deposits , 1986 .

[76]  E. Hoek,et al.  Rock slope engineering , 1974 .

[77]  D. G. Fredlund,et al.  Effect of soil suction on slope stability at Notch Hill , 1989 .

[78]  J. M. Duncan,et al.  The accuracy of equilibrium methods of slope stability analysis , 1980 .

[79]  P. R. Vaughan,et al.  Pore pressure changes and the delayed failure of cutting slopes in overconsolidated clay , 1973 .

[80]  N. Janbu.  Application of composite slip surfaces for stability analysis , 1954 .

[81]  M. S. Rosenbaum,et al.  Probabilistic slope stability analysis using a microcomputer , 1985, Quarterly Journal of Engineering Geology.

[82]  J. A. Charles,et al.  The stability of slopes in soils with nonlinear failure envelopes , 1984 .

[83]  Malcolm G. Anderson,et al.  Pore water pressure and stability conditions on a motorway embankment , 1980 .

[84]  A. Skempton.  Long-Term Stability of Clay Slopes , 1964 .