Landslides and Their Stabilization

This book was written with the objective of providing geotechnical engineers with a practical guideline on how to cope with landslides as well as of acquaint­ ing them with the present state of physical fundamentals and scientific expla­ nations for the phenomenon of landslides. The book is based on my personal experiences, gathered over decades of work as geotechnical engineer on construction sites in Austria and many other parts of the world, which I also use in my lectures at the Technical University of Graz, Austria. The method of stabilizing lands lides by short-circuit conductors has been developed by myself and has been patented in Germany and Italy. A number of publications already exists (see References) on this method, and of course I also deal in this book with its theoretical and practical aspects. Here I want to thank my assistants, Messrs. J. Dalmatiner, K. Eigenberger, E. Garber, H. Kienberger, R. Pötscher, and W. Prodinger, for working with me on various projects and for assisting me in the drafting of some chapters of this book, Mr. A. Trippl for preparing the illustrations, and my wife for many a Sunday worked through with me.

1 Introduction.- 1.1 Definition.- 1.2 Economic Significance of Landslide Stabilization.- 2 Characteristic Types of Landslides and Alternatives for Their Stabilization.- 3 Main Causes of Landslides.- 3.1 Geological Causes.- 3.2 Morphological Causes.- 3.2.1 Excessive Steepening of Slope Inclinations.- 3.2.2 Excessive Load Pressure on Slope Head.- 3.2.3 Weakening of Slope Toe.- 3.3 Physical Causes.- 3.3.1 Decay of Cohesion with Time.- 3.3.2 Diagenetic Cohesion and Its Decay as Related to the Danger of Landslides.- 3.3.3 Progressive Failure—Engineering Geology of Overconsolidated Plastic Clays.- 3.3.4 Landslides in Stiff, Fissured Clay.- 3.3.5 Effects of Earthquakes.- 3.4 Physicochemical Structure Changes of Silt and Clay Soils.- 3.4.1 Relief from Load Pressure and Resulting Water Absorption.- 3.4.2 Increase of Water Pressure in Soils.- 3.4.2.1 Increased Water Inflow to Water-Bearing Layers.- 3.4.2.2 Closing of Natural Drainage (Springs, Water Outlets).- 3.4.3 Development of New Cracks and Fissures or the Opening of Water Passages Previously Closed by Impermeable Soil.- 3.4.4 Salting of Highways—Ion Exchange.- 3.4.5 Adjacent Reducing and Oxidizing Soil Layers (blue clay/brown clay)—Natural Electroosmosis.- 3.4.6 Quick Clay.- 3.5 Action of Water in Soil.- 3.5.1 Action of Pore Water.- 3.5.1.1 Concentrated Pore-Water Action at Potential or Actual Slip Surfaces or at Walls of Cracks in Clayey-Silty “Homogeneous” Soils.- 3.5.1.2 Concentrated Pore-Water Action at the Zone of Division between Clayey-Silty Soils of Different Nature.- 3.5.1.3 Pore-Water Acting in Relatively Permeable Silty Sand Layers of Several Decimeters Thickness Interposed between Two Relatively Impermeable Silty-Clayey Layers.- 3.5.1.4 Pore-Water Acting More or Less Uniformly in Whole Mass of Clayey-Silty Layers of Several Meters Thickness.- 3.5.2 Action of Water (from a Constant Strong Source) that is Streaming in Soils.- 3.5.2.1 Sandy Soils.- 3.5.2.2 Clayey-Sandy Silt Soils.- 3.5.3 Action of Flowing Surface Waters.- 3.5.3.1 Water in Vertical or Steep, Fissured Soil Layers.- 3.5.3.2 Water Mixed with Superficial Soil (Debris Avalanches).- 3.5.3.3 Water Undercutting Slope Toes.- 3.5.4 Solifluction.- 4 Theoretical Basis for the Calculation of Slope Safety.- 4.1 Safety Conditions in a Slope with Slope-Parallel, Planar, Infinite Slip Surface.- 4.2 Methods for Calculating Slope Safety Regardless of Subsoil Structure.- 4.2.A Definition of Safety.- 4.2.B Position and Shape of Slip Surfaces.- 4.2.C Which Calculation Method Yields the Most Accurate Results Regarding Safety?.- 4.3 Critical Evaluation of Methods of Calculating Slope Safety and Suggestions for Improvement.- 4.3.1 Remarks in Principle Regarding the Methods Listed in 4.2.C.- 4.3.1.1 Planar Test Surfaces.- 4.3.1.2 Curved Test Surfaces.- 4.3.2 Simplified Eigenberger Method.- 4.3.2.1 Homogeneous Soils.- 4.3.2.2 Stratified Soils.- 4.3.2.3 Concentrated Loads.- 4.3.2.4 Simplification with Pore-Water Pressure (Quick Lowering of Water Table).- 4.3.2.5 Extended Test Surfaces of Any Shape.- 4.3.3 Calculation of Slope Safety after Eigenberger’s Simplified Method—Examples.- 4.3.3.1 Cohesionless, Homogeneous Slopes.- 4.3.3.2 Cohesive, Homogeneous Slopes.- 4.3.3.3 Cohesionless, Stratified Slopes.- 4.3.3.4 Cohesive, Stratified Slopes.- 5 Field and Laboratory Investigations.- 5.1 Field Investigations.- 5.1.1 Aerial Photography.- 5.1.2 Geodetic Surveys.- 5.1.3 Geological Investigations.- 5.1.3.1 Seismic Investigations.- 5.1.3.2 Geoelectric Investigations.- 5.1.4 Soil Exploration by Boring and Extraction of Disturbed and Undisturbed Soil Samples.- 5.1.5 Measuring Penetration Resistance of Sounds.- 5.1.6 Measuring Pore-Water Pressure with a Piezometer.- 5.1.7 Deformation Measurements at the Surface and at Different Depths below the Surface.- 5.1.8 Measurement Techniques for Electric Soil Potentials, pH-Values, and Redox Properties.- 5.1.8.1 Measurement of Soil Potentials.- 5.1.8.2 Measurement of Soil pH-Value.- 5.1.8.3 Measurement of Redox Properties of Soil.- 5.1.9 Measurement of Natural Water Content at the Surface with Radioactive Cobalt.- 5.2 Laboratory Investigations.- 5.2.1 Determination of Natural Water Content.- 5.2.2 Oedometer Test and Determination of Permeability Coefficient.- 5.2.3 Cylinder Compression Test.- 5.2.4 Determination of Internal Friction Angle and Cohesion.- 5.2.5 Investigations with X-Rays.- 5.2.6 Testing of Models in the Centrifuge.- 6 Methods for the Stabilization of Landslides.- 6.1 The Morphology of the Terrain Remains Unchanged.- 6.1.1 Moving Layers are Intersected by Construction, but without Arresting the Slide Movement.- 6.1.1(I) Tobacco Factory, Ftirstenfeld, Styria, Austria.- 6.1.1(II) Foundation of the Lueg Bridge, Brenner, Tirol, Austria.- 6.1.1(III) Foundations for Cable-Car Supports and Powerline poles.- 6.1.1(IV) Foundation of the Limberg Bridge, Franz-Josefs-Railway, Lower Austria.- 6.1.2 Stabilizing Moving Soil Layers.- 6.1.2(I) A Landslide in Turkey.- 6.1.2(II) Stahlberg Freeway, German Federal Republic.- 6.1.3 Stabilizing Moving Structures: Stabilization of an Abutment for a Freeway Overpass near Graz, Austria.- 6.1.4 Stabilization by Reduction of Pore-Water Pressure.- 6.1.4.1 Reduction of Pore-Water Pressure with Drainage Trenches.- 6.1.4.1(I) Stabilization of a Slope near Retznei, Styria, Austria.- 6.1.4.1(II) Landslide Graz-Ruckerlberg, Austria.- 6.1.4.1(III) Landslide Kleinsölk, Styria, Austria.- 6.1.4.1(IV) Budapest, Dunaújváros, Hungary.- 6.1.4.2 Reduction of Pore-Water Pressure by Horizontal Borings from the Ground Surface.- 6.1.4.2(I) Landslide Graz-Ries, Austria.- 6.1.4.2(II) Memphis, Tennessee, United States.- 6.1.4.3 Reduction of Pore-Water Pressure Using Wells with Horizontal Drainage—Landslide Kirchschlag, Lower Austria.- 6.1.4.4 Reduction of Pore-Water Pressure with Short-Circuit Conductors (after Veder).- 6.1.4.4.1 Overview.- 6.1.4.4.2 Practical Applications.- 6.1.4.4.2(I) Landslide near St. Marein, Styria, Austria—Powerline Pole.- 6.1.4.4.2(II) Landslide on the West Freeway near Viehdorf, Lower Austria.- 6.1.4.4.2(III) Sarukuyoji Landslide, Japan.- 6.1.5 Increase of Internal Friction—Solidification of Soil.- 6.1.5.1 Solidification by Grouting (Claquage, Soil Fracturing).- 6.1.5.1.1 Overview.- 6.1.5.1.2 Practical Applications.- 6.1.5.1.2(I) Hart, near Gleisdorf, Styria, Austria.- 6.1.5.1.2(II) Märzzuschlag Tunnel, Styria, Austria.- 6.1.5.2 Drainage and Consolidation by Electroosmosis (after Casagrande).- 6.1.5.2.1 Overview.- 6.1.5.2.2 Practical Application—Kootenay Channel, British Columbia, Canada.- 6.1.5.3 Consolidation by Compounds of Magnesium, Calcium, Aluminum or Iron.- 6.1.5.3.1 Overview.- 6.1.5.3.2 Practical Applications.- 6.1.5.3.2(I) Mooskirchen, Styria, Austria.- 6.1.5.3.2(II) Construction of Lime Piles.- 6.1.5.3.2(III) Sonnenberg Road, Switzerland.- 6.2 The Morphology of the Terrain is in Part Significantly Changed.- 6.2.1 Improvement of Stability Conditions in Sliding Slopes or Embankments.- 6.2.1.1 Down-Grading to Relieve Slope Head of Load Pressure—Headrace, Rossegg Power Plant, Carinthia, Austria.- 6.2.1.2 Replacement of Too Heavy an Embankment Fill—Krummbach Bridge, Styria, Austria.- 6.2.2 Steep Cutting Slopes of Loose Soil are (Temporarily) Retained by Shot-Concrete Skins that may be Reinforced and Anchored—Tokyo, Japan, and the Zwenberg Bridge for the Tauern Railway, Carinthia, Austria.- 6.2.3 Installation of Stone Wedges at Slope Toe to Increase Friction, Drain and Ballast the Toe—Ybbsitzer Heights, Lower Austria.- 6.2.4 Soil Exchange at Embankment Base—Embankment Slide near Oberpullendorf, Burgenland, Austria.- 6.2.5 Lining the Bottom and Sides of a Cut with Gravel—Tailrace Channel, Silz Power Plant, Tirol, Austria.- 6.2.6 Installation of Terzaghi Filter to Check Erosion of Easily Moving Layers of Fine Sand.- 6.2.7 Installation of Stone Ribs or Stabilized Soil Material Parallel to Slope—Brick-Clay Pit, Budapest, Hungary.- 6.2.8 Ballasting Fills as Support for Embankment Toes.- 6.2.8(I) Freeway, German Federal Republic.- 6.2.8(II) Vermont, United States.- 6.2.9 Retaining Walls.- 6.2.9.1 Gravity or Cantilever Retaining Walls.- 6.2.9.2 Bore-Pile or Diaphragm Walls without Anchoring—Construction of the Olympic Road, Rome, Italy.- 6.2.9.3 Anchored Walls of Load-Bearing and Non-Load-Bearing Bore-Pile or Diaphragm-Wall Panels.- 6.2.9.4 Anchored Wall Constructed from Top to Bottom—Anchor Wall near Peggau, Styria, Austria.- 6.2.9.5 Other Retaining-Wall Constructions.- 6.2.9.5(I) “Krainer” Crib Walls.- 6.2.9.5(II) Gabionades.- 6.2.9.5(III) Reinforced Earth.- 6.2.9.5(IV) New “Ebenseer” Wall.- 6.2.9.5(V) Soil Nailing.- 6.3 Synoptic Description of Characteristic Landslides.- 6.4 Additional Stabilization Measures.- 6.5 Durability of Stabilization Measures.- 6.6 Symbols Used in Soil Profiles.- 7 Physical Chemistry of Landslides in Silt and Clay Soils.- 7.1 Introduction.- 7.2 Highly Disperse (Colloidal) Soil Components.- 7.2.1 Colloids—Common Properties.- 7.2.2 Clay Minerals and Their Properties.- 7.2.2.1 Montmorillonite as Example for Layered Silicates Capable of Swelling.- 7.2.2.2 Mechanism of Water Uptake and Swelling in Clay Minerals.- 7.2.2.3 Influence of Cations on Water Absorption, Swelling, and Decrease of Shear Strength—Ion Exchange.- 7.2.2.3.1 Influence of Road Salting and Sewage Waters on Slides.- 7.2.2.3.2 Influence of the pH-Value of Water in Soil.- 7.2.2.3.3 Thixotropy—Quick Clay.- 7.2.2.4 Electric Charge of Clay Particles and Related Phenomena.- 7.2.2.4.1 Electrochemical Double-Layer.- 7.2.2.4.2 Electroosmosis.- 7.2.2.5 Electric Soil Potentials, Reducing and Oxidizing Soils, Correlation between Soil Potentials and Landslides.- 8 Closing Remarks.- References.