Landslides and Their Stabilization

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.