Advanced Soil Mechanics, Study notes of Soil Mechanics and Foundations

Download Advanced Soil Mechanics and more Study notes Soil Mechanics and Foundations in PDF only on Docsity!

Advanced Soil Mechanics

Stefan Van Baars

© Edited and published by Stefan Van Baars. Edition May 2016

Key words: soil mechanics, foundation engineering, tunnelling

CONTENT

• I SOIL IMPROVEMENT
• 1 Introduction
• 2 Mechanical compaction
  • 2.1 Surface compaction
  • 2.2 In-depth compaction
• 3 Injection techniques.....................................................................................................
  • 3.1 Permeation grouting..............................................................................................
  • 3.2 Jet-grouting
  • 3.3 Fracture grouting
  • 3.4 Compaction grouting
• 4 Dewatering & drains
  • 4.1 Introduction
  • 4.2 Vertical drainage
• 5 Ground freezing...........................................................................................................
  • 5.1 Introduction
  • 5.2 Brine freezing (indirect cooling)
  • 5.3 Nitrogen freezing (direct cooling)
  • 5.4 Thermic Design
• 6 Geotextiles and reinforced soil
  • 6.1 Geotextiles............................................................................................................
  • 6.2 Reinforced soil / Terre armée
• 7 Ground exchange
  • 7.1 Natural soils..........................................................................................................
  • 7.2 Artificial heavy or light products
• II TUNNELLING
• 8 Tunnel types.................................................................................................................
• 9 Cut & cover tunnel
  • 9.1 Open building pit
  • 9.2 Classical cut & cover
  • 9.3 Aqueduct
  • 9.4 Wall-Roof method
• 10 Tunnel Boring Machine (TBM)
  • 10.1 Open face TBM
  • 10.2 Hydro shield or slurry shield (SS) TBM
  • 10.3 Earth Pressure Balanced shield (EPB) TBM
  • 10.4 Hard rock TBM
  • 10.5 Support pressure
  • 10.6 Pneumatic caisson.................................................................................................
  • 10.7 Settlements
• 11 Drill & blast (rock) tunnelling
  • 11.1 German Method or Core Method
  • 11.2 Old Austrian Tunnelling Method or Old ÖTM
  • 11.3 New Austrian Tunnelling Method or NÖTM
• 12 Immersed tunnel
  • 12.1 Construction method
  • 12.2 Chin-nose and jack-leg support.............................................................................
  • 12.3 Advantages and disadvantages..............................................................................
• 13 Jacked box tunnel........................................................................................................
• III SHALLOW FOUNDATIONS
• 14 Types of shallow foundations
• 15 Elastic stresses and deformations
• 16 Boussinesq
• 17 Flamant........................................................................................................................
• 18 Deformation of layered soil
• 19 Bearing capacity of a strip footing..............................................................................
  • 19.1 Lower bound
  • 19.2 Upper bound.........................................................................................................
• 20 Prandtl & N c
• 21 Reissner & N q
• 22 Meyerhof & N 
• 23 Table of the bearing capacity factors
• 24 Correction factors
  • 24.1 Inclination factors i
  • 24.2 Shape factors s
• 25 CPT, undrained shear strength and Prandtl
• IV PILE FOUNDATIONS........................................................
• 26 Cone Penetration Test (CPT)......................................................................................
• 27 Compression piles
  • 27.1 Pile types
  • 27.2 Bearing capacity
  • 27.3 CPT, SPT and HDP
  • 27.4 Tip resistance using Meyerhof (Prandtl, Terzaghi or Brinch Hansen)
  • 27.5 Tip resistance using a CPT method (Koppejan)
  • 27.6 Shaft resistance...................................................................................................
  • 27.7 Settlement of piles
• 28 Tension piles
  • 28.1 Differences between tension and compression piles
  • 28.2 Reduction of the cone value qc due to excavation................................................
  • 28.3 Reduction of cone resistance due to tensile pile force
  • 28.4 Clump criterion
  • 28.5 Edge Piles
  • 28.6 MV-pile or Jacket-grouted pile
• V UNDERGROUND MEGASTRUCTURES........................
• 29 Underground megastructures
• 30 Sustainable resources
• VI BUILDING PIT
• 31 Building pit
  • 31.1 Introduction
  • 31.2 Pit collapse
  • 31.3 Pit design
• VII WALLS AND LATERAL STRESS
• 32 Walls
  • 32.1 Wall types...........................................................................................................
  • 32.2 Soldier pile wall (Berliner wall)
  • 32.3 Sheet pile wall
  • 32.4 Combi wall
  • 32.5 Bored pile wall
  • 32.6 Diaphragm wall
• 33 Lateral stresses in soils
  • 33.1 Coefficient of lateral earth pressure
  • 33.2 Elastic material
  • 33.3 Elastic material under water
• 34 Rankine
  • 34.1 Mohr-Coulomb
  • 34.2 Active earth pressure
  • 34.3 Passive earth pressure
  • 34.4 Neutral earth pressure
  • 34.5 Menard-penetrometer and CAMKO-pressuremeter
  • 34.6 Groundwater
• 35 Coulomb
  • 35.1 Active earth pressure
  • 35.2 Passive earth pressure
• 36 Tables for lateral earth pressure
  • 36.1 The problem
  • 36.2 Example
  • 36.3 Tables
• 37 Sheet pile walls...........................................................................................................
  • 37.1 Homogeneous dry soil
  • 37.2 Pore pressures
• 38 Blum
• 39 Sheet pile wall in layered soil
  • 39.1 Computer program
  • 39.2 Computation of anchor plate
  • 39.3 Horizontal bedding constants for subgrade reaction models
  • 39.4 Finite Element Modelling
  • 39.5 Example quick design
• 40 Sheet pile profiles
• VIII ANCHORS, STRUTS AND WALES
• 41 Supports
• 42 Anchors......................................................................................................................
  • 42.1 Anchoring
  • 42.2 Anchor installation
  • 42.3 Soil nailing
  • 42.4 Holding capacity of anchor plate
  • 42.5 Holding capacity of a grouted anchor
  • 42.6 Overall stability
• 43 Struts
• 44 Wales
• IX FLOORS.............................................................................
• 45 Floatation & Archimedes
• 46 Natural floor & heave
• 47 Unsupported under water concrete floor
• 48 Supported under water concrete floor
  • 48.1 General...............................................................................................................
  • 48.2 Floatation of the floor
  • 48.3 Transfer of forces to piles & fracture of the pile joint
  • 48.4 Fracture of the floor
• X GLOBAL STABILITY & FAILURE................................
• 49 Failure modes
• 50 Global translation (sliding)
• 51 Global rotation (circular sliding)
  • 51.1 Safety factor
  • 51.2 Fellenius
  • 51.3 Bishop
  • 51.4 Global failure
• XI DEWATERING
• 52 Groundwater flow
  • 52.1 Hydrostatics
  • 52.2 Groundwater head...............................................................................................
  • 52.3 Darcy..................................................................................................................
  • 52.4 Permeability
  • 52.5 Flow in a vertical plane
• 53 Flow net......................................................................................................................
  • 53.1 Potential and stream function
  • 53.2 Flow under a structure
• 54 Flow towards well
  • 54.1 Confined aquifer
  • 54.2 Unconfined aquifer
  • 54.3 Semi-confined aquifer
  • 54.4 Superposition
  • 54.5 Examples
• 55 Dewatering
  • 55.1 Open dewatering and wellpoint drainage.............................................................
  • 55.2 Dewatering problems
  • 55.3 Hindrance for the surroundings
• XII SAFE DESIGN
• 56 Limit states and design rules
  • 56.1 Limit states
  • 56.2 Design rules
• 57 Material and load factors
  • 57.1 Design theory
  • 57.2 Load factors
  • 57.3 Material factors...................................................................................................
  • 57.4 Inadequate standards
• 58 Control sensors

I Soil improvement

2 Mechanical compaction

The goal of mechanical compaction is the reduction of the amount of pores. The less pores, the higher the stiffness of the ground and also the higher the strength (angle of internal friction). For cohesive soils like clay and peat, this reduction can only be achieved by consolidation and creep of the material, which means dewatering is required. For these soils with a low permeability, dewatering is a very slow process. Since mechanical compaction is a quick load technique, it will not work well for these soil types. For non-cohesive soils like sand and gravel, or mixed soils, there are good possibilities for this technique. There are two types of mechanical densification techniques:

1. Surface compaction
2. In-Depth compaction

2.1 Surface compaction

There are different types of machines for surface densification:  Surface vibrators,  Vibrating rollers,  Vibro rammers,  Explosion rammers,  Impact slabs

Figure 2 - 1. Surface vibrator.

Figure 2 - 2. Vibrating roller.

Figure 2 - 3. Vibro rammer.

Figure 2 - 4. Explosion rammer.

Figure 2 - 5. Impact slab.

For sandy soils, this vibration technique, with or without water injection, works fine. For clayey soils, one cannot decrease the amount of pores, but one can increase the strength, stiffness and permeability (for drainage to speed up the consolidation), by vibrating gravel or small stones into the ground.

Figure 2 - 7. Vibration needles, with water injectors at the tip. (Photo: BIUG Geotechnik)

Figure 2 - 8. Vibrator (Rüttler) in sandy soils and gravel (Schotter) injection in clayey soils.

3 Injection techniques

Injection techniques are techniques in which mixtures of materials are injected under pressure in the pores and other open spaces of the underground in order to decrease the permeability or to increase the strength and/or stiffness. One needs large injection pipes and large machines for this.

There are several grouting techniques: a) Permeation grouting: a very fluid liquid grout (water and cement) is injected in the pores (of mostly sand) to make it more impermeable and stronger. b) Jet-grouting: Soil is mixed with a powerful grout beam. The beam is rotated to make columns or walls. c) Fracture-grouting: a very fluid liquid grout (water and cement) is injected with high pressure in order to create horizontal cracks (unfortunately mostly vertical cracks appear). The horizontal cracks are made for compensating settlements.. d) Compaction Grouting: Very stiff grout is blown up like a balloon in order to compensate settlements.

Figure 3 - 1. Injection pipes and machinery.

Figure 3 - 2. Grouting techniques.

3.2 Jet-grouting

The Jet-grouting technique can be used for different purposes. An example is the underpinning of a shallow foundation that is settling too much. In this way, more or less a deep foundation is made.

By combining a long line of grouting columns even a retaining wall can be made.

In fact, besides the walls, also the floor can be jet-grouted. In this way a complete swimming pool can be made in a small and difficult to access back yard.

Figure 3 - 5. Foundation support.

Figure 3 - 6. Retaining wall from jet-grouted columns.

Figure 3 - 7. Jet-grouted swimming pool.

There is a risk in jet-grouting. The grouting tubes are never installed exactly at where the design requires. Also these tubes are never installed fully perpendicular. Due to this, the centres of the columns are never as designed. Also the radiuses of the columns are never exactly as designed. This can cause small leaks in the grouted floor, which are very difficult to locate and to repair. A famous case is the tunnel under the Big Market Street in Den Hague in the Netherlands, where this problem caused major problems. The final, very time and money consuming method, was to install air-locks and seal off the whole tunnel, pushing out the ground water and repairing the leaks, all under air-pressure.

3.3 Fracture grouting

Fracture grouting is mainly used for lifting buildings, which have settled too much. This mostly happens due to insufficient deep constructed shallow foundations and settlements caused by excavations like building pits and tunnels. The grout pressure should be far more than the vertical pressure at that particular level in the ground.

Figure 3 - 8. Designed (left) and constructed (right) grout floor with leak.

Figure 3 - 9. Fracture grouting (Pictures Hayward Baker, USA).