Feb.20th, 2013
D R A F T
of the course CEB0007361/Lecture GEOENGINEERING – FOUNDATIONS
by
Włodzimierz Brząkała, PhD, DSc, Associate Professor
contents
Subject
1. Examples of soil-foundation interaction 1
2. Linear models of the subsoil behaviour 1
3. Foundations on the Winkler subsoil;
beams and plates on elastic subsoil 3
4. Underground mine workings and surface subsidence. Protection
against mining damages 3
5. Construction and types of retaining structures.
Stability criteria of retaining walls 1
6. Earth pressure theories; applications of the Prandtl solution 2 7. Corresponding limit states - cohesion;
final completion test – 45min 2
8. Geoengineering Failure Histories;
final completion test – 45min. 2
General outcomes:
the course completes the scope of the graduate course called Foundations (Level I) focusing on the presentation of selected new geoengineering technologies and some relevant calculation techniques.
Special attention is paid to the soil-foundation interaction which enables a more realistic evaluation of subsoil actions. Both basic models, the elastic settlements and the ultimate bearing capacity, are developed.
A special approach is required when analyzing mining influences on foundations.
Students get the background knowledge to cope with more advanced problems of geoengineering and gain a skill in foundation design.
1. Examples of soil-foundations interaction (1 hr)
Statically indeterminate foundation beam on 3 elastic supports
Elastic supports and fixities of a frame structure
Long beam loaded with a moving force
Long pipeline resting on an inhomogeneous subsoil
Contact forces under stiff plates and water pressure effects
A hybrid retaining wall.
Outcomes:
Students discover that structural calculations can be loaded with errors of the range up to 20-40%, if the soil-structure interaction is ignored; the foundation (or structure) stiffness – related to the subsoil stiffness – governs the redistribution of contact forces for design purposes, the rising of the water horizon introduces new calculation situations.
2. Linear models of the subsoil behaviour (1 hr)
The Winkler model, the subsoil coefficient
Elastic half-plane
Finite elastic layers
Evaluation of parameters – the inverse analysis
Limitations of the linear models, no-tension joints, nonlinearities etc.
Outcomes:
Students look for a balance between model simplicity and acceptable accuracy for design purposes;
shortcomings of the linear models are discussed in detail, global and local models (analogs) of the subsoil are introduced;
the question “When the Winkler model (hypothesis of the elastic subsoil coefficient) can be acceptable?” is addressed.
3. Foundations on the Winkler subsoil; beams and slabs on elastic subsoil (3 hrs)
The Euler-Bernoulli beam (strip foundation)
The force fundamental solution (infinite beam, concentrated loading force)
The moment fundamental solution (infinite beam, concentrated loading moment)
General boundary conditions
Semi-finite and finite beams – The Bleich virtual forces
Variable subsoil coefficient – solutions in terms of polynomial expansions
Foundation beams as virtual strips within rectangular slabs supporting an array of columns
Equations and analytical solutions for slabs.
Outcomes:
A bridge to the courses Strength of Materials and Ordinary Differential Equations, practicing with the superposition principle and the Green functions, application of virtual loadings as a prototype for the Boundary Element Method, longitudinal variability of internal forces in beams on the elastic subsoil, design of deformable continuous footings.
4. Underground mine workings and surface subsidence;
Protection against mining damages (3 hrs)
Mining technologies
Area of influence and subsidence curves
Parameters of the ground surface subsidence, mining categories
Tolerance of engineering objects to deformations
Discontinuous mining deformations and mining dynamical excitations
Subsoil redistributed actions on foundations
Subsoil additional actions on foundations
Precautions against mining damage
Designer’s question: structural accommodation or high resistance?
Outcomes:
15-20% of Poland’s territory is in contact with mining influences (including dewatering of open-pits, historical mining activity, mining induced quakes, etc.) – and close to urban regions or industrial ones, students acquire a description and classification of CE-problems.
Design in difficult geoengineering conditions, evaluation of bending moment changes (mining curvature) and tensile/compressive axial forces (mining strains); individual analysis of the allowable differential settlements of CE-objects, shape optimization of foundations; some aspects are also useful for foundations on swelling and shrinking soils or other origins of ground movements Students get a background for further contacts with mining engineers and municipal authorities.
5. Construction and types of retaining structures.
Stability criteria of retaining walls (2 hrs)
Massive gravity walls, abutments
Concrete cantilever retaining walls
Embedded structures - slurry walls
Setting of loadings, positioning of the structure, eccentricity reduction
EQU criterion (rotation failure),
GEO criteria: sliding failure, bearing failure, failure by (rotational) slip in surrounding soil, other failure criteria: anchors, slurry trench,
HYD and UPL due to the Eurocode EC7
STR in concrete design, etc.
Outcomes:
Students acquire technical information (useful to make a rational selection) about characteristic features of each construction type in the context of: required functions, safety, bearing capacity, durability and costs; most recent technologies, such as the “Top & Down” construction processes and the floor strutting method, are discussed; soil anchors are also useful for masts, suspension bridges, hydrotechnical structures, deep tunnels (against up-lift).
The criteria meet the geotechnical requirements of the Eurocode EC7 design code, minimal values of allowable safety margins confirm the correct position and shape of the construction; other failure criteria that are of interest: pull-out capacity of anchors, slurry trench stability, design of concrete elements, etc.)
6. Earth pressure theories;
applications of the Prandtl solution (2 hrs)
The Coulomb-Poncelet theory
The Prandtl solution and its applications
Technical methods for the earth-pressure reduction
The EC7 approach to the earth pressure evaluation Outcomes:
Most frequently, the limit equilibrium equations formulated in stresses can be solved only for several simple cases, therefore some additional simplifications are necessary; for the ultimate passive earth pressure such simplifications can be dangerous (overestimated values by the Poncelet approach);
a rational shape of the wall can reduce the earth pressure substantially.
7. Corresponding limit states – cohesion (1hr)
Limit states of stresses for cohesive soils
Examples: earth pressure, foundation bearing capacity
Final Test #1.
Outcomes:
Solutions for cohesive soils result from corresponding solutions for noncohesive ones.
8. Geoengineering Failure Histories (1 hr)
The Leaning Tower of Pisa – a sequence of many geoengineering faults
Old monumental Buildings in Mexico City – very large settlements
Reclamation of a pond with liquid uranium wastes in Kowary – reinforced soil cover
Final Test #2.
Outcomes:
Some spectacular situations as a background for profound geoengineering analyses: role of human errors, insufficient geological data, lack of experience with new technologies, poor prediction of environmental changes
Note about the Final Tests:
2 calculation tasks (20min+10min, 7pts.+4pts)
3 detailed questions (3x5min, 3x3pts)
marks (at least 10 pts. to pass)
The better result of both Final Tests will be taken.
Outcomes:
It is expected that the students – engineers to be – will become skilful in simple calculations for design purposes; therefore 11 pts. - of the total of 20 pts. – are assigned to the calculation part of the test.
