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Grävpålar - Dimensionering, utförande och användningsområden

Shiltagh, Sam (2010) VGTM01 20092
Structural Mechanics
Civil Engineering (M.Sc.Eng.)
Abstract
Foundations of buildings and structures are laid with various methods, both deep and shallow foundations. Piling is the most common method of deep foundations while spread footings are often used in shallow foundations, especially in buildings with column frame. An alternative is to use a composite pile foundation where piles and spread footings or piles and a base slab are used to carry the loads.

Bored piles are in-situ concrete piles formed by excavating or boring a hole in the ground and filling it with concrete or reinforced concrete. The use of bored piles has so far been limited in Sweden; therefore there are no Swedish standards for the design of bored piles. However, there are Swedish guidelines from 1979 for the design of... (More)
Foundations of buildings and structures are laid with various methods, both deep and shallow foundations. Piling is the most common method of deep foundations while spread footings are often used in shallow foundations, especially in buildings with column frame. An alternative is to use a composite pile foundation where piles and spread footings or piles and a base slab are used to carry the loads.

Bored piles are in-situ concrete piles formed by excavating or boring a hole in the ground and filling it with concrete or reinforced concrete. The use of bored piles has so far been limited in Sweden; therefore there are no Swedish standards for the design of bored piles. However, there are Swedish guidelines from 1979 for the design of bored piles founded in frictional soils, published by the Swedish Commission on Pile Research. These guidelines are however not valid for bored piles in clay or boulder
clay.

The purpose of this study is to present and evaluate various design methods in order to make an appropriate choice of design methods and to present guidelines to assess when bored piles are appropriate based on technical and economical aspects.

Owing to the method of construction, bored piles can be formed with various sizes, ranging from large piles which are a few meters in diameter with depths that reach one hundred meters to small and short piles. This huge variation in dimensions makes bored piles useful for deep foundations as well as shallow foundations. Bored piles have many advantages compared to driven piles; they are environmentally friendly
because they generate low levels of noise and ground vibrations, are able to carry heavy transverse loads as well as vertical loads and they are economically advantageous compared to driven concrete piles at moderate depths. Bored piles, also known as drilled shafts, have many advantages compared to spread footings especially in boulder clay and other dense soils. Bored piles have a much shorter production time, require less labor and are often cheaper to produce. Bored piles and spread footings were compared in two buildings with column frame. One of the buildings is founded in sand and the other in boulder clay. The results show that bored pile foundations are technically feasible and also provide lower production cost for both buildings compared to spread footing foundations.

A bored pile’s total resistance consists of base and/or skin resistance. The resistance may be determined by load tests or by ground investigation. Bored piles founded in cohesion soils and boulder clay are often designed by the Total Stress Analysis which is the most reliable method of analysis. Design of bored piles in frictional soils is more complicated and is based on the Effective Stress Analysis or empirical methods.

Bored piles resist transverse loads by mobilization of passive earth pressure around the pile. A bored pile have a large diameter with low risk for buckling, therefore it may be considered as a rigid body when considering the failure mechanisms rotation or translation as the transverse load resistance is designed. The bending moment capacity of a bored pile is usually calculated by assuming that the bored pile rotates around its base, but it may varies depending on the degree of freedom of rotation at the connection with the structure.

Bored piles bearing capacity is often decided by the size of the displacements. Bored piles settlement may be calculated in the same way as for spread foundations e.g. by the traditional 2:1 method or by using normalized load-displacement curves. Use of the above mentioned methods will result in short-term settlements which are sufficient, if the utilization of the base resistance doesn’t exceed tow-thirds in the ultimate limit state.

In connection with the introduction of Eurocodes, standards for execution of bored piles have come. Eurocodes don’t contain any design methods for determining the geotechnical bearing capacity of bored piles, but they provide guidelines regarding how the bored piles should be constructed, how the geotechnical resistance will be calculated and which partial- and safety factors should be used for soil parameters, material and ground resistance when determining the design value of bored piles load capacity. (Less)
Please use this url to cite or link to this publication:
author
Shiltagh, Sam
supervisor
organization
course
VGTM01 20092
year
type
H3 - Professional qualifications (4 Years - )
subject
keywords
Cohesive Soils, Frictional soils, Boulder Clay, Piling, Foundation, Geotechnical Engineering, In-situ concrete piles, Bored piles, Drilled shafts, Eurocodes, Finite element method, FE modeling
report number
TVSM-5165
ISSN
0281-6679
language
Swedish
id
3566941
date added to LUP
2013-08-01 14:10:12
date last changed
2013-10-07 13:11:50
@misc{3566941,
  abstract     = {Foundations of buildings and structures are laid with various methods, both deep and shallow foundations. Piling is the most common method of deep foundations while spread footings are often used in shallow foundations, especially in buildings with column frame. An alternative is to use a composite pile foundation where piles and spread footings or piles and a base slab are used to carry the loads. 

Bored piles are in-situ concrete piles formed by excavating or boring a hole in the ground and filling it with concrete or reinforced concrete. The use of bored piles has so far been limited in Sweden; therefore there are no Swedish standards for the design of bored piles. However, there are Swedish guidelines from 1979 for the design of bored piles founded in frictional soils, published by the Swedish Commission on Pile Research. These guidelines are however not valid for bored piles in clay or boulder 
clay.

The purpose of this study is to present and evaluate various design methods in order to make an appropriate choice of design methods and to present guidelines to assess when bored piles are appropriate based on technical and economical aspects.

Owing to the method of construction, bored piles can be formed with various sizes, ranging from large piles which are a few meters in diameter with depths that reach one hundred meters to small and short piles. This huge variation in dimensions makes bored piles useful for deep foundations as well as shallow foundations. Bored piles have many advantages compared to driven piles; they are environmentally friendly
because they generate low levels of noise and ground vibrations, are able to carry heavy transverse loads as well as vertical loads and they are economically advantageous compared to driven concrete piles at moderate depths. Bored piles, also known as drilled shafts, have many advantages compared to spread footings especially in boulder clay and other dense soils. Bored piles have a much shorter production time, require less labor and are often cheaper to produce. Bored piles and spread footings were compared in two buildings with column frame. One of the buildings is founded in sand and the other in boulder clay. The results show that bored pile foundations are technically feasible and also provide lower production cost for both buildings compared to spread footing foundations.

A bored pile’s total resistance consists of base and/or skin resistance. The resistance may be determined by load tests or by ground investigation. Bored piles founded in cohesion soils and boulder clay are often designed by the Total Stress Analysis which is the most reliable method of analysis. Design of bored piles in frictional soils is more complicated and is based on the Effective Stress Analysis or empirical methods.

Bored piles resist transverse loads by mobilization of passive earth pressure around the pile. A bored pile have a large diameter with low risk for buckling, therefore it may be considered as a rigid body when considering the failure mechanisms rotation or translation as the transverse load resistance is designed. The bending moment capacity of a bored pile is usually calculated by assuming that the bored pile rotates around its base, but it may varies depending on the degree of freedom of rotation at the connection with the structure.

Bored piles bearing capacity is often decided by the size of the displacements. Bored piles settlement may be calculated in the same way as for spread foundations e.g. by the traditional 2:1 method or by using normalized load-displacement curves. Use of the above mentioned methods will result in short-term settlements which are sufficient, if the utilization of the base resistance doesn’t exceed tow-thirds in the ultimate limit state.

In connection with the introduction of Eurocodes, standards for execution of bored piles have come. Eurocodes don’t contain any design methods for determining the geotechnical bearing capacity of bored piles, but they provide guidelines regarding how the bored piles should be constructed, how the geotechnical resistance will be calculated and which partial- and safety factors should be used for soil parameters, material and ground resistance when determining the design value of bored piles load capacity.},
  author       = {Shiltagh, Sam},
  issn         = {0281-6679},
  keyword      = {Cohesive Soils,Frictional soils,Boulder Clay,Piling,Foundation,Geotechnical Engineering,In-situ concrete piles,Bored piles,Drilled shafts,Eurocodes,Finite element method,FE modeling},
  language     = {swe},
  note         = {Student Paper},
  title        = {Grävpålar - Dimensionering, utförande och användningsområden},
  year         = {2010},
}