Pile foundation analysis is based on a number of simple assumptions that affect the accuracy of the results. Calculated results should always be reviewed by the design engineer along with engineering judgment to ensure that the values are appropriate. Also, the results of the analysis should be compared with the results of the load test.
The designer responsible for designing the pile foundation should consider the following 5 factors before arriving at any decision regarding the design of the pile foundation.
1. Functional importance of structure
- The type, purpose and function of the structure influence decisions regarding subsurface investigation programs, analytical methods, manufacturing processes and inspections, and performance monitoring.
- Generally, the proposed structure should be assessed on the basis of the consequences of failure, that is, the potential for loss of life and property, economic losses both local and national, compromise with national defense, and adverse public opinion. The designer should be aware of these factors so that a rational approach can be adopted during the analysis, design and construction of the project.
- To reduce the chance of failure as well as reduce cost, the designer must implement appropriate factors of safety into the design. These safety factors are based on the functional importance of the structure, the level of confidence in the foundation’s parameters, the adequacy of analysis tools, and the level of construction control.
2. definition of failure
- Structure or foundation failures can be classified as true collapse or functional failure.
- Functional failure can be caused by excessive deflection, unacceptable differential movements, excessive vibration and premature deterioration due to environmental factors.
- For critical structures, failure to meet functional requirements can be as serious as the actual collapse of a structure. Therefore, designers need to know not only the degree of protection against collapse but also the effects of settlement and vibration on functional performance.
3. factor of safety
- The factors of safety represent the reserve capacity that a foundation or structure has against collapse for a given set of loads and design conditions. Uncertain design parameters and loads require a higher factor of safety than is necessary when the design parameters are well known.
- For most hydraulic structures, designers must have a high degree of confidence in soil and pile parameters and analysis. Therefore, uncertainty in analysis and design parameters should be reduced rather than requiring a high factor of safety.
- For less critical structures, it is permissible to use larger factors of safety if it is not economical to reduce uncertainty in analysis and design by performing additional studies, tests, etc. In addition, factors of safety must be selected to ensure satisfactory performance. terms of Service. Failure of critical components to perform as expected can be just as damaging as an actual collapse.
- Therefore, it is imperative that in choosing a design approach, designers consider the functional importance of the project, the degree of uncertainty in the design parameters and analytical approach, and the potential for failure due to both collapse and functional inadequacies.
4. Soil composition considerations for analysis
- The functional importance and economic considerations of the structure will determine the type and degree of foundation exploration and testing programmes, pile testing programmes, disposal and leak analysis, and analytical models of the pile and structure.
- The foundation testing program for critical structures should clearly define the parameters required for the design of pile foundations, such as soil type and profile, soil strength, etc.
- Although pile load tests are typically expensive and time-consuming, they are invaluable for verifying or modifying a pile foundation design during the construction phase. A well-planned and monitored pile load test program will typically save money by allowing the designer to use a reduced factor of safety or by modifying the required number or length of piles required.
- Pile load test programs should be considered for all large structures that require a pile foundation.
- Depending on the type of foundation material, nature of loading, groundwater conditions and functional requirements of the structure, a detailed seepage analysis and/or pile disposal analysis may also be required to adequately define the pile-soil. Resultant parameters required for load transfer mechanism and adequate pile design.
- Where differential movement between monoliths is a concern, an accurate estimate of pile settlement can be important, especially if monoliths have significantly different load levels.
- It may be satisfactory to analyze pile foundations for a small, lightly loaded structure based on conservative assumptions for pile parameters and crude structural models; However, a detailed single pile analysis would be required to establish the proper pile parameters for a larger, more substantial structure. Perhaps it will also be necessary to use a structural model that is able to consider the actual structural rigidity to ensure correct load distribution to the piles.
5. Manufacturing & Service Ideas
- No matter how thorough and thoroughly researched a design is, it is only as good as its execution in the field. The proof of the entire design and manufacturing process lies in the performance of the final product under service conditions. Therefore, the designer must consider the analysis and design of a structure and its foundations as parts of an engineering process that culminates with the successful long-term performance of the structure for its intended purposes.
- The designer prepares specifications and instructions for field personnel to ensure proper execution of the design.
- The designer should discuss important aspects of the design with construction personnel to ensure that important design features are fully understood.
- For critical structures a representative of the Design Office should be present in the area on an ongoing basis. One such example would be a major pile testing program where pile testing and data gathering are critical to both a successful test program and validation of design assumptions.
- Another important activity that requires close collaboration between the sector and the designer is the installation of foundation piling. The designer should be involved in this phase to the extent that he is convinced that the design is being executed properly in the field.
- As a general principle, designers should make frequent visits to the construction site not only to ensure that the design intent is being met, but also to improve future designs and meet the built record, through the construction processes and Familiarize yourself with the problems.
- Once the project is in operation, the designer should receive feedback on how well the structure is meeting its operational objectives. This may require that equipment be a part of the design or may take the form of feedback from operational personnel and periodic inspections.