4 Specific needs
Ground anchors can only be designed efficiently on the basis of a sound knowledge of the construction project, of the structural requirements of the anchor and of the geotechnical properties of the ground. Anchor testing and the verification of design parameters are necessary elements in the construction procedure for economical installation of effective ground anchors.
The responsibilities of all parties involved in the design, execution, testing and maintenance of the ground anchors shall be defined. Table 1 shows, as a guide, an appropriate separation of design and execution activities.
|Overall design activities||Specialist execution activities|
1. Provision of site investigation data for construction of ground anchors
2. Decision to use ground anchors, required trials and testing and provision of a specification
3. Acquisition of legal authorisation and entitlement to encroach on third party property
4. Overall design of anchored structure, calculations of anchor force required. Definition of safety factors to be employed.
5. Definition of ground anchor life (permanent/temporary) and requirement for corrosion protection.
6. Specification of anchor spacing and orientation, anchor loads and overall stability requirements.
7. Specification of minimum distance from the structure to mid fixed length to ensure stability of the structure.
8. Specification of load transfer mechanism from the anchor to the structure.
9. Specification of any sequence of anchor loading required of the structure and the appropriate load levels.
10. Specification of systems for monitoring ground anchor behaviour and for interpretation of results.
11. Supervision of the works.
12. Specification of maintenance for ground anchors.
13. Instruction to all parties involved of key items in the design philosophy to which special attention should be directed.
|1. Assessment of site investigation data with respect to design assumptions.
2. Selection of ground anchor components and details.
3. Determination of fixed anchor dimensions.
4. Detailing of the corrosion protection system for the ground anchor.
5. Supply and installation of the ground anchor system.
6. Supply and installation of the ground anchor monitoring system.
7. Quality control of works.
8. Execution and assessment of anchor tests.
9. Evaluation of on-site anchor tests.
10. Maintenance of ground anchor as directed.
Sufficient information to assist in the design and installation of ground anchors should be provided prior to, and updated during, the execution of the works.
NOTE The whole design or some parts of the design may be performed by the client, the main contractor, a specialist contractor or by a consultant.
4.2 Planning of anchor works
The following shall be provided prior to the initial supply and installation of the ground anchor system:
- details of the ground anchor project and the construction sequence and programme;
- a site investigation report incorporating a geotechnical classification and engineering properties of the ground in which the ground anchors are to be located;
- information on all other boundary conditions, including underground services, existing foundations and requirements relevant to the location and performance of the ground anchors;
- details of ownership of the ground into which the anchors are to be installed;
- details of any agreement required to gain access to ground into which the anchors are to be installed.
The amount of investigative and design work depends upon the type and size of the project, the complexity of the ground and the degree of risk involved.