A robust design and certification methodology for installing foundations of geographically distributed infrastructures

Assume that you have a series of foundations (e.g. foundations of bus stop poles; foundations of #windturbines or ESB poles, etc.) distributed in a large geographical area (e.g. a county, a country, or a large area of the ocean), how is it possible to ensure that the design output would be safe and also cost effective?

One may say that the worse case design scenario can be resulted a safe output. However. It is obvious that the result is not optimised. On the other hand, an engineer may say that having proper design input parameters give you different design options making the output optimised. The question then arises how we can manage gathering the design parameters in a proper way and design some options on one hand and ensure that the design options will be properly installed/constructed in different geographical points that may not be possible to properly survey in advance, on the other hand.?In other words, a robust design and construction of?geo-structures distributed in a very?large geographical area rely on the harmonised contribution of all different parties involved in the project. This is not achievable without having a systematic approach in design and to arrange the required interaction between PSDP (project supervisor for the design process) and PSCS (project supervisor for construction stage) and involving Health Safety and Environment (HSE) concept in all design and construction steps of the project.

The below procedure is a robust design methodology suggested by the author under directorship of David Lally to Transport Infrastructure Ireland for installing bus poles distributed in a large #geographical area of Ireland and it was successfully implemented. The similar methodology can be adapted for installing foundations of #windfarms or other geographically distributed #infrastructures .

Description of the proposed design methodology

Regarding the number of the bus stop poles and their distribution in a large geographical area, collecting all design input data and prediction of geotechnical behaviour at the beginning of the project are difficult. To overcome this, according to Eurocode 7, an ‘ observational method’ (also known as ‘learn-as-you-go method’ in geotechnics) can be employed for the project. This helps that the project economically executes due to increasing knowledge of the properties and behaviour of the ground.?

Figure 1 shows the proposed, designed methodology for the project. The project starts with the reviewing all available information provided by the client. This can be including (but not limited to):

1- The coordination of the poles?

2- Conceptual design drawings

3- Clients criteria for design and construction

4- Acceptable design regulations and standards

5- Vendor lists and information

6- Products/material specifications and installation methods

7- Traffic information?

8- Previous available design reports or drawings (good practices)

A desk study is necessary for collecting essential data for designing the foundations and the investigation program. The examples of information and documents that can be used for providing a desk study report include:?

1- Local climate condition

2-?Characteristic wind pressures

3- Topographic maps

4- Previous experience from the area (i.e. consulting with local governmental offices, City Councils, local labs, etc.)

5- Previous investigation close-by to the location of the bus stop (i.e. collecting geotechnical, geological and hydrological information from GSI, EPA, CFRAM etc.)

6- Buried services (i.e. collecting data from local agencies, city councils or online services)

7- Road geometry and traffic consideration for each bus stop

8- Previous geotechnical investigation in the area

The desk study helps to screen the relevant data for each bus stop and provides pre-design information. In case the desk study shows that more information may be needed for the design process, a rapid site visit will be executed for a specific area or a bus stop. The rapid site visit does not include the detail site investigation. To avoid any askew in the design process, the collection of data and processing them will be according to acceptable standards and regulations. The below codes are acceptable standards, can be used for the project:

? Eurocode 1- Actions on structures

? Eurocode 2- Design of concrete structures

? Eurocode 3- Design of steel structures

? Eurocode 7-Geotechnical design

? BS EN 40- Lighting column (Design and verification, the specification for characteristic load)

? AA-STR-06004 and 06028 Early thermal cracking of concrete

? AM-STR-06007 The assessment of reinforced concrete half-joints

? AM-STR-06038 The management of sub-standard road structure

? AM-STR-06042 Structural review and assessment of road structure

? AM-STR-06051 The conservation of the road structures

? AM-STR-06052 The protection and repair of concrete road structures

? CC-GSW-01500 Guidance on Specification for Traffic Control and Communications

? TII Specification for Works Series 000 to 1700?

? TII Specification for Traffic Control and Communications

? TII regulations and guidance for Drainage?

? TII regulations and guidance for Ducts

? TII regulations and guidance for Pavement?

? Other relevant TII documents

Following the desk study and a rapid site visit, a pre-design process is necessary to:

1- Specifying rules for the design of foundations and repair of previous pavements or structures affected by the new construction

2- Reviewing the design concept according to the regulation and available concepts or previous design practice provided by the clients?

3- Specifying design parameters

4- Categorising regions for a group of bus poles based on site characteristics achieved in the desk study process

5- Specifying required tests and validations

6- Planning of new site investigations for each pole and region (see next section for more detail)

The pre-design process provides a basis for developing modelling scenarios of the main design process.?Different scenarios are developed based on soil conditions (categorised during desk study for a group of poles), the geometry of the bus stops and loading cases and values (especially regarding the wind load characteristic value of each bus stop /region of the group of bus stops). The design output consists of design alternatives, drawings, schedules and diagrams for each alternative and relevant design restrictions and considerations.

Regarding different scenarios and the existing uncertainty in the ground conditions of each or group of bus stop poles in different regions, the design specification, sizing and considerations for construction phases can be different. Thus, the design output includes different alternatives for sizing of foundations, specifying the reinforcement, and so on. The suitability of each alternative for each bus stop can be proved after site investigation and surveying during the construction phase. The arrangement for interaction between PSDP and PSCS to prove the suitable alternative for a specific site is described in the next sections. The designer certifies the design and provides the inputs information for risk assessment. This can be done through issuing design schedules, reports or design certification forms.?

Subsequently, a design risk assessment is proceeding for each alternative to identify the hazard during the construction period and to provide measures for eliminating the hazard or reducing the risk of construction to an acceptable level. This process includes planning for safety and health and describing the way that measures of safety and health plan would be controlled. In case the project supervisor for the design process (PSDP) was ensured about safety in design, the design will be issued for approval to PSCS and the client representative (if needed). This process may include providing safety assessment schedules, reports and certification forms.

Notably, the design is not issued for construction, unless a new site investigation, described in the next section, prove that the ground condition of a target bus stop (i.e. executed for construction), is suitable for one of the pre-defined design alternatives.

In case the new site investigation shows that one of the design alternatives is appropriate regarding the ground condition, the design is eventually issued for construction. This process may be needed a post-validation of design and providing as-built drawings, regarding the condition of the ground and other constructional issues. While there will be extra attention to provide suitable design alternatives according to information reviewed during the desk study process, it is possible that the site investigation shows that none of the pre-defined design alternatives is suitable for a specific bus stop, considering the nature of proposed method (i.e. observational).?Meanwhile, the design needs to be revised based on the new geotechnical site investigation and is issued for construction only after reviewing a new risk assessment.?

Proposed surveys and investigations

As aforementioned above, the suggested observational method for the project consists of surveying and geotechnical investigation during the construction period.

A preliminary survey executes during the construction period for each bus stop to collect all the necessary physical information and details of topography and drainage. Considering the buried services for each bus stop, the location of the bus stop is firstly prepared. This may include a minor site levelling or a slightly deep excavation, regarding the design considerations issued for the location.

During site preparation, detailed geotechnical data are collected using a static cone penetrometer (i.e. by using an AMS static cone penetrometer). The static cone penetrometer provides an in-situ measurement for soil consistency. The result can be reported as standard penetrations (Test N values) that are convertible to strength (unconfined compression) and cohesion of the soil or CBR values. The proposed in-situ test is also helpful for verifying the suitability of the hard stand of a bus stop after construction.

The above data in addition to a detailed description of the soil, drainage conditions and buried services and topography, etc. are referred to the designer/ PSDP for reviewing. As there is a database for the pre-assumed conditions of each bus stop (collected during the desk study process), the new survey enables comparing of observed ground parameters with the presumed conditions. Subsequently, as mentioned in the previous section, providing one of the design alternatives was suitable for the site condition, the designer/PSDP issues the final design for construction.?

Arrangement for obtaining any necessary consents

During the desk study process, the arrangement will be necessary to collect design data from:

1. The client at the initial phase of the project, especially for accurate coordination, design concepts, material and installing specifications, vendor lists, and previous design reports, etc.?
2. Local road authority for collecting data relevant to buried services, traffic data, bus schedules, etc.
3. Online services to collect data relevant to buried services
4. Irish Water, ESB, broadband providers and all other service providers that their buried services are affected by the project
5. Geological Survey Ireland (GSI) and Environment Protection Agency (EPA), Catchment flood risk assessment and management for collecting available geotechnical, geological and hydrological data

Arrangement for inspection and certification of the works

The periodic inspection and certification of the project will be done by the PSDP as below:

1. Certifying the desk study report for the designer(s)
2. Issuing the design certificate of alternatives for approval of the client and reviewing by the PSCS
3. Certifying the temporary work design for construction
4. Issuing health and safety plan for the construction stage
5. Certifying the design risk assessment results
6. Certifying the site investigation plan for each bus stop/region
7. Certifying the results of the site investigation for issuing the design for construction or revise the design
8. Reviewing and certifying the results of concrete samples
9. Periodic inspection of the construction activities based on an agreed schedule with PSCS as below:

• Rapid site visit/inspection, after desk study and before starting the design process
• During site investigation?
• After preparing the foundation formwork and arranging reinforcement for pouring concrete?
• After finishing the job in each bus stop/region

Arrangement for interaction with the PSDP and the PSCS

A project supervisor for the design process (PSDP) is appointed for the project to ensure the coordination of the work of designers throughout the project. Satisfying HSA (health and safety authority) criteria to ensure safety in different aspects of the project, the PSDP 1) identifies the hazards, 2) guides designers for eliminating the hazard or reducing the risk, 3) communicates with the project supervisor of construction stage (PSCS) regarding safety and health plan and 4) notifies the authority and the client of non-compliance with any written issued directions.?

Regarding the suggested methodology in previous sections and HSA criteria, the PSCS and the PSDP interact to ensure the safe managing of the project in below areas:

1. The PSCS develops the health and safety plan issued by the PSDP before construction commences
2. The PSDP issues the site investigation plan to the PSCS for each bus stop?
3. The PSCS supervises the site investigation program during commencing of the construction stage and reports to the PSDP the result of the site investigation for each bus stop or the group of the bus stop under construction
4. The PSDP informs the client and PSCS about all hazards arising from the design or from technical, planning or time-related aspects of the project
5. The PSDP reviews the site investigation, decides about the suitable design alternative for final construction stages or issues direction to the designer to revise the design, and issues a design method (according to the approved site investigation data), drawings and design schedule, and defines all measures for reducing the hazards or eliminating the risk. These include certification for temporary design works and the permanent structures
6. The PSDP issues the concrete sampling plan/ and hard stand in-situ test plan for each bus stop and reviews the result when the tests were confirmed by the PSCS?
7. The PSCS provides all necessary file information to the PSDP

Figure 2 shows a sample design output of the design.

Figure 2- A sample of design output (the geographical coordinations and bus stops were masked for the purpose of this article)