Helical piles | Foundation solutions | GTL International

SIBA GAS FIELD DEVELOPMENT, IRAQ

Portfolio Categories: Oil and Gas.

Project Description

The Iraq Ministry of Oil has selected a consortium led by Kuwait Energy Iraq Limited Company (KEIL) for the development of the Siba Natural Gas Field. KEIL is planning to conduct a full field development in the Siba Field.

The Project will further develop into constructing gas processing facilities and three main export pipelines to pre-identified metering stations.

It has been estimated that the Siba gas field holds approximately 2.9 billion cubic meters (m3) of gas.

Siba Gas Field is situated in the southern part of Iraq, in Basrah Governorate, about 30 km southeast of Basrah and extends northeast to the Shatt Al Arab River. The field is an anticline NE-SW structure with multiple culminations separated by structural lows. The field is about 21 km long with a width between 6 and 13 km. Its area is about 200 km2

GTL was appointed during FEED as Geotechnical and Foundation Engineering Consultants and later included Engineering Design for piled foundations.

Topography

The Siba field itself is approximately 21km long and 6-13 km wide. It is located within the Zagros Foreland Basin. This Basin is bounded to the east by the Zagros Mountains, to the west by the Arabian Plate and to the south by the offshore areas of the Arabian Gulf. To the northwest lies the Euphrates Valley. The general gradient of the plain is 1m per 20 km. The main geomorphological units of the accumulation fluvial origin are terraces, alluvial fans, sheet run-off plains, flood plains, shallow depressions, marshes and lakes, and sabkhas. There are a number of individual marshes and lakes that have developed in shallow depressions in different parts of the Mesopotamian Flood Plain and are distributed in three main areas. The oil field is located in an area known as Central Marshes, which lies to the north of Euphrates

Geology

The whole Iraqi territory could be classified into seven physiographic provinces. In the middle part, the Mesopotamia Plain is developed which starts from the Arabian Gulf and extends to the northwest for about 730 km, attaining to a height of about 150 m (a.s.l.), near Baiji. It comprises of alluvial sediments of the Tigris and Euphrates Rivers with their distributaries, and Shat Al-Arab, exhibiting different geological hazards, like floods, piping, sabkhas, seawater intrusion and depressions.

The near-surface geology in the project area comprises Quaternary deposits underlain by Tertiary Pliocene age sedimentary rocks of Dibdiba and Mahmudia  Formations.  These references indicate that the base of the Quaternary age deposits in the project area is approximately 100 m below the existing ground surface level. The Quaternary deposits comprise Holocene age flood plain deposits (up to about 20 m thick) underlain by Pleistocene age sediments of the Euphrates and Tigris Rivers. In general, the Holocene age flood plain sediments comprise silts, clays and sands. The vertical boundaries between different materials may be both gradual and abrupt and the thickness of individual layers may vary from a few centimetres to a few meters. The clays often contain carbonate nodules and gypsum (as powder of fine crystals). The sands are usually fine-grained, grey and brown and may contain pebbles. Thicker beds of sand may be present in abandoned (buried) river channels.

The Pleistocene sediments comprise interbedded pebbly sands, sandy gravels, sands, silts and silty clay. The sands are deposited as thin layers inter-bedded with silts and clay or as thick sequence. The sands may be cemented by gypsum or carbonates forming horizons of sandstone like material.

The Tigris and Euphrates rivers carry large quantities of salts, and due to the combined effects of excessive irrigation and flooding, and a high water table with poor surface and subsurface drainage these salt s have concentrated at the surface of the soil. Degradation of soil quality has also occurred due to contamination by pesticides, untreated industrial discharge, oilfield operations, construction of large dams, and untreated (or partially treated) sewage originating upstream. These anthropogenic impacts have compounded the high naturally occurring salinity levels.

Despite this widespread degradation, because of the low hydraulic conductivity, low groundwater flow velocities, and seasonal fluctuations in the flow direction, it is likely that contamination from point sources (e.g. oilfield discharges) has migrated only limited distances in groundwater (MOEN,2006).

The near-surface geology in the project area comprises Quaternary deposits underlain by Tertiary Pliocene age sedimentary rocks of Dibdiba and Mahmudia  Formations.  These references indicate that the base of the Quaternary age deposits in the project area is approximately 100 m below the existing ground surface level. The Quaternary deposits comprise Holocene age flood plain deposits (up to about 20 m thick) underlain by Pleistocene age sediments of the Euphrates and Tigris Rivers. In general, the Holocene age flood plain sediments comprise silts, clays and sands. The vertical boundaries between different materials may be both gradual and abrupt and the thickness of individual layers may vary from a few centimetres to a few meters. The clays often contain carbonate nodules and gypsum (as powder of fine crystals). The sands are usually fine-grained, grey and brown and may contain pebbles. Thicker beds of sand may be present in abandoned (buried) river channels.

The Pleistocene sediments comprise interbedded pebbly sands, sandy gravels, sands, silts and silty clay. The sands are deposited as thin layers inter-bedded with silts and clay or as thick sequence. The sands may be cemented by gypsum or carbonates forming horizons of sandstone like material.

The Tigris and Euphrates rivers carry large quantities of salts, and due to the combined effects of excessive irrigation and flooding, and a high water table with poor surface and subsurface drainage these salt s have concentrated at the surface of the soil. Degradation of soil quality has also occurred due to contamination by pesticides, untreated industrial discharge, oilfield operations, construction of large dams, and untreated (or partially treated) sewage originating upstream. These anthropogenic impacts have compounded the high naturally occurring salinity levels.

Despite this widespread degradation, because of the low hydraulic conductivity, low groundwater flow velocities, and seasonal fluctuations in the flow direction, it is likely that contamination from point sources (e.g. oilfield discharges) has migrated only limited distances in groundwater (MOEN,2006).

Helical Pile Design

Over 800 piles were designed at various depths and diameters to accommodate a modular type construction. 

The foundation pile design was undertaken as a limit state design, whereby a distinction was made in ultimate limit states (ULS) and serviceability limit states (SLS).

Limit states are related to design situations, which was classified in persistent, transient, accidental and seismic design situations. 

In accordance with the superstructure operation states, accidental design situations are mentioned and classified in the foundation pile design.

Value Proposition

This Value Proposition centres around the removal of work-scope from the camp and the reduction in uncertainty in the labour rates and productivity.

In general, this was achieved by

  • Reduction in the numbers of people to be accommodated at the camp. The number generated at the Concept Stage did not allow for Iraqi personnel who would commute from the towns local to the field.
  • Reduction in the civil scope, especially the volumes of sand/ soil to be moved
  • Use of technology to increase the productivity of construction to remove a significant amount of site work

This Value Proposition is for the reduction in the Cost and the Schedule for the Permanent Accommodation Camp (PAC) by the use of Helical (Screw) Piles. The VP does not cover other civil scopes associated with foundations but the cost reductions will be of the same magnitude.

Independent Concept Report

The key risks, constraints and drivers that are recognised to have an impact on project cost are:

  • Civils material quantities – uncertainty related to the material volume required for the site
  • Preparation due to lack of geotechnical data and to the preliminary level of layout definition.
  • Civils construction norms – uncertainty related to site preparation man-hour norms and / or productivity due to lack of local contractor input (e.g. to assess manpower and / or machinery availability).
  • Civils site labour rate – uncertainty related to man-hour cost as rates are expected to be
  • driven by the level of activity in the region.
  • Facilities site labour rate – same as above civils site rates, uncertainty related to rates for labour on processing facilities (i.e. modules installation, hook-up, commissioning).
  • Equipment and material cost – uncertainty related to the overall cost of equipment, bulks, line pipe and buildings depending on the market, as well as the outcome of the tendering phase.
  • Facilities construction norms – uncertainty related to site installation man-hour norms andConstruction security    uncertainty related to overall project security cost depending on potential future unrest in the region which might significantly increase the security levels required as well as the manpower and infrastructure costs. / or productivity due to lack of local contractor input (e.g. to assess manpower and/or machinery availability).

The Value

Costs are reduced by approx 85%.

The schedule is reduced. This has not been specifically calculated but saving in of 50% to 80% on schedule is expected. Example – concrete foundations for fence would be circa 40 working days. HSP foundations for fence would be circa 10 working days.

The uncertainty associated with costs of civil works (materials, labour, equipment) is reduced HSE and Security exposure is reduced due to the shorter duration

Conclusions

The use of Helical Screw Piles significantly reduces the costs associated with

  • Removing sand and replacing with engineering-grade soils (eliminated completely)
  • Laying concrete foundations (maybe one building only)
  • The additional costs associated with the uncertainties around labour and equipment costs

The use of helical screw piles reduces the time taken to install modular units but only if dimensional control is utilised such that the units ‘fit-first-time’.

The significant reduction in site man-hours feeds through a reduction in exposure to HSE and Security incidents. The less time spent on site the less likelihood of incidents occurring. The ‘Cost of Safety’ has not been factored into the cost calculations.

The PAC is a small scope of work but the costs can be projected to cover civil works for the Base, CPF, River Gathering Station, Hubs and trunklines.

Telecommunications Infrastructure – India

Portfolio Categories: Infrastructure.

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Project Description

GTL were commissioned to undertake both the concept and feasibility design of a telecommunications infrastructure throughout India, consisting of 22,000 lattice type masts. With an overall timeframe for delivery of just three years, the project had an ambitious building schedule with challenging targets.
GTL designed various piled grillages, supported by six to eight piles.

Biofuel Plant, Fujairah, UAE

Portfolio Categories: Oil and Gas.

gtl-case-studies_65048041

Project Description

GTL were approached by Petrofac to undertake both geotechnical investigation and the provision of a concept foundation design, along with a constructibility report. This project was an investment of $800m in the construction of a biofuel refinery in Fujairah.

Preparation

The preparation of studies, engineering designs, and the selection of appropriate technology is currently underway to construct the facility in the eastern Emirate. The refinery has a design capacity of one million tonnes per year of biofuel products, including bio-diesel, green diesel, bio-jet, bio-naphtha and bio-LPG.

International Cooperation

An incorporated consortium of major international companies and financial institutions has been established for the project, which will be built on a 460,000 meters-square area of land, in proximity to the Fujairah Free Zone and the Port of Fujairah.

Stadium Design – Milwaukee, USA

Portfolio Categories: Construction and Infrastructure.

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Project Description

The construction of a uniquely designed stadium has provided significant long-term investment for the greater Milwaukee region. Getting the project completed on-budget meant looking at every cost alternative. Upon the recommendation of geotechnical engineers, the design and implementation of a test pile program was recommended to determine the most cost-effective deep foundation pile system. For testing, two types were selected: both the straight, parallel-sided steel piping, and the uniformly-tapered steel piles. The results showed that the mono-tapered pile was the most economical choice for our project.

Geotechnical Ground Conditions

Examining the results on an installed cost-per-ton basis showed that the Mono pile achieved a 400-ton ultimate capacity at the 77-ft. range. The pipe, by comparison, required an embedment of over 100ft to obtain an ultimate capacity of 300-tons. Using conventional equipment, the Mono piles required significantly less time and hammer blows to penetrate to the stipulated design depth, thus achieving outlined capacity, and at much shorter embedment depths.
Importantly, it was also recognized that by investing a relatively small amount of money in a test pile program at the early stages, millions were saved in the deep foundation work designated for driven piling.

BP Exploration, Northstar Island, Alaska

Portfolio Categories: Oil and Gas.

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Project Description

This case regards GTL’s involvement with BP and their exploration of Northstar Island, an oil-drilling and refinement facility in the Beaufort sea – six miles offshore from Alaska’s North Slope. Being the very first offshore oil production facility situated in an arctic region of the United States, this manmade 4.5 acre gravel island presented a specific set of challenges.

Geotechnical Ground Conditions

The area of North Slope is known for its adverse weather conditions: of long winters and short summers. In spite of this, GTL took on this exploration project, driving piles with APE 200 and Delmag 62 impact hammers to facilitate access.
Inevitably, the PN&D encountered difficult soil conditions. A series of holes, ranging from small-to-large in diameter, were predrilled and filled with a combination of steam and hot water to facilitate access, filling the full length intended for the piles themselves. Once complete, the steel piles would subsequently be put in place.
Thus, in the process, this pilot hole procedure – via thermal manipulation and facilitation – was pioneered. Furthermore, the combined lengths of open cell sheet pile wall totalled approximately 800ft, with the project utilizing 1,049 sheets at up to 60ft in length.

Portfolio Categories: Construction.

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Project Description

As a major transportation improvement project in the heart of downtown Orlando, Florida, this project involved twelve structures at the busy junction of Interstate 4 and the East-West Expressway. The deep foundations consisted of 60,000 meters of driven piles, with the distinguishing feature being the extensive use of steel H-piles on such a large scale transportation project in Florida. The inherent advantages of steel pile ensured the success of the foundation work.

Garraf Oil Field Development, Iraq

Portfolio Categories: Oil and Gas.

Garraf

Project Description

Garraf oil field is located in the province of Thi Qar, approximately five kilometres north-west of Al-Refaei city and 85km north of the city of Nasiriya. The field is owned by PETRONAS Carigali Iraq Holding (PCIHBV, 45%), Japex (30%) and North Oil Company (25%). Development works for the oil field started in early 2011. Initial production started in August 2013. The onshore oil field was discovered in 1984 and contains oil in Cretaceous reservoirs. The field is 17.5km long and 5.5km wide. It is estimated to hold 1.3 billion barrels of oil reserves. The current production capacity of the field is 35,000 barrels of oil per day (bopd). It is expected to increase to 230,000bopd by 2017. GTL was appointed during FEED as Geotechnical Consultants and later included Engineering Design for piled foundations. GTL also undertook preliminary pile testing and CAT 2 checking for structures. Piles were eventually supplied and installed by the EPC Contractor. GTL is now in discussions regarding their involvement with the plant expansion.

Geotechnical Ground Conditions

The project was classified as Geotechnical Category 2, in accordance with DMRB (Design Manual Roads and Bridges) Volume 4 Part 1 Section 1 HD22/08, Managing Geotechnical Risk, Chapter 3. Geographically, the FCP site was situated within the regional fertile basin fed by the Euphrates River. The site lies along the fringes of the Garraf River to the east, a tributary of the Euphrates River. The notable features within the local area were the lake and road that formed on the crest of an embankment. Geologically the site was considered young as the ground has been formed by secondary or tertiary geological processes; alluvial clays from the Euphrates River delta and wind-blown sand formations from the desert. Geological records showed the site to be situated within a stable tectonic plate therefore the ground has not been influenced by mountain-building events. As a result, there is the limited thickness (geological memoirs suggest approximately 15 to 30m) of superficial (drift) deposits attributable to the sediment deposits from the adjacent river systems. Sandstone bedrock was recorded beneath superficial deposits of the local region. The exploratory borehole logs recorded numerous layers of clays, which GTL considered to be of alluvial origin, differentiated by changes in colour, strength or variations in the relative proportion of sand. Minor layers at depth of silt were also recorded. Garraf Development is assigned to Seismic Zone 1 and the ground conditions encountered are categorised for seismic design purposes as Soil Profile SD. The facilities are assigned to occupancy category 2.

Pile Design

Over 1000 piles were designed at various depths to accommodate a modular type construction. Piles were designed to The foundation pile design was undertaken as a limit state design, whereby a distinction was made in ultimate limit states (ULS) and serviceability limit states (SLS). Limit states are related to design situations, which was classified in persistent, transient, accidental and seismic design situations. In accordance with the superstructure operation states, accidental design situations are mentioned and classified in the foundation pile design.

Acknowledgements

Gavin Rixon – Project Director Karsten Richter – Lead Geotechnical Engineer Stephen Whitham– Geotechnical Engineer

Vodafone Foundation – Westway

Portfolio Categories: Infrastructure.

Vodafone Foundation – Westway

Project Description

GTL was employed by Vodafone/Babcock to design, supply and install a foundation solution to accommodate a Vodafone 2G/3G Street Pole – Type 7000 series.

GTL were tasked with providing a complete solution that could be constructed including tower erection in two days. The limited footprint was to accommodate the 12m mast and equipment cabinet.

Geotechnical Ground Conditions

Construction drill with digger

Construction drill with digger

The soil investigation indicated clay overlaid with sands and gravels. Dynamic Probe results were used for the design of the piles.

However, during pile installation underground obstructions were encountered at 2000mm.

Helical Pile Design

GTL designed for additional dead load to provide stability against OTM of the grillage that was deemed necessary resulting from the information attained whilst installing.

Due to these unforeseen obstructions GTL revised the design accordingly.

The obstructions reduced the depth of the driven pile from 3000mm design depth, to an actual depth of 1800 ~ 2000mm.

This reduced the factor of safety of the piles from 3:1 to 1.25:1 (without the mass of the grillage being considered); this was considered to be insufficient. In order to increase the factor of safety to an acceptable level the grillage was modified by the introduction of a continuous steel plate (15mm thick) welded to the underside of the grillage with the depth of the grillage then being filled with concrete. The additional weight increased the deadweight of the grillage base.

GTL designed the helical piled foundation compound with loads of 3kN in compression, 4kN in Tension and 15kNm moment force.

To mitigate time lost GTL adapted their piles on site and subsequently installed them to refusal.

In parallel the grillage was modified to incorporate the design amendments.

GTL continue to utilise this balanced solution where high rock head is encountered.

Rapid Deployment Site – Church Farm

Portfolio Categories: Infrastructure.

Large drilling machine, detail of screw bit.

Large drilling machine, detail of screw bit.

Project Description

GTL were employed by Hutchinson 3G to design, supply and install their Rapid Deployment Site (RDS). The main objective was to create a complete compound by utilising the Helical (screw) piled grillage foundation. This design incorporated security fencing, equipment and electrical cabinets whilst providing capacity for the forces generated by the 18m high timber monopole.

Geotechnical Ground Conditions

The soils investigation indicated superficial deposits overlaying stiff sandy gravely clay.

The site investigation of a borehole with SPT and Dynamic Probes Super Heavy were used for the design of the piles.

Helical Pile Design and Testing

GTL designed the helical piled foundation compound with loads of 9kN in compression, 10kN in Tension and 86kNm moment force.

GTL carried out a static analysis using a combination of end bearing and shaft friction to generate the required pile capacity in tension and compression.

Development Subsequent to the success of this generic site model GTL in partnership with H3G went on to develop various other RDS solutions that have been rolled out throughout the United Kingdom.

Generally the GTL RDS solution is designed to be installed within 48 hours and is defined as both a permanent and temporary structure. The concept is that the GTL RDC replaces traditional concrete foundations and construction methods.

There are three options available for installing the RDS

  • Helical pile solution
  • Gravity solution
  • Structural anchoring

Network Rail Helical Screw Piles – Wadbrook Axe LC

Portfolio Categories: Infrastructure.

Railway cross-junction

Project Description

GTL were employed by Murphy’s to design, supply and supervise the installation and testing of helical (screw) piles for Network Rail FTN/GSMR node site south of Chard in Devon.

Geotechnical Ground Conditions

The soils investigation indicated superficial deposits overlaying stiff sandy gravely clay.

The site investigation of a borehole with SPT and Dynamic Probes Super Heavy were used for the design of the piles.

The site sloped away from the RDS base toward the boundary.

This change in level was taken into account in the design of the piles under lateral loading as it would affect the pile capacity.

Helical Pile Design and Testing

GTL designed the helical piles for a RDS narrow base, with loads of 70kN in compression and 37kN in Tension.

GTL carried out a static analysis using a combination of end bearing and shaft friction to generate the required pile capacity in tension and compression.

GTL predicted the settlement and movements under load using industry recognised software in Oasys Pdisp and Alp.

The tension test yielded results of 2.5 mm at 100% of safe working load compared with predicted settlements of 2 mm at design Stage.