Deep Foundation Construction

Proper site characterisation can eliminate significant risks involved in the design and construction of pile foundation both in liquefiable and non-liquefiable soils, emphasizes Dr Parthasarathy, CMD, Sarathy Geotech & Engineering Services.

How is the civil construction industry of India evolving with respect to cutting-edge technologies, quality control, R&D, best practices, etc?

India is one of the fastest growing economies, but we are decades back in implementing emerging and newer technologies. However, it’s better to be late than never; there are some projects commissioning new technologies and quality control methods as per international standards, and following the best construction practices. I think in the coming decade, we should be at par with the more advanced Western practices.

What are the challenges in construction of deep foundations in India with respect to project type, size, and site condition?

As we are aware, the Government of India has committed large investments in the infrastructure pipeline being developed across the length and breadth of the country. Geographically, the stratigraphy varies widely for example, there are deep alluvial deposits in the northern region, which is also an earthquake prone zone; it has no bedrock vis-à-vis the regions of the deccan plateau, and deep-seated high strength massive rocks are present. Both this stratigraphy poses huge risks for the deep foundation construction industry; thus, it is imperative to thoroughly understand the stratigraphy and its behaviour to foundation loading that will help mitigate construction risks and avoid delays in project schedules.

Inadequate geotechnical Investigation has been experienced in many civil engineering projects for saving time or cost: what impact would this have on the structures?

Any time and cost overruns of projects is significantly attributed to the foundation problems, which are mainly due to inadequate and/or improper geotechnical investigation. Adequate site characterisation eliminates costly over designs or conservative designs - both case studies are available in abundance.

Regardless of the size of project, adequate and thorough site investigation is very important in the design and construction of deep foundation. Good site investigation helps in choosing appropriate type of equipment, tooling, and construction methods.

What are the challenges in design and construction of pile foundation in non-liquefiable and liquefiable soil?

Pile foundation is generally accepted in liquefiable soils, provided adequate precautions are taken care in the designs, which otherwise will result in loss of support due to inadequate resistance from the additional seismic loads. It is always desired and necessary to comply with the codal provisions viz. Euro code, ISO, Bureau of Indian Standards, AASHTO etc.

Liquefaction potential assessment again will lead to the quality of geotechnical investigation. The standard penetration test (SPT) which is routinely performed in a site investigation campaign necessitates energy transfer to normalise the N value to the desired energy level and thus avoid wrong qualification of liquefiable soils or otherwise. Proper site characterisation can eliminate significant risks involved in the design and construction of pile foundation both in liquefiable and non-liquefiable soils.

What is Continuous Flight Auger (CFA) Pile Technology and its benefits?

CFA piles are faster compared to other methods like bored piles and do not induce vibration and noise. They are also economical on large scale projects. They have not been popular yet in India although a pilot project was commissioned by DFI a few years back.

What are the various codes, standards, and guidelines in India for design, installation, construction, and testing of pile foundation and excavations?

Some codes of Bureau of Indian Standards (BIS) requires revision, which is under works. For conventional testing like static load test, BIS has been followed. For non-destructive testing, only pile integrity test has been codified, while other methods like the High Strain Dynamic test, is yet to be released. In the absence of local codes, many projects adopt international codes like ASTM, ISO etc.

However, there are no codes, guidelines, or standards for deep excavation, which these days are to the depth of 15 to 20m and are not uncommon. Efforts are being made to develop these codes in various professional forums and we hope that BIS will consider to codify soon.

What, according to you, are the right practices for Quality Control/Quality Assurance of deep foundation testing?

QA/QC of deep foundation stems from the contract document. Design basis has to be developed by the principals for geotechnical investigation, interpretive methods, compliance to codal provisions, testing methods and numbers.

Absence of a thorough design basis results in conflicts among different stakeholders. Empanelling experienced and qualified agencies (geotechnical, designers, project managers, contractors, testing agencies) will automatically improve the QA/QC methods. Training and skill development is essential when newer methods are adopted. In fact, even for conventional methods deploying experience and trained resources, will to a great extent ensure quality.

For drilled shafts and bored piles, the following QA/QC methods are available:

Prior to pouring concrete: (Available in India and commissioned on projects, yet to be popular.)

• Shaft Quantitative Insepection Device (SQUID) determines quantitatively the thickness of contaminated material at the bottom of borehole prior to concreting.
• Shaft Area Profile Evaluator (SHAPE) determines the eccentricity, radii and volume of pile borehole excavation.

After pouring concrete:

• Pile Integrity Test - very popular and adopted in every project – IS code
• Crosshole sonic logging test - being adopted in major infrastructure projects
• Thermal Integrity Profile - commissioned in one project, not popular yet although an advanced method
• High Strain Dynamic Test – very popular being adopted extensively
• Conventional static load test - very popular and adopted compulsorily on all projects
• Conventional static load test with instrumented piles - adopted in important projects
• Bidirectional Load test – some projects have adopted but not popular yet in India.

You have been credited for bringing the most advanced geotechnical investigation boring machines to India to deploy at the High-Speed Rail Project and also other advanced geotechnical services. Please share some of your experiences in geotechnical engineering deployed at mega infra project sites, which not only saved time and cost but also ensured safety of the engineers?

We are proud to have introduced 3 units of new imported multipurpose geotechnical machines TMG CSR 183 from TMG manufacturers Inc., USA. Initially deployed at the High Speed Rail Project, subsequently, in Indore Metro, Delhi Metro, and Chennai Metro. Currently, a unit is on a project in Saudi Arabia.

The advantage these machines have are:

• Compact
• Can do SPT with automatic hammer
• CPT with 20T force (piezocone)
• Rotory drilling and wireline drilling
• Moving from location to location is very easy
• High quality undisturbed samples by static push
• Safe operations.

These have high pull capacity to handle large diameter drill pipes, while the production has been relatively very high in the country. The only challenge is to bring awareness to clients on the advantages on the schedule and quality of the data, which will reflect in the construction schedule and cost economics.

I wish that these kind of machines could be manufactured in India and be affordable for the geotechnical community, and thereby ensure uniformity in the data acquisition practices and help all the construction projects of the country. Operating high-end machines is again a challenge and requires a talent pool. With great difficulty we have equipped the machines to meet the current needs, but there will be a continual requirement.

How do you view the skill development programs in India specific to geotechnical engineering and foundation/underground structure construction?

Skill development is the need of the hour. The rate at which our infrastructure investments are being planned is in conflict with the capacity available. Though information is accessible for free unlike three decades ago, what is lacking is the skill and learning from experience. It is important therefore to develop skilled resources for projects at all levels.

What kind of positive impact do programs like DFII have in enhancing the performance of geotechnical and foundation industry?

DFII creates a platform for people to share experiences and for others to learn from them. There are many initiatives and programmes being planned by DFII, which will create a huge impact on the skill development and for building an employable resource pool. Skilled resources on projects ensure quality, safety, and time saving. When these are accomplished on projects, a modern infrastructure will drive our country’s economy.