Geotechnical Investigation: Why and How?

A.M. Shingarey, M.D., Geotech Services, Nagpur, explains the logic behind doing Geotechnical Investigation, the appropriate way of doing it, and presents two case studies that support his views.

Introduction

Geotechnical Investigation (GI) is seldom considered important in civil engineering projects by the stakeholders, structural consultants, or architects, primarily because of their ignorance of the subject. The common practice is to save a tiny fraction of the project cost required for investigation, but in doing so, they inadvertently suffer huge time and cost overruns, often leading to national losses. At times, there is a lack of transparency in the working, where incorrect project reports or wrong designs result due to insufficient, incorrect or dishonest data, or due to facts not reported to the project owner.

Importance of appointing a Geotechnical Consultant

Awarding work to the “lowest” bid in case of consultants has jeopardized professional excellence and ethics. In the 32 years of our geotechnical consultancy, our team at Geotech Services has tried to reinforce the importance of Geotechnical investigation to all our collaborators and clients.

The scope of GI depends on size of project, nature of project, and geology of the area. For all sizes and type of projects, a Geotechnical Consultant should be appointed (and not selected through the process of tendering). The scope of GI should not be dictated by a structural consultant or an architect.

Responsibilities of a Geotechnical Consultant

• Deciding scope of the investigation
• Choosing the right agency for work
• Supervision on the ‘field work & ‘laboratory testing’ of the agency
• Approving the report
• Design of excavation protection scheme / ground improvement/ de-watering/ borrow area material necessary for the project
• QA/QC on the works related to geotechnical engineering (e.g. ground), improvement, pile load tests, compaction control etc.

Estimate

A few government departments like PWD/Railways/CPWD/Irrigation have fair rates for geotechnical works. But public sectors like the Metro rail in particular, have very low and non-workable rates for laboratory testing. It is imperative for them to study the rate analysis of other departments and make amendments. Unrealistic rates lead to manipulation of results without conducting any testing. For example, many agencies quote Rs. 1500 to 2000 /per meter for drilling + sampling+ laboratory tests + report and recommendations, which is just not possible without manipulation. As their work at field or laboratory is never supervised, reliability is always questionable. In fact, this is the prime reason for cost and time overruns in infrastructure projects, but either this is unknown to the authorities or is covered by all responsible parties. Consultants should prepare an estimate with fair and workable rates and not deliberately use lower rates to bag the project.

Time period

Almost all consultants and departments allocate a very short time period for the process of investigation. This is the main reason why drilling contractors are tempted to be dishonest. During actual work, either drilling is not continued up to the required depth, or a few bores are not drilled at all. On many occasions, faulty rock cores preserved from previous work are submitted and not drilled fresh for the site under investigation.

The ground reality is that all projects have sufficient time at their inception, so the geotechnical investigation should be planned and initiated in advance.

Tendering Process

All tenders should be evaluated with 80% weightage given to technical capability and 20% to the financial bid. Geotechnical consultants should evaluate technical competence of the bidder based on the following technical information from various investigation agencies:

• Drilling facilities: Quantity and type of drilling rigs owned by the agency and its sub-contractors
• Laboratory tests facilities: This will include equipment, staff (technicians), certification (NABL)
• Managerial staff: Their qualifications and experience
• Storage facilities: For storing and processing samples.

After submission of the above information, the consultant should:

• Visit the office or laboratory of the agency for onsite assessment of field and laboratory facilities.
• Observe working condition of the machinery & equipment
• Discuss with operating staff the various tests to gauge their technical knowledge
• Study previous reports issued by the agency.

Standard formats can be designed to allot marks for each activity assessed to help make a comparison of all the bidding agencies.

No Negotiations

Once an agency has won the bid by the standard evaluation process, one should resist making further monetary negotiations. A few thousand rupees will not make a difference to the project; legitimate profit and good working relations are more important as it will facilitate “ease of doing business”. In India, hard negotiations and bringing down the cost of everything is what management people rejoice in, but they are unaware of the ground reality. The Procurement department people sitting in the head office, only compare rates and negotiate, without giving any consideration to technical competence or experience.

Unfortunately, how much is lost by choosing the ‘lowest’ bidder is never realised by them. One who is an expert in the field will never be available at ‘lowest rates’, which is true in all fields. Qualified professionals must be adequately remunerated.

Supervision

The consultant should visit the site during drilling /field tests and also the laboratory of the agency when tests are being performed. If necessary, 5% of the tests can be sent to other reputed laboratories for comparison or the consultant should witness them.

Deviations

Many a times, the ground conditions differ to a great extent than predicted so that the quantity of drilling needs to be increased or reduced. Moreover, few fields or laboratory tests which are not covered in bidding may have to be performed or specifications may have to be altered. This process should be entirely under the control of the consultant, and the owner, structural designer and architect should not interfere in the same. Owners must keep faith in the geotechnical consultant and approve any deviation or financial implication.

Timely payments

This is a big hurdle in the Indian scenario. Often, companies resort to numerous ways to delay payment, which is an unprofessional practice. In corporate companies, the process of getting payment is long and complicated, with no single person or department guaranteeing the same. In jest one may say that for getting back one’s security deposit, one may have to take another birth! Corruption in corporate companies and government departments have ruined the system. All bad roads, slope failures, bridge collapses, pavement distress, or poor-quality civil work are the result of awarding to the ‘lowest’ bidder and deliberately ‘delaying’ payments.

Conclusion

The evaluation of bidders and the tendering system needs a complete revival, for projects to have quality work with negligible time and cost overruns.

Case Study 1: Rehabilitation of Railway Embankment

Two 32-meter-high embankments for two separate bridges were constructed by the Department of Railways on the Nagpur- Chindwara rail line when it was converted to broad gauge from narrow gauge. For the first bridge embankment, the ground investigation along with borrow area testing and design was conducted by our firm in 2014 (Photo -1). It has shown no distress or excessive settlements to this day.


At the second bridge, no detailed investigation or design was done, and embankment was constructed assuming slopes and berms, in the year 2014. This embankment started settling by nearly 3 to 4 meters, exhibiting huge cracks every year (photo2). Heaving of ground was noticed 50/60 meters beyond the toe (Photo-3). The department went on sealing cracks and levelling it with local material. But the excessive settlements continued till 2018, and the last span of the bridge could not be placed.

GSPL was appointed for cause analysis and rehabilitation. Investigation was possible only along the toe. It revealed that the top 6 meter layers were of plastic clay. A seasonal drain (named Lal Nallah) was buried under the embankment without any diversion or treatment. A thick stone layer was also placed on the lower berms to arrest the heave, but without results.

After a detailed study and analysis, rehabilitation scheme was designed. The end portion was removed to 10 meters height and the ground at toe in nearly 12 meters width was excavated to 6 meters depth. A gabion structure was built to support the embankment and the remaining portion was reconstructed in 2019.


Twenty-one settlement gauges were placed for observation. To this date, the maximum number of settlements observed are between 19 to 73 mm only. But for want of this rehabilitation the rail line project costing Rs.1700 crores was delayed by six years and the cost of rehabilitation was an additional Rs. 16 crores.

Case Study 2: Road Project

A concrete road was constructed at a cost of ~Rs. 340 crores 4 years ago near Shegaon in Maharashtra. During the initial visits, when the borrow area material was tested by us, we categorically informed the highway department of PWD that the road is planned on 2/3 high embankment and sufficient borrow area material of the desired quality is not available. The road was also passing through an area where the backwaters of river Purna remains stagnated at many locations for over four months.


Stabilization of the original ground and quality improvement of the embankment material was recommended. However, the contract being EPC, making any amendments was beyond the power of the engineer in-charge, and the contractor was not ready for any deviations in the contract. This clearly indicates that the DPR itself was inadequate.


The road was built as per contract. Within a very short period of time, the pavement exhibited deep and wide cracks, which are continuing till date {photo 5).

Conclusion

From the information given above, readers will realize the huge amount of national waste in terms of projects’ money, natural materials, productive time, and labour, is resulting because of minor initial issues of investigation. Whether the private sector or the government, negligence of authorities is rampant, making the problem severe. We hope that all the stakeholders involved in civil engineering projects will give some deep thought to this subject and strive to bring about the necessary changes.