An inside story of Inadequate Geotechnical Investigations by Amol Shingarey, MD, Geotech Services, Nagpur
In 1991, the Ground Board of the Institution of Civil Engineers, London, published a report on inadequate site investigation leading to construction delays and additional costs. The findings were based on a study of 5000 Industrial buildings, 8000 commercial projects, and 200 roads & bridges; of which 37%, 50%, and 35%, respectively, suffered time & cost overruns due to inadequate site investigations. The report concludes with recommendations of awareness programs for clients, planners, architects, engineers, builders, and quantity surveyors, and also insurance and property development companies, with the aim of highlighting the significance of site and ground investigation on civil engineering and building projects.
In India, many news articles are published in newspapers on project delays, cost overruns etc, without studying the root cause. Recently it was reported that:
- Out of 1,673 projects, 445 projects reported cost overruns, totalling to more than Rs 4.4 lakh cr.
- 557 projects were delayed by an average of 45.69 months.
- It has also been observed that project agencies are not reporting revised cost estimates and commissioning schedules for many projects, which suggests that time/cost overrun figures are under-reported.
- Delay & cost overrun is attributed to:
- Tie up for financing
- Detail engineering report
- Tendering process
- Law & order problems
Two case studies cited below reveal the truth:
Case Study 1 – Railway Bridge Project
A 13 span railway bridge was constructed by designing foundations with “safe bearing capacity (SBC) of 25 tons per sq.m.” Investigation was done by a civil contractor having no experience in Geotechnical investigation, was quoted the “lowest”. In the first monsoon itself, majority of the foundations were exposed due to scouring. But no distress was observed due to total or differential settlement. The only problem was of scouring; hence it was recommended that ‘Rock Apron’ on the up & down stream and a cut off up to 3 meters, to the foundation by joining them to a bed level with a nominal raft, would be sufficient to prevent scouring.
But this simple solution could not be digested by the authorities. A national level academic institution was appointed as consultant. It conduced ‘Plate load tests’ (PLT) on 50% locations at the foundation level. Actually, PLT is not an appropriate test for this type of soils. Water table was very high at the test level, though cautioned not to dewater during the test. The ‘expert’ from the Institute did not agree. Ultimately, SBC’s determined by him varied in the range of 5 tons to 26 tons per sq.m. Then they recommended for total rehabilitation of all the foundations by providing 6 piles around each of the old open foundations, with heavy cap and shear connections. The original cost of bridge was Rs. 2 cr., whereas rehabilitation cost was Rs. 8 cr., with 3 years of time delay for a project costing Rs. 650 cr.
Case Study 2 – Irrigation Project
An Irrigation project in Maharashtra was planned at Rs.384 cr. in 1984. Detail investigation was done only for the main dam, and no proper investigation for either Geotechnical or Material was done for the canals. A 70 km main canal flows mostly below the natural ground. The depth below ground varies from approx. 8 to 14 meters. The canal itself is only 6 meter deep, with 1 meter free board and 18 meters width at the bottom. The canal was designed with a slope of 1:1.5 without any consideration to the soil properties and surrounding field conditions. Slopes of canal were lined with only 100 mm plain concrete to prevent water seepage. A blanket of local soil was provided as a layer of “Cohesive Non Swelling Soil” (CNS), under concrete lining to prevent it from ‘swell pressure’ of the soils in cuts. The concrete lining failed at many locations, as the soil used in the blanket was not at all CNS.
CNS was a granular soil with least ‘Cohesion’, and could not resist swell Pressure, consequently concrete lining started failing in the first monsoon itself.
To prevent slope failure, retaining wall of size 9 meters in the bottom and 0.5m on the top & 6 m high was constructed to prevent further failures. Thankfully it was constructed only in 400m trial length. This also failed in the next season. The failure was so severe that the entire retaining wall moved nearly 9 meters, breaking bottom concrete slab of canal up to the centre of the canal.
After analysis it was found that Factor of Safety was only 0.89 against 1.4, which is unsafe!
The total project cost was Rs 372.22 cr. in March 1983 when estimated and escalated (repeated- consider risen) to Rs 13,739 cr. up to 2012, to nearly Rs 16,000 cr. in 2020.
The canal has also a divided forest and restricted movement of wild animals. The environmental impact of this project is beyond calculations. (Photo of tiger crossing district road during the daytime on 7th July 2022).
Similarly, when a Detail Project Report (DPR) is prepared, before any tendering process, it should be done very systematically, as all the designs & quantities are derived from this. But these DPRs are made in haste and in a casual manner, which become a source of all deviations in the future. The following example will explains how.
DPR Example: A metro rail tender for a DPR published in June 2019, gave a time limit of 6 weeks (Inception report - 10 days, Field work - 4 weeks, final report submission - 6 weeks) - all from the date of award of work; with total drilling: 360rmt. and 979 no. of laboratory tests. No laboratory, with ongoing work in-hand, can complete such a job in the stipulated timeline. In such works, drilling is done in haste. Many boreholes are not even drilled to the reported depth; and many of the lab tests are not performed at all, by filling up the data. The drillers working at field are neither trained nor are they supervised. Moreover, the rates of tests mentioned were extremely low and not at all workable. The following comparison will give a clear picture:
Comparison of rates of few laboratory tests
|S.N.||Test||Delhi Metro in Rs./no||Indian Railway in Rs./no|
|2||Atterberg‟ s Limits||161.65||535.18|
The example and case studies mentioned above are just a tip of an iceberg, as there are countless cases in all fields of civil engineering. But surprisingly, very few are aware, many are not “affected” and the issue remains unsolved, incurring huge loss to the nation.
DFII- Deep Foundation Institute (India), has taken over this issue for the improvement and formed a committee for “Geotechnical Characterisation for Foundations” (DCGCF) to work on it. The committee has identified following four activities for improvement:
- Creating awareness amongst the top management and decision makers about cost & time overrun due to inadequate geotechnical Investigations.
- Assistance & advice to stakeholders for enhancement in “Tendering Process” for defining scope of work, time schedule and selection of appropriate agency.
- Training of Laboratory & Field personnel from geotechnical Investigation agencies.
- Training to fresh civil Engineers for early insight in the subject.