hyderabad
The six-member expert team of the National Dam Safety Authority (NDSA) that has examined sinking of piers in the Block-7 of Medigdda (Laxmi) Barrage of Kaleshwaram Project has faulted the planning and design of the project and stated that a combination of issues involving planning, design, quality control and operation and maintenance have led to the damage.
The NDSA committee visited the barrage site on October 23 and 24 after the drift of some piers was noticed on the October 21 evening and it also held a meeting with the authorities of the Irrigation department on October 24. While making serious remarks on the project, the 43-page report has mentioned that the panel was given information on only 11 of the 20 aspects (data/inputs) sought from the State government.
“The primary reason for the failure is the settlement of the barrage raft. The piers, being monolith with it, have also settled, moved and cracked. This could occur due to several possible reasons such as piping, wherein transportation of foundation material has occurred. Inadequate bearing capacity of the foundation material (sand), failure of upstream secant piles due to barrage load also led to the failure,” the report explained.
Further, there appears to be deficiencies due to lack of stringent quality control during the construction of sub-surface contiguous secant piles and plinth connected between the raft and cut-offs. “Gaps might have been created in the secant pile formation making the barrier permeable, leading to piping and subsequent progressive failure,” the panel observed.
Stating that the barrage has been designed as a floating structure the committee said it was constructed as a rigid structure. The contiguous secant pile type cut-offs adopted by the project authorities were taken up to rock both at upstream and downstream of the barrage and it has changed the structure behaviour from the designed way.
“The department has also not inspected or maintained the cement-concrete blocks or launching aprons since commissioning of the barrage in 2019-20 and it has progressively weakened the barrage, leading to its failure. The distress condition developed in one block of the barrage is adversely affecting its functionality and under the present condition it is rendered useless until fully rehabilitated,” the NDSA panel concluded.
Two other barrages constructed in the upstream of Medigadda Barrage, Annaram and Sundilla barrages have also similar designs and construction methodologies, making them prone to similar failure modes. Signs of boiling already exist downstream of Annaram Barrage and it is a precursor to failure, the report said and suggested that the two barrages too should be examined urgently for signs of piping/distress.
What more the NDSA report says
A detailed investigation may be carried out to determine the causes of failure. Telangana government may look into issues raised in the report, undertake measures to remedy the barrage.
Project designs and drawings need to be examined along with the results of geo-technical and geological investigations. Dam Safety Act, 2021 provisions not complied with. Likelihood of piping failure of other blocks resulting in a similar failure is very much possible. All piers and rafts of the barrage must be surveyed, particularly the adjoining Blocks (6 and 8) of the damaged Block (7). Before formulating remedial measures, extent of settlement and damage to the raft need to be ascertained.
