The six-member expert team of the National Dam Safety Authority (NDSA) that examined the sinking of piers in the Block-7 of Medigdda (Laxmi) Barrage of the Kaleshwaram Project has faulted the planning and design of the project in its report and stated that a combination of issues involving planning, design, quality control and operation and maintenance have led to the damage.
After the drift of some piers was noticed on the October 21 evening, the NDSA committee visited the barrage site on October 23 and 24 and held a meeting with the authorities of the Irrigation Department on October 24. The 43-page report has made made castigating remarks on the project. It has mentioned that information on only 11 of the 20 aspects (data/inputs) were submitted by 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, the committee has observed that there appears to be construction deficiency 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 expert committee stated in the report.
The NDSA committee stated that the barrage has been designed as a floating structure but 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.
Taking the downstream cut-off up to the impermeable strata alters the uplift pressure due to blocking the sub-surface flow. The construction methodology adopted for transverse cut-offs has imposed different conditions than what was assumed in the design. The alignment of the flared-out wall provided upstream of the barrage hydraulic deficient, the panel pointed out.
“The Department has also not inspected or maintained the cement-concrete blocks or launching aprons since the commissioning of the barrage in 2019-20 and it has progressively weakned 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 in the report.
