Evaluation of Intake Cofferdam Work Implementation Methods At the Muara Tawar PLTGU Project

Abstract

Purpose: The construction of a new intake in the Muara Tawar PLTGU must be carried out by demolishing the existing walls of the canal.  There was a shift in the intake cofferdam in the Muara Tawar PLTGU project which caused a delay in the duration of the work so that the contractor suffered losses. The evaluation of the implementation method of the intake cofferdam work aims to analyze the existing stability conditions in several conditions against shear and overturning, analyze the safety of the existing profile, redesign the cofferdam so that it does not experience a shift, and propose a new method of installing the cofferdam.

Methods/Design: The evaluation method was carried out by collecting data based on field observations and interviews with four existing conditions: (1) Cofferdam flooding due to seepage; (2) Flooding due to tides; (3) Conditions if the cofferdam is fully installed; (4) Flooding due to rain. Data analysis techniques accordance with SNI 1729: 2020 Specifications for Structural Steel Buildings.

Findings: The evaluation results show that the intake cofferdam at the Muara Tawar PLTGU has shifted due to the absence of locks on other buildings. The shift value is obtained from the calculation of shear stability ≤ 1.5. In terms of overturning moment stability, the cofferdam experienced overturning because the overturning moment stability value ≤ 1.5. The cofferdam structure bar force fulfills in resisting the forces that occur in the cofferdam.

Practical implication: With the shift, a redesign is carried out, namely adding anchor locks to 12 joints using mechanical anchors with each baseplate using 2 22 mm diameter anchors.