Semantok Dam is located in East Java province, in the district of Nganjuk. Approximately 670 km east-south-east of Jakarta, the capital of Indonesia.

The dam will be the longest in Southeast Asia with a dam crest length of 3,100 meters.

The dam with a zonal type random fill with a clay core will have a height of 31.56 meters. Later, this dam can accommodate water with a total capacity of 32.67 million cubic meters, so that during the dry seasons this dam can supply water. It is also expected to irrigate 1554 Ha land and generate 1.01 MW electrical power.

PT BAUER Pratama Indonesia was appointed to construct the cut-off wall for the Semantok Dam by Hutama – Bangunnusa KSO as main contractor.

An un-reinforced secant pile wall, diameter 880 mm with a depth up to 25 m cast with plastic concrete, was constructed for a cut-off wall. Spacing 640 mm c/c to have a minimum wall thickness of 600 mm after overcutting. The specification of this wall is to have a cut-off wall with an elasticity modulus equal to maximum 5 times of the surrounding ground material. Permeability test was mandatory for this wall, and the coring position is on the overcutting area (in between the primary & secondary). Works were carried out from various working platform levels which follow the cut-off trench level that is equal to the pile cut off level. Due to the low plastic concrete strength, special attention was paid to the secondary pile drilling process to avoid cracking the primary pile.

 

 

All permeability tests, which are the key to the success of this project, produced results much higher than the requirement.

• Employer: Directorate General of Water Resources, Ministry of Public Works and Housing of Indonesia
• Client: Hutama Karya – Bangunnusa
• Execution: P.T. Bauer Pratama Indonesia

 

Location

The site of the Semantok Dam is located in the East Java province, near the city of Nganjuk.

 

 

Scope of works

• Cut-off wall
• Construction material: plastic concrete
• 1104 nos Secant Piles of Ø 880 mm, drilling depth 7.5 to 23 m
• Total length of cut-off wall alignment: 703 m

 

Geological conditions

• Clay 0 – 2 m
• Tuff rock 2 – 4 m
• Sandy clay 4 – 8 m
• Tuff rock 8 – 10 m
• Sandstone 10 – 15 m
• Siltstone 15 – 19 m
• Sandstone 19 – 20 m

 

 

 

Equipment

Two units BAUER BG 28 were deployed

 

Miscellaneous

The requirement of verticality of the drilled holes are 1:100, each of the piles must be checked by ultrasonic verticality tests. There are several cases of flooding throughout the construction period. To prevent our equipment from being trapped in flood, an escape route (evacuation ramp) was identified and flood sensors installed. Monitoring staff also standby to monitor the upstream area 24/7.

 

Construction period

November 2019 – June 2020