Dewatering Importance for Structures
Dewatering is essential to prevent the damage to structure foundations specially in case of high salinity water intrusion regions; therefore, BNB’s respective client Matrix Pharma engage the services of BNB dewatering division to counter the water intrusion issue. On 22nd of December, 2018 BNB started the project of dewatering, to reduce the water level for base foundation construction. BNB had started drilling work on 23rd Dec, 2018 and drilled 50ft. borehole with 8” diameter. The drilling completed on 24th Dec, 2019 and cased the well with 5” diameter across casing. BNB moreover introduced Piezometers, the installation including all works required that installation of two bore holes (at distance 5.0 & 20.0 ft. from production well) of relatively smaller borehole depth (40 ft. each) and dia 4”.
These wells are constructed for measuring water level before and during the pumping through submersible pump of water from production well. After all these processes of well construction on 28th Dec, 2019 installation of submersible pump (2 HP) took place for water quality and quantity. Guide line of 1.5” dia had been placed. This yield test was operational for approx. 48 hours. But this submersible pump was not giving the significant discharge for dewatering as it produced 48 GPM discharge, to mitigate this issue the specialized group of BNB enhanced the efficiency of submersible pump and on 31st Dec, 2018 we installed another submersible pump of 3 HP for increasing discharge. After the upgrade of submersible pump’s efficiency increased the discharge to about 55 GMP. Dynamic Water Level (DWL) within in the pumped well is measured and recorded at a particular time with flow and rechecked after an interval of timings as provided in the recording form. This process was continued till the completion of 48 hours. The Original Static Water Level (OSWL) in the pumped well has been taken after finishing of the activity. The required levels in the production well are measured through a sounder to measure the water level fluctuations (drawdown) in the well. According to the same interval of timings as provided in the recording form, this process of pumping with help of submersible pump was continued till the completion of 48 hours.
This area is near to the Korangi Creek so, the recharge factor is very high and recovery of static water level is considerably high. It is very challenging to sustain the draw down. BNB recommended 33 nos. of borehole with effective submersible pump, which can maintain 70 GMP within construction site with 20’ x-factor, and submersible pump depth should be maintained at 35ft. to 40ft.
After implantation on BNB recommendations with adequate submersible pump sets, BNB’s client successfully able to achieved the dry land targeted depth and place the safe and sound foundation to continue the projected factory building.