This is a brief report on construction of 200*150 mm boring works at, Pharpu, Gorkha. The Deep Tubewell Drilling Site was located at Gorkha. The GPS Coordinate of the well drilling site is 27°59’27.95″N, 84°36’38.49″E about 3.9 kms road distance from Gorkha Municipal Office and 100m ahead of Nare Pipal Tree. The drilling site is accessible through connected to Road network. Then the Rig Machine including other accessories and manpower were mobilized to the site on 2080/02/27.
Photograph
Photograph 1 Machine Mobilization at site
Photograph 2 ground clearance
After Site Mobilization, the drilling work on the site at Gorkha work was started on 2080/02/28.The drilling work was continued smoothly and achieved 132 m of penetration. After this depth, the drilling work was stopped as the well has penetrated sufficient depth. During the drilling operation; the cutting samples were collected. Representative sample of each layer were collected. The driller has also prepared litholog on the basis of cuttings, nature of progress of the well penetration. According to driller’s lithological log & well penetration rate, the well was designed. The whole drilling work was carried in the direction and close supervised of office representative.. After the completion of the drilling work on the basis of aquifer layer presence of the well the screen pipe and casing pipe were lowered.
Photograph 3 Machine Setup after site clearance
Photograph 4 Drilling and Lowering Works
Total length of casing and screen used
200 mm MS Casing Pipe – 60 m
200 mm Perforated Screen – 36 m
150 mm MS Casing Pipe – 8 m
150 mm Perforated Screen – 28 m
Total length – 132 m
Note: +0.5 m above the ground level.
Well development
The well development by air compressor and pump test work was done after installation of Tube well. Compressor was used during drilling time and Development of tube well by pump has been carried out immediately after installation of the pipe assembly. The well development has broad objectives:
– To repair damage done to the formation (aquifer) by the drilling opera1on so that the natural hydraulic properties are restored
– To alter the basic physical characteristics of the aquifer near the borehole so that the water will flow more freely to the well.
Over pumping
After the development of well by air Compressor, well was again developed by over pumping before carrying out pump test. In this method, the water well is pumped at a higher rate than the well will be put into service. This process removes fines from the water bearing formation and create graded zone outside the well screen.
Pump Test
The continuous test was conducted by using submersible pump. In this test, the well was pumped at constant rate for 24 hrs. The pumping test data and measurement taken during the pumping test are shown in Annex A. The static water level was 28 m. The dynamic water level after 24 hr. was 72.4 m at 4 lit/sec discharges and the Transmissivity is:
Transmissivity (T) = 2.1*10-4 m2/sec
Hydraulic Conductivity (K) = 3.55*10-6 m/sec
Recovery Test
After 6 hr. of pump operation, constant rate pumping test was stopped. Recovery test was conducted immediately after pump had stopped. It took 1 hr 35 minutes to recover water level to initial level.
Conclusion
The well was drilled up to the depth 132 meters below the ground surface. The Perforated screen pipes were installed on the basis of aquifer presence on the well. Perforated screen of 3.2 mm screen opening size were used in well. Well was developed by air compressor for 4 hrs. A tube well’s performance was satisfactory and was successful.
Suggested preferable submersible pump according to well’s performance for the tube well at this site is 10 HP Texmo branded submersible pump of with 160 m head. Lowering depth of pump was suggested at 78 m with 2 inch outlet.