Precipitation on the tube well in the pit Construction

Abstract: In high water table areas for infrastructure construction, dewatering, construction of infrastructure to provide a dry working environment is the key. This paper describes the precipitation tube well Technology in a project-based construction applications.

Keywords: foundation pit; tube wells, precipitation

1 Project Overview and geological conditions
An Engineering major for the clay soil excavation, excavation slope of 1:3, according to the construction site above the actual situation, excavation slope without supports. Down the drainage pit excavation for the key, open digging, should reduce the water table to below the excavation surface 0.5m, non-disturbance of natural ground, reserve pit at the bottom 30cm thick layer of protection. foundation pit drainage ditches and tube wells mainly precipitation.

Engineering Geology is divided into the lower three layers: the upper part of the artificial accumulation of filling the main, central part of the wavy brick red clay, sandy conglomerate based in the lower part of the bedrock.

2 materials and equipment investment plan
Tube wells: wells using concrete pipes, well pipe diameter φ300mm, wall thickness of 50mm, the lower part of the precipitation for the 1.0m tube, the upper filter for the non-sand concrete pipe.

Pumps: drainage ditches 22kW using two sets of mud pump, deep wells within each configuration a platform 150QJ20-26 / 4 type deep well pump, a control switch for each pump configuration.

3 Pit Dewatering ideas
3.1 General construction methods
Excavation slope of 1:3, water content of soil material at this stage is moderate, direct excavation pit in the second phase of excavation at 52.0m elevation using the following drainage ditches and drainage tube wells, the second stage, from 52.0m The following elevation before excavation started to play deep in the 52.0m height, seven days after the end of the cutoff wall construction of tube wells precipitation started to reduce soil diving, excavation below the water table to improve efficiency, while increased rainfall effect, the use of drainage Ditch the way aid precipitation, and the third stage is used in the excavation after the end point as a set of wells, tube wells and wells, tube wells while reducing the use of ditches and groundwater, to ensure that structural construction in arid lands.

3.2 layout of drainage ditches
Rectangular pit, length 50.6m, width 21m, with the excavation pit, when the pit depth close to 52.0m, the pit along the four weeks (other than the basic outline, set the pit edge slope drains within 0.3m , 1.40 or in the pit every 30 ~ 40m to set up a set of 0.8m diameter wells, ditch width 0.3m, ditch excavation lower than 0.4m, lower catchment drains bottom than 0.8m. As the pit excavation, drainage ditches and collection wells along with the classification set to deepen, until it reached the design elevation Bottom up. excavation to a predetermined depth, then drain and set on the perfect finishing wells, trench wall to be unstable puzzle or the use of dry masonry sand bags for flooding supporting.

3.3 Layout of precipitation tube well
Pumping down tube around the pit from the pit rim Jingyan 1.5m arranged in the pit of the layout of a row of left and right side tube wells, three wells arranged on each side, the number of tube wells arranged according to the effect of precipitation increase or decrease. Well Center from the building Edge 1.5m, well spacing of 7m, well-head diameter of 600mm, well pipe section installed, removed section by section, with the excavation to excavation of the surface above 30cm, the structure normal water level elevation during the construction of the well control 48.0m the following to ensure that soil water table below the pit bottom 0.5m.

3.4 deep well construction methods
3.4.1 Construction Program
Wells, setting out to do → wellhead, casing → safety drill in place, drilling pit backfill sand cushion → → → dipping well pipe wall and backfill the hole wall of the filter layer pumping control circuit → → Installation → precipitation test pumping work well
3.4.2 Hole
Uses XY-600 Model rig drilling into the hole. Aperture 600mm diameter selected according to design requirements or four-leaf cone drill, a hole. BWT450/12 support for the mud pump, maximum working pressure of not less than 1.2MPa, the input slurry amount not less than 5L / S, can be drilled Control in 2.5 ~ 4m / h, in the clay layer from the mud, sandy soil into the pool of qualified use of mud slurry, strictly control the proportion of 1.1 to 1.2 mud, mud viscosity 18 20 seconds, the amount of sand is less than 5.0%, the proportion of the general outflow from the hole in the 1.2 to 1.3, filtered by the high sedimentation tank into the lower pool, tested before they can be pumped to the drilling cycle.

3.4.3 deep well system equipment
Tube wells: wells using concrete pipes, well pipe diameter φ300mm, wall thickness of 50mm, the lower part of the precipitation for the 1.0m tube, the upper filter for the non-sand concrete pipe.

Pumps: 1 for each deep wells within the configuration table 150QJ20-26 / 4 type deep well pump, a control switch for each pump configuration.

3.4.4 dipping well pipe, filter clay backfill and sealing
To maintain the drill pipe concentric with the shaft, the outer wall of well-oriented wood banding, drilling frame does not move, with the original rig lifting concrete pipe, the amount of the hole at the end of elevation in the complex is correct, complete records. The bottom of the first blind configure a concrete pipe with hardwood tray with a rope hanging embrace, slowly drop hole, until a predetermined depth. blind tube connected filter tube, the mouth of the good prices, outer layer of 80 mesh nylon cloth bag, two connector 200mm, with a non-woven dressing , away from it and then 3 to 4 hairs fixed vertical bamboo, galvanized iron wire hoop with 10 # tight-sand backfill tube.

3.4.5 Wash the hole, pumping
Well pipe installed, it should immediately wash the hole, without delay. Well, after washing, the amount of water to meet the requirements, which officially began pumping and observation wells test record by the water table. Edge into the well while improving the measurement side plus side analysis of wells, the water level until the required water level dropped to pit its structure see tubewell columnar structure: Links to free download http://www.hi138.com
3.4.6 plugging
The construction of the infrastructure project is completed, approved by the supervising engineer, began plugging orderly stop pumping, ensure quality, do not stay hidden. In order to ensure safety block, opened before the backfilling with gravel, clay filling the upper 0.5m compaction.

4 The use of tube wells Management
4.1 Organization
In the deep well set up before the rain began construction group, composed of the leaders in charge of one, two construction workers, and with two full-time electrician, working two generators, on-site arrangements for 6 people on duty 24 hours a day.

4.2 power supply system to ensure
Power to the system using anti-notching dedicated line connection of the downstream side, and with standby power grid, electrical power failure in the system, start the backup power supply, and ensure the normal operation within 5 minutes to work full-time electrician and generator for the protection.

Measures to ensure the well running 4.3
4.3.1 strict management system, broken down to each person the responsibility to make site specific work for each specific person responsible for the implementation.

4.3.2 the establishment of field work management system, and to ensure normal system operation, so that the scene always under control.

4.3.3 in the field setting up a dedicated office space, check each well in time, each pump working conditions, problems in a timely manner.

4.3.4 Generator every day and full-time electrician check the line is intact, sooner or later try to start again, once the electrical power system can guarantee the normal operation of the generator. Meanwhile prepare the pump, wires, fuses and other spare materials.

5 Security measures
5.1 Construction of power by the Security specification, two levels of protection in line with three distribution requirements, to ensure "a machine, a gate, a drain, a box" can be realized,
5.2 Under construction needs, with hand pump, regular inspection, strengthening the operation and maintenance and repair work, identify problems and rectification, and strive to take preventive measures.

5.3 Private non-random pull wiring, arrange electrical wiring.

5.4 In order to prevent staff stepped wells, tube wells to be higher than the demolition ground 30cm.

5.5 Deep requirements during construction and operation may not fall into the debris in the pipe, the sand filtration layer material should be clean, not a lump of clay folder.

5.6 above the surface excavation section tube wells installed, removed section by section, with the excavation to excavation of the surface above 30cm, reserved for the late set of pit wells.


References:
[1] National Water Resources and Hydropower Construction Technology Network <<Water Resources and Hydropower Engineering Construction Manual>> (vol. 1, (Volume 5), China Electric Power Press, 2004. Links to free download http://www.hi138 . com