Installation of Tubewells

After completion of a bore hole to the desired length, the tubewell assembly is to be lowered and fixed in position as soon as possible. The bore hole is usually drilled a little more than the installed depth of the tubewell to accommodate the materials which may cave in or settle in the bore hole before installation of the tubewell. The sand trap, strainers, blind pipes, housing pipes, etc are assembled near the tubewell and marked serially. The components of the tubewell are than lowered one by one as required starting from the bottom end. Each component of the tubewell is to be properly screwed or welded to another and slowly lowered vertically with the help of clamps. When the lowering of the tubewell is complete, it is kept suspended from the top of the bore hole and clean sand or properly designed cleaned shrouding gravel is dropped in the bore hole. The coarse sand or shrouding material is filled to at least 10 to 15 m above the top of the upper strainer. These materials grip the strainers and the blind pipes on the out side and hold the tubewell in position. The remaining space of the bore hole may be filled with clayey materials to prevent percolation of contaminated water from the surface.

It is important that the entire tubewell is installed straight and vertical. In case of large diameter tubewells, guides are placed at a certain distance apart for concentric installation, to permit uniform filing of shrouding materials around the well and satisfactory operation of the pumping unit and without damage.

Disinfection of Tubewell

Tubewells are contaminated during construction mainly due to the use of contaminated surface waters for sinking. Sometimes contaminating materials are used to stabilize the bore hole against collapse and caving. Tubewells in Bangladesh are also contaminated due to submergence in flood or under storm surges. The contaminated tubewells need disinfection by the following procedure:

a. Prepare about 50 l of chlorine solution with a chlorine concentration of 50 mg/l (dissolved 0.150 gms of bleaching powder containing 33% chlorine in 1 liter of water).

b. Open the base of the tubewell and pour the chlorine solution in the pipe slowly. The chlorine solution will fill the pipe and then enter into the aquifer through the strainer.

c. Dismantle the tubewell and submerge/wash smaller components in the chlorine solution and wipe all the surfaces of larger components with the same chlorine solution. Then reassemble and fix the tubewell.

d. Wait for at least six hours and than pump out the water until traces of chlorine can be smelled in water produced by the tubewell.

e. When the pumping of the tubewell is completed, the disinfected tubewell is ready for regular use.

Telecommunication Circuits in Building

The design of telecommunication systems is beyond the scope of this post, but the provision that has to be made for them within a building in described here.

In many cases all that is needed is a route by which the telephone service can bring in a telephone cable to an instrument. Telephone cables are quite small and if the position of the outlet for the telephone receiver is known it is sufficient to install a 20 mm conduit from out side the building to the outlet with the same number and spacing of draw-in points as are used for any other conduit system.

Some buildings may have an internal telephone system which may consist of extensions to the public telephone or may be an entirely separate installation. Here again the essential matter for the electrical services designer is to agree on the outlet positions with his customer and to arrange for them to be linked to each other by conduit or trunking.

Trunking can be useful alternative to conduit when the system is a complex one needing many cables with a large number of junctions. Telephone cables do not have a protective sheathing and therefore need the mechanical protection of conduit or trunking. Where practicable, a separation of at least 1.8 m shall be maintained between conductors of communication systems on buildings and the lighting conductors.

Requirements for Inspection and Testing of Pile Driving Equipment

Pile diving equipment shall be inspected by an engineer at regular intervals not exceeding four months. A register shall be maintained at the site for recording the result of such inspection. Pile lines and pulley blocks shall be inspected by the foreman before the beginning of each shift for any excess wear or other defects.

Defective parts of pile drivers, such as sheaves, mechanism slings and hose shall be repaired by only competent technicians and duly inspected by foreman in-charge of the rig. The findings of such inspection shall be recorded in the register.

For every hoisting, machine, chain, rig, hook, shackle, swivel and pulley block used in hoisting or suspending, safe working loads shall be ascertained. Every hoisting machine and all gears shall be marked with the safe working loads and the conditions under which it is applicable.

Tests shall be performed in case of doubt and half of the tested load shall be taken as the safe working load. No part of any machine or any gear shall be loaded beyond the safe working load.

Groove Welds

Groove Welds: This post provides the requirements for the design of connectors (Groove welds) and connecting elements such as plates, stiffeners, gussets, angles, brackets, etc. The requirements for groove welds are stated here following AWS : D 1.1 : Structural Welding Code-Steel.

Effective area

Effective area of groove welds shall be considered as the effective length of the welds times the effective throat thickness.

The effective length of groove weld shall be the width of the part joined.

The effective throat thickness of a complete penetration groove weld shall be thickness of the thinner part joined.

The effective throat thickness of a partial-penetration groove weld shall be as shown in Table-1.

Table-1: Effective throat thickness of a partial-penetration groove welds.

Welding Process	Welding Position	Include Angle of Root of Groove	Effective throat Thickness
Shielded Metal Arc Submerged Arc Gas Metal Arc Flux-Cored Arc	All	J or U Unit	Depth of Chamfer
		Bevel or V joint ≥600
		Bevel or V joint <600 ≥450	Depth of Chamfer minus 3 mm.

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The effective throat thickness of a flare groove welds when flush to the surface of bar or 90⁰ bend in a formed section shall be as shown in Table-2. Random sections of a production weld for each welding procedure, or such test sections as may be required by design documents, shall be used to verify that the effective throat is consistently obtained.

Table-2: Effective throat thickness of a Flare groove welds.

Type of Weld	Radius (R) of Bar or Bend	Effective throat Thickness
Flare Bevel Groove	All	5/16 R
Flare V- Groove	All	½ R*
Use 3/8 for Gas Metal Arc Welding (except short circuiting transfer process when R≥12mm.

Limitations

The minimum effective throat thickness of a partial penetration groove weld shall be as shown in Table-3. Minimum effective throat thickness is determined by the thicker of the two parts joined, except that the weld size need not exceed the thickness of the thinnest part joined though a large size is required by calculation. For this exception, particular care shall be taken to provide sufficient pre-heat foe soundness of the weld.

Table-3: Minimum effective throat thickness of a partial-penetration groove welds.

Material Thickness of Thicker part joined, mm	Minimum Effective Throat Thickness,mm
To 6 Inclusive	3
Over 6 to 12	5
Over 12 to 20	6
Over 20 to 40	8
Over 40 to 60	10
Over 60 to 150	12
Over 150	16

Health Hazard during Excavation

Mechanical ventilation shall be provided where gases and fumes are likely to be present in trenches. All personnel working shall be provided with protective respiratory equipment. All trenches/tunnel shall be provided with emergency exits.

Clothes worn by the workmen shall not be of such nature and materials as to increase the chances of inflicting injuries to themselves and others. Wearing of loose garments shall be strictly avoided.

Workman using necked flames (such as welding), where steel is used for ladder or shoring purpose or where metal obstruction has to

Precautionary measures shall be taken against the emission of dust, small particles, toxic gases and other harmful substances in quantities hazardous to health. Such measures may include local ventilation, use of protective devices, medical check-up etc. Exhaust ventilation shall be employed in enclosed spaces.

A copy of all pertinent regulations and notices concerning accidents, injury and first aid shall be prominently displayed at the work site.

A first aid box or cupboard shall be provided for every 150 workmen and be accessible. The provision shall also include a stretcher and cot with accessories for every 300 workmen.

In case of site where more than 600 workmen are employed at any one time, or in which more than 300 workmen are employed at any one time and 15 Km from the nearest health service facility, provision of an ambulance shall be made.

The precautionary measures provided shall meet the requirements of the local health authority. The owner shall ensure that all precautionary measures have been taken and been inspected by the Authority prior to commencement of such work.

Placing of concrete

To ensure the requirements of strength, impermeability, and durability of the hardened concrete in the actual structure, the operation of placing concrete is most important. Before placing concrete it should be determined that forms are tight, clean, properly braced and moistened or oiled.

As far as placing concerned, the main objective is to deposit the concrete as close as possible to its final position so that segregation is avoided and the concrete can fully be compacted. To achieve this objective, the following rules should be followed:

1. The concrete should be placed in uniform layers, not in large heap or slopping layers.

2. Hand shoveling and moving concrete immersion or poker vibrator should be avoided.

3. The thickness of a layer should be compatible with the method of vibration so that entrapped air can be removed from the bottom of each layer.

4. The rates of placing and of compaction should be equal.

5. Where good finish and uniform color are required on columns and walls, the form should be filled at a rate of at least 6 ft per hour, avoiding delays.

6. Each layer should be fully compacted before placing the next one, and each subsequent layer should be placed whilst the underlying layer is still plastic so that monolithic construction is achieved.

Collision between concrete and formwork or reinforcement should be avoided. For deep sections, a long down pipe or tremie ensures accuracy of location of the concrete and minimum segregation. Concrete should be placed in a vertical plane. When placing in horizontal or sloping forms, the concrete should be placed vertically against and not a way from, the previously placed concrete.

Placing concrete by tremie is particularly suited for deep forms, where compaction by the usual methods is not possible, and for underwater concreting. In the tremie method, high workability concrete is fed by gravity through a vertical pipe which is gradually raised. The mixed must be cohesive, without segregation or bleeding, and usually has high cement content, a high proportion of fines and contains a workability aids.

SHALLOW EARTHQUAKES CAUSE MORE DESTRUCTION THAN INTERMEDIATE ONES

The earthquake of Magnitude 7.4 Hindu Kush Region, Afghanistan 2002 March 03 12:08:19 UTC gave a finding that shallow earthquakes cause more deaths and damage than intermediate ones. About 150 people were killed in this earthquake. However, the casualty and damage toll would likely have been much higher if the quake had occurred within 35 km (20 miles) of the Earth's surface. Shallow earthquakes cause more damage than intermediate and deep ones since the energy generated by the shallow events is released closer to buildings and therefore produces stronger shaking than by quakes that are deeper within the Earth.

On February 4, 1998, a magnitude 5.9 shallow earthquake struck 70 km (45 miles) northwest of the March 3 quake. That earthquake killed at least 2,323 people, injured 818 and destroyed 8,094 houses in the Rostaq area of Afghanistan. A magnitude 6.6 earthquake, also shallow, hit the same area on May 30, 1998, and killed at least 4,000 people and destroyed many homes in Badakhshan and Takhar Provinces.

By comparison, on February 20, 1998, a magnitude 6.4 earthquake occurred about 60 km (35 miles) east of the March 3, 2002 earthquake, at a depth of about 235 km (145 miles) below the surface. That earthquake killed only one person and destroyed 35 houses in northern Pakistan.

Shallow-depth earthquakes: 

1998 Feb 04 14:33:21 37.075N 70.089E 33 km 5.9M at least 2,323 killed 

1998 May 30 06:22:28 37.106N 70.110E 33 km 6.6M at least 4,000 killed 

Intermediate-depth earthquakes: 

1998 Feb 20 12:18:06 36.479N 71.076E 236 km 6.4M 1 person killed 

2002 Mar 04 12:08:22 36.533N 70.100E 256 km 7.3M about 150 killed

Arahant Ven. Shadhanananda Mohasthobir

Rajbon Temple, Rangamati