VERTICALITY, TUNNELS AND PIPELINES SETTING DURING CONSTRUCTION
How To Set Verticality, Tunnels, and Pipelines For Construction?
As a building rises the vertical alignment must also be controlled. This can be done by extending building centre lines at right angles to each other out to fixed points clear of the structure.
These lines can then be projected up the building and marked, allowing accurate measurements from these marks at each floor. Alternatively an optical plumb can be used to project a fixed point up through openings in the floors of the building so as to provide a set of reference points at each level.
The standard of setting out for tunnels must be high using carefully calibrated equipment, precise application and double checking everything. An accurate tunnel baseline is first set out on the surface using the methods described above.
Transference of this below ground can be done by direct sighting down a shaft if the shaft is sufficiently large to allow this without distortion of sight-lines on the theodolite. With smaller shafts, plumbing down may be used.
A frame is needed either side of the shaft to hold the top ends of the plumb-lines and to allow adjustment to bring them exactly on the baseline. The plumb-line used should be of stainless steel wire, straight and unkinked, and the bob of a special type is held in a bath of oil to damp out any motion.
By this means the tunnel line is reproduced at the bottom of the shaft and can be rechecked as the tunnel proceeds.
Many tunnels are nowadays controlled by lasers, the laser gun being set up on a known line parallel to the centre line for the tunnel and aimed at a target. Where a tunnelling machine is used, the operator can adjust the direction of movement of the machine to keep it on target so that the tunnel is driven in the right direction.
For other methods of tunnelling, target marks can be set on the soffit of rings, the tunnel direction being kept on line by adjusting the excavation and packing out any tunnel rings to keep on the proper line.
Lasers are also used in many other situations, usually for controlling construction rather than for original setting out since their accuracy for this may not be good enough. The laser beam gives a straight line at whatever slope or level is required, and so can be used for aligning forms for road pavements or even laying large pipes to a given gradient.
For the latter, the laser is positioned at the start of a line of pipes and focused on the required base line. As each new pipe is fitted into the pipeline a target is placed in the invert of the open end of the pipe, using a spirit level to find the bottom point, and the pipe is adjusted in line and level until the target falls on the laser beam. Bedding and surround to the pipe are then placed to fix the pipe in position.
Rotating lasers are also widely used and once set up give a constant reference plane at a known level. Use of a staff fitted with a reflector allows spot levels to be obtained anywhere in the area covered by the laser. Earthmoving equipment fitted with appropriate sensors can also be operated to control the level of excavation or filling with minimum input other than by the machine operator.
Friday, February 10, 2012
CONCRETE MIXING TECHNIQUES TIPS TRICKS BASICS AND TUTORIALS
MIXING OF CONCRETE TUTORIALS
Links On Concrete Mixing Tips and Tutorials
Concrete is one of the most used materials in civil and structural construction. May it be a high rise building, or a bridge that carries a heavy load, even in simple household projects, concrete is used.
An important aspect on the design of such is the desire to have a good concrete mix. Below are links to articles that teaches basics and advance concrete mixing techniques.
How To Mix Concrete
Concrete is a mixture of cement, sand, gravel and water. Variations in the ratio of the ingredients produces a mix suitable for different jobs but we will be instructing you on a general puepose mix suitable for most garden tasks and shallow foundations not house foundations. Mix 1 part cement, 2 parts sand and 4 parts of gravel. What you use to measure the parts depends on how much concrete you need normally buckets are the best measure, one part being a level bucket full. Read more...
The Perfect Concrete Mix Design
Is there such a thing as a Perfect Mix Design? If you are looking for one mix design recipe that will work perfectly for every job and every application, the answer is definitely "NO". However, there is a right mix design for every job and every application, and with the right knowledge and good communication between a concrete contractor and his supplier, you can find The Perfect Mix Design for every one of your jobs. Read more...
High Strength Concrete Mix Design
The type of concrete generally with compressive strength of 6000psi (40MPa) or greater is called as HSC. We need high strength concrete in our modern infrastructures in order to put the concrete into service at much earlier stage, To build up high rise building by reducing column sizes and increasing available space or in case of long span bridges Now what is mix design? Although the American Concrete Institute (ACI) doesn't use the term, preferring mix proportioning. Read more...
Concrete Mix Evaluator
Concrete mix design is no longer just a recipe of proportions of cement, sand, stone and water. Today the concrete supplier is held responsible for the performance of the in-place concrete. Curling, cracking, dusting, color variation, moisture transmission, and strength, are all concerns for the quality of the in-place concrete. Much of what happens is outside the responsibility or control of the concrete producer. Concrete of good quality can become undesirable in the hands of an inexperienced finisher, but poor concrete, that of inappropriate proportions, will doom the final product regardless of the experience of the concrete finisher. Read more...
How to Properly Mix Concrete
How to hand mix concrete so it delivers maximum strength and durability. Mixing isn't complicated and when done well, the concrete should last a lifetime. Mixing bags of concrete isn't complicated. You add some water, stir it up and pour it out. But to get the most strength from the concrete, you have to recognize when it has just the right amount of water mixed in. Too little water and the particles in the mix won't stick together. Too much water weakens the concrete. In this article, we'll show you what the perfect mix looks like. We'll also show you a mixing technique that will ensure thoroughly mixed concrete with a minimum of effort. Read more...
Links On Concrete Mixing Tips and Tutorials
Concrete is one of the most used materials in civil and structural construction. May it be a high rise building, or a bridge that carries a heavy load, even in simple household projects, concrete is used.
An important aspect on the design of such is the desire to have a good concrete mix. Below are links to articles that teaches basics and advance concrete mixing techniques.
How To Mix Concrete
Concrete is a mixture of cement, sand, gravel and water. Variations in the ratio of the ingredients produces a mix suitable for different jobs but we will be instructing you on a general puepose mix suitable for most garden tasks and shallow foundations not house foundations. Mix 1 part cement, 2 parts sand and 4 parts of gravel. What you use to measure the parts depends on how much concrete you need normally buckets are the best measure, one part being a level bucket full. Read more...
The Perfect Concrete Mix Design
Is there such a thing as a Perfect Mix Design? If you are looking for one mix design recipe that will work perfectly for every job and every application, the answer is definitely "NO". However, there is a right mix design for every job and every application, and with the right knowledge and good communication between a concrete contractor and his supplier, you can find The Perfect Mix Design for every one of your jobs. Read more...
High Strength Concrete Mix Design
The type of concrete generally with compressive strength of 6000psi (40MPa) or greater is called as HSC. We need high strength concrete in our modern infrastructures in order to put the concrete into service at much earlier stage, To build up high rise building by reducing column sizes and increasing available space or in case of long span bridges Now what is mix design? Although the American Concrete Institute (ACI) doesn't use the term, preferring mix proportioning. Read more...
Concrete Mix Evaluator
Concrete mix design is no longer just a recipe of proportions of cement, sand, stone and water. Today the concrete supplier is held responsible for the performance of the in-place concrete. Curling, cracking, dusting, color variation, moisture transmission, and strength, are all concerns for the quality of the in-place concrete. Much of what happens is outside the responsibility or control of the concrete producer. Concrete of good quality can become undesirable in the hands of an inexperienced finisher, but poor concrete, that of inappropriate proportions, will doom the final product regardless of the experience of the concrete finisher. Read more...
How to Properly Mix Concrete
How to hand mix concrete so it delivers maximum strength and durability. Mixing isn't complicated and when done well, the concrete should last a lifetime. Mixing bags of concrete isn't complicated. You add some water, stir it up and pour it out. But to get the most strength from the concrete, you have to recognize when it has just the right amount of water mixed in. Too little water and the particles in the mix won't stick together. Too much water weakens the concrete. In this article, we'll show you what the perfect mix looks like. We'll also show you a mixing technique that will ensure thoroughly mixed concrete with a minimum of effort. Read more...
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