Caisson work

One aspect of improper decompression that has been reported is aseptic bone necrosis. Bone is poorly vascularized and poorly innervated thus, gas bubbles trapped between the periosteum and the bone may lead to necrosis. Being poorly innervated there is no warning until too late. It is insidious. Bone necrosis has been associated with high pressures, hard work, prolonged exposure, and most important inadequate decompression Thus far bone necrosis has been seen only in caisson work. Aseptic bone necrosis at a later date could provide a basis for compensation claims. 

Helium is of great assistance to the diver and in caisson work. After prolonged exposure at great depths much time is absorbed in bringing the diver to the surface every 33 feet of depth gives... 

The construction of many caissons can proceed simultaneously on a site because it does not rely on the availability of piling rigs is not governed by availability of material or space constraints. Hence, construction can be relatively quick provided that labor resources are available in abundance. Based on past experience, caisson work down to a reasonable depth would not be slower than conventional piling works. Depending on the soil conditions and diameter of the caisson, a dig of 0.75 m to 1.2 m can be constructed each day. Typically, a 1.5 m diameter caisson about 20 m deep would normally take about 3 weeks to construct. 

Although the JARLAN-type breakwater concept has been used more or less successfully worldwide, it has a basic drawback (see Fig. 12.6) which requires a further development of this concept. For this purpose, it was necessary to investigate first the key processes which contribute to the wave damping by friction (local losses and vortices) and by destructive interference of the incident and reflected waves over the full range of BjL ratios (i.e., over the full range of incident wave periods). The experimental results in Fig. 12.5 well illustrate how a traditional JARLAN-type caisson works. 

M. Nonchemical physical exposures in the workplace are important because they can cause systemic effects that mimic chemical toxidromes. The most important example is heat stress, which is a major occupational health issue. Other relevant nonchemioal, work-related physical exposure types include ionizing radiation, nonionizing radiation (such as ultraviolet, infrared, and microwave exposure), and increased barometric pressure (eg, among caisson workers). Except for extremes of exposure, the adverse effects of these physical factors are generally associated with chronic conditions. 

The hand-dug caisson thrives in an environment where conventional piling equipment struggles e.g. hill sites and congested sites. Being of relatively large diameter (to be able to fit a worker therein), the caisson has potentially large structural capacity - typically above 500 ton. Where the rockhead is near the ground surface, say less than 20 m, the caisson can be socketted into rock to derive full structural capacity. Caisson construction works well on hill slopes and in residual soil... 

Construction of a hand-dug caisson is essentially a well digging exercise. During the excavation of caisson wells, the soil conditions can be assessed and buried objects can be examined. Such wells have been used in forensic work of failed structures where the soil conditions and pile conditions (depth and quality) can be examined (Yee 2003). 

Typical rock bearing values used for caisson design are generally derived from work done for drilled shafts e.g.Tomlinson(1995 and 1997), Poulos and Davis (1980), HK GEO (1996), Hilletal. (2000). As can be expected, suggested bearing values vary significantly probably because experience from... 

Hand-dug caisson construction involves workers working in deep shafts subjected to risks. Common causes of accidents involve falling objects, ingress of water and persons falling down the shaft. Health risks would include dust inhalation and noise damage hearing. Some of the safety precautions recommended would include ... 

In this case, micropiles were used to support part of the 1-78 dual highway, which crosses the Delaware River between Pennsylvania and New Jersey. It was thought that the New Jersey pier was to be founded on solid rock but excavation revealed that the solid rock was nonexistent. So two alternatives were considered the installation of six 36 in. caissons, each with a working load of360 tons (3,203 kN) and the placement of 24 minipiles, each of nominal working load of 100 tons (890 kN). 

Changing the operation to work in the dry through the use of limpet dams or caissons (Figure 4.4) can remove the hazards associated with changing water levels. Care should still be taken to ensure inundation does not occur due to excessive water levels, waves, ground water or other means. 

We live in an environment in which the air above us in the atmosphere creates pressure around us. We experience changes in pressure when we fly in airplanes or climb mountains. Some people experience changes in pressure when they go scuba diving or work in tunnels or caissons. 

Pressures greater than that at sea level occur in underwater diving and in certain kinds of constmction work, such as caisson construction. Caissons are watertight structures for... 

A caisson worker must work under water at a depth of 60 ft digging a tunnel under a river. Assuming a 33 ft column of water is equivalent to 1 atm, determine the following ... 

Detonators and explosives should not be stored in tunnels, shafts, or caissons. Detonators and explosives are carried separately into the working chambers. The blaster or powderman is responsible forthe management aspects. 

Divers and caisson workers may suffer from pain in the joints if they return to the surface too quickly after working in deep water or under elevated air pressure. In these conditions, air contained in the body tissues, which was dissolved under l)igh pressure, is released to form air bubbles (mostly nitrogen gas) in the joints and elsewhere to produce unpleasant symptoms. The bends is the name of the illness resulting. Mild cases affect the elbows, shoulders, ankles and knees. As the illness develops, the pain increases in intensity and the affected joint becomes swollen. Serious cases of the bends may affect the brain and/or the spinal cord. In cases of brain damage the patient may suffer visual problems, headaches, loss of balance and speech disturbances. Spinal cord damage may cause paralysis of the limbs, loss of sensation, pins and needles and pain in the shoulders and/or hips. The problem is obviated by reducing the rate of change of pressure to which the workers are subjected to a level at which the bubbles of gas do not form. 

While work is being carried out in a coffer-dam or caisson, an inspection must be carried out at the beginning of each day or shift, and a thorough examination conducted at least once every seven days, after explosives have been used, or where substantial damage has occurred due to falling materials (Reg. 18). The result of the examinations must be recorded in Form 91 (Part 1 Section B), a copy of which should be held on site. Thorough daily and shift inspections should be carried out and while they do not have to be recorded, it is prudent to do so. 

Such physician shall at all times keep a complete and full record of examinations made by him. The physician shall also keep an accurate record of any decompression illness or other illness or injury incapacitating any employee for work, and of all loss of life that occurs in the operation of a tunnel, caisson, or other compartment in which compressed air is used. 

All parts of caissons and other working compartments shall be kept in a sanitary condition. 

Head frames shall be constructed of structural steel or open frame work fireproofed timber. Head houses and other temporary surface buildings or structures within 100 feet of the shaft, caisson, or tunnel opening shall be built of fire-resistant materials. 

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