CAISSON WORKS(prof. harmfulness and prof. diseases). Occupational hygiene in the caisson. The caissons represent a device consisting of a working chamber, a shaft pipe extending upwards from it, ending at the top with a hardware chamber, and a sluice connected to the hardware chamber. The working chamber is that part of the caisson, in which the actual caisson work is carried out, i.e., excavation and excavation. Usually it is made of reinforced concrete, but it can be iron and even wooden. The shaft pipe is designed to lower people and materials into the chamber and to raise the excavated soil from it. It consists of separate links, built up one on top of the other as the caisson is lowered, and has a strictly vertical ladder for people. The hardware chamber contains simple mechanisms that serve to lift soil from the working chamber and lower materials into it and are usually serviced by two workers inside it. The lock has a special purpose of both medical and industrial nature, representing a chamber (or chambers), in which any air pressure intermediate between the external pressure and the pressure in the caisson can be created, without changing the pressure in the caisson itself. The creation of such intermediate pressures is necessary in order to protect people from the risk of injury and disease associated with pressure changes, as well as to maintain the necessary pressure in the working chamber at the time of people going outside or discharging soil and materials. The working chamber usually employs from 6 to 14 people. When the caisson has reached the soil of the required stability, further excavation work is completed, the working chamber is filled with concrete, like the first link of the shaft pipe; the rest of the caisson is removed, and thus formed. the unfilled space in the masonry is also filled with concrete, after which the abutment is ready. Appointment K. r. consists in the fact that if the strength of the soil is insufficient for a given structure (when there is an aquifer under it) or if it is necessary to carry out work on the bottom of rivers, etc., abutments and supports are brought under the structure being erected (bridge, building, etc.) , brought to solid ground, as a result of which you have to pass through the water. For this purpose, in the corresponding layer, water is pushed aside by air injected under pressure into a special device called a caisson. The value of air pressure corresponds to the depth of the caisson; it is assumed that for every 10 m the depth of lowering the caisson, the pressure of the air supplied to it should increase by 1 atmosphere. Air is pumped into the caisson by compressors from the compressor station through air ducts. Since the air is very hot during compression, if special measures are not taken to cool it, it enters the caisson significantly heated, as a result of which in such cases the t ° in the caisson turns out to be excessively high. This also happens when the air distribution network is not insulated and is exposed to solar heating. In winter, non-isolation of the air duct network leads to the opposite results: the air in the caisson may come chilled, and the temperature in the caisson may be excessively low. Since air for compressors can be taken in an unfavorable (in terms of its dustiness) place, and since when it passes through compressors lubricated with oils, it can become contaminated with the latter, sometimes the air in the caisson can also be heavily polluted. Humidity in the caisson is always inevitably very high, exceeding 90% and often reaches full saturation. It is especially high in locks during the period of sluices, because due to the decrease in pressure, which constantly occurs in the lock, fog is formed in it and vapors condense into water. The same phenomenon takes place in the working chamber during the periods of landing of the caisson, carried out by lowering the pressure in it. Ventilation in the caisson depends on the amount of air supplied to it, as well as on the quality of the soil; with soils that are easily permeable to air (sandy), the ventilation of the caisson and, in particular, the working chamber is carried out satisfactorily; in the case of soil that is poorly permeable to air (clay, silty), ventilation of the caisson can suffer significantly if it is not provided with special measures. To ensure the necessary purity of air (freeing it from impurities of oils, condensate and dust), tanks are included in the air duct network, which, if necessary, can be equipped with filters. -swarm would provide at least three times its exchange in 1 hour in the working and hardware chambers.Under the existing conditions, this rate provides about 50 m 3 air per person. The lack of ventilation of the caisson is all the more important because, due to the very high humidity in the caisson, conditions that are unfavorable for the thermoregulation of the body are more easily created and, therefore, occur more quickly. disorders in the latter, which has a direct impact on the occurrence of decompression sickness. In addition, in the prevention of caisson diseases, the temperature regime in the caisson is of great importance. The most suitable temperature is within 17-22°, legalized by the Decree of the NCT of the USSR of 5/II, 1930, and at the highest limits it would be very useful to give an appropriate speed to the movement of air in the working chamber (up to 0.6"m in 1 sec.) to ensure the necessary heat transfer of the body. Caisson b-ni, their pathogenesis, symptomatology, treatment and prevention. The transition of the body from normal pressure to increased pressure entails a change in its tissues and organs, gradually acquiring pressure. environment. If this transition takes place gradually and over a period of time sufficient for the body to adapt to the changed pressure conditions, and if there are no stalemate in the body. changes that prevent this adaptation, then the body safely tolerates the transition to high pressure and stay in it. If one of these conditions is violated, then corresponding damage in the body is inevitable. Practically at To. it boils down to the fact that in the period of direct sluice ("compression"), when the pressure in the sluice rises too quickly or when the person in the sluice suffers some kind of stalemate. process in the hearing aid or nasopharyngeal space, perforation of the tympanic membrane can easily occur due to unbalanced pressure in the cavum tympani with external pressure. Therefore, the legislation of all countries prescribes the increase in pressure in the sluice in accordance with a special time table. In particular, the legislation of the USSR requires a gradual increase in pressure from normal to one additional atmosphere within 5 minutes; from one additional atmosphere to two atmospheres - 3 minutes, and in total from normal pressure - 8 minutes; from two to three atmospheres-2 min. (from the norm 10 min.); from three to four atmospheres-2 min. (from the norm 12 min.). On the other hand, it is required that people descending "41 "42 in the caisson, did not suffer from any stalemate. changes or processes in the hearing aid or nasopharyngeal space. Nevertheless, even if all precautions are observed, a person in the airlock, especially “a poorly trained person, may experience an unpleasant sensation and even acute pain in the ears due to the equalization of pressures on the eardrum from inside and outside. In this case, passing air through the Eustachian tube (by the Valsalva method or swallowing) opens it, due to which the pressure in the tympanic cavity quickly equalizes and discomfort and pain quickly disappear. That. damage to the tympanic membrane that may occur during the compression period are purely mechanical in nature and do not actually belong to caisson diseases. all the doors in the caisson open in the direction of greater pressure), and the people who passed through the lock pass through this chamber into the shaft pipe, go down the stairs to the working chamber, where they remain all the time of their shift. This time depends on the pressure in the caisson, and according to the new rules of 1930, at pressures up to 1.75 additional atmospheres, it should not exceed 7 hours. per day, from 1.75 to 2.5 additional atm. - 6 hours, from 2.5 to 3 atm. - 5 hours, from 3 to 3.5 atm.-4 hours. and over 3.5 atm.-2 hours, and in all these cases, mandatory two shifts are established for a person per day (with the exception of pressures over 3.5 atmospheres, for which one shift is established), including the specified time he spends in caisson in two steps. In this case, the specified time also includes the time of sluice, sluice, descent into the working chamber and ascent from it. During a stay in compressed air, usually a person does not experience any noticeable disturbances. At the end of work in the caisson, people go back to the lock for reverse locking (“decompression”); the door from the airlock to the equipment chamber is closed, and a slow decrease in pressure begins in the airlock until it is reduced to normal. Usually, the pressure reduction is carried out by the medical officer on duty. staff. The pressure reduction is carried out in accordance with special rules and, according to the legislation of the USSR, it must comply with the following. norms: when transferring a person from pressure to 1 ext. atm. in normal pressure, pressure reduction should last 5 minutes, from R / z ext. atm. to normal - 10 min. , from 1 "/" add. atm. to norm.--20 min., from 2 add. atm. to norm.-30 min., from 3 add. atm. to norm.-45 min., from 4 add. atm.up to norm.-1 hour.The most serious and life-threatening disorders in the body occur in the after compression period.If decompression is carried out quickly, in violation of the established norms, then in this period there may be cases of perforation of the eardrum with bleeding from the ears, but already due to the excess of internal pressure over external.However, such cases are rare, because violations of the norms of pressure reduction must be too gross for this.Decompression diseases depend on the fact that tissues and organs saturated with air (ch. arr. nitrogen) in during the stay of the body under pressure, they do not have time to get rid of it during decompression and the body goes into normal pressure with excess gas in the tissues. Saturation of the body with air (saturation) occurs through the blood, which transfers it from the lung tissue by diffusion to all tissues and organs. back to normal pressure, the reverse process occurs - desaturation of tissues and body fluids from excess gas. Its speed depends on the degree of saturation of the body with air (and this latter depends on the magnitude of pressure, the duration of its action and the saturation abilities of individual tissues), but the essence lies in the desire of excess gas (nitrogen) to pass from tissues saturated with it into the blood and get through it. into the exhaled air and leave the body with it. If the degree of saturation of the body with nitrogen is significant, then it is natural that significant amounts of nitrogen enter the blood vessels, the emboli of which, clogging various vessels, can cause corresponding disorders in the body. That. caisson diseases are a consequence of gas embolism of various localizations. Depending on the latter, all caisson diseases can be divided schematically into 3 groups. The 1st group includes local skin lesions in the form of skin emphysema, partly explained by gas embolism of the skin vessels, partly by the release of gas directly in the fiber; the phenomena of emphysema explain pruritus, although some consider itching to be caused by irritation of the posterior roots of the spinal cord with gas bubbles in the cerebrospinal fluid. Skin lesions are characterized by mottling or marbling, depending on the embolism of the superficial cutaneous veins. This group also includes the most common damage to the joints, bones and muscles in caissons (caisson rheumatism, "break" Russian caissons). The most frequent cases of caisson articular rheumatism, especially diseases of the knee joint. These cases are not uncommon even at relatively low pressures (up to 2 atm.). The mechanism of origin of these lesions is not entirely clear. It can be assumed that it comes down to pressure on the nerve endings of gas accumulations under the fascia, under the periosteum, in the yellow marrow of tubular bones, and also in the joint cavities. Symptoms of these diseases: increased tendon reflexes, sensitivity of the nerve trunks, swelling of the affected limb, friction noise, effusion and crunch in the joint. The 2nd group includes lesions of the central nervous system from embolism of its vessels and from the accumulation of gas bubbles in it. These lesions can affect both the spinal cord and the brain. Cerebrospinal lesions manifest themselves in the form of paraplegia (usually spastic), monoplegia, paralysis of the bladder and rectum, disorders of sensitivity and coordination, etc. These phenomena can be transient if gas accumulations and emboli resolve. If destruction of the nervous tissue occurs (chap. arr. in the posterior columns and posterior sections of the lateral columns of the thoracic part of the spinal cord) or hemorrhages into it (hematomyelia), then these phenomena remain persistent and often, after a few weeks, end fatally. Cerebral symptoms are reduced to dizziness, headaches, speech disorders, confusion, stupor. Collapse and death can occur as a result of gas embolism of cerebral vessels. Hemiplegia and convulsions, which are the result of focal softening of the brain, often join the above-mentioned brain phenomena. Accumulations of gas in the labyrinth can cause the onset of deafness and Meniere's symptom complex. Finally, the 3rd group includes phenomena that depend either on the slipping of large emboli into the right heart or on embolism of the coronary vessels with cardiac arrest and death per syncopen, or on blockage of the pulmonary vessels with the onset of death per asphyxiam. The latter case is characterized by severe shortness of breath with intense asthma attacks due to developing pulmonary edema. While the 1st group of caisson b-hers also occurs at relatively low pressures and is characterized by localized and transient lesions, the 3rd group is a generalized lesion, always with a rapid and violent lethal outcome and occurs after the transition from the highest pressures ( 4-3 atm.); The 2nd group occupies an intermediate position, develops after being under pressure of significant degrees (2.5-3.5 additional atm. ) and may either be limited to localized transient or persistent lesions or be characterized by generalized lesions with a fatal outcome. All diseases from compressed air are combined under common synonyms: aeropathy, aeremia, pneumatemia, etc. In experiments on animals and autopsies on people who quickly died in the decompression period, the right heart was found to be distended with a large amount of gas, and the venous system filled with gas bubbles. As a result, the blood foams when opened. Multiple gas embolisms were found in the coronary vessels. In the spinal cord in cases of paralysis during autopsy, hemorrhages and focal softening were found with localization mainly in the lower thoracic and upper lumbar parts, which is explained by their weaker vascularization. On the part of the lungs, edema and interstitial emphysema were detected during autopsy. The liver, spleen and kidneys are also affected at autopsy, although in vivo they did not give any symptoms. Cases have been noted of finding huge gas accumulations under the jejuni mucosa.-■ The rate of tissue saturation with gas, resp. nitrogen, depends on their properties. Thus, blood saturation occurs within 55 seconds, while adipose tissue is saturated slowly and at the same time it absorbs 5 times more nitrogen than blood and other tissues. That. this tissue, which makes up to 20% of the body weight and is weakly vascularized, will also be slowly released from the gas in the decompression stage, representing during this period a reservoir for nitrogen absorbed under pressure. Therefore, nervous tissue, subcutaneous tissue, bone marrow, joints (especially knees) are most often affected. To combat caissons, resp. decompression b-n I m and it is important, first of all, the corresponding prof. selection of workers. These should be people with a good cardiovascular system, able to cope with the transport of portions of gas from tissues to the lungs, with a slight development of adipose tissue, with a stable nervous system, etc. Working conditions (temperature, etc.) should not create obstacles to the normal functioning of the body, which is especially important in the decompression period; everything that can lower the body's resistance during this period (cooling, colds, etc.) can be a direct cause of decompression sickness and must be carefully eliminated. It is extremely important to comply with the norms of staying under pressure, and especially the norms of ejection. The latter plays a cardinal role in the prevention of caisson diseases. In addition to strict observance of the rules of egress and the appropriate conditions in the lock (proper t °, clean air, sufficient ventilation), it is important after a person leaves the caisson to excite his cardiac activity, for which it is advisable to immediately give workers hot tea or coffee, provide them with or (in a special room) a short rest to bring the thermostatic apparatus to a stable state, change clothes and dry in order to avoid colds. - Caisson diseases can occur not immediately after leaving the caisson, but also after a few (up to 24) hours. Therefore, it is necessary to observe appropriate precautions and some time after leaving the caisson. Special and special medical supervision at To. inevitable and necessary. are regulated in the USSR by the rules of the NCT of the USSR for No. 38 of 5 / P 1930, which normalize the issues of arrangement, equipment and maintenance of caissons, auxiliary premises and devices for them, prescribe all the necessary safety and hygiene measures when working in a caisson, measures to to the prevention of caisson diseases, establish rules for the organization of medical service, state contraindications to admission to K. r. and prescribe obligatory methods of treatment of caisson diseases. According to the Decree of the NCT of the USSR No. 156 of April 30, 1929 (section XI, paragraph 5), an additional two-week vacation is established for caisson workers due to the special hazard of work. The most effective way to treat decompression sickness is recompression, return to pressure, at which the person worked. To do this, the caisson work must always be provided with a treatment lock with appropriate equipment, where sick people can be brought in. Even in case of paralysis if defeats unstable, the person easily and quickly completely restores the health in to lay down. gateway. Lech. the lock must be equipped with beds, electric lighting, heating devices, equipped with a special window for monitoring the condition of the b-th from the outside and have a chamber for transferring medicines to the b-nom, etc. without changing the pressure in the lock. The recompression method is based on the fact that, under pressure, gas emboli decrease in size and dissolve, passing again in a dissolved state into the tissues. After recompression, when the person feels completely healthy, they begin to slowly and carefully reduce the pressure. The room in to lay down. the gateway of the sick person should occur as soon as possible and in any case not later than 12 hours later. after the onset of symptoms. Of the palliative measures, it is necessary to point to painkillers, a high rate. (expansion of blood vessels and acceleration of blood circulation), soothing ointments, massage, baths. These measures can be applied only in mild cases (occurring from low pressures up to 2 atmospheres). Lit.: Bobrov N. and Brener V., Quantitative and morphological study of blood in caisson workers, Labor Hygiene, 1927, L "" 7; Gushcha A., On the issue of the effect of increased atmospheric pressure on blood composition, Arkh. bislogical nauk, vol. XIX, issue 1, 1915 (lit.); Lpb about in B., On the influence of underground work on a person. Vrach, 1901, Lg "20-21 (lit.); R and v about sh O., Caisson works from the point of view of labor protection, Gig. Labor, 1924, L "° 6; Solovtsova A., On the question of the effect of caisson work on the blood, Russian doctor, 1914, No. 13-14, 17, 22-23; Heller R.., Die Caissonkrankheit, Dissertation, Zurich, 1912. See also foreign literature to the article Decompressive diseases. M. Jacobson.

CAISSON WORKS(prof. harmfulness and prof. disease). Occupational hygiene in the caisson. The caissons represent a device consisting of a working chamber, a shaft pipe extending upwards from it, ending at the top with a hardware chamber, and a sluice connected to the hardware chamber. The working chamber is that part of the caisson, in which the actual caisson work is carried out, i.e., excavation and excavation. Usually it is made of reinforced concrete, but it can be iron and even wooden. The shaft pipe is designed to lower people and materials into the chamber and to raise the excavated soil from it. It consists of separate links, built up one on top of the other as the caisson is lowered, and has a strictly vertical ladder for people. The hardware chamber contains simple mechanisms that serve to lift soil from the working chamber and lower materials into it and are usually serviced by two workers inside it. The lock has a special purpose of both medical and industrial nature, representing a chamber (or chambers), in which any air pressure intermediate between the external pressure and the pressure in the caisson can be created, without changing the pressure in the caisson itself. The creation of such intermediate pressures is necessary in order to protect people from the danger of damage and disease associated with pressure changes, as well as to maintain the necessary pressure in the working chamber when people go outside or when soil is given out and materials are fed. The working chamber usually employs from 6 to 14 people. When the caisson has reached the soil of the required stability, further excavation work is completed, the working chamber is filled with concrete, like the first link of the shaft pipe; the rest of the caisson is removed, and thus formed. the unfilled space in the masonry is also filled with concrete, after which the abutment is ready. Appointment K. r. consists in the fact that if the strength of the soil is insufficient for a given structure (when there is an aquifer under it) or if it is necessary to carry out work on the bottom of rivers, etc., abutments and supports are brought under the structure being erected (bridge, building, etc.) , brought to solid ground, as a result of which you have to pass through the water. For this purpose, in the corresponding layer, water is pushed aside by air injected under pressure into a special device called a caisson. The value of air pressure corresponds to the depth of the caisson; it is assumed that for every 10 m the depth of lowering the caisson, the pressure of the air supplied to it should increase by 1 atmosphere. Air is pumped into the caisson by compressors from the compressor station through air ducts. Since the air is very hot during compression, if special measures are not taken to cool it, it enters the caisson significantly heated, as a result of which in such cases the t ° in the caisson turns out to be excessively high. This also happens when the air distribution network is not insulated and is exposed to solar heating. In winter, non-isolation of the air duct network leads to the opposite results: the air in the caisson may come chilled, and the temperature in the caisson may be excessively low. Since air for compressors can be taken in an unfavorable (in terms of its dustiness) place, and since when it passes through compressors lubricated with oils, it can become contaminated with the latter, sometimes the air in the caisson can also be heavily polluted. Humidity in the caisson is always inevitably very high, exceeding 90% and often reaches full saturation. It is especially high in locks during the period of sluices, because due to the decrease in pressure, which constantly occurs in the lock, fog is formed in it and vapors condense into water. The same phenomenon takes place in the working chamber during the periods of landing of the caisson, carried out by lowering the pressure in it. Ventilation in the caisson depends on the amount of air supplied to it, as well as on the quality of the soil; with soils that are easily permeable to air (sandy), the ventilation of the caisson and, in particular, the working chamber is carried out satisfactorily; in the case of soil that is poorly permeable to air (clay - silty), ventilation of the caisson can suffer significantly if it is not provided with special measures. To ensure the necessary purity of air (freeing it from impurities of oils, condensate and dust), tanks are included in the air supply network, which, if necessary, can be equipped with filters. Days

Caissons and caisson works- Previously, this name (French Caisson) was applied to floating boxes, open at the top, in which masonry is erected, so that the box gradually sinks and finally sits on the bottom, and the masonry can be continued, as on land (see Pontoon box). Currently construction practice by the word K. means only a closed box from above, from which, after sinking to the bottom, the water is displaced by condensed air, so that the workers can move freely in it. Undermining the bottom under the edges of the box, they gradually deepen it until they reach a hard layer, which can serve as a reliable sole for the structure. This method of arranging the bases is generally called pneumatic. This method was tested for the first time in 1839 by the French engineer Triger when laying a coal mine in an aquifer in the Chalons mines near the Loire River and then was applied in 1850 in England by engineer Hughes to construct the foundations of the Rochester Bridge across the Midway River. The piers of this bridge were raised on cast-iron columns, 2.15 m in diameter, filled with concrete. In order to be able to perform work in the column, its internal space was filled with condensed air with the help of blowers, which displaced water from it through the lower, open hole. Two chambers were installed above the column - airlocks, which communicated through tightly closed doors both with outside air and with the working space in the column. The workers entered the lock chamber through the outer door and, closing it behind them, connected the chamber with condensed air to the working space of the column with the help of a crane. After complete equalization of pressure, it was possible to open the door leading from the lock chamber into the column and go down. In a similar way, only in the reverse order, the workers were released, and before opening the door leading out of the lock, compressed air was released from it with a tap. Through the same locks, the soil extracted from the bottom was carried out and materials were introduced to fill the columns with concrete. In this way, the sole of the bridge foundations was lowered to a depth of 18 m. When it turned out that compressed air makes it possible to work successfully and continuously both at great and shallow depths, regardless of various obstacles, such as the onset of floods, etc., this method began come into common use in the construction of bridges. The era of building large railway lines that came after this caused a rapid improvement in the pneumatic method of arranging foundations. In FIG. 1 shows a section of the bull of the bridge of the St. Petersburg-Warsaw road across the Neman, near the city of Kovno, built by the engineer Cezanne (C?zanne 1859), modeled on the Chegedinsky bridge built by him earlier over the Teissa River.

The caisson is a reinforced concrete or steel structure open from below (Fig. 1, a), consisting of a ceiling and side walls. The thickness of the walls of the caisson decreases from top to bottom, and they end with a console with a steel knife. The cavity at the bottom of the caisson is called the working chamber. It produces soil excavation, as the caisson descends under the action of its own weight, as well as the weight of the over-caisson masonry erected from concrete above the ceiling in the process of immersing the caisson into the ground. By supplying compressed air to the working chamber, water is squeezed out of it, which makes it possible to develop the soil dry.

Figure 1. Caisson: a - immersion of the caisson; b - caisson foundation; 1 - console; 2 - caisson masonry; 3 - pipes for compressed air; 4 - compressor station; 5 - central lock chamber; 6

Prikamerki; 7 - mine pipes; 8 - ceiling of the caisson; 9 - knife; 10 - working chamber of the caisson; 11 - masonry of the above-foundation part of the support; 12-concrete filling mine; 13 - concrete filling the working chamber; 14 - solid soil; 15 - weak ground.

Compressed air is generated by the compressor station and is supplied through pipes both to the working chamber of the caisson and to the lock apparatus. The latter consists of a central lock chamber and two closets - one for workers, the second for materials. The sluice apparatus is installed on two shaft pipes, which are assembled from separate metal links and used for lifting and lowering workers, as well as vertical transport of materials and soil. The descent of workers into the chamber of the caisson is carried out in the following order. Compressed air is released from the passenger cubby, which allows the outer door of the cubby to be opened inward, into which workers enter. The door is closed and compressed air is supplied to the closet from the central lock chamber. When the air pressure in the chamber becomes equal to the air pressure in the central lock chamber, the door between them is opened and the workers go into this chamber, and then they descend into the caisson chamber along a metal ladder installed in the shaft pipe. The lifting of workers into the central lock chamber and their exit to the outside is carried out in the reverse order.

The change in pressure from normal to increased (the locking process) and from increased to normal (the sluice process) in the passenger chamber must be done in such a way that the workers can gradually adapt to the new conditions. The time required for sluice and sluice, the greater, the higher the air pressure in the caisson.

To be able to squeeze out water from the working chamber of the caisson, the excess (above normal) air pressure in it must somewhat exceed the hydrostatic pressure at the level of the bottom of the caisson knife. The highest overpressure at which

people are allowed to work in a caisson, equal to 400 kPa. This determines the maximum depth of immersion of the caisson from the water level of 40 m.

After reaching the design depth of the foundation, the caisson chamber is filled concrete mix(Fig. 1b). Then the lock apparatus and shaft pipes are dismantled; the vertical shaft is filled with concrete mix. As a result, a massive deep foundation is obtained, on which the masonry of the above-foundation part of the support is erected.

Caissons are made at the place of lowering (on the natural surface or the surface of an artificial island) or away from it. In the first case, caissons with a width b, not exceeding 15 m, are made with a massive structure (Fig. 2, a); with a greater width, the side walls (consoles) are made massive, and the ceiling is hollow, consisting of beams (ribs) located in one (transverse) direction (Fig. 2, b) or in two mutually perpendicular directions (Fig. 2, c) , and slabs. The thickness of the slabs and beams is usually taken from 50 to 100 cm. The device of voids is resorted to in order to reduce the weight of the caisson during its manufacture and removal from the linings. In the manufacture of the caisson aside, its delivery to the dive site is carried out afloat. To give the caisson buoyancy, the structure is made as light as possible. For this purpose, not only the ceiling of the caisson is made hollow, but also its consoles (Fig. 2, d), the thickness of the beams (ribs) is taken from 20 to 40 cm, and the plates - about 15 cm.

According to sanitary standards, the height of the working chamber of the caisson should be at least 2.2 m. the slope of the lower section to a height of about 50 cm is assumed to be 1:1. The console is finished with a bench about 25 cm wide, which is reinforced with a knife made of sheet or profile steel. Reinforce caissons in accordance with the calculation of the forces arising in the cross sections of their elements during the construction of foundations.

Figure 2. Types of caissons: a - massive construction; b, c - with a hollow ceiling; g - with hollow ceiling and consoles.

The advantage of caissons over other types of foundations is that they allow the construction of a deep foundation in any hydrogeological conditions. In the working chamber of the caisson, it is possible to survey and even test the foundation soil, which is very valuable.

Caissons also have significant drawbacks, which primarily include the harmful effects of excess pressure on the body of workers, a large volume of concrete masonry in a massive foundation structure and the high cost of caisson

works. If it is allowed to stay under overpressure up to 175 kPa for no more than 7 hours a day, then under a pressure of 350-400 kPa the maximum residence time is only 2 hours, of which 1 hour is spent on locking and locking processes and only 1 hour is used for useful work . In this regard, the cost of caisson work increases sharply with an increase in the depth of immersion of the caisson into the ground.

Caissons and caisson works

Previously, this name (French Caisson) was applied to floating boxes, open at the top, in which masonry is erected, so that the box gradually sinks and finally sits on the bottom, and the masonry can be continued, as on land (see Pontoon box). At present, building practice under the word K. understands only a closed box from above, from which, after immersing it to the bottom, water is displaced by condensed air, so that workers can move freely in it. Undermining the bottom under the edges of the box, they gradually deepen it until they reach a hard layer, which can serve as a reliable sole for the structure. This method of arranging bases is generally called pneumatic. This method was tested for the first time in 1839 by the French engineer Triger when laying a coal mine in an aquifer in the Chalons mines near the Loire River and then was applied in 1850 in England by engineer Hughes to construct the foundations of the Rochester Bridge across the Midway River. The piers of this bridge were raised on cast-iron columns, 2.15 m in diameter, filled with concrete. In order to be able to perform work in the column, its internal space was filled with condensed air with the help of blowers, which displaced water from it through the lower, open hole. Two cameras were installed above the column - air locks, which communicated through tightly closed doors both with outside air and with the working space in the column. The workers entered the lock chamber through the outer door and, closing it behind them, connected the chamber with condensed air to the working space of the column with the help of a crane. After complete equalization of pressure, it was possible to open the door leading from the lock chamber into the column and go down. In a similar way, only in the reverse order, the workers were released, and before opening the door leading out of the lock, compressed air was released from it with a tap. Through the same locks, the soil extracted from the bottom was carried out and materials were introduced to fill the columns with concrete. In this way, the sole of the bridge foundations was lowered to a depth of 18 m. When it turned out that compressed air makes it possible to work successfully and continuously both at great and shallow depths, regardless of various obstacles, such as the onset of floods, etc., this method began come into common use in the construction of bridges. The era of building large railway lines that came after this caused a rapid improvement in the pneumatic method of arranging foundations. In FIG. 1 shows a section of the bull of the bridge of the St. Petersburg-Warsaw road across the Neman, near the city of Kovno, built by the engineer Cezanne (Cézanne 1859), modeled on the Chegedinsky bridge built by him earlier over the Teissu River.

The bull consists of a pair of cast-iron columns (one column is visible in the section), 3.22 m wide at the top and 3.50 m at the bottom. The column is made up of separate cast-iron links bolted together. The lower part of the column is separated by a ceiling from the rest, and two downcomers or mine pipes to the bell with airlocks installed at the top. Parts of the columns around the shafts, above the ceiling of the working chamber, remained open from above and were filled with water to sink the columns to the bottom. As the lowering progressed, new links of columns were built up and the shafts lengthened, at the top of which a bell with locks was again placed. These works were carried out from permanent scaffolding. The soil was raised through the shaft pipes in buckets, with the help of a handle and gear wheels installed inside the bell, and at the same time one bucket was raised and the other was lowered. After the columns were immersed to the required depth, the working chamber was filled with concrete, which formed a sufficiently strong layer to counteract the pressure of water from below. After that, water was pumped out of the upper parts of the columns, the shaft pipes and the ceiling of the working chamber were removed, and the rest of the space inside the columns was also filled with concrete. Concrete-filled tubular supports, lowered pneumatically, constitute a transitional step to the coffered foundations in modern form, in which K. of small height supports a masonry pillar that forms the support of the bridge. The upper part of the column in them is replaced by metal sheathing of small thickness, and sometimes the support is left without any sheathing, since the entire load is supported by masonry. In some cases, in order to save even more metal, they also make the chamber itself, that is, the working chamber, from masonry, in the form of a vault of clinker bricks, using metal only for shafts and locks, which, moreover, are removed after completion of work and suitable for further use. In America, wooden knuckles were also successfully used. Metal K., the most common, consists of a lower working chamber, usually from boiler iron, connected by means of vertical pipes (mines) to lock chambers (Fig. 2).

Sometimes the same shaft is used both for lowering workers into the chamber and for lifting the soil, sometimes separate shafts are arranged for the entry and exit of workers (the middle shaft in Fig. 2) and for excavation (both extreme shafts in the same Fig. .). Cranes are built into the walls of the airlock, on which a rubber tube from a blower is put on from the outside of the airlock to force air into the working chamber. The outer outline of the working chamber corresponds to the intended outline of the support. It can be oval, rectangular or polygonal. The height of the working chamber was: in the K. of the bridge across the Danube in Pest - 2 m, in the newest K. in France - 2.2 m, across the Elbe near Stendal - 2.6 m, across the Mississippi near St. Louis - 2.75 m, through the East River in New York (wooden k.) - 2.9 m. The ceiling of the chamber must be very solid, since during the sinking of the k. it supports the entire array of stone superstructure. Therefore, it is made up of a number of transverse and longitudinal beams of an I-section, between which arches of brick are removed. From below, the ceiling is sheathed with boiler iron, holes are left in it for mine pipes of a round or elliptical section. In order to avoid buckling of the side walls of the working chamber, a number of consoles or brackets made of boiler iron sheets are placed under each cross member of the ceiling. These brackets are attached both to the ceiling and to the walls of the chamber. At the same time, they serve as those ribs to which the iron sheets that make up the walls of the chamber are attached from the outside. The consoles are interconnected in two or three places in height by light beams. Sometimes the gaps between the brackets are filled brickwork(Fig. 3.).

Knife The chamber, i.e., the lower edge of K., is arranged so firmly that it cannot be damaged if, when immersed in the ground, K. gets on a stone or other solid body. The knife is usually reinforced with an iron square and two or more narrow strips of boiler iron. The walls of the working chamber are also reinforced with squares in several other places along the height (Fig. 2 and 3). The allowable stress of boiler iron in K., under ordinary conditions, is taken up to 1500 kg per square meter. see. The weight of the caisson (in kg) can be taken in preliminary calculations at 280 BUT+130AT, where BUT- bypass (in meters), B - chamber area (in sq. m). When constructing a working chamber from masonry, the K. knife is made of metal, and on top of it there is a metal flat ring that serves as the basis for the masonry of the chamber, and at the top of the vault a metal ceiling is closed up, from which shaft pipes go up (bridges across the Oder in Stettin and across the Elbe near Lauenburg, the Marman viaduct on the Garonne flood, the overpass on the Bessarabian branch of the Southwestern Railways). A gigantic example of a k. with a wooden working chamber represents the construction of a bridge over the East River in New York, where two wooden k. with a base area of ​​1594 and 1632 square meters were built for coastal abutments. m. To prevent a fire hazard, the walls and ceiling of the second, later built by K., were sheathed inside with boiler iron. Air locks are a very important part of the capital, and the success of the work, and sometimes the safety of the workers employed in the capital, depend on their rational design and proper operation. To avoid the installation of shaft pipes, locks are sometimes placed in the K. chamber itself, directly under the ceiling. This location provides great convenience for removing the soil excavated in the K., but at the same time, the locks can easily be damaged during sudden precipitations of the K., and therefore the location of the locks inside the working chamber is unsafe. When placing locks outside the working chamber above the ceiling itself, it is necessary to leave space for them in the masonry. Elevation of the locks above the water surface requires the construction of shaft pipes, which have to be increased as the K. lowers and, at the same time, the locks are removed and rearranged. In addition, it greatly complicates the excavation of soil, as well as the descent and exit of workers. But the location of the locks above the water horizon is the safest, and therefore this location is most often used. Gateways are single-chamber, two- and three-chamber. The first are used only when they are assigned exclusively for the movement of workers, and the excavation is carried out through other pipes. If the soil is carried out through the same pipe along which the worker moves, then in order to be able to continuously take out the soil, it is necessary to give the lock such dimensions that it is possible to put a certain amount of soil in it, which is sometimes thrown out, closing for this time the communication between the lock and the shaft pipe . At the same time, the excavation of the soil is interrupted for a while. After each ejection of the soil, it is necessary to re-inject compressed air into the lock (the bridge across the Oka on the Ryazhsko-Vyazemskaya railway). In two chamber locks, when soil is ejected from one chamber, its rise to the second chamber does not stop (Kovrovsky bridge across the Klyazma on the Nizhny Novgorod railway). The three-chamber sluice has the advantage that the excavation is carried out continuously; while one side chamber is being emptied, the excavated soil is folded into the second side chamber (bridges across the Dnieper near Kremenchug, Liteiny bridge across the Neva). In FIG. 4 and 5 show a three-chamber sluice of the Gaertner system.

Medium chamber B serves for entry and exit of workers, and two side C not communicating with the camera B, - for lifting and folding the soil. Main camera A is in constant communication with the shaft pipe, and hence with the working chamber. The soil is lifted with the help of a bucket elevator placed in the shaft, and the contents of the scoops fall out into the tray d, which can be moved with the help of a handle so that the right and left side chambers are alternately filled with soil. To dump the soil out of the chamber, open its valve at the bottom p which can be controlled from outside. Workers can descend into the mine through a hatch b at the bottom of the chamber B without interfering with the lifting of the soil. In addition, this chamber has two doors, of which one is external, and the other serves to communicate with the main lock chamber. A. Through such a gateway, up to 40 cubic meters can be taken out of K. m of soil per day. The essential accessories of locks are shutter doors and cranes. There are special mechanisms for opening and closing them. The cranes are controlled by a worker who fits in the lock (crane operator). One of these taps is connected to the outside air and, after closing the door leading from the working chamber to the lock, this tap is used to release compressed air from the lock. The second valve connects the airlock with the blower and serves to fill the airlock with compressed air after the workers enter the airlock and close the outer door. Shaft pipes are made of round or oval section, and one wide pipe or two pipes of small diameter are placed under the lock. If the soil is mined by elevators, then the dimensions of the mine pipes are quite significant, depending on the diameter of the pulleys and the size of the scoops. Air pipes are either copper or cast iron. In view of the fact that K. is constantly lowered, and the blower is often placed on barges, a metal air duct is connected to K. and to the air reservoir of the machine by rubber pipes with a spiral wire inside. The tube connected to the sluice is equipped with a valve that opens inwards, so that the air that is filled with K. cannot escape if the blower pipes and the machine are damaged. In general, it is necessary to take all possible measures so that the air pressure inside the k. could not fall below a certain limit, since in this case the working chamber can be instantly flooded, and the workers in it die. The excavation of soil is sometimes carried out with the help of a bucket elevator in an open pipe, lowered by the lower end into a hole dug in the working chamber, so that the pipe is always filled with water and compressed air does not have access to it (Cologne bridge over the Rhine). The inconvenience of this method lies in the fact that when the elevator breaks, it is necessary to correct it with the help of a diver, stopping work for a considerable time. Therefore, they usually prefer to lock the soil by installing a bucket elevator in a shaft pipe (Arzhanteilsky bridge across the Seine, a bridge across the Dnieper near Kremenchug), or by removing the soil with buckets lifted by workers using a winch installed inside the lock (bridges across the Oka on the Ryazhsko-Vyazemskaya railway, through Klyazma near Kovrov on the Nizhny Novgorod railway), or in bags (the bridge across the Volga near Syzran). Loose and liquid soils can also be removed mechanically, by the action of compressed air, using a sand pump. It consists of a gas tube laid vertically in the masonry (4-9 cm in diameter), the upper end of which is brought out and bent down so that the sand pouring from it can be lowered into the water or into a substituted vessel. In the working chamber, the tube ends with a tap, not reaching the bottom by 0.5 m. To remove the soil, a tap is opened, and then the compressed air, rushing into the pipe, carries with it the sand thrown up by shovels, and sometimes a funnel is placed under the pipe into which sand is poured (a bridge over the East River near New York). For the same purpose, in some cases, jet pumps are used, in which the crushed soil is carried away by a fast current of a water jet under high pressure (the bridge across the Mississippi at St. Louis). The descent of K. into the water at a shallow depth, up to 4 m, is carried out from permanent scaffolding (Fig. 6), but at a more significant depth, K. is installed on a barge or on a pontoons, the ship is flooded by loading it with stones, and the surfaced K. is brought between two by barges to the place designated for diving.

Sometimes floating scaffolds (the embankments of the port of Antwerp) or pontoons (the Tay bridge in Scotland) are used to lower the bridge. In all these cases, the movement of K. is directed by chains, with the help of which it is suspended from permanent or floating scaffolds. After launching K. into the water, they begin to erect it above the ceiling masonry, and as it rises, K. descends, and its movement is directed all the time by the chains supporting it. Having reached the bottom, K., together with the masonry located on the ceiling, settles to a more or less significant depth. Locks are installed on the mine pipes in advance and the air duct is connected to the blower, which can be installed either on the shore or on a ship anchored near the coffered scaffolds, and immediately start pumping air (Fig. 7).

Compressed air displaces water from the working chamber, so that the bottom in it is exposed. Then workmen enter the K. and dig under the lower edge of the K., which, as a result, sits deeper. Taken out from under the K. and over the entire surface of the bottom occupied by the K., the soil rises up into the lock, from there it is thrown out, onto barges or into the water. At the same time, above the ceiling of K., masons continue laying. As the shaft deepens, the masonry grows, the shaft pipes grow, and when the shaft finally sinks to the required depth, the entire working chamber, as well as the shaft pipes, are laid with a stone - and the foundation of the structure is ready.

In the past, it was decided to resort to the use of K. only if it was necessary to build foundations at depths of 9 to 10 m under water, at present this method is already used for depths of 3 to 4 m. The limit at which the use of K. becomes already profitable, consider the depth from 4 to 5 m. The most significant caisson work in Russia was performed during the construction of the Kyiv railway bridge (the first caisson work in Russia, in 1867, the builder was Major General A. E. Struve), the Kremenchug bridge across the Dnieper and the bridge of Emperor Alexander II (Liteiny) across the Neva, in St. Petersburg. Then follow the Alexander Bridge across the Volga at Syzran and many other railway bridges. Condensed sometimes up to 3 or more atmospheres, the air of the C. has a certain effect on the human body, which makes it necessary to take certain precautionary measures to preserve the health of people working in the C.. Only completely healthy and strong people should be allowed to do this work, and medical supervision should be established over them. A work shift should last no more than 6 hours. As the pressure increases, the duration of the shift must be reduced accordingly. It is necessary to let out workers from K. carefully. To accurately control the pressure in the working chamber K., manometers must be installed.

An underground or underwater part of a structure that transfers to its soil base the static load created by the weight of the structure, and additional dynamic loads created by wind or the movement of water, people, equipment or ... ... Collier Encyclopedia