Loading and unloading operations at the construction site. Loading and unloading works
Loading and unloading works in construction
Loading and unloading operations of the main material elements of construction processes (non-metallic materials, building structures, timber, metal, etc.) are now almost completely mechanized. For the mechanization of loading and unloading operations are used
general construction and special machines and mechanisms. According to the principle of operation, all machines and mechanisms that carry out loading and unloading operations are divided into the following groups: those that operate independently of vehicles and that are part of the design of vehicles. The first group includes special loading and unloading and conventional erection cranes, loaders of cyclical and continuous action, mobile belt conveyors, mechanical shovels, pneumatic unloaders, etc. The second group includes dump trucks, transport devices with self-unloading platforms, self-unloading facilities, etc. Special loading and unloading and conventional cranes (beam cranes, overhead cranes, gantry, tower, pneumatic wheeled and caterpillar boom cranes, truck cranes, etc.) are widely used for loading and unloading reinforced concrete and metal structures, equipment, materials transported in packages , containers, etc. Cranes equipped with special gripping devices and grabs can work on loading and unloading timber, crushed stone, gravel, sand and other bulk small-sized materials.
Loaders in construction have become widespread. The widespread use of loaders in construction is due to their high mobility and versatility. The most widely used in construction are universal single-bucket loaders, auto-loaders and multi-bucket loaders.
Bucket loaders (continuous action) are designed for loading bulk and small-sized materials into dump trucks and other vehicles.
Forklifts are general purpose material handling machines. They serve for the mechanization of reloading and lifting and transport operations on sites, mainly with a hard surface. The main working body is a telescopic lift with forks.
Types of soils, their technological properties.
In the construction industry, soils are called rocks that occur in the upper layers of the earth's crust. The properties and quality of the soil affect the stability of earthworks, the complexity of development and the cost of work. To select the most efficient way of performing work, it is necessary to take into account the following main characteristics of soils; density, moisture, cohesion, looseness and angle of repose. Density is the mass of 1 m3 of soil in its natural state (in a dense body). Humidity is characterized by the degree of saturation of the soil with water, which is determined by the ratio of the mass of water in the soil to the mass of solid particles of the soil and is expressed as a percentage. With a moisture content of more than 30%, the soils are considered wet, and with a moisture content of up to 5%, they are considered dry. Cohesion is determined by the initial shear resistance of the soil. From the density and adhesion between soil particles mainly. depends on the productivity of earthmoving machines. The classification of soils according to the difficulty of their development, depending on the design features of the earth-moving machines used and the properties of the soil, are given in the ENiR. So, for single-bucket excavators, soils are divided into six groups, for bucket-wheel excavators and scrapers - into two, and for bulldozers and graders - into three groups. When developing soils manually, they are divided into seven groups. Building codes and regulations set the slope steepness values for permanent and temporary earthworks, depending on their depth or height. The slopes of embankments of permanent structures are made more gentle than the slopes of cuts. Steep slopes are allowed when constructing temporary pits and trenches.
Due to the fact that some of the processes performed in the production of earthworks are associated with the passage of electric current through the soil (dehumidification by electroosmosis, thawing by current), the electrical conductivity of the soil is also of practical importance. Since the mineral particles that make up the soil are usually not conductors, the electrical conductivity of the soil depends on the degree of its saturation with moisture. In the process of earthworks, one has to deal with the phenomena of freezing and thawing of the soil, and these processes can be natural and artificial. Therefore, the thermophysical characteristics of soils are also important - their heat capacity and thermal conductivity. They are also more dependent on soil moisture, as the corresponding values for water are much higher than for mineral particles.
Types of earthworks
According to the duration of use, earthworks can be permanent or temporary. Permanent structures are constituent elements of facilities under construction and are intended for their normal operation. Such structures include canals, excavations and embankments of roads and railways, dams of hydraulic engineering and regulatory structures, water wells, etc.
Temporary earthworks are arranged during the construction of an underground or buried part of buildings, engineering networks, communications, etc. After that, they are partially or completely eliminated. The recesses, in which the width is commensurate with the length, but not less than 1/10 of the length, are called pits, with a width of less than 1/10 - trenches. Pit pits are dug out, as a rule, during the construction of the buried part of bulk structures (foundations, basement floors: technical rooms designed to accommodate equipment for sanitary and technological systems). Trenches are dug when laying linearly extended communications, external networks of water supply, sewerage, gas supply, heating, power supply, etc. When arranging excavations at construction sites that do not have width restrictions, as well as in order to ensure the maximum level of mechanization of earthworks, earthworks with a trapezoidal cross profile. Its main characteristics are depth (h), width along the bottom (b) and on top (B), laying of slopes (a), slope base, slope angle. The depth of development is determined by the difference in the marks of the day surface of the working (edge) and the bottom (slope base).
The width along the bottom of the excavation is equal to the width of the structure element being erected in the excavation (A) plus the size of the gaps (c), depending on the nature of the processing of the external surfaces of the element. The value of the broadening of the bottom of the pit (c) must be at least 0.6 m. In recesses of a rectangular profile, the value of the broadening, in addition, depends on the depth of the recess and the type of wall fastening. The width along the top of the excavation is determined as the sum of the width along its bottom (b) plus the value of the two slopes (a). Under the laying of the slope is understood the value of the projection of the slope line on the horizontal.
The reciprocal of the slope is called the slope factor (m). The value of m is determined by the type of soil, the degree of its watering, the duration of the excavation and its depth. The more monolithic the soil and the greater its water content, the greater the steepness of the slope of the excavation. With a depth of excavations of more than 6 m, it is necessary to install small horizontal platforms called berms. Slopes below berms tend to be less steep than those above berms. The exception is when the soils below the berms are dry and stronger than in the upper horizons. In temporary recesses, the steepness of the slopes is assumed to be greater than in permanent ones.
GROUND AT CONSTRUCTION SITE PLANNING
There are the following most common methods for determining L CP. :
a) analytical (method of static moments);
b) grapho-analytical (Kutinov's method);
c) graphic;
d) on the basis of a chess balance sheet;
e) based on linear programming (transport problem).
1 Grapho - analytical method
Based on the construction of graphs of progressive results on the sides of the construction site. The average distance of soil movement in this case is found by the formula
L CP \u003d L x 2 +L y 2, m
where: L x , L y - respectively horizontal and vertical projection L SR, m.
L x =W x /∑V Bi
where: W x , W y - the area of the figures, limited by the graphs of the cumulative results of excavation and embankment along the horizontal and vertical sides of the site, respectively, m 3.
2. Graphical method
after plotting the progressive totals on the sides of the construction site, parallel to the X and Y axes, the middle lines are drawn, spaced from the axes at a distance of V H /2 and V B /2. After that, the points of intersection of the middle lines with the graphs of cumulative totals are set and they are demolished on the site plan. At the intersection of the projection lines from the points, we obtain the position of the centers of gravity of the embankment and excavation, respectively. As L SR, the distance between the obtained centers of gravity is taken
3. Analytical method.
It is based on finding the centers of gravity of the cut and fill by the method of static moments of the cut and fill points relative to the X and Y axes according to the formulas
X V DH =S B y /∑V Bi =∑ V Bi х X Bi /∑V Bi , m
Y V DH =S B x /∑V Bi =∑V V i х X V i /∑V V i , m
X H CT =S H y /∑V H i =∑V H i x X H i /∑V H i , m
Y N CT =S N x /∑V N i =∑V Hi x X Hi /∑V Hi, m
where: S B y , S H y , S B x , S H x - static moments of excavation and embankment relative to the Y and X axes, respectively, m 4 ; V Bi , V Hi - the volume of the i - point of excavation or embankment, respectively, m 3 ; X Bi , X Hi , Y Bi , Y Hi - coefficients of the centers of gravity of the i -th point of the cut or embankment in the coordinate axes XOY.
After finding the centers of gravity of the excavation and embankment, L СР is determined as the distance between them according to the Pythagorean theorem
L CP \u003d (X V C.T. - X N C.T.) 2 + (Y V C.T. - Y N C.T.) 2, m
4. Based on the chess balance sheet
The distribution of soil from cut points to fill points can be carried out in the following ways:
a) common sense
b) by the smallest distances
At the final stage, the following soil movement distances are determined:
a) the total average distance of soil movement within the construction site L СР
L O CP =(∑V ij x L ij +∑V kj x L kj +åV p j x L p j)/(∑V ij +∑V kj +åV p j) , m
where: V ij , V kj - volume of soil moved from excavation points i or “pit” to embankment points j, m 3 ; L ij , L kj - distance of soil movement from excavation points i or “pit” to embankment point j, m.
b) the average distance of soil movement from the leveling cut to the leveling embankment L CP
L PL SR =∑V ij х L ij /∑V ij , m
c) the average distance of soil movement from the pit to the leveling embankment L CP
L K CP =∑V to j x L kj /∑V kj , m
When determining L O CP, the volumes of soil of the reserve and dump in case of a distance of removal or delivery of soil is more than 3. . .5 km are not taken into account.
5. Based on linear programming methods
average travel distance
L 0 SR \u003d L PL. SR. m
37 The calculation of LIA is to determine the required amount pumping units, filter pitch and depth of their immersion.
S=h gr +0.5+e ; m
where S is the required lowering of groundwater, m
h gr - groundwater height
e is the height of the capillary rise of water, m;
where k is the filtration coefficient
where Y is the pressure at the design point, m
H is the thickness of the aquifer
A \u003d √F u / π; m
where A is the reduced radius of the dewatering system, m
F u - reduced area of the inner contour of the wellpoint system, m
R=A+2*S*√k*H ; m
where R is the radius of influence of the system, m
Q c =(2*π*k*m*(H-Y))/(lnR/A); m 3 / day.
where Q c is the total inflow of water, m 3 / day.
Q c h \u003d Q c / 24; m 3 / hour.
where Q c h is the total inflow of water per hour, m 3 / hour.
where m is the average flow thickness, m.
N y =L ktotal /L before; PCS
where N y is the number of pumping units, pcs;
L ktot - the total length of the collector, m;
L before - the maximum length of the collector
L k = L ktot / N y ; m
where L k is the length of the collector per 1 unit, m
Q y =Q c / N y ; m 3 / day.
where Q y is the inflow of water to one installation, m 3 / day.
Q y h \u003d Q y / 24; m 3 / day
where Q y h is the influx of water to one installation per hour, m 3 / day.
n=L k /2*G; PCS
where n is the required number of wellpoints, pcs;
G – step of wellpoints, m.
q= Q y h / n; m 3 / day
where q is the water inflow to each wellpoint.
The limiting flow rate of one wellpoint is determined according to the schedule.
The distance from the aquiclude to the reduced GWL at the wellpoint is determined at a different step:
y g ’ \u003d y n -h in + ξ * Q y / (k * h) + 1.34 * 10 -7 * ξ 1 * Q y 2; m
where y g ’ is the distance from the aquiclude to the lowered GWL, m;
y n - the height of the pump axis above the aquiclude, m;
h in - the estimated suction lift of the pump
ξ - value depending on the service life of the installation at the facility
ξ 1 - coefficient of pressure loss in the suction system, day 2 / m 5.
Let's define the condition of water filtration:
y g \u003d H-S * (1 + 2 * π * Ф * m ’ / (N * n * ln (R / A)); m
where m ’ is the flow thickness on the wellpoint line, equal to y;
Ф – coefficient of resistance filtering;
According to the curve, we determine the pitch of wellpoints
Scraper traffic patterns
Depending on the size of the earthen structure, the location of cuts, embankments, cavaliers or dumps, the following schemes of their movement are most often used during the operation of scrapers: elliptical, "eight", spiral, zigzag, shuttle-transverse and shuttle-longitudinal.
Work "along the ellipse" (Fig. 1, a) and "eight" (Fig. 1, b) is applicable when erecting embankments from one- and two-sided reserves, when arranging excavations with laying soil in embankments, dams and caves, during planning work in industrial and civil construction. When working with the "eight" in one pass, the scraper performs two operations of loading the bucket and two operations of its unloading, which shortens the path of the idle run and, as a result, increases the productivity of the scraper.
Fig.1. Scraper movement pattern
a - along an ellipse; b - eight; in - in a spiral; g - zigzag; e - according to the shuttle-transverse scheme; e - according to the shuttle-longitudinal scheme; rectangles show loading areas; shaded rectangles - unloading areas
The spiral scheme (Fig. 1, c) is used in the construction of wide embankments from bilateral reserves or wide excavations with a height or depth of up to 2.5 m. At the same time, work is carried out without the arrangement of exits and exits.
Work "in a zigzag" (Fig. 1, d) is carried out during the construction of embankments up to 6 m high from reserves with a grip length of 200 m or more.
The shuttle-transverse scheme (Fig. 1, e) is used more often when erecting embankments and dams with a height of less than 1.5 m when working from bilateral reserves or when constructing canals and excavations up to 1.5 m with laying soil in dams or cavaliers. The productivity of the scraper along the zigzag is 15% higher, and with the shuttle-transverse - by 30% compared to the elliptical scheme.
The shuttle-longitudinal scraper movement pattern (Fig. 1, f) is used in the construction of embankments 5 ... 6 m high with slopes not steeper than 1: 2 ° with soil transportation from bilateral reserves.
The traffic pattern for each specific case should be chosen taking into account local conditions so that the traffic paths are the smallest. The greatest slopes of earth-carrying roads should be for scrapers: in the freight direction - when lifting - 0.12 ... 0.15, and when descending - 0.2 ... 0.25; in an empty direction - when lifting 0.15 ... 0.17, and when descending 0.25 ... 0.3.
Physical methods of drilling.
The main physical methods of drilling are thermal and hydraulic. Electrohydraulic, plasma, ultrasonic and some other methods are under development and production testing.
With the thermal method of drilling, rocks are destroyed by a high-temperature heat source - an open flame. The working body of the thermal drilling machine is a thermal drill with a fire-jet burner (Fig. VI. 3, a), from which a high-temperature gas jet is directed to the bottom of the well at supersonic speed. A mixture of finely dispersed kerosene with gaseous oxygen is fed into the combustion chamber through a nozzle. Formed inside the chamber, gaseous combustion products with a temperature of up to 2000°C under the action of pressure inside the chamber fly out at a speed of about 2000 m/s through the holes in the bottom of the burner and act on the bottom of the well. With the help of water, the burner is cooled and the destroyed rock is removed from the well.
Mobile thermal drilling machines on caterpillar and automobile tracks and hand-held thermal drills have, in principle, a similar device. A manual thermal drill (Fig. VI. 3, b) is a metal casing rod with a diameter of 30 mm, in which there is a burner with a cooling system. Kerosene and gaseous oxygen enter the burner at a pressure of 0.7 MPa, and water for cooling - at a pressure of 1.3 MPa.
Mobile thermal drilling machines can drill holes and wells with a diameter of up to 130 mm and a depth of up to 8 m, and hand-held thermal drills can drill holes with a diameter of 60 mm and a depth of 1.5 ... 2 m.
A variation of thermal drilling is the drilling of holes with the help of heated compressed air. In this way, holes are drilled with a diameter of 50 ... 70 mm and a depth of up to 2 m in frozen soils. For drilling, an installation consisting of a compressor, a heater and an air heater is used. From the compressor, compressed air is supplied through hoses to the heater through air tubes built into it and a preheating coke oven. A jet of compressed air, heated in an air heater to 90°C, is directed into the soil through a sleeve with a perforated tip, warms it up, loosens it and throws it out of the well.
The thermal method of drilling holes in comparison with the mechanical one is more efficient, and its productivity is 10...12 times greater when drilling the rocks of the crystalline structure.
The hydraulic drilling method (Figure VI. 3, c) is used to develop wells in light loams and quicksand. With this method, water is injected into the well through a string of pipes and a special slender nozzle attached to the bottom of the string. Water erodes the bottomhole, and the pipes sink into the ground. The hydro mass formed by the erosion of the soil is squeezed out under the pressure of water along the outer walls of the casing pipe, which is extracted from the soil by a winch. With the help of hydraulic drilling, wells up to 8 m deep can be drilled at a speed of up to 1 m/min.
Soil compaction with rollers
Rolling is carried out by self-propelled and trailed pneumatic rollers. The compaction force is achieved due to high contact stresses created by the gravity of the roller and the ballast load on the rolling plane (line) (up to 8 MPa).
Pneumatic rollers can be single-axle (weighing 10 - 25 tons), two-axle trailed (weighing up to 50 tons) and semi-trailed (single or two-axle weighing up to 100 tons). With light rollers, the required compaction of loose soils with a layer of 20-30 cm is achieved with a working width of up to 2.5 m. Heavy trailed pneumatic rollers weighing 25-50 tons provide soil compaction with a layer of 35-50 cm with a working width of 2.5-3.3 m semi-trailed pneumatic rollers are most effective, they provide high-quality compaction of cohesive and non-cohesive soils with a layer of 40 - 50 cm with a grip width of 2.7 - 2.8 m. ). Trailed and self-propelled drum rollers are less efficient than cam rollers due to the large area of pressure distribution.
To increase the contact pressure on the compacted soil and achieve high performance, cam or lattice rollers are used. The cams are steel profile pins 200 - 300 mm long, welded around the circumference to the drum shell. Such rollers are used to compact only cohesive soils. When compacting soils from coarse rocks, instead of cams, steel gratings from a corner or other steel profile are welded to the surface of the drums. Cam and lattice rollers provide soil compaction with a layer of 25 - 50 cm with a capture width of 2.7 - 3.3 m in 4 - 10 passes along the track.
Rolling of each layer of soil is carried out, as a rule, according to a spiral-ring pattern. The length of the grip is assumed to be 250 - 300 m. When compacting soils on grips of small width (it is difficult to turn the rollers), mainly self-propelled drum rollers are used, moving in a reciprocating pattern.
61. Compaction and vibrocompaction of soils.
The method of soil compaction by tamping is based on the transfer of shock loads to the compacted soil. Unlike vibration and vibrotamper methods, this method has a significantly higher impact energy due to the high speed of load application at the moment of impact of the working body with the soil, due to which this method provides compaction
cohesive and non-cohesive soils in layers of great thickness (practically up to 2 m). The method of soil compaction by tamping has found the widest application in industrial construction when arranging soil cushions under the base of the foundations of buildings and structures, process equipment and floors. This method is also used for ramming pits in subsiding soils when constructing columnar foundations.
The combined method of soil compaction is based on the use of various combinations of the impact on the soil of static, vibration, vibrotamping and tamping loads. This method allows you to compact all types of soils and is mainly used for a wide range of works.
The method of soil compaction by vibration is based on the transmission of mechanical harmonic vibrations from working bodies (drums, wheels, plates, vibrating heads) to the compacted soil. The vibration method is divided into superficial and deep. The method of surface vibrocompaction of the soil is characterized by the fact that during operation the compacting working body is located on the surface of the soil and, making oscillatory movements, acts on it. With the deep method, the compacting working body is located inside the soil during operation.
The surface vibration method has found application in the compaction of non-cohesive and weakly cohesive backfill soils. The deep vibration method can be effectively used in the compaction of sandy soils, especially those in a water-saturated state. Depending on the main parameters of vibration, which are the frequency and amplitude of oscillations, vibration machines for surface soil compaction can also operate in vibro-impact mode. The amplitude of their oscillations is much larger, and the frequency of oscillations is less than that of vibration machines. In this case, vibration machines are called
vibrotamping, and the method of compaction is vibrotamping. The method of compacting soils by vibrotamping has found application in construction when compacting backfills in cramped places.
62. Deep compaction of soils.
Compaction with soil piles, displacement of soil during its radial compaction in the process of punching or punching wells and subsequently filling them with soil and layer-by-layer compaction
Deep compaction methods:
Physical
Soak
Drainage (vertical drainage)
Mechanical
Vibrocompaction
Soil compaction with piles
Soil compaction with pneumatic punches
Compaction with a spiral screed
Sealing with a working body in the form of a screw pile
Combined
water + vibration
(hydro-vibration compactor)
When compacting the soil, it is necessary to ensure optimal moisture, at which the least energy consumption is required.
With sequential compaction, work is performed in a checkerboard pattern. The impact method is used to form wells. Duration of compaction of 1 layer - 30 sec. With 10-15 hits. For bulk and subsidence soils to a depth of 5-25 m. The surface (buffer) layer should be compacted.
Deep vibration compaction - for sandy water-saturated bases: bulk and alluvial sands. The implementation of the method is carried out by successively immersing the vibrating bar into the soil while simultaneously supplying water through the internal cavity, after immersing the vibrating bar to the required deep water supply stops and is carried out in addition to 4-5 lifting-lowering dry . Deep compaction with pre-soaking - for the device of subsidence properties reduced by deformability and compaction of soils: loess, loam, silty soils with a high filtration coefficient of at least 0.2 m / day. The compaction process is carried out under the action of the soil's own mass during soaking, and is quite long 2-3 months. Reducing the time of soil compaction up to 3-7 days is achieved with the use of additional compaction due to comflet explosions.
63. Quality control of soil compaction.
The quality of soil compaction can be controlled by the following most common methods: standard, cutting rings, radioisotope, probing, stamping, waxing, hole method. The choice of one or another method depends on the equipment of the laboratory, the nature of the structure, the volume of the embankment being erected and their class. seals determine the optimum moisture content and the maximum standard density using the SoyuzdorNII device. The method of cutting rings in determining the density of the soil skeleton in embankments is based on determining the density of wet soil in the volume of a metal ring with a capacity of 300 ... 400 cm3 (d / h = l), pressed into the compacted layer, and the moisture content of this soil. due to its simplicity, it is the most acceptable and widespread. Currently, radioisotope methods are most widely used in construction practice, since soil field laboratories on large earthworks were equipped with devices that use the absorption and scattering of gamma radiation and neutrons. The method of static and dynamic sounding as one of the types of control of the degree of compaction of soils in embankments and backfills is the most efficient and simple of all existing methods of control. The stamp indentation method is used to determine the strength of soil foundations. In particular, this method is widely used to control the quality of soil compaction of foundations under the floors of industrial buildings and foundations. The waxing method is mainly used to control soil compaction in winter conditions. clods. The quality of the soil laid in the body of the embankment can be considered acceptable if the number of control samples with a soil density deviating from that specified by the project does not exceed 10% of the total number of control samples taken on the site, and the density of the soil skeleton in the samples should be no more than 0.5 g/cm3 below the density required (minimum).
64. Closed development of soils by a puncture method.
A puncture is the formation of holes due to the radial compaction of the soil when a pipe with a conical tip is pressed into it. The indentation is made with a hydraulic jack. A pipe link with a tip is laid in the pit and, after alignment with a jack, is pressed into the ground for the length of the rod stroke. After the rod returns to its original position, a pressure pipe (ramrod) is inserted into its place, and the process is repeated. At the end of the indentation of the first pipe link to the full length, the ramrod is removed, the next link is lowered into the pit, which is butt welded to the one already crushed into the ground. Next, the welded link is crushed, and the cycle is repeated a sufficient number of times until a puncture over the entire length of the section that cannot be dug in the traditional way. For each cycle, the pipe advances by 150mm. This method is practiced in highly compressible soils, holes are “pierced” for pipes with a diameter of 100 to 400 mm at a depth of more than 3 m. In slightly compressible soils (sand, sandy loam), in order to ensure the stability of the walls, in addition to the horizontal force, it is necessary to apply transverse and vibration effects. At the same time, holes with a diameter of up to 300 mm are made.
65. Closed development of soil by punching.
The method is used for laying steel pipes with a diameter of 500 mm to 1800 mm, or collectors of square (rectangular) cross-section at a distance of up to 80 m. The technology is as follows: pipe links are sequentially pressed into the soil, inside which the soil is developed and removed by means of a screw installation. In easily eroded soils, removal is carried out by the hydromechanical method (the soil inside the pipe is washed away with a jet of water and the pulp is pumped out with a pump). Often pipes are used as cases for placing the main pipelines in them. The method of horizontal drilling in closed excavation.
Drilling is used for laying pipelines in clayey soils with a diameter of 800 to 1000 mm for a length of up to 100 m. The end of the pipe is equipped with a cutting crown of increased diameter, the pipe is driven by a motor installed on the edge of the pit. The translational movement of the pipe is reported by a rack jack with an emphasis on the back wall of the pit. The soil that fills the pipe from the inside can be removed through the pipe being laid using a screw installation using a hydromechanical method by washing out the soil inside the pipe with a jet of water and then pumping out the pulp with a pump (in easily eroded soils) or bailers with an extension of their handle.
Purpose and types of piles.
According to the method of deepening into the ground, the following types of piles should be distinguished:
a) driven reinforced concrete, wooden and steel, immersed in the ground without excavation with the help of hammers, vibrators, vibropressing and indenting devices, as well as reinforced concrete shell piles buried by vibratory drivers without excavation or with partial excavation and not filled with concrete; b) reinforced concrete shell piles, buried by vibratory drivers with excavation of the soil and partially or completely filled with a concrete mixture; arranged in the ground by filling drilled wells with a concrete mixture or installing reinforced concrete elements in them; and driven piles, in addition, on low-compressible soils you. Hanging piles should include piles of all types, based on compressible soils and transferring the load to the foundation soils with their side surface and lower end. Driven reinforced concrete piles with a cross section of up to 0.8 m incl. and shell piles with a diameter of 1 m or more should be divided: a) according to the method of reinforcement - into piles and shell piles with non-stressed longitudinal reinforcement with transverse reinforcement and prestressed with rod or wire longitudinal reinforcement (from high-strength wire and reinforcing ropes) with transverse reinforcement and without it; b) according to the shape of the cross section - into square, rectangular, tee and I-section piles, square with a round cavity, hollow round section; c) according to the shape of the longitudinal section - into prismatic, cylindrical and with inclined side faces ( pyramidal, trapezoidal, rhomboid); d) according to design features - into solid and composite piles (from separate sections); hollow piles with a closed or open lower end or with a camouflage heel. Stuffed piles are divided into: a) stuffed open, arranged by immersing inventory pipes, the lower end of which is closed by a shoe or concrete plug left in the ground, with the subsequent extraction of these pipes as the wells are filled with concrete mixture; in the form of a pipe with a pointed lower end and a vibrator fixed on it; Drilled piles according to the device are divided into: a) bored piles of a solid section with and without widening, concreted in wells drilled in silty-clay soils above the groundwater level without fixing the walls of the wells, and in any soils below the groundwater level - with fixing the walls wells with clay mortar or inventory retrievable casing pipes; b) bored hollow circular cross-section, arranged using a multi-section vibrocore; the formation of widening with an explosion and filling the wells with a concrete mixture; with or without broadening, laying monolithic cement-sand mortar and lowering cylindrical or prismatic solid-section elements with sides or diameters of 0.8 m or more into the wells; reinforced concrete pile.
Separate concreting
Classification of construction cargo and modes of transport. Transportation of building materials
During the construction of any building or structure, certain transport and handling operations are performed related to the delivery of various materials, semi-finished products and products from the places of manufacture to the construction site. The elements delivered for the construction of the structure are called construction materials.
Depending on the physical and geometric characteristics, building materials are divided into 9 types: bulk (sand, crushed stone, gravel, soil); powdered (cement, lime, gypsum, chalk); doughy (concrete mixture, mortar, lime dough); small pieces (brick, blocks, etc.); piece (window and door blocks, floor slabs and coatings); lengthy (trusses, timber, columns); liquid (gasoline, lubricants); large-volume (sanitary cabins, block rooms, etc.); heavy (reinforced concrete elements of considerable mass, construction machines, etc.).
Based on the variety of construction cargoes, a wide variety of means of their transportation have been used in construction, and appropriate means of loading and unloading them have been developed.
Transportation of building materials is carried out by vertical and horizontal transport.
Vertical transport designed to perform loading operations at the factories supplying building structures, unloading operations when receiving materials and products arriving at the construction site, when transporting goods vertically from the ground to the place of work.
Horizontal transport they transport construction goods from the place of their receipt to construction sites and directly at the facilities themselves, if not individual buildings are being erected, but a whole construction complex.
Horizontal transport in relation to the construction site is divided into external and object. By external transport, building materials, structures are delivered to the construction site from supplying plants, quarries, warehouses to the facilities under construction. Object transport move construction cargo within the construction site.
In construction, the transportation of goods is carried out by all types of modern transport. The choice of vehicles depends on the type of cargo being transported; dimensions and weight of structures and parts; method of transportation; dimensions of spatial elements; transportation distance; permissible speed of cargo transportation; method of unloading cargo; type of road, slopes, outdoor temperature and transported cargo; transportation conditions.
Vehicles are:
- cyclic action: a) rail - railways of normal (broad) or narrow gauge; b) trackless - automobile and tractor;
– continuous action – hydraulic; conveyor (with the help of a conveyor) and suspended.
Vehicles are selected on the basis of their technical and operational indicators (carrying capacity, possible speed of movement, productivity, road requirements, coverage, cost of operating vehicles and roads, ease and reliability in operation and the possibility of using to move other goods); the conditions in which they will be applied (the relief of the construction site, the dimensions of the structure in the plan and the relative height position of cuts and embankments, the volume of earthworks, deadlines, operating parameters, the availability and condition of roads, etc.).
Automobile transport widely used for the delivery of construction materials to the construction site. In construction, vehicles with a carrying capacity of up to 12 tons and trailers for caterpillar tractors with a capacity of 9–12 m 3 are most common. This is due to the possibility of their wide application for the transportation of various materials, a large range of carrying capacity, and a relatively simple road design.
Tractor transport used to deliver goods over short distances and in case of off-road. Advantages: high productivity, the ability to use on objects with different volumes of work, less demanding on roads and dependence on weather conditions in comparison with road transport, the ability to use on steep slopes (up to 0.15).
Disadvantages of tractor transport: low travel speeds, limited use for long hauling distances. The economical hauling distance, when caterpillar tractor transport can compete with automobile transport, does not exceed 600–800 m.
Railway transport is mainly an external transport for transportation over long distances.
Railways of the construction site are arranged with a wide gauge of 1520 mm if railway transport is provided for in the project of the enterprise under construction; as well as with a large volume of cargo delivered by him to the construction site (more than 1 million tons per year). Narrow-gauge roads with a width of 750 mm are used when transporting goods from quarries to the construction site, if for some reason it is impossible to use more efficient modes of transport - cars, trolleys, long-range conveyors.
The use of railway transport is limited by the high cost of the railway track, as well as the track conditions: maximum slopes - 0.03–0.05; curvature radii for wide gauge - 200–300 m, for narrow gauge - 60–100 m.
Special modes of transport
Specialized vehicles are designed to transport certain categories of goods: concrete mix, mortar, powdered building materials, large-sized reinforced concrete structures, etc.
For bulk transportation of powdered materials (cement, lime, gypsum, etc.), cement trucks equipped with self-unloading devices are used.
Large-sized reinforced concrete structures are transported mainly by road trains, consisting of an automobile tractor and specialized trailers and semi-trailers.
Depending on the type of transported construction cargo, semi-trailers are used: plate carriers, bulk carriers, panel carriers, farm carriers, sanitary cabin carriers, block carriers.
Special types of transport include vehicles for technological purposes, in which the processes of transportation are combined with the technological processing of this construction cargo:
- truck mixers - they simultaneously carry out the processes of preparation and transportation of the concrete mixture to the construction site;
- truck-mounted concrete pumps - combine the transportation of the mixture over long distances and its laying;
- concrete trucks - combine the transportation of the mixture and its mixing.
Of the special types of (in-building) transport, belt conveyors, cable cars and pipelines are used.
Belt conveyors are most widely used in factories of reinforced concrete products (concrete products) for the transportation of aggregates, concrete mix, small-piece materials (bricks, etc.).
Suspended rope transport is used to deliver construction materials in conditions of rugged terrain and water barriers.
Pipeline transport is used to deliver some building materials: soil washed out by water, concrete mixture, mortar for plastering, cement, etc. are moved through pipes.
Loading and unloading work at a construction site
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Loading, unloading and warehousing of materials are the most time-consuming in the overall process of moving goods. In order to reduce manual costs in loading and unloading operations and to facilitate heavy labor, it is necessary to increase the degree of mechanization of these works.
The organization of loading and unloading operations should ensure their comprehensive mechanization with the utmost reduction in the number of transshipments. The composition of mechanized complexes includes both general construction and special machines and mechanisms.
General construction machines (tower, shooting, gantry, overhead cranes, beam cranes, excavators of various types) are used for loading and unloading piece, heavy, long and large-volume structures and materials, as well as bulk materials and containers with low-flowing materials.
The use of special loading and unloading machines determines the type of cargo.
Special loading and unloading machines are cyclic and continuous.
The most widely used in construction are various self-propelled loaders and belt conveyors.
Loaders (universal single-bucket, multi-bucket, auto-loaders) have high mobility and versatility.
Universal shovel loaders can be equipped with a bucket, fork lift, jaw gripper, dozer blade, ripper, excavator bucket and other working parts. They are used not only for loading and unloading operations, but also for moving various goods over short distances.
Forklifts, as well as universal shovel loaders, have various interchangeable working equipment - crane booms, jaw grippers, buckets, forklifts and other devices. They are used on sites with a hard surface.
Bucket loaders are classified as continuous machines and are used to load bulk materials into vehicles.
Belt conveyors are also continuous machines and are used for loading and supplying loose, small-piece and some dough-like materials (concrete mixtures) to the place of laying.
Conveyor systems consisting of individual conveyors can be several kilometers long.
In order to reduce manual labor, increase the productivity of vehicles, ensure better safety of transported goods and create conditions for the mechanization of loading and unloading operations in construction, containerization and packaging methods are widely used. The essence of these methods is to combine small-piece building materials at factories that produce them (brick, ceramic stones, small wall blocks, etc.), or at the bases of production and technological equipment (finishing materials, roofing, electrical materials, etc.) into enlarged packages or containers.
A package is a batch of cargo laid on a special pallet, a container is a multi-turn volumetric device. There are universal containers used for the transportation of various categories of goods, and special ones, designed for the transportation of a certain type of cargo. With the help of handling and transport vehicles, packages and containers are moved from the place of production or assembly to the construction site or factory.
Depending on the method of delivery, goods are divided into piece, bulk and bulk. All of them, in turn, are divided into other types:
piece - into small pieces (weighing up to 50 kg) - wooden and metal products, roofing and heat-insulating materials, packages, packaged pieces, etc.; building structures - panels, trusses, blocks (sanitary cabins, elevator shafts); rolled metal - rod, corner, channel; and lashes of pipes; containers and packages; sets of cargoes (piece cargoes selected for the technological stage); lengthy; technological equipment and construction vehicles (when transported to facilities); forest - round wood,;
bulk - for bulk (, non-metallic materials) and blocky (rock, rubble); porous aggregates for concrete (thermolite, agloporite); powdery and dusty materials (cement, lime, ash, mineral powder); bulk - on water; semi-liquid cargoes (concrete and mortar mixes); bitumen and mastics (heated up to 200°С); binder load - hot asphalt; lime milk; liquid fuel.
The most effective form of material and technical support (MTO) of the facilities under construction is a complete set - a complete supply of materials, products and structures on time, subordinating the MTO system to the technological rhythm of in-line industrial construction. Complete delivery of goods to the construction site is calculated in advance and prepared by the production and technological equipment management service (UPTK).
There are three main types of kits: technological, delivery and transport. Technological kit - a set of material resources required for the construction of an object or its part (floor, section, grip), delivery kit - part of the technological kit supplied to the construction site in order of priority by timing, transport kit - part of the supply kit delivered to the construction site for one flight, taking into account the technological sequence of the construction of the object.
In order to improve the storage of goods in the UPTK and at the facility, as well as to increase the level of mechanization of loading and unloading operations, containers and packages are widely used during picking. A container is an inventory special reusable container for bulk piece building materials and products, adapted for mechanized loading, unloading, short-term storage of goods. By carrying capacity, containers are divided into low-tonnage (0.625 and 1.25 tons), medium-tonnage (2.5 and 5 tons) and large-tonnage (10, 20 and 30 tons). A package is an enlarged batch of piece cargo (boards, joinery, bricks). Packaged goods are transported on pallets, which by their design are divided into flat, rack and box.
In addition to the advantages discussed above, the equipment provides: centralized delivery of material resources directly to the construction site; improvement of warehousing and loading and unloading operations; reduction to a minimum of stocks of materials at the construction site; liquidation of intermediate warehouses of materials in all parts of construction organizations; high labor productivity.
Loading and unloading works currently continue to be very labor intensive, they employ about 10% of all workers in construction. To reduce the labor intensity of these works, they should be carried out in strict accordance with the PPR, which reflects the volume of cargo transportation by nomenclature and terms, the organization of storage facilities at the facility, the location and equipment of construction cargo unloading points, the procedure for unloading and storing main cargo.
Loading and unloading operations must be carried out in a specially designated area with an even and durable surface (concrete, crushed stone, plank) and in compliance with. It is allowed to carry out work on planned unpaved areas capable of absorbing the design (according to the project) load from stored goods, vehicles and hoisting and transport machines.
Carrying out loading and unloading operations should be mechanized as much as possible. The level of mechanization is determined by the coefficient
where Q - the amount of cargo loaded or unloaded in a mechanized way 20bsh - the total amount loaded or you. loaded cargo.
A large number of specialized loading and unloading machines are used in construction. According to the principle of operation, they are divided into machines and installations of cyclic, continuous and pneumatic action, as well as machines designed to work with bulk materials in railway transport:
cyclic machines - used when working with bulk cargo: equipped with a straight shovel, dragline, loading buckets or special loading equipment; planner excavators; single-bucket universal loaders; electric forklifts; special loaders and unloaders; cyclic machines used to work with piece cargo include various types of self-propelled jib cranes; conventional design and loader cranes; gantry loader cranes, timber loaders, electric pilers, electric hoists;
machines of continuous action - designed for scooping, transportation and loading of bulk and small-piece cargo in a continuous stream: bucket loaders; conveyors (belt, bucket belt, elevators, screws);
pneumatic machines - used for cargo processing of powdered and pulverized building materials: pneumatic unloaders of suction and suction-pressure action; pneumatic screw lifts and pumps; chamber and jet pumps; aeration installations; pneumatic bottom and tank unloaders;
machines and installations for unloading railway cars and platforms with bulk cargo: various types of unloading machines operating on the conveyor principle of loading and transporting cargo; machines and installations for restoring the flowability of frozen materials based on loosening (vibratory rippers, vibro-impact action, drill-cutting rippers) and cutting; gondola car cleaning machines; hatch lifts; shunting devices (for the movement of wagons along the unloading fronts).
Transportation of building materials includes loading at the place of departure and unloading at the place of arrival. The processes of loading and unloading are currently fully mechanized; for these purposes, machines and mechanisms of general and special purposes are used.
According to the principle of operation, all mechanisms for loading and unloading operations are divided into two groups that operate independently of vehicles and mechanisms that are part of the design of vehicles.
- 1. The first group of mechanisms includes all types of cranes, cyclic and continuous loaders, mechanical shovels, mobile belt conveyors, pneumatic unloaders, etc.
- 2. The second group includes dump trucks, vehicles with self-unloading platforms, autonomous vehicles for self-unloading and loading, etc.
Cranes boom automobile, pneumatic-wheeled and caterpillar, tower, gantry, bridge, beam cranes are widely used for loading and unloading reinforced concrete and metal structures, equipment, materials transported in packages, containers, etc. Cranes equipped with special grippers and grabs are used for loading and unloading timber, crushed stone, gravel, sand and other loose and small-sized materials. Cranes equipped with special bucket bunkers are used to supply the concrete mix to the work site.
Loaders are widely used in construction. With their help, they perform a significant amount of loading and unloading operations due to their high mobility and versatility. The most widely used in construction are universal single-bucket loaders, multi-bucket loaders and forklifts.
Single-bucket self-propelled loaders are equipped with a bucket for loading and unloading loose and lumpy materials. As attached and replaceable equipment, they can be equipped with fork lifts, jaw grip, bulldozer blade, ripper, backhoe excavator bucket. Single-bucket loaders are produced with front dumping of the bucket, unloading to the side and unloading back. At construction sites, loaders are used to unload and move goods over short distances, move them to lifting and transport mechanisms, to load receiving hoppers of mortar and concrete units, and for various auxiliary works.
Bucket loaders (continuous action mechanisms) are designed for loading bulk and small-sized materials into dump trucks and other vehicles. This is a self-propelled machine, on the frame of which a scooping mechanism is fixed - a feeder and an elevator or conveyor. Such machines are produced in several types; they differ in the design of the feeder - raking screws, scooping ball head, raking paws, etc.
Forklift trucks have a telescopic fork lift as a working body; crane boom, bucket, clamps for piece cargo and other devices are used as interchangeable equipment.
Loaders with a telescopic boom are widely used, which can be called universal, as they are able to load bulk building materials, containers, and can also be used as lifts with a platform for workers. Lifted loads reach (from different manufacturers) 3.2...4.5 m, lifting height - up to 13 m. , various buckets, crane hook, buckets for concrete. The speed of movement of loaders reaches 25 km/h. Two- or four-wheel drive, hydrostatic transmission and 90° rear axle swivel provide high power and agility. The advantage of this type of loaders is the full lifting and lowering of the boom within 10 s, extension and retraction - up to 14 s, respectively. The telescopic loader can be used due to this as a controlled belt conveyor for moving goods through openings into and out of the premises. When the loader is working with an aerial platform, all the control functions of the mechanism and boom can be switched to the platform.
Self-unloading vehicles, in addition to dump trucks and cement trucks, include cars with craneless self-unloading devices for long structures or autonomous crane devices. building dwelling
The mass use of small-piece materials and products at construction sites has led to packaging - the formation and fastening into an enlarged unit of such goods, which ensure their integrity, safety when delivered under established conditions and allow mechanizing loading and unloading and storage operations. Special technical means are used - packages, universal and special containers, designed to transport a certain type of cargo.
Transport and loading and unloading operations in construction have a large share, they account for over 42% of the total labor intensity of construction and installation works. Therefore, it is very important to use mechanization as widely as possible, and in some cases complex mechanization, in the performance of these works.
Complex mechanization of loading and unloading operations. involves mechanized loading and unloading of goods and containers with a minimum number of reloads, with the lowest cost and labor intensity, while maintaining the original quality of goods in transit.
Transport in relation to the object under construction is divided into external and intra-construction; the latter is used within the construction site for the delivery of materials and structures to workplaces (to the crane operation area).
For the production of loading and unloading operations, mechanisms are used: tower and boom cranes (caterpillar and pneumatic wheels), forklifts, universal bucket loaders, etc. The use of an integrated system of containerization and palletizing of goods is effective, as well as the delivery of prefabricated structures in enlarged units using special vehicles in a strict technological their installation sequence.
Handling equipment used for loading and unloading operations must meet the requirements of GOSTs, and load handling equipment must have a stamp indicating the maximum load capacity. Organizations developing load gripping devices must have special permits from the supervisory authorities (Gosgortekhnadzor, etc.).
Loading and unloading operations are classified as the most labor-intensive, which encourages the widespread use of various means of mechanization that reduce the number of workers, reduce the downtime of vehicles and protect goods from arbitrary falling. Prefabricated reinforced concrete structures for their capture, lifting and delivery to the place of unloading are equipped with load-gripping loops or special devices (holes; protruding consoles, etc.).
Specialized vehicles are used for the transportation of long structures or structures that need to be laid and strengthened during transportation in special ways: trusses, beams, panels, floor slabs, sanitary cabins, etc. Most often, a road train includes a truck tractor and specialized semi-trailers-dissolutions.
Wall panels are transported on backbone, cassette and platform panel carriers. Spatial load-bearing frame of backbone panel carriers has a trapezoidal cross-section and a small loading height. More versatile are cassette panel carriers. Rafter and sub-rafter trusses are transported by semi-trailers. Floor slabs and coatings, as a rule, are transported on slab semi-trailers; beams, respectively, on bulk carriers.
Structures and products whose dimensions exceed the allowable dimensions (width - 2.65 m, height from the level of the carriageway - 3.8 m) are considered oversized and are transported according to special rules, with the permission of the traffic police.
Structures, as a rule, have two support points, under which wooden linings of rectangular section are laid. Structures with one-sided reinforcement (slabs and beams) are transported in the working (design) position - the working reinforcement is at the bottom. Panels that are not designed to work in a horizontal position, as well as products made of lightweight concrete with a thickness of less than 200 mm, are transported in a vertical position ("on edge"). The columns are transported in a horizontal position - flat. Trusses 18 and 24 m long are transported in a vertical (design) position, and 30 m long - in an inclined position: they are supported on wooden linings and fixed in the knots of the upper belt. Wall panels without working reinforcement rest on linings located in 0.5 m increments. They are transported in a vertical position, fixed on both sides; panels in an inclined position are fixed on one side.
The used loading and unloading mechanisms are divided into those operating independently of vehicles (self-propelled automobile and pneumatic wheel cranes - loaders, pneumatic wheel and caterpillar excavators with crane equipment, universal loaders, mobile and adjustable belt conveyors, pneumatic or auger unloaders, mounted mechanical shovels, etc. .) and included in the transport facilities (dump trucks, vehicles with self-loading platforms, vehicles with devices for self-unloading, etc.).
Loaders have received the greatest practical application in construction. With their help, up to 15-20% of all volumes of loading and unloading operations are now performed, which is explained by their versatility and high mobility. Universal shovel loaders, auto loaders and multi-bucket loaders are widely used. Loaders are front, semi-swivel and full-swivel. In loading and unloading operations, front loaders are most often used, equipped with quick-detachable buckets, crane equipment, fork lifts, jaw buckets and other working bodies. Due to their versatility, mobility and high cross-country ability, shovel loaders are effectively used in small-scale dispersed construction, as well as in lifting and transport operations within the construction site (transportation and supply of packages, wall materials, buckets and bunkers with concrete, mortar, etc.) . Bucket loaders are used for loading bulk and fine bulk materials.
Forklifts, like construction loaders, are equipped with interchangeable working bodies (beamless boom, bucket, jaw gripper, etc.), but are used mainly on hard-surfaced sites - at on-site warehouses or construction industry enterprises. Mobile belt conveyors are used for loading loose, lumpy and small-tonnage cargo. To unload powdered and bulk materials from covered wagons, mechanical shovels are used, operating on the principle of pulling scrapers, and pneumatic unloaders are used to unload cement.
Self-unloading vehicles are equipped with devices for craneless self-unloading of long loads, containers and hydraulically controlled jib cranes. The use of such tools is especially effective for servicing dispersed facilities with small amounts of construction work, which, in particular, is typical, for example, for agricultural construction. Self-unloading vehicles also include cement trucks, consisting of an autotractor, a tank and a suction unloading device.
Tank unloading is based on the property of aerated cement (saturated with air) to flow like a liquid.
Pipes from gondola cars are unloaded either to a warehouse, and then to a pipe carrier, or immediately to a pipe carrier, which is more efficient. Pipes are unloaded by automobile and pneumatic wheel cranes of the required carrying capacity. When unloading pipes on pipe trucks, the latter are installed parallel to the track opposite the car, and the crane is installed between them. When unloading pipes from gondola cars, end grips are used, consisting of two or more ropes with hooks at the ends. In order to avoid damage to the edges of the pipes, the hooks are provided with sponges made of soft material. For temporary storage of pipes, rail, road and base warehouses are organized, which are high-row and low-row, up to 8 and 3 m high, respectively.
High-row ones are more efficient, since they provide a higher level of mechanization of loading and unloading operations, reduce the storage area and improve the quality of pipe storage.
When loading and unloading insulated pipes and sections, it is necessary to take measures to ensure the safety of the insulation coating. It is not allowed to hit the pipe against the pipe, about the racks of trailers, dropping rigging devices onto the surface of the pipes, etc. Soft grippers (towels, etc.) should be used for their slinging, and the booms of pipe-laying cranes should be wrapped with shock-absorbing rubber gaskets at least 20 mm thick.
Schemes of complex mechanization of loading and unloading operations can be as follows. Cars with finished parts, structures, containers and packages are fed under the crane hook with their transfer to the installation site or to the area where these materials or semi-finished products will be used. Bulk cargoes in a quarry or in a warehouse are loaded into a dump truck by a universal or frontal shovel loader. The dump truck unloads aggregates into the warehouse of the construction concrete plant, from where they are fed to the batchers by a scraper installation. Cement is usually delivered to the site by cement trucks with a capacity of up to 60 m 3 , unloaded by a special air device using compressed air.
Covered wagons and gondola cars are unloaded by screw pneumatic unloaders with a capacity of up to 90 t / h, which supply cement into the hatch of a cement truck with a carrying capacity of 10 to 22 tons. The cement unloaded from them is fed through the pipeline into storage silos, and then to batchers of concrete mixers.
To organize the transportation of bulk construction cargo, it is necessary to use specialized containers and packaging equipment for technological purposes, circulated in a closed system: the supplier is the construction site. The range of goods for delivery in containers and packages is quite extensive - these are bricks, parapet slabs, window and door blocks, pipeline blanks for internal plumbing systems, parquet and boards, glassine, roofing material, electrical materials, glass, heat-insulating materials, facing products, paints, etc. . (more than 70 items).
Containers and packages are loaded by rolling cargo from the unloading platform of a vehicle or by forklifts equipped with a set of interchangeable working equipment, including grippers for pipes and rolled materials. Containerization and packaging can dramatically reduce the complexity of loading and unloading operations, improve the use of mechanization and ensure better safety of transported goods. Containers and packages can also be unloaded by special self-unloading vehicles. Warehouses of reinforced concrete plants, central pipe welding or pipe insulation bases are usually equipped with gantry or overhead cranes that unload vehicles and wagons.
The choice of a more rational option for complex mechanization of loading and unloading operations is made according to specific indicators of technical and economic efficiency.