The underground part of any building is hidden under the ground, so it is not even possible to visually inspect it, unlike ground structures. A qualitative survey of the foundation of existing buildings is facilitated by pits dug from the outside of the structure or from the inside. Their location is determined depending on the design of the building itself, the distance to nearby buildings, and also on the level of the foundation footing.
When is an Underground Inspection Necessary?
Checking the condition of the foundation and the base under it is required in the following cases:
- increase in the number of storeys of the building;
- technical re-equipment of production;
- overhaul associated with increased loads;
- the appearance of significant cracks on the facade and distortions of openings;
- development of unacceptable drawdowns;
- the need to build nearby foundations, etc.
Often, the problems of the underground part of the structure are indicated by external damage on the walls, which are determined visually, as well as the jamming of several doors at once, located in the same plane or not far from each other. In these cases, experts give an unequivocal conclusion that the structure is experiencing deformations, and this is most likely due to the weakness of the base or the beginning of the destruction of the foundation.
During the overhaul of the facility, which involves increased pressure on the ground, it is mandatory to conduct a survey of its underground part, for which it is necessary to dig pits.
In some cases, it is enough to study the technical documentation. But in the absence of it or the occurrence of significant subsidence, confirmed by systematic observations, as well as during work related to the reconstruction of old buildings, it is impossible to do without a direct examination of the state of the foundation and foundation.
Inadmissible deformations, distortions and subsidence of buildings can occur for various reasons that appear immediately, over the years or after the soil thaws. The sources of problems are:
- atmospheric water seeping into the ground and soaking the base;
- groundwater resulting from leaks from water supply or sewerage networks, as well as reservoirs and heating mains;
- groundwater rising above the permissible level;
- insufficiently compacted base or backfill;
- freezing or washing out of the soil;
- displacement of soil layers relative to each other, etc.
When pitting, soil samples are taken at the base of the foundation, visually inspect the structure and, if necessary, take samples of materials (concrete, mortar, stone) for further laboratory research. Often they open the fittings.
Rules for the construction of pits
The pit is a dug hole that exposes the wall of the tape, the support of the columnar or the side of the slab foundation. The locations of the recesses are determined based on specific conditions. Problem areas are prioritized, and if it is necessary to survey long-length zones, the choice is left to sites that can least of all become an obstacle to passers-by or people living nearby.
When marking pits, builders should not start only from the convenience of working conditions and accessibility of the territory. Research is almost always carried out in populated areas, so the presence of pedestrians near the object cannot be eliminated. But others also need to remember that the foundation survey is only temporary, and the ongoing activities are necessary, appropriate and not critical.
Without fail, the pit must be laid in places where the deformation of the walls is clearly visible. Also drilling can be done:
- in the busiest areas of the building;
- in each independent part of a multi-section house;
- in the areas of additional supports.
Sites where the condition of the soil or foundation is defined as emergency require special attention. In this case, in addition to the problem area, reliable zones are examined where a pit is arranged, after which the results of the study are compared. For the foundation of the reconstructed object, drilling and inspection of structures together with the base is carried out at the installation sites of load-bearing columns and walls. And in the case of a partial superstructure - only in the area of reorganization.
The number of holes depends on the initial purpose of the foundation revision. When reconstructing or overhauling a building that does not provide for an increase in loads, it will be enough to perform 2-3 control pits. When eliminating the flow of water in the basement or on the ground floor, pits are dug in each of the flooded areas, and when the basement is deepened, one pit is made near all walls. In the most loaded areas, double-sided pits are allowed.
In places of change in the level of laying the foundation or a significant jump in the height of the structure, additional pits are often arranged.
Each hole is dug below the depth of the foundation by half a meter. Depending on the tightness of the territory and the size of the deepening, the walls of the pit are made with slopes or strengthened with vertical shields with spacers. The minimum area of the bottom of the pit in relation to its depth is:
- 1.25 m2 - up to 1.5m;
- 2 m2 - from 1.5 to 2.5 m;
- more than 2.5 m2 - from 2.5 m.
In buildings with basements, drilling is carried out from the inside, which significantly reduces labor costs when excavating. The pits, in this case, have, as a rule, a depth of 0.8-1.2 m and dimensions along the bottom - 1.0 * 1.0 m.
As a result of the foundation survey, they find out or clarify:
- the depth of the underground part;
- overall dimensions in plan;
- type and strength of the structure;
- the presence of defects and damage;
- class of concrete and brand of stone (according to samples - in the laboratory);
- condition of the waterproofing layer;
- violation of the position relative to the vertical axis;
- the presence of any amplification.
The state of the artificial and natural base is determined by the soil sample taken in the same pits. In some situations, additional drilling is required.
Options for opening foundations
One of the walls of the pit, designed to examine the strip foundation, is the vertical surface of the underground structure itself. For free-standing columnar foundations, there are three options for opening them:
- double-sided - the pit is dug out in two adjacent parties foundation reinforced concrete pad;
- angular - the pit is also located on both sides, but not for the full length of the faces of the base of the foundation, but only half;
- perimetric - the structure is exposed from three sides completely, and from the fourth - partially.
A two-sided pitting scheme is used in the event of significant sedimentary deformations in the pit digging zone, with an asymmetric shape of the foundation sole, or when considering the possibility of increasing the load on the supporting structures after the reconstruction of the object. Corner pit is arranged at the same size sides of the reinforced concrete base in terms of and the absence of subsidence processes. For industrial buildings, they also take into account the uniformity of loads from equipment and the inadmissibility of its dismantling or moving to another place in the future.
Digging a hole around the perimeter is used in critical situations when a maximum inspection of the underground part of the building or a thorough analysis of soil conditions is required. But the opening of the foundation, in this case, is allowed to be carried out not immediately along the entire perimeter, but only in sections that are no more than one and a half meters long, otherwise the building under investigation may collapse.
It is not uncommon for a building that is small in area and number of storeys to dig much more pits than for a huge production workshop with similar designs. The fact is that the process of responsible examination is more influenced by specific conditions, visual assessments, as well as preliminary control measurements and studies, rather than the human factor. It happens that with minimal verification, significant discrepancies between the underground structure and the technical documentation and even previous studies are revealed. It is then that additional research is required.
Inspection of foundations with the help of pits is carried out by specialized organizations in the presence of terms of reference, project documentation for the work with a clear indication of the location and size of the pits, as well as permission from supervisory authorities.
The presence of professionals and the guidance of engineers when digging holes is necessary in order to:
- excess soil from under the foundation was not accidentally removed to avoid additional subsidence;
- when the pit is flooded, problem areas could be quickly examined, since with intensive pumping of water, the rock is additionally washed out, including the sand cushion;
- the specialist was able to adjust the dimensions of the pit to be able to perform more accurate measurements;
- correct soil samples and samples of materials were taken.
Upon completion of work, each pit is filled with layer-by-layer compaction. Further, from the outside, the blind area is restored in accordance with all the rules, and from the inside - the floor.
Negative moments of drilling
Before you decide to examine the foundations by digging out the pits, you need to understand that the work will entail certain inconveniences that can affect not only the owner of the building, but also others. Namely:
- noise during the destruction of the blind area or concrete floor;
- dust and dirt;
- the appearance of moisture;
- the probability of flooding in case of untimely pumping of atmospheric waters;
- damage to waterproofing;
- difficulty in moving around the house;
- the impossibility of exploitation of the surveyed areas.
But, despite the difficulties, it is necessary to understand the importance of the arrangement of pits, provided for a visual acquaintance with the problems of foundations and the foundation under them. Inconvenience, in this case, is temporary.
Drilling of oil and gas wells is carried out by a drilling crew whose duties include:
preparatory work
work related to drilling and fixing wells and separation of layers, prevention and elimination of complications and accidents.
Preparatory and final work, preventive maintenance of drilling equipment. Works on testing productive horizons during drilling and after perforation.
Final work after completion of well construction.
The entire process of well construction is supervised by a drilling foreman, appointed from among technicians or engineers with extensive experience in drilling a well. Preparatory work conducted prior to the start of well drilling includes the following operations:
Installation and testing of small-scale mechanization devices - disconnection.
Checking instrumentation - instrumentation.
Centering the tower, checking the horizontalness of the rotor.
Equipment for the traveling system.
Run-in of diesel engines and testing of drilling equipment.
Drilling fluid preparation.
Pit drilling and installation of a pit pipe.
Drilling and descent directions.
Before putting the drilling rig into operation, the correct installation of the equipment is checked and it is tested without load. First, individual units are checked, and then the entire installation. To do this, start the engines of power units and compressors, turn on the clutches and test the operation of the transmission, gearboxes, winches, pumps, and the rotor at idle.
During the running-in of diesel engines, the output and fuel consumption are checked, the pressure and temperature in the fuel system, the tightness of the entire piping and instrument readings. After testing all the mechanisms and equipment of the drilling rig, a kermak rope with a kermak is suspended. Hang machine keys, connect the drill hose to the riser and swivel; assemble a square. They make a tooling for the traveling system, for this they first make a small tooling from a rope with a diameter of 9 mm and drag the traveling rope with diameters from 25 to 38 mm. After the wire rope has been pulled, one end of it is attached to the lifting shaft of the drawworks, and the other end is attached to the device for attaching the dead end. Next, assemble the lifting hook. Check the centering of the tower, the horizontalness of the rotor.
Prior to the start of work, the drilling rig is equipped with bits, casing pipes for the direction and conductor, drill pipes, small-scale mechanization devices, instrumentation for drilling, a pit for a leading pipe, the necessary supply of water, clay and chemicals. At the drilling rig, it is necessary to have a room for rest and meals (shift camp), a dryer for overalls, fire-fighting equipment, a set of hand and auxiliary tools, a first-aid kit with medicines, industrial sanitary equipment, as well as instructions and posters on safety, industrial sanitation and fire-fighting measures. The stock of fuels and lubricants must be stored in closed containers and have a clear inscription on the name of the materials stored in them. The construction of the well begins with the installation of a mine direction - to strengthen the wellhead from erosion by the flushing fluid. With stable rocks, the mine direction is established during the construction of the tower. For this purpose, they dig a shaft 7 m deep, in which a direction is established from pipes. After setting the direction, the shaft is covered with broken stone and poured with cement mortar. In those cases when unstable rocks lie from the surface, they drill under the direction with the help of a rotor to a depth of 30 m. After that, the direction from the pipes is lowered into the drilled well, it is centered and the space between the walls of the well and the direction is filled with cement. The upper end of the direction should reach the chute, through which the flushing fluid flowing from the well is directed to the circulation system.
Once the derrick is centered and the rotor is in place, the drilling for the kelly hole is started. The hole is required to lower the kelly during drill pipe extensions and during periods when drilling is not in progress. They drill under the hole with a turbodrill or a rotor. For drilling under the hole with a turbodrill, a bit, a turbodrill and a Kelly are preliminarily assembled above the wellhead. The pit is drilled with a depth of 17 m, then two screwed casing pipes (two-pipe) with a diameter of 219 mm are lowered into the pit, the upper end of the two-pipe is equipped with a visor to facilitate the insertion of the end of the leading pipe into the pit.
The acceptance of the drilling rig is documented by an act confirming the suitability and correct installation of the equipment. In addition, certificates are drawn up for testing injection lines and pneumatic systems, limiters for lifting the traveling block under the crown block, for testing grounding devices, for testing the block for overloading the traveling system. The commission checks the condition of access roads and territories, the condition of receiving bridges and racks, the floors of the drilling rig, the serviceability of equipment and machinery, the serviceability of mid-flight ladders on the tower, the serviceability of instrumentation, the presence of fencing on moving and rotating parts of mechanisms and equipment. All malfunctions and shortcomings identified during the acceptance of the drilling rig must be eliminated before the rig is lowered.
When drilling a well for more than 2 months, monthly technical discussions should be held, at which the results of the work are summed up and the features of the drilling technology for the next period are considered.
Well drilling can be started if the following documents are available:
a) geological and technical outfit (GTN)
b) a regime-technological map, and when drilling wells with a depth of 3000 m or more, in addition, a drilling technology project;
c) an act on the commissioning of the installation with permission to start drilling of the Gosgortekhnadzor bodies
d) drilling order.
Installation and testing of small-scale mechanization devices, connecting a drill hose, hanging machine keys, checking instruments, centering the derrick, checking the horizontalness of the rotor, equipping the traveling system, drilling under a hole and lowering the direction.
Before putting the drilling rig into operation, the correct installation of the equipment is checked and it is tested without load. At the beginning, they check individual units, and then the entire installation, for this they start the engines of power units and compressors, then turn on the clutches and test the operation of the transmission, gearboxes, pump winches, and the rotor at idle. During the running-in of diesel engines, the supply and consumption of fuel, the pressure and temperature in the oil system, the tightness of the entire piping are regulated.
After testing the equipment and mechanisms, a rope with a hook is hung on the drilling rig. Then hang the machine keys. Then connect the drilling hose to the riser. On the other side, the neck of the swivel is attached. Then the traveling block is dragged onto the drilling rig with a kermak and the equipment is started. After the tackle system is equipped, the lifting hook is assembled. Next, check the centering of the drilling rig. The centering of the tower is checked by pulling the rope through the center of the well. A plumb line is installed on the lifting hook, which must coincide with the center of the rotor and the center of the intersection of the stretched ropes. The mounted drilling rig is put into operation after acceptance of the commission appointed by the management of Bashneft-Drilling TEGB LLC.
Check: the condition of the territory and access roads; the condition of the receiving walkways, racks, floors of the drilling rig; serviceability of machines and equipment; instrumentation; protection of moving and rotating parts of equipment; certificates for testing the injection lines and pneumatic system, lifting limiter of the traveling block and grounding devices. Also check the list required documents before the start of drilling.
