Circular pipe culvert construction plan (1)
1. Project overview:
2. Construction preparation:
(1), Remove debris and tidy up the site; (2) Inventory and install the main construction machinery; (3) Install the water and electricity supply facilities at the construction site; (4) Organize the construction reasonably to ensure clear responsibilities and reasonable division of labor; (5) Prepare enough materials for construction.
3. Construction plan:
(1) Channel and reinforced concrete cover culvert:
1) Construction setting out. Carefully review the construction drawings to understand the design intent. According to the location and elevation of the structure determined in the drawings, accurately calculate the coordinates and axis direction of the piles in the structure, and then carry out construction stakeout according to the calculated specific position. In order to facilitate inspection and verification after excavation, the foundation axis control piles should be extended to the foundation Fix the hole. After the stakeout is completed, lay out the side lines of the structural foundation according to the structural dimensions of the foundation, and apply for review by the resident supervision engineer. Only after confirmation can the excavation of the foundation pit be carried out.
2) Excavation of foundation pit.
A. According to the on-site construction equipment conditions and construction environment, the foundation is excavated with an excavator and repaired manually. During the excavation, specialized surveyors are dispatched to measure the base elevation in time to prevent over-excavation. phenomenon occurs. For areas with groundwater, a water collection ditch should be dug around the foundation pit during foundation excavation to maintain good drainage and ensure that there will be no water hazards during the entire construction period of the excavation.
B. For some foundations with Grade I non-self-weight collapsible loess, after the foundation is excavated, it should be tamped with a heavy hammer, and a light penetrator should be used on site to detect the bearing capacity of the foundation to meet the design requirements. Pour the foundation concrete. If the bearing capacity of the foundation is insufficient, lime should be replaced depending on the specific situation. The thickness and width of the cushion layer are calculated through the bearing capacity of the foundation. When replacing lime, the proportion of lime and soil should be 3:7 by volume, and they are mixed together at the mixing station. After mixing, the lime-soil mixture is transported by a transport truck, and is paved and leveled manually, and the thickness of each layer is controlled. At about 20cm, the compaction degree of the lime soil is tamped with a small air tamper, which meets the approval of the supervision engineer. Other measures can also be used to treat the foundation according to the actual situation.
3) Templates and brackets:
A. The basic concrete formwork adopts bamboo plywood with standard size and smooth surface. The formwork must ensure that its surface is smooth and there is no leakage between the board seams. Pulp and other requirements.
B. Before installing the formwork, apply a release agent on the surface of the formwork. Do not use oil that easily sticks to the concrete or discolors the concrete.
C. In order to prevent the formwork from shifting and deforming when erecting the formwork, supports are set up outside the formwork when erecting the foundation side formwork. The side formwork of the platform body is set up to fix the tie rods. The tie rods poured into the concrete are designed according to the requirements for pulling out the tie rods. The tie rods are covered with plastic pipes. After the formwork is removed, the tie rods are pulled out and reused.
D. After the formwork is installed, in order to ensure that the position is correct, self-inspection of its plane position, flatness, verticality, top elevation, node connection and vertical and horizontal stability must be carried out. Only after passing the form can it be reported to supervision. The engineer will conduct random inspections and the supervising engineer will approve the pouring before pouring. When pouring concrete, if it is found that the formwork exceeds the allowable deviation value, it may be corrected in time.
4) Concrete pouring and maintenance:
a. Material selection. The laboratory strictly controls that all raw materials must meet the design and construction needs.
b. The culvert concrete is mixed centrally, transported by tanker, and poured by crane. The quality of various raw materials is strictly inspected before mixing. Concrete is mixed centrally at the mixing station, transported by tanker, and put into the mold using the hanging bucket method. When pouring concrete, strict inspection must be carried out on the concrete transported to the construction site. Such as concrete slump and workability.
c. Before pouring, check the brackets, formwork, and embedded parts. The debris and accumulated water in the formwork should be cleaned up. If there are gaps in the formwork, they must be filled tightly.
d. In order to prevent segregation when the concrete is dumped from a high place into the mold, when pouring the foundation, the dumping height of the crane shall not exceed 2 meters and it will fall through the string tube.
e. The concrete is poured in layers in a certain thickness sequence and in the horizontal direction. The upper layer of concrete is poured before the lower layer of concrete is initially set. When the upper and lower layers are poured at the same time, the distance between the upper layer and the lower layer should be maintained at more than 1.5 meters. The pouring thickness No more than 30cm.
f. The concrete is vibrated by plug-in vibrator. The movement should not exceed 1.5 times of the vibrator’s radius of action, and a distance of 5 to 10 centimeters should be kept from the side formwork.
g. Concrete pouring is carried out continuously. If it is interrupted for any reason, the interruption time should be less than the initial setting time of the concrete in the front layer.
h. After the concrete pouring is completed, it should be cured as soon as possible after the grout is collected. The concrete should be cured by sprinkling water, and the curing time should not be less than 7 days.
5) Treatment of construction joints:
Since the foundation platform body and platform cap are poured separately, construction joints should be carefully handled, and construction joints should be removed manually.
Within 1-2 days after the treatment layer concrete is poured, the cement mortar and loose layer on the surface should be roughened. The roughened concrete surface should be rinsed with water. Before pouring the sub-layer concrete, a layer of 1 layer should be laid on the horizontal joints. ~20cm of 1:2 cement mortar. The on-site pouring construction of reinforced concrete, concrete arch ring and cover slab concrete should be carried out continuously to avoid construction joints. When the culvert is long, it can be carried out in sections along the length direction. The joints It should be located at the settlement joint of the culvert body.
6) Treatment of settlement joints:
The setting of settlement joints is based on the design drawings. One settlement joint is set 4 to 6 meters per wall of the cave body. The structure of the settlement joints is strictly implemented in accordance with the construction drawings. . The settlement joints must be set up to form a vertical line from top to bottom, and the foundation wall is poured in sections according to the designed length of the settlement joints. When pouring, first use wooden boards as blocks at the settlement joints. After the concrete reaches a certain strength, remove the wooden block blocks and paste foam plastic at the settlement joints.
7) Paving at the bottom of the cave:
The bottom surface of the culvert and channel foundation is leveled and hardened. The surveyor controls the base elevation and pours the concrete with the design number. If the concrete in the culvert is When the slope is too large, a 5% reverse slope should be added to the foundation at the bottom of the culvert to make the foundation step-like to ensure the stability of the foundation.
8) Prefabrication, transportation and installation of cover plates:
Prefabrication of cover plates. ① Processing and binding of steel bars: The steel bars are cut, bent and made on-site in the steel bar workshop according to the drawing requirements. They are welded and tied in strict accordance with the specifications, and the dimensions are accurate during installation. ② Support of the formwork: The formwork uses high-hardness bamboo glue formwork, and it should have sufficient rigidity to prevent obvious deflection deformation when pouring concrete. Before installing the formwork, apply a release agent on its surface. Do not use oil that easily sticks to the concrete or discolors the concrete. During the erection process, pay attention to check whether the inside of the formwork is in contact with the steel bars to ensure that the structural components have sufficient protective layer thickness; secondly, pay attention to check the direction of the upper and lower sides of the formwork. For diagonal culverts, pay attention to the diagonal direction to avoid occurrences. Reverse error. ③ Mixing and pouring of concrete: Strictly follow the construction mix ratio provided by the laboratory, and use a forced mixer for centralized mixing. The minimum mixing time should comply with the requirements of the construction specifications. When mixing, the cement and aggregate should be mixed. Before mixing, some mixing water should be added first, and all the water should be evenly injected into the mixing cylinder within the first 15 seconds of mixing. The mixed mixture should be evenly distributed and consistent in color when viewed with the naked eye. The mixture is transported by tank truck and poured manually. The mixture transported to the site must be inspected (including the slump, workability, etc.) of the mixture. Before pouring, the bracket formwork and embedded parts must be inspected and the formwork must be cleared. Any gaps in the formwork must be filled tightly to remove debris and accumulated water. During the pouring of concrete, dedicated personnel should be assigned to check the stability of brackets, formwork, steel bars and embedded parts. If any looseness, deformation or displacement is found, they should be dealt with in a timely manner. ④Concrete curing: After the concrete pouring is completed, the concrete should be artificially sprinkled with water and cured as soon as possible after the surface grout is collected. The sprinkling curing should be maintained for at least 7 days. The structure should be continuously kept moist before being dismantled and touched.
Transportation and installation of cover plates: The finished concrete can only be transported after its strength reaches 70% of the design strength. It is transported to the site by a trailer and lifted and installed by a Y-16T crane. Before installation, check the size of the culvert. During installation, place 1cm thick linoleum between the bottom of the plate and the culvert cap, and then place the cover plate. For culverts with a longitudinal slope of ≥4% at the bottom of the culvert, after the cover plate is installed, the steel bars should be fixed with ф18 bolts at both ends. After the bolts are installed, the holes should be filled with No. 10 cement mortar. After the installation is completed, saw off the lifting rings on both sides, fill one end of the board with linoleum and the other end with No. 20 cement mortar.
9) Backfilling of the table back:
When the strength of the casing reaches more than 80% and the cover plate is hoisted, backfilling can be carried out. That is, after the base behind the table is 2.0m away, press Fill 10% lime soil from the 1:1 side slope to the top of the culvert. All the back filling must be filled in layers and rolled with a small roller compactor. Use small flat plates for places near walls, edges, dead corners, etc. The vibrator is used for compaction. During the filling process, the two sides of the culvert must be symmetrically compacted and compacted in layers. The compaction degree must reach more than 95%. It is strictly prohibited to fill the soil on one side and use a large roller compactor for compaction. When filling the top of the culvert with soil, the strength of the cover plate must reach the design strength.
(2) Reinforced concrete circular pipe culvert:
1) Excavation of foundation:
a. Before excavation of foundation, accurately release the center line position and use Cross bolts for precise position and elevation control.
b. Foundation excavation uses an excavator and manual excavation. During excavation, surveyors release the base elevation in a timely manner, and over-excavation is strictly prohibited. After the foundation is excavated, if the bearing capacity of the base is insufficient, the lime will be replaced depending on the specific situation. The thickness and width of the cushion are calculated through the foundation bearing capacity check. When replacing lime, the proportion of lime and soil should be 3:7 by volume, and they should be mixed together at the mixing station. After mixing, the lime-soil mixture should be transported by a truck and manually paved and leveled. The thickness of each layer should be controlled. At about 20cm, the compaction degree of the lime soil is tamped with a small air tamper, which meets the approval of the supervision engineer. Other measures can also be used to treat the foundation according to the actual situation.
2) Basic formwork and bracket:
a. The basic concrete adopts a fixed combination steel form with high strength, good stiffness, standard size and high turnover rate. The combination steel form must ensure its Requirements include smooth surface, accurate shape, and no grout leakage between board seams.
b. Before installing the formwork, apply release agent on the surface of the formwork. Do not use oil that easily sticks to the concrete or discolors the concrete.
c. In order to prevent the formwork from being displaced and protruding when supporting the formwork, supports should be set up outside the formwork when supporting the side formwork.
d. After the formwork is installed, in order to ensure the accurate position, its plane position, flatness, verticality, top elevation, node connection and vertical and horizontal stability must be inspected. Only after passing the formwork can it be reported to the supervision engineer. Concrete can be poured only after random inspection and approval by the supervision engineer. During pouring, if it is found that the formwork may exceed the allowable deviation value, it should be corrected in time.
3) Pouring and maintenance of foundation concrete:
Culvert concrete is mixed centrally, transported by tanker, and poured by crane. The quality of various raw materials is strictly inspected before mixing. Concrete is mixed centrally at the mixing station, transported by tanker, and put into the mold using the hanging bucket method. When pouring concrete, the concrete transported to the construction site must be strictly inspected. Such as concrete slump and workability.
Before pouring, check the brackets, formwork, and embedded parts. The debris and accumulated water in the formwork should be cleaned up. If there are gaps in the formwork, they must be filled tightly.
In order to prevent segregation when the concrete is dumped from a high place into the mold, when pouring the foundation, the dumping height of the crane shall not exceed 2 meters and it will fall through the string tube.
Concrete is poured in layers in a certain thickness sequence and in the horizontal direction. The upper layer of concrete is poured before the lower layer of concrete is initially set. When the upper and lower layers are poured at the same time, the pouring distance between the upper layer and the lower layer should be maintained at more than 1.5 meters, and the pouring thickness should not exceed 30cm.
Concrete is vibrated using plug-in vibrator. The movement should not exceed 1.5 times of the vibrator’s radius of action, and a distance of 5 to 10 centimeters should be maintained from the side formwork.
Concrete pouring is carried out continuously. If it is interrupted for some reason, the interruption time should be less than the initial setting time of the previous layer of concrete.
After the concrete is poured, it must be cured as soon as possible after the grout is collected. The concrete must be cured by sprinkling water, and the curing time shall not be less than 7 days.
After the foundation is completed, use a crane to place the reinforced concrete round pipes steadily on the concrete foundation. It is required that each pipe section is straight and smooth, and the height difference between adjacent pipes is not more than 5mm. The joints of the pipe sections are filled with asphalt fluff. . To ensure that there is no water leakage between pipe joints, the outside of the pipe joint joints is wrapped and sealed with 15cm wide linoleum, asphalt and reinforcement materials, and then a layer of asphalt is applied to the outside to ensure that there is no external moisture. Leakage into the culvert.
4) Construction of the eight-character wall at the culvert:
After the culvert is completed, let the surveyors set the position of the eight-character wall at the opening on both sides.
Accurate positioning , and control the elevation well, and start erecting the formwork.
The template uses bamboo plywood of standard size and smooth surface. The template must ensure that its surface is smooth and there is no leakage of slurry between the board seams. Before installing the formwork, apply a release agent on the surface of the formwork. Do not use oil that easily sticks to the concrete or discolors the concrete.
In order to prevent the formwork from shifting and deforming when erecting the formwork, supports are set up outside the formwork when supporting the foundation side formwork. The side formwork of the platform body is set up to fix the tie rods. The tie rods poured into the concrete are designed according to the requirements for pulling out the tie rods. The tie rods are covered with plastic pipes. After the formwork is removed, they can be pulled out and reused.
After the formwork is installed, in order to ensure the correct position, it is necessary to conduct self-inspection on its plane position, flatness, verticality, top elevation, node connection, and vertical and horizontal stability. Only after passing the formwork can it be reported to the supervision engineer for random inspection. , can only be poured after approval by the supervision engineer. When pouring concrete, if it is found that the formwork exceeds the allowable deviation value, it may be corrected in time.
The process of pouring concrete for the eight-character wall is the same as pouring the foundation concrete.
Platform backfilling:
When the strength of the eight-shaped wall concrete reaches more than 80%, platform backfilling can be carried out. The backfill should be made of well-graded natural gravel and constructed symmetrically. Due to the construction work, If the area is small, use a small roller compactor to compact it. Use a small flat vibrator to compact the areas close to the wall, edges, dead corners, etc. During the filling process, the two sides of the culvert must be compacted symmetrically and compacted in layers. The solidity must reach more than 95%, backfill to the height of the construction roadbed (exceeding the upper top surface of the culvert), and then fill with soil together with the roadbed.
Circular pipe culvert construction plan (2)
1. Quantity of projects
This contract section *** has a 285×250 double-hole box culvert 52.5m/ 2 blocks, 285×250 double hole box culvert 60m/2 blocks, 300×250 box culvert 101.4m/1 block, 450×300 box culvert 210.4m/1 block, reinforced concrete round pipe culvert 182m/2 blocks.
2. Team and Construction Period Arrangement
It is planned to arrange three culvert construction teams, each with 42 people, totaling 126 people. After the start of construction, if there is insufficient manpower, they will be recruited from the local area.
The first culvert team constructed 285×250 double-hole box culverts with 52.5m/2 units and the 285×250 double-hole box culverts with 60m/2 units; the second culvert team constructed 300×250 box culverts with 101.4m/1 unit and reinforced concrete round pipe culverts of 182m /2 blocks; Culvert Team Three is constructing 450×300 box culvert 210.4m/1 block.
Construction schedule: 30 days of construction preparation from October 28, 2004 to November 26, 2004; 70 days of construction from November 27, 2004 to February 4, 2005.
3. Construction method
1. Reinforced concrete circular pipe culvert
1.1 Foundation project
Foundation pit excavation uses manual and mechanical combinations After excavation and foundation pit inspection, the gravel cushion is laid and compacted in layers with a small vibratory roller, with a compaction degree of more than 95%. The foundation concrete is poured in two steps before and after the pipe joints are installed, focusing on controlling the combination of new and old concrete and the combination of the pipe base concrete and the pipe wall, and performing timely maintenance.
1.2 Culvert construction
The culvert is prefabricated by a designated manufacturer. After passing the inspection and transported to the construction site, the full length of the culvert, the configuration of the pipe sections, and the accurate position of the end wall are accurately calculated. Installation starts from the downstream, so that the joints are installed facing the upstream, and each section of the culvert is closely attached to the laid base, so that the force on the culvert is even.
Anti-collision measures should be taken during the loading, unloading, transportation and installation of pipe sections to avoid damage or cracks to the pipe sections; the loading, unloading, installation of equipment and storage sites for culverts must be approved by the supervising engineer, and the installation must be strictly in accordance with the specifications Specify operations.
1.3 Joints
Install the joint rubber ring according to the design requirements and fill the joints with M10 mortar. The width of the joint shall not be greater than 1cm, and the joint shall be smooth. It is prohibited to increase the joint width to meet the culvert length requirements.
1.4 Filling soil at the back and top of the culvert
After the culvert is completed, it can only be filled when the strength of the culvert masonry mortar or concrete reaches 70% of the design strength
Carry out backfilling. The backfilling soil must meet the quality requirements. The embankment gap at the culvert shall be filled with soil within a range of no less than 2 times the hole diameter from both sides of the culvert body. It shall be filled horizontally in layers, symmetrically, and compacted (compacted) at the same time. When filling the soil with machinery, in addition to complying with the above regulations, the thickness of the filling soil on the top of the culvert must be greater than 1m before the machinery is allowed to pass. When rolling with a vibratory roller, it is prohibited to activate the vibration source.
Strictly control the thickness and density of the layers, and assign a dedicated person to supervise and inspect. The inspection frequency is 1 point every 50m2. If it is less than 50m2, at least 1 point is inspected. Each point must be qualified and compacted by small machinery. The layering thickness of backfill soil is 0.1~0.2m. The compaction degree must reach 95%.
2. Reinforced concrete box culvert
2.1 Foundation treatment
Use manual and mechanical excavation. Pay attention to waterproof and drainage facilities before excavation. Set up jump excavation for deformation joints, and provide temporary support work when necessary.
The base must be leveled and compacted, and the bearing capacity of the base must be tested. If it cannot reach 150Kpa, it needs to be filled with gravel or gravel.
After the base meets the design requirements for bearing capacity, the concrete cushion shall be constructed according to the design requirements.
2.2 Binding of the bottom plate and side wall steel bars
Measure and set out the lines on the cushion and draw the steel bar layout and the edge lines of the formwork, then tie the bottom plate and side wall steel bars, tie the side When reinforcing the wall, temporary brackets are set up with steel pipes on the outside to prevent the steel cage from deforming. The protective layer of the main steel bars is 3cm (the wall steel bars are tied with bimodal pads on the side of the inner mold), the protective layer of the lower bars of the floor is 4cm, the anchoring length of the steel bars is 35d, the overlap length is 42d, and the percentage of steel bar lap joints is not greater than 25%.
2.3 Internal support and internal mold construction
The internal support is built with φ50 steel pipes. The vertical and horizontal spacing is no more than 1m, the vertical spacing is no more than 1.2m, and the top is equipped with an adjustable bracket. Support the top longitudinal beam, arrange the cross beam on the longitudinal beam, and the top mold on the cross beam. The transverse steel pipes of the inner support should be connected to the inner mold with steel pipe clips at the horizontal and vertical belt nodes (double steel pipes are used for both the horizontal and vertical belts of the inner and outer molds) to play the role of horizontal internal support. The inner mold is made from a large flat template of 1.5㎡. The surface is required to be smooth and free of errors, and sealing strips are added to the joints of the template.
2.4 Binding the roof steel bars and external formwork
The roof steel bars should be padded with bimodal pads. They should be tied in strict accordance with the specifications and design requirements. The support stirrups should be spot welded appropriately to ensure The upper layer of steel mesh does not deform.
The outer formwork is assembled using ordinary steel formwork. The outer formwork is fixed using φ16 tie rods that pull the inside and outside, and logs or steel pipes are used as auxiliary supports.
2.5 Concrete pouring
The concrete is commercial concrete. Filling and filling into the silo are carried out by a crane and a feeding funnel, and vibration is carried out by a plug-in vibrator.
2.6 Deformation joint treatment
The box culvert body is provided with deformation joints every 10 to 18 meters (including the foundation). Whenever the soil quality of the foundation changes and the junction of foundation filling and excavation, All are equipped with deformation seams with a seam width of 2 to 3cm.
The rubber waterstop of deformation joints adopts QZ5-400 rubber waterstop.
Where the box culvert is set up with deformation joints, the surrounding concrete should be thickened by a circle, and the thickness should be 25cm. Insert a 3cm thick oil-soaked cork board on the inside of the deformation joint setting, and fill it with water-stop sealing paste on the outside. In order to ensure that the entire deformation is vertical and on one section, two separate formworks (clamping waterstops) must be erected at the plug of the vertical formwork, and connected with the inner and outer formwork with screw rods, and the oil-immersed wooden boards correspond to the hollow tubes Use glue to stick to the plug steel mold.
2.7 The backfill on both sides of the box culvert and the top of the culvert are filled with soil.
The backfill is the same as that of the round culvert.
IV. Quality and Safety Assurance Measures
1. Quality Assurance Measures
1.1 When mechanical excavation of the culvert foundation, reserve 20cm for manual excavation and cleaning to reach the design elevation. Finally, check whether the cross-sectional dimensions and bearing capacity meet the design requirements. Only after the supervisor has passed the inspection and signed the signature can the next process be entered.
1.2 The steel bars must be inspected for their factory certificates and randomly inspected. They can only be used if they pass the test. The steel bars must be straightened, rusted, and descaled before use; welders must hold certificates to work, and the welding heads must be Official operations are allowed only after passing the test.
1.3 Steel bars must be limited when installing. The steel bars must be marked first and then tied. The vertical main bars and horizontally distributed steel bars must be tied firmly according to the design location requirements to form a standardized construction and strictly ensure the protective layer of the steel bars. thickness.
1.4 Concrete construction scaffolding and supports should be erected firmly, and the formwork should be horizontal and vertical to prevent formwork from occurring; tamping should be carried out by dedicated personnel, and the layering thickness and distribution points should be strictly vibrated to prevent the occurrence of honeycombs and Pockmarked noodles.
1.5 When constructing the masonry masonry of the culvert project, the stones must be carefully selected, the mortar must be mixed in strict accordance with the mix ratio, and the masonry shall be built using the extrusion method. The overlap between layers shall meet the requirements of the masonry specifications. It should be facing down, and it is forbidden to build it upright. The mortar is full and the mortar joints are uniformly concave.
1.6 Settlement joints and waterproof layers shall be constructed in strict accordance with the design and construction specifications to achieve no leakage. If water seepage is found, repairs should be made as soon as possible.
1.7 The filling at the back of the culvert shall be constructed strictly in accordance with the specifications and shall be rammed and filled symmetrically on both sides. Only when the filling thickness at the top of the culvert is greater than 1m can construction machinery be allowed to pass through to prevent cracking of the concrete and other man-made damage.
2. Safety assurance measures
2.1 A distribution box must be set up at the construction site, and the incoming and outgoing cables must have sleeves so that the incoming and outgoing wires are not messy. It is strictly prohibited to use fancy wires or plastic wires, and wires must not be dragged anywhere or tied to scaffolding.
2.2 On-site machinery and equipment must be operated in strict accordance with safety technical operating procedures, and illegal operations must be eliminated. It is strictly prohibited to operate machinery and equipment after drinking.
2.3 When excavating the foundation pit, the excavation should be based on the designed slope, and temporary support work should be done to prevent collapse. Equipped with water pumping equipment to prevent slope collapse and leakage accidents caused by water immersion.
2.4 When installing the formwork, the inside and outside should be firmly supported, and the tamping personnel should wear insulating and anti-electricity gloves; when dismantling the formwork, the prescribed procedures should be followed, and the formwork, materials, and tools should not be thrown directly down.
2.5 When working at heights, safety belts must be worn and protective fences must be set up around the area. People must be careful when moving around. People with fear of heights, heart disease, and myopia are strictly prohibited from working at heights.
2.6 Strengthen on-site security and protection work, and the layout of the construction site complies with the requirements of fire prevention, flood prevention, explosion prevention, lightning protection and other safety regulations.
2.7 The lighting fixtures, guardrails, fences, and warning signs installed on site should be regularly maintained to maintain their normal functions, and required safety warning signs should be hung in dangerous locations.