What are technical procedures (including operating procedures)?
Answer: Technical specification (including operating specification) is the concretization of technical standards and specifications, and it is a technical regulation on construction technology, operation method, use of equipment and tools, construction safety technology, etc. of building installation project according to the requirements of technical standards and specifications.
Briefly describe the relationship between deflection value of subgrade top surface and compaction degree.
Answer: The deflection value of subgrade top surface is the deformation value under load, which reflects the overall strength of subgrade, while the compactness reflects the compactness of each compacted layer of subgrade. Only when the compactness of each layer meets the requirements can the subgrade deflection value meet the requirements.
What are the main types of special subgrade?
Answer: Subgrade in landslide area, rockfall area, debris flow area, karst area, permafrost area, loess area, expansive soil area, saline soil area, aeolian sand area, snow damage area and salivation area.
What are the common diseases of embankment slope?
Answer: dike slope collapse, gully erosion, protective body sliding, protective erosion, rapids hanging, etc.
What is flexible pavement?
Answer: Flexible pavement refers to the pavement with low rigidity and low tensile strength, which mainly depends on compressive strength and shear strength to bear the vehicle load. Except cement concrete pavement and block pavement, all types of pavement are flexible pavement.
What is a rigid pavement?
Answer: Rigid pavement refers to the pavement with high rigidity and high bending and tensile strength, generally referring to cement concrete pavement.
What is the maximum particle size requirement of graded crushed stone as base and subbase?
Answer: When graded macadam is used as base, the maximum particle size of macadam should not exceed 40mm (square hole sieve), and when subbase is used, the maximum particle size of macadam should not exceed 50mm (square hole sieve).
How to evaluate whether the compacted specimen meets the requirements?
Answer: After the last layer of sample is compacted, the height of the sample beyond the top of the test tube shall not exceed 6mm. Samples with excessive height shall be invalid.
What's the effect on the quality if the proportion of oilstone is too large?
Answer: The correct choice of asphalt-aggregate ratio is an important factor to ensure the quality of asphalt pavement. Too much asphalt is not only wasted, but also causes diseases such as flooding, softening, oil coating and skin coating.
What's the effect on the quality if the oil-stone ratio is too small?
A: Too little asphalt is used, the aggregate is not firmly bonded, and the compaction is loose, pitted and permeable, which leads to the early damage of the surface layer.
What requirements should asphalt pavement base meet?
Answer: (1) has sufficient rigidity and strength.
(2) It has good stability.
(3) The surface is smooth and dense, and the camber is consistent with the surface layer.
(4) Good combination with the surface layer.
How to evaluate the area of honeycomb pits on concrete surface?
Answer: (1) Honeycomb pits appear after concrete pouring and formwork removal, and the honeycomb depth shall not exceed 1cm.
(2) In a component, the pit area of each inclined plane shall not exceed 1% of the surface area.
(3) When pits appear on several sides of the component, the degree of honeycomb pits of the component should be expressed by the side with the highest percentage of pit area.
What are the disadvantages of cement concrete pavement?
Answer: 1) has joints; 2) It cannot be opened to traffic immediately after construction; 3) Difficulties in digging and repairing; 4) It is too reflective in the sun; 5) The demand for cement is large; 6) There are too many preparations before pouring concrete.
What are the manifestations and characteristics of hole collapse?
Answer: The characteristics of hole collapse are that the water level in the hole suddenly drops, small bubbles appear at the orifice, the slag output increases obviously without footage, and the load of the drilling rig increases obviously.
What are the main factors that affect the strength of concrete?
Answer: (1) Quality of raw materials, sand, cement and water.
(2) Grading composition of aggregate
(3) Mix proportion and water cement ratio
(4) Mixed mass
(5) Transportation
(6) Vibrating and leveling
(7) Maintenance
(8) Temperature
What should be done before pouring concrete?
Answer: Before pouring, the supports, templates, steel bars and embedded parts should be inspected. Sundries, accumulated water and dirt on steel bars in the formwork shall be cleaned up. The template should have gaps and be packed tightly, and the inner surface of the template should be coated with release agent.
What are the basic requirements for dry paving flaky?
Answer: (1) When laying, large stones should be selected and staggered, packed tightly and not loose.
(2) The edge of masonry should be straight, smooth and firm.
Which piles do you usually need to nail in midline survey?
Answer: (1)20M pile or 50M pile.
(2) Piling 100 meter pile
(3) 100 meter pile and kilometer pile
(4) The starting point, midpoint and end point of the curve
(5) indicating pile
What are the instruments commonly used in highway measurement?
Answer: Compass, theodolite, leveling instrument, flatbed instrument, hand-to-line instrument, infrared range finder and total station.
What are the main factors that affect the angle measurement results?
Answer: (1) collimation axis and horizontal axis errors.
(2) the leveling error of leveling tube
(3) Error caused by irregular operation
(4) Errors caused by natural conditions
(5) reading errors.
What kinds of wires are commonly used on highways?
Answer: Closed conductor, attached conductor and branch conductor.
What is the main content of restoring alignment?
Answer: (1) Repetition and recovery of traverse intersection.
(2) Repetition and recovery of conductor turning point
(3) stacked on the recycling route.
(4) Re-survey and additional leveling base points along the line.
What are the main items of bridge completion survey?
Answer: (1) Measure the centerline and span of the bridge.
(2) Measure the dimensions of pier or tower and anchor.
(3) Check the bridge deck elevation.
In bridge construction, under what circumstances do you need to carry out river-crossing leveling to check the elevation of leveling points set on both sides of the river?
Answer: When the width of the river is greater than 150m, river-crossing leveling should be carried out to check the elevation of bench marks on both banks.
What are the methods of elevation lofting?
Answer: (1) The horizontal direct measurement method is suitable for flat places;
(2) The hanging steel rule method is suitable for deep foundation pit or high pier;
(3) The trigonometric leveling method is suitable for deep foundation pits or high piers.
What are the conditions of measuring instruments that are considered unqualified?
(1) is corrupted;
(2) overload or misoperation;
(3) The display is abnormal;
(4) functional problems;
(5) Exceeding the specified weekly inspection and confirmation interval;
(6) The integrity of the instrument seal has been destroyed.
As a material of surface concrete, what characteristics must it have?
A: High bending tensile strength, high wear resistance, good frost resistance, and the lowest possible expansion coefficient and elastic modulus.
What does 7-day unconfined compressive strength mean?
Answer: (1) Wet cultivation at 25℃ for 6 days in non-frozen areas and soaking in water 1 day.
(2) Wet cultivation at 20℃ for 6 days and water immersion for 65438 0 days.
Is the asphalt used for asphalt surface layer good or not? What should I choose according to it?
Answer: According to regional climate conditions, construction season temperature, pavement type, construction method, etc.
Pavement cement concrete has high requirements for gravel. What are the main technical indexes of crushed stone in the specification?
Answer: Crushing value index, acicular particle content, silt content and organic matter content of crushed stone.
What is the content of the quality inspection stage?
Answer: ① incoming inspection, such as inspection of raw materials.
(2) Construction process inspection, such as process inspection and concealed engineering inspection.
(3) Final inspection, such as completion inspection and project completion inspection.
What are the basic contents of construction quality inspection, evaluation and acceptance of building projects?
Answer: Sampling inspection of partial and sub-project contents, inspection of construction quality assurance data and inspection of project appearance quality.
What should be done in time after the subgrade earthwork is basically completed?
Answer: The construction unit should restore all the piles, and check the center line and elevation of subgrade, subgrade width, slope gradient, intercepting ditch and drainage system together with the quality supervision personnel according to the requirements of the design documents, and make a renovation plan according to the inspection results to carry out the renovation of subgrade and drainage ditch.
How are the types of sand named according to the grain gradation?
Answer: Sandy soil can be divided into three categories: coarse sand, medium sand and fine sand, with coarse sand particles with a particle size of 2-0.5 mm accounting for more than 50%; Particles with a particle size of 0.5-0.25mm account for more than 50% in medium sand and 0.25-0.074mm in fine sand.
How to calculate the crushing value of aggregate?
Answer: The aggregate crushing value is tested twice in parallel. After each test, the ratio of the calculated fine material quality to the total test amount is the aggregate crushing value, which is expressed as a percentage, and the result only needs to be taken after one decimal point.
What sampling work should be done for asphalt mixture during asphalt concrete construction?
Answer: Marshall stability, flow value, porosity, saturation, asphalt extraction test and mineral aggregate gradation after extraction.
How many stages does asphalt mixture design include?
A: There are three stages: target combination design, production combination design and production combination verification.
What is the compressive strength of cement concrete?
Answer: The concrete compressive strength specimen is a cube with a side length of 150mm as the standard specimen. The concrete strength shall be subject to the standard curing of the specimen for 28 days and the strength measured by the specified method.
How many steps are there in the mix design of cement concrete?
Answer: (1) Calculate the preliminary mixture ratio;
(2) put forward the benchmark mixture ratio;
(3) Determine the mixture ratio of the laboratory;
(4) Conversion of "field mixture ratio".
According to the gradation principle, the asphalt mixture structure can be divided into several categories.
Answer: Suspended dense structure, skeleton gap structure and discontinuous grading structure.
What are the advantages of SMA asphalt pavement?
Answer: It has the advantages of skid resistance, wear resistance, compactness, durability, fatigue resistance, rutting resistance, and reducing low-temperature cracking.
What does quality management mean?
A: Establish a quality policy, implement all the functions and work contents of the quality policy, and evaluate and improve the work effect.
What systems does the quality control system include?
A: Regular meeting system, coordination system, acceptance system and quality responsibility system.
What method can be used to reinforce the wet and weak foundation?
A: Chemical consolidation and drainage consolidation.
What are the applicable scopes of bored piles?
Answer: (1) dense soil layer, no groundwater;
(2) Weathered rocks without groundwater;
(3) There is a small amount of groundwater, and the soil layer or weathered rock layer is relatively dense.
What are the structural characteristics of bridge pile foundation?
Answer: Solid section, hollow section, large buried depth and many forms of pile group arrangement.
What is the basis for the division of extra large bridges, large bridges, medium bridges and small bridges in the technical standards of highway engineering?
Answer: The total length and standard span of the bridge.
What are the geosynthetics commonly used in asphalt pavement?
Answer: Plastic grille, glass fiber grille, geotextile.
What conditions should be met for cement concrete expansion joint plate?
Answer: No deformation during construction, high elastic recovery rate and good durability.
What are the granular subbase suitable for all levels of highways?
Answer: Graded gravel subbase, graded crushed stone subbase and interstitial crushed stone subbase.
What are the types of bridge foundations?
Answer: Rigid foundation, pile foundation, pipe pile, open caisson, diaphragm wall, etc.
52, the applicable conditions of underground continuous wall?
Answer: It is suitable for underground retaining walls, water retaining cofferdams, bridge foundations bearing vertical and lateral loads, underground structures with large plane size or complex terrain, and can be used to remove soil layers with high underground confined water such as karst in time.
53. What are the main construction technologies of bridge superstructure?
Answer: segmental cantilever balanced construction, hole-by-hole construction, incremental launching method construction, swivel construction and cable hoisting construction.
What factors should be considered in the calculation of common bearings?
Answer: Design load, camber, settlement value, etc.
Generally speaking, various loads and external forces acting on highway bridges are divided into several categories.
Answer: Permanent load, variable load and accidental load.
Before using the hanging basket to pour the main girder, the hanging basket must be pre-pressed. What is its purpose?
Answer: (1) Verify the reliability of the hanging basket;
(2) eliminating inelastic deformation;
(3) Determine the actual deformation of the hanging basket under different loads.
After the prestressed tendons are tensioned, how to deal with the channels?
Answer: After the prestressing tendon is tensioned, the channel shall be washed clean, the accumulated water shall be blown away, and grouting shall be carried out as soon as possible. Each index of mud must meet the design or specification.
How to inject mud into the channel after the prestressed tendons are tensioned?
Answer: grouting pump is used to start grouting from the lowest point of the beam, and the grouting holes at both ends of the beam are grouted at one time until the specified consistency of cement slurry fills the whole channel.
In order to ensure the strength of lime stabilized soil base, what should be controlled in construction?
Answer: (1) The amount of lime and ash are uniform;
(2) Mixing uniformity of lime stabilized soil;
(3) Compaction of lime stabilized soil;
(4) Maintenance of lime stabilized soil.
The main feature of highway engineering projects is linear structure, which requires a lot of investment. What kind of highway construction industry does it belong to?
A: capital-intensive and labor-intensive.
What is the function of bridge bearing?
Answer: (1) transfer the supporting reaction of the superstructure, including vertical force and horizontal force caused by dead load and live load;
(2) Ensure the self-change of the structure under the action of live load, temperature change, concrete shrinkage and creep.
Shape, so that the actual stress of the upper and lower structures conforms to the static diagram of the structure.
How many kinds of bearings are there for beam bridges?
Answer: Fixed bracket and movable bracket.
What principles should be followed in the arrangement of fixed bearings and movable bearings?
Answer: It should be based on the principle of facilitating the pier and abutment to transmit longitudinal horizontal force.
What material are the bearings of beam bridges usually made of?
A: It is usually made of steel, rubber or reinforced concrete.
What effect does coarse aggregate particles with scale have on concrete quality?
A: Gravel made of weathered rocks often contains particles with rust on the surface. This kind of particle has a yellowish brown surface and is called hydrotalcite. For limestone, under the action of water and carbonate, soluble new substances increase relatively. This is the characteristic of weathered limestone. This kind of weathered rock is reddish brown, rough and fragile, which will adversely affect the strength and frost resistance of concrete and even lead to quality accidents. Therefore, there are clear restrictions on the content of coarse aggregate with water rust on the surface in the specification.
How to leave sand and gravel on site to ensure the quality of sand and gravel?
Answer: The site for stacking sand and gravel should be flat and solid; The sand pile should be square, and the gravel should be piled up according to the particle size specification; Gravel piles are strictly prohibited from being trampled by cars; It is best not to use bulldozers and grab buckets to pile up sand and load soil to prevent soil from being brought into the sand and gravel.
How to deal with unstable cement?
Answer: Some high-quality active mixed materials can also be added to cement with poor stability, which can overcome the problem of poor volume stability of cement caused by high content of free calcium oxide to some extent.
Why can't different kinds of cement be mixed?
Answer: The cement commonly used in engineering includes ordinary cement, slag cement and pozzolanic cement. These different types of cement contain different mineral components, and the proportion of each mineral component in cement is also different, so different types of cement have different chemical and physical characteristics.
How to keep the site cement?
Answer: Cement entering the site must be inspected first, especially bagged cement. It should be carried out in strict accordance with the variety, brand, label and factory date. Need rain, moisture and heat insulation.
What is the reason for the displacement of reinforced concrete structure?
Construction survey error, incorrect setting-out; The setting-out error of construction survey is too large, and it is not corrected or adjusted in time, which makes the error accumulation increase gradually; The formwork support system is inexperienced or miscalculated.
Template support is not firm, and displacement occurs under the lateral pressure of newly poured concrete and the vibration of vibrator;
The formwork support method at the reserved hole is wrong, or the support is not firm, and the impact during concrete pouring and vibration during tamping make the formwork shift;
The embedded parts are not fixed firmly, which causes the embedded parts to shift when pouring concrete.
The concrete pouring method is wrong.
What is a pitted surface?
Answer: On the local surface of reinforced concrete structure, the loss of cement mortar is in the form of dense mottled pits, and the surface is embedded with coarse aggregate. This phenomenon is called pit.
72. What causes the pockmarked surface?
(1) The template assembly is not tight, which leads to slurry leakage at the joint of the plate and pits along the joint of the template.
(2) The wooden formwork is not fully wetted by water; The template is not coated with isolation agent. When the formwork is removed, the local "oil film" on the surface of light concrete is stuck off, and the surface of heavy concrete is stuck off, forming a pitted surface.
(3) The formwork renovation and cleaning are poor, the deformed formwork assembly is not tight, the board surface bonding mortar, concrete crumbs and other sundries are not removed, or the removal is not complete, which makes the concrete surface rough.
(4) The vibrator is not properly selected, the vibration is not dense, and it depends entirely on the vibrator, and there is no artificial tamping, especially no artificial tamping shovel to insert the mold.
What is tendon exposure?
Answer: The main reinforcement and stirrup of reinforced concrete structure are not wrapped by concrete, but are exposed intermittently or continuously, which is called exposed reinforcement.
What are the causes of cracks on the surface of reinforced concrete structures?
Answer: (1) The concrete consistency is improper, and the aggregate sinks after entering the mold, resulting in segregation. Mortar, pebbles and big pebbles are distributed from top to bottom. Because of this layered distribution, the shrinkage is different, leading to cracks.
(2) The concrete is not cured in time according to the construction operation procedures, or it is not covered, so that the surface free water evaporates too quickly and cracks are generated.
(3) After the formwork is removed, the temperature difference between concrete and the outside world is too large, resulting in cracks in reinforced concrete.
(4) Plastic cracks, that is, cracks, are easy to appear when the foundation temperature is greatly different from the outside temperature after about 4 hours of concrete pouring.
(5) Improper cement selection, and no cement with smaller shrinkage is used.
(6) Too much cement and too high water-cement ratio.
(7) The sand used is too fine, which usually refers to silt, or the silt content of sand is too large.
What are the causes of cracks in reinforced concrete floor parallel to the direction of main reinforcement?
Answer: (1) Concrete is composed of solid, liquid and gas. Because the expansion coefficient of cement stone (12× 10-6) is quite different from that of stone (3~4× 10-6), temperature stress or shrinkage stress will occur when the temperature changes. Because the main reinforcement in the floor slab does not shrink, it produces a kind of self-restraint stress on concrete, which makes the floor slab produce short and thin cracks along the direction of the main reinforcement.
(2) When the thermal insulation material is removed in winter construction, the concrete is directly connected with the external low temperature, and cracks occur due to the excessive temperature difference between concrete and air temperature.
(3) In summer, when the floor is constructed, it suddenly rains heavily after being exposed to the hot sun, which leads to the sudden cooling of the formwork and cracks.
(4) The wooden formwork will also produce cracks if it is not wet.
What is the main reason for cracks in cast-in-place floor slab perpendicular to the direction of main reinforcement?
Answer: The main reason why cracks appear in the cast-in-place floor perpendicular to the main reinforcement direction is that the rigidity of the formwork support system is not enough. When the concrete is poured into the mold, the supporting system is deformed, and the newly solidified concrete can't bear the tensile stress caused by this deformation, resulting in cracks. In addition, if the formwork is removed too early, the strength of the concrete itself can't keep up with the dead weight, or the concrete after formwork removal can keep up with the dead weight, but with other construction loads, the floor slab will crack.
What are the quality analysis methods?
Quality analysis methods include: causal analysis diagram, primary and secondary analysis diagram and quality histogram.
How to strengthen the measurement work?
Strengthening measurement work mainly includes: 1) using measuring instruments correctly and reasonably; 2) Measuring instruments shall be verified and maintained; 3) Measuring instruments shall be properly kept; 4) Reform the methods of measuring instruments and realize the modernization of testing methods.
What is a concealed work?
Concealed engineering refers to those parts of the project that cannot be re-examined because the work results of the previous process are covered by the next process.
What is the basic method of total quality management?
It can be summarized as a process, four stages, eight steps and seven tools.
What are the common subgrade deformations and damages?
Settlement, subgrade settlement in the vertical direction, uneven settlement of subgrade, leading to local damage of pavement, subgrade settlement has two situations:
A, subgrade subsidence, due to improper selection of filler, unreasonable filling method and insufficient compaction, under the comprehensive action of load and water temperature, the subgrade sinks downwards;
B, foundation settlement, the original ground is soft soil, which was not treated or replaced before filling, resulting in insufficient bearing capacity, foundation settlement and embankment settlement.
(2) Slope collapse, such as spalling, slump and collapse.
(3) The subgrade slides along the hillside, and the subgrade is filled on the steep hillside. If the original ground is flat, without chiseling or digging steps, and the toe of the slope is not treated as necessary, the subgrade will move down along the ground in whole or in part under the action of water infiltration or load and self-weight, and the subgrade will lose its overall stability.
(4) Subgrade damage caused by unfavorable hydrogeological conditions, such as landslide, strewn at random, debris flow, avalanche, deep edge collapse, earthquake, rainstorm, etc., can lead to large-scale subgrade damage.
What are the basic requirements of cement stabilized gravel base?
(1) For gravels, solid and clean granular materials shall be selected according to the transportation location of the materials.
(2) The dosage of cement should be accurately controlled according to the design requirements. When mixing, it must be dry mixed evenly first, and then wet mixed with water until the color of the mixture is consistent.
(3) In the process of watering and mixing, the water consumption is slightly greater than the optimal water content to compensate for the evaporation of water during construction.
(4) Under the condition that the mixture is at the optimum water content, it will be rolled by a heavy roller to the required degree of compaction, and the compaction thickness of each layer shall not exceed 15cm.
(5) During the construction of cement stabilized macadam, it is advisable to adopt sectional flow operation, and the time from adding water to the end of rolling should not exceed 4 hours.
(6) After passing the rolling inspection, immediately cover or spray water for curing, and the curing period is generally not less than 7 days.
(7) The original construction records are complete.
What requirements should be met for the maintenance of concrete?
(1) The surface of concrete slab should be covered with straw bag and straw curtain before the final set of concrete, and it should be watered evenly every day to keep it moist;
(2) In areas with large temperature difference between day and night, heat preservation measures should be taken within 3 days after concrete slab pouring to prevent shrinkage cracks of concrete slab;
(3) Vehicles are prohibited from passing during the curing period of the concrete slab and before joint filling, and only after reaching 40% of the design strength can people pass;
(4) The curing time should be determined according to the growth of concrete strength, which should generally be 14-2 1 day. The covering can only be removed after the curing period, and no trace can be left on the board.
What are the contents of raw material quality inspection before asphalt pavement construction?
(1) Asphalt shall be tested according to specifications: penetration, softening point, ductility, flash point, melting point, etc.
(2) Fabric: compressive strength, abrasion value, grading composition, relative density, water content, water absorption, soil and impurity content, flat slender particle content and asphalt adhesion, loose square units, etc.
(3) Sand and stone chips, relative density, gradation composition, water content and silt content;
(4) mineral materials; Relative density, screening test, water content. .
What problems should be paid attention to when measuring and setting out culvert?
Answer: Check whether the topographic profile of vertical and horizontal axes of culvert is consistent with the design drawings, and pay attention to the correctness of culvert length and culvert bottom elevation. For skew culverts, curved culverts and culverts on steep slopes, the influence of intersection angle, widening, superelevation and longitudinal slope on the concrete position and size of culverts should be considered, and the position, direction, length, height and slope of wing wall, I-wall and top of culvert wall should be paid attention to, so as to meet the technical requirements.
86. What is prestress?
A: In the tensile area of concrete, steel bars are stretched by prestress. When the steel bar is stretched to a certain value, the steel bar is anchored on the concrete, and then the tension is relaxed. At this point, the reinforcement elastically retracts. Because the steel bar has been anchored, the resilience is transferred to the concrete, which makes the concrete under pressure. Usually, this pressure is called prestress.