The cause of manhole cover sinking is well cover sinking in well seat. In recent years, we have found that some cast iron well covers in many cities have good walls and well seats have not sunk, but the cast iron well covers have sunk in the well seats, and the height difference between the well covers and well seats has formed several centimeters. By analyzing the causes, we find that in order to prevent the well covers from jumping, such cast iron well covers are seriously deformed, mostly uneven and rusted, and the gap between the well covers and the well wall seats becomes large and loose. And a rubber band is installed between the well seat and the rubber band is damaged after aging, which causes the well cover to sink.
One of the most common cases is the sinking of the composite well cover. Through our observation and analysis, the sinking of the composite well cover is related to the unreasonable design of the well cover structure and the material and production technology used for the well cover. Most of the composite manhole covers in China are made of unsaturated polyester resin, and the filling materials are short glass fiber, quartz sand, Magnesium Oxide, calcium carbonate, fly ash, reinforcing bar and other raw materials. The welding technology of the steel bar is not even strict. The most serious problem of the production of the composite cover is its poor aging resistance, which is totally out of line with the national standard. Use requirements.
The non-standard composite well cover sinks in the well seat, but the original steel bar is separated from the composite material. Although the composite well cover has certain compressive strength, its tensile strength is poor. In order to enhance the tensile strength, the non-standard composite well cover basically adds steel bar and sand; some even add bamboo bar instead of steel bar, the composite material is non-metallic, and the steel bar is metallic, The difference of thermal expansion coefficient between the two materials.
Under different temperatures (early, middle, late, winter and summer), the interface of metal materials will form stress, and the metal will become more brittle under the temperature difference, which is the most fatal defect of cast iron manhole cover. At present, due to the problems of production technology, the sulfur content of cast iron in smelting has not been effectively controlled. In addition, repeated rolling of vehicles will lead to the separation of steel bars and composite materials, and finally the manhole cover will be lost To remove the bearing capacity, not to mention the composite well cover with bamboo strips.
The use of non-standard well covers usually results in natural deformation, fracture or even damage after one or two years of installation, especially for long-span well covers such as telecommunication, electric power, water supply, etc., which is extremely obvious. This kind of non-standard composite cover covers the most cheap manhole cover of the composite shaft and the steel strip. The exposed reinforcement shows that the composite performance is poor, the aging resistance and the tensile strength are poor. The defects of the long span well covers such as telecommunication, power and water supply are very obvious. The reason of sinking is that the well cover is not designed according to the actual requirements due to the use of non-standard production process and products.
