Cause of sinking of the manhole cover The manhole cover sinks in the well seat. In recent years, we have found that in many cities, the cast-iron manhole covers are intact and the wells have not sunk. Prevent the manhole cover from bouncing. Such cast iron manhole covers are severely deformed, most of which are uneven, corroded, and the gap between the manhole cover and the well wall seat becomes large and loose. An rubber ring is installed between the well and the well seat. The rubber ring is damaged after aging, which causes the well cover to sink.
One of the most common situations is the sinking of composite manhole covers. According to our observation and analysis, the sinking of composite manhole covers is related to the irrational structure design of the manhole covers. The materials used in the manhole covers and production processes are related. Most domestic composite manhole covers are made of unsaturated polyester resin as the bonding material. The filler materials are short glass fiber, quartz sand, magnesia, calcium carbonate, fly ash, and steel bars. It is not even tight. The biggest problem produced by this composite manhole cover is the poor anti-aging performance, which completely does not meet the national standards and fails to meet the requirements for use.
The non-standard composite manhole cover sinks in the well base, and the original steel bar is separated from the composite material. Although this composite manhole cover has a certain compressive strength, the tensile strength is poor. Reinforcement and sand and gravel are basically added to the manhole cover; some even added bamboo strips instead of rebar. Composite materials are non-metallic materials and rebars are metallic materials. The two materials have different thermal expansion coefficients.
At different temperatures (early, middle, late, winter, summer), the metal material interface will form stress, and the metal will become more brittle under the temperature difference. This is the most fatal defect of the cast iron manhole cover. At present, due to production technology problems, It can effectively control the sulfur content of cast iron in smelting, and repeated rolling of the vehicle will cause the steel bars and composite materials to detach, and eventually cause the manhole cover to lose its bearing capacity, not to mention the use of bamboo composite manhole covers.
The use of non-standard manhole covers generally deforms and breaks or even breaks after installation for one or two years, especially for large-span manhole covers such as telecommunications, power, and water supply. Such defects are extremely obvious. This kind of non-standard composite manhole cover has broken steel bars and exposed composite material. The cheapest manhole cover is exposed. The exposed steel bar proves that its composite properties are poor. Aging resistance is poor. Tensile strength is poor. Large-span manhole covers such as telecommunications, power, and water supply. Very obvious. The reason for the sinking is that due to the use of substandard production processes and products, the manhole cover design was not designed according to actual requirements.
