Problems Existing in inspection manhole cover installation

Problems Existing in Municipal Road Inspection Wells

The cracking, damage and subsidence of the inspection manhole cover around the asphalt concrete road inspection manhole cover (10-35cm) is a common road quality problem at present, which is called the common road quality problem around the manhole cover. No matter what form the nodular manhole cover structure is, it cannot be avoided.

The harm of this common quality problem:

1. Lightly affects driving comfort, and seriously affects driving safety.

2. Increase road maintenance costs.

External manifestations of common road quality problems around manhole covers

1. The pavement around the manhole cover is cracked and damaged, and the manhole cover sinks

2. Scope of road damage around the manhole cover:

According to the survey, more than 95% of the damaged roads around the manhole cover are within the range of 10-35cm.

Conclusion: The pavement range affected by the installation of the manhole cover is the same as the damage range around the pavement. Only if there are defects in the installation process, the pavement around the well will be damaged.

Pathogenic defects of common manhole cover installation methods

Defect 1: The manhole cover seat slurry is not full, the support pads are random, and there are large or large gaps under the manhole cover seat, resulting in insufficient bearing capacity of the manhole cover seat slurry layer.

Defect 2: Insufficient strength of manhole cover seat slurry material.

Defect 3: The filling material in the installation groove is arbitrary, and concrete is not used or not all concrete is used.

Several common operations that cause quality defects in manhole cover installation:

Operation 1: First lay cement mortar, put the manhole cover on the back seat, and then pour the surrounding concrete. (Some people do not even pour concrete, but only use cement mortar.) The disadvantage of this method is that it is difficult to accurately adjust the elevation of the manhole cover, and it must be adjusted repeatedly.

Operation 2: First adjust the elevation of the manhole cover with pads, then fill with cement mortar, and then pour the surrounding concrete.

The disadvantage of this installation method is that when the distance between the manhole cover seat and the wellbore installation base surface is too small, the concrete is not easy to penetrate and fill; it is not easy to plug the cement mortar by hand. It is difficult to ensure the quality, resulting in insufficient strength of the seat slurry. At present, the problems of large subsidence of manhole covers on roads are mostly caused by this installation method.

Operation 3: When installing a manhole cover with a concrete manhole cover seat, no cement mortar is used under the cast iron manhole cover seat, or only iron sheets and steel bars are used to support the manhole cover seat, and then the surrounding concrete is poured.

This operation method causes the cast iron manhole cover to sit with a gap, and the manhole cover seat is deformed or vertically displaced under the vehicle load. When installing a manhole cover with a concrete manhole cover seat, it is necessary to install the concrete manhole cover seat first, and then place the cement mortar under the seat ring.

This operation method is easy to cause the seat slurry to be not dense, resulting in the instability of the concrete manhole cover seat ring after being put into use, which drives the instability of the entire manhole cover.

Check the reasons for the improper installation of manhole covers

Reason 1: There is no standard process for the installation of cast iron inspection manhole covers in the current construction specifications of road engineering and pipeline engineering, and there are various installation methods.

Reason 2: The operators often work independently in the installation and construction of the manhole cover, and have strong randomness.

Reason 3: During the installation process, there is a lack of inspection and supervision ; after the installation is completed, the quality is not easy to check, and it is difficult to judge whether there are hidden dangers.

Reason 4: There are many construction units who are not clear about the installation regulations of the manhole cover in the drainage code.

Conclusion: The lack of a unified, scientific and reasonable standard installation process for cast iron manhole covers is the fundamental reason for the installation defects of inspection manhole covers.