The structure of a manhole typically consists of the foundation, chamber, cylinder, collar, base, and cover. Generally, manholes are square in shape, and the material now commonly used is pre-cast concrete, which can be directly utilized during construction. The manhole is a crucial structure, yet it is often overlooked. For instance, the sinking issue of a manhole. While sinking does not usually harm the manhole itself, it can significantly impact the connected piping.
Severe settling of manholes can easily lead to pipe cracking, which could result in substantial water leakage from water pipes. Gas pipes are even more hazardous, and combined with complex road conditions, it can easily trigger explosions and other issues. The settling of manholes can also damage road surfaces, causing significant difficulties for traffic. The settling of manholes mainly includes the following aspects.
Firstly, there's the mortar layer, typically situated between the well shaft and the well base. Its primary function is simply to level the manhole, aligning it with the road gradient. However, due to this, the mortar layer is usually thin, resulting in less bearing capacity. Consequently, under load, it can easily be damaged due to its limited bearing strength. Therefore, accurately calculating the amount of mortar layer is crucial during construction.
Another issue is the backfill soil problem. Backfill soil refers to the soil originally excavated from the surrounding area, which is then filled back in after the construction is completed. This part often has issues with compaction. The uneven settlement of this soil relative to the well can lead to sinkholes around the inspection well and even cracks in the asphalt concrete pavement; moreover, the loose backfill soil layer cannot withstand the impact loads from vehicles. Insufficient bearing capacity of the backfill soil can cause the inspection well to shift, leading to subsequent settlement. This problem is easily resolved by ensuring the backfill soil is properly compacted.
