There is a Pakistani customer who wants to buy inspection manholes and asked some questions about inspection manholes. Our factory produces inspection manholes of various materials. In order to let customers know more in detail and make more correct decisions, we introduced to customers three inspection manholes made of different materials, the following table sorts out the physical and chemical properties of inspection manholes made of three different materials, for customer reference. According to this table, you can choose the inspection manhole that meets your requirements.
| Physical Performance | Character | SMC Plastic Inspection Manhole | HDPE Inspection Manhole | PVC Inspection Manhole |
| Weather Resistance | Small shrinkage range, small shrinkage value, can be constructed and operated at -45℃,not afraid of sudden cooling. Can be used in cold weather.There is no sign of brittleness. In a hot environment, there is no sign of deformation after long-term exposure to sunlight | The shrinkage range is large, the shrinkage value is large, and the directionality is obvious. The shrinkage value of HDPE is 25%-60%, so it is easy to deform and warp. It is easy to cause thermal expansion and contraction, and it is easy to become brittle when operating at a temperature below 0°C, especially it cannot be used in cold weather and permafrost environments. In a hot environment, long-term exposure to the sun is easy to deform | The range of shrinkage is average, and the shrinkage value is medium. In the air, due to light and ultraviolet light, water temperature, atmospheric chlorination, and chemicals encountered during product use, it is easy to cause color loss, brittle aging, and poor weather resistance. | |
| Intensity | Lightweight and high strength, like steel | Lightweight and low strength according to the material | ||
| Electric Performance | Flame retardant level reach FVO (the highest level of non-metallic materials) | Cannot be used as flame retardant material | Has a certain flame retardant effect, but not as obvious as composite resin | |
| Thermal Performance | SMC plastic inspection manhole plastic has good thermal performance, its specific heat is large, 2-3 times that of metal, and its thermal conductivity is relatively low, only 1/100-1/1000 of metal. High temperature cooling almost no deformation | High temperature, easy to deform after cooling | High temperature, easy to become brittle after cooling | |
| Aging Resistance | Slow aging rate | Moderate aging | Fast aging | |
| Heat Resistance | Can be used as a missile protection device, effective protection, not troubled by high temperature, also can be used normally in low temperature environment, ordinary materials can withstand the temperature of 200 ℃, special materials can be as high as 400 ℃ | Between 80°C-90°C, there are signs of softening, at 130°C it becomes a high elastic state, and at 160°C-180°C it begins to change into a viscous fluid state | The molecular weight of industrially produced PVC is generally in the range of 50,000-120,000. It has a large polydispersity. The molecular weight increases with the decrease of the polymerization temperature. There is no fixed melting point. It starts to soften at 80-85℃ and becomes high elastic at 130 ℃ State, at 160-180 ℃ began to transform into a viscous fluid state | |
| Expansion Coefficient | Low, no change in thermal expansion and contraction | High, thermal expansion and cold contraction, easy to deform, brittle | ||
| Fatigue Resistance | Good | Poor fatigue resistance, easy to break on impact | ||
| Chemical Performance | Acid/Alkali Resistance | Resistant to strong acid and alkali | Resistant to weak acids and alkalis, but not resistant to strong acids and alkalis | |
The customer wanted to refer to the problems and prevention of our urban road inspection manholes. We sent a document to the customer and introduced the problems and prevention of domestic urban road inspection manhole.
Prevention and Cure on the Troubles of Inspection Manholes in Urban Roads
According to the requirements of the regulations, various pipelines in municipal engineering should have an inspection manhole at a certain distance to facilitate inspection and maintenance at any time to ensure their safe operation and unimpeded flow. Inspection manholes bring convenience at the same time. It also affects the plate integrity, structural stability, appearance aesthetics and service life of urban roads to a certain extent.
Existing problems and causes of inspection manholes
① The damage to the existing road first appears around the inspection shaft. ② Inspection manholes cause discomfort when walking (cars) and are difficult to cure, and also affect the overall appearance of the road. ③ Due to the congenital deficiency during construction and the restriction of maintenance itself by objective conditions, although some inspection manholes have been repaired several times, the effect is always unsatisfactory.
Analysis of the cause of the problem of inconsistency between the inspection manhole and the road surface
There are many reasons for the inspection manhole to make the road surface uneven. But it is mainly due to the uneven settlement of the inspection manhole and the road surface. Conventional inspection manholes are composed of foundation, manhole chamber, manhole neck, manhole circle and manhole cover. As a whole structure, the manhole neck, manhole ring and manhole cover of the inspection manhole are located in the pavement structure layer of the road, while the manhole chamber is located below the road pavement structure layer. In the construction of inspection manholes and roads, the order of construction is to lay the pipeline first and reserve the manhole position, then build the inspection manhole after the pipeline laying is completed, and finally complete the road construction. Due to the influence of various factors such as construction conditions, rainy season precipitation, foundation treatment, and geological conditions. It is difficult to form a whole with the inspection manhole and the road structure layer. At the same time, the treatment of the pavement structure layer around the inspection manhole is also a weak link in Shi Dingzhong.
The inspection manhole is not connected with the surrounding road surface, especially in the asphalt concrete road surface. The occurrence of inspection manhole hazards is a relatively long gradual process. in the early stages of road construction. The road is basically level with the manhole, but over time and under load. Both the road and the inspection manhole have subsidence and poor deformation. Coupled with the influence of groundwater, the backfill soil around the inspection manhole is relatively loose, which makes the chamber and neck of the inspection manhole (especially the brick inspection manhole) slightly deformed. Thus affecting the road structure layer. This kind of situation usually begins to appear about half a year after the completion of the road. At first, it appears as a circumferential crack along the periphery of the manhole cover of the inspection manhole. As time goes by, the crack further expands, and then there are obvious circumferential cracks along the periphery and the surrounding subsidence. At this time, when the vehicle is driving, you will obviously feel bumps and jumping. at the same time. Due to the uneven change of soil pressure around the manhole, it is easy to damage the manhole circle of the inspection manhole. Due to the subsidence of the inspection manhole, the rainwater cannot be drained in time when it rains, and ponding is formed around the inspection manhole, which penetrates into the subgrade along the cracks, destroying the stability of the subgrade and making it lose its original strength and function. This in turn leads to further propagation of cracks on the surface
Big, the sinking is more serious. Due to the different soil quality and backfill quality around the inspection manhole, etc. After being soaked in water, it will cause water and soil loss, and cause the road surface around the manhole to collapse. This is a vicious circle process, which affects the comfort of driving at the slightest, and is related to the service life and safety of the road, and even leads to quality accidents. Some unreasonable practices in construction will also accelerate the above-mentioned damage process. The common ones are: ① Defects in the construction process of the inspection manhole itself, including errors in elevation control. The installation of inspection manhole covers and manhole rings does not meet the requirements, the size of the foundation pit of the inspection manhole does not meet the construction requirements, the strength of the lining material is low, the quality defects during the inspection of the masonry of the manhole, and the management of the construction is not standardized, etc.; ②The quality of the surrounding backfill is poor; ③ Insufficient bearing capacity of foundation.
The above content is based on the problems and reasons listed in a certain city in China. The customer in Pakistan has made some references to these content. The specific problems are still investigated and collected according to the city where the customer Pakistan is located. If customers from other countries want to refer to the above content to purchase inspection manholes, please refer to them according to local conditions. Customers are best to leave us a message to contact us. We will recommend inspection manholes for you according to your specific situation. For these problems in a certain city, we also listed some solutions.
Construction Improvement Measures
According to the above-mentioned mechanism and cause analysis of inspection manhole defects, combined with actual construction experience, the following improvement measures can be taken to avoid inspection manhole defects from the source.
Strictly control the elevation of the inspection manhole
The elevation of the location of the inspection manhole should be coordinated with the vertical elevation and cross slope of the road to avoid height differences. before asphalt paving. The elevation of inspection manholes should be strictly controlled. When laying out the line, the longitudinal and transverse slopes of the road must be satisfied at the same time. For this reason, the crosshairs can be used for precise positioning. The elevation of the manhole frame of the inspection manhole shall be measured in four directions along the longitudinal and transverse slopes of the road, so as to avoid the formation of one side higher than the road surface. Generally speaking, the elevation difference is easier to control during construction, but it is difficult to maintain after construction. Therefore, it is necessary to ensure that the manhole frame and its bottom structure are solid to prevent deformation. When paving asphalt, adjust the paving thickness in time to make the inspection manhole and the road surface smoothly connected, and the height difference between the road surface and the manhole frame shall not exceed 5mm. When placing the inspection manhole circle. At least 3 height-adjusting jigs must be placed between the manhole circle and the top of the manhole wall, and checked with a small cross or ruler to ensure that the top of the manhole circle is evenly close to the small cross line. Considering the impact on the inspection manhole when the snowplow is working in winter in the north, it is advisable that its installation height should be 0-5mm lower than the road surface.
Improving the Construction Method of Manhole Bore
Since the road construction is mainly based on large-scale mechanical construction, in order to improve the efficiency of mechanical construction, after the shaft wall is raised to the top elevation of the subgrade, it should be carried out simultaneously with the construction of the road base and surface course, and the height should be increased layer by layer. When the construction reaches the final surface layer, install the manhole ring and manhole cover to ensure that the asphalt concrete around the manhole cover can be integrated with the main road surface to ensure the compaction effect. When the manhole ring is installed, the mortar should use high-strength grade mortar. The construction of the manhole body should be done as follows: ① In order to improve the compressive strength of the manhole wall, the manhole wall material within 40-50 cm below the road surface elevation (including the thickness of the manhole cover seat) can be changed to plain concrete with a strength grade of C25 or above . If the connecting part of the inspection manhole body and the road surface is a masonry structure. Block strength should not be less than MU10. 20 cm thick under the asphalt concrete layer (belonging to the pavement structure layer) and 30 cm wide around the inspection manhole shall be poured with grade strength C25-C30 concrete. And ensure that the strength of the concrete reaches more than 75% of the design strength before applying T to the asphalt concrete layer on the pavement. ② Improve the connection between the manhole frame and the manhole body of the inspection manhole. Add teeth at the bottom of the manhole frame, or drill holes and pre-embed bolts at the bottom of the manhole frame to be embedded in the wall or concrete to increase stability. On the side of the inspection manhole frame, the connection method of drilling pre-embedded bolts through the manhole wall concrete is fixed, so that the manhole frame, manhole body, and the structural layers around the manhole cover frame are connected into a firm and unified whole. Avoid the displacement of the manhole cover frame due to mechanical rolling during road construction and road use.
The customer in Pakistan said that the above improvement measures are also a reference for them. Other customers can refer to the product performance table in this article to determine what material inspection manhole is suitable for them to buy.
Construction method of combined cover installation and manhole ring reinforcement
For problems in inspection manhole engineering. Based on the previous construction experience, a set of construction methods for manhole cover installation and manhole circle reinforcement are summed up.
1) Well circle reinforcement and manhole cover installation should be carried out before asphalt surface construction, and according to the design requirements of the manhole cover size and the same manhole circle. Determine the shape and size of the manhole ring reinforcement. Generally, it is a square with the manhole head as the center, and the outer wall of the manhole is 25 cm wider. A cutting machine is used to slit to excavate the pavement structure within the reinforcement range of the manhole ring. A small part of the pavement structure can be reserved for manual chiseling to ensure that the groove wall is straight and tidy.
2) According to the design requirements of the reinforced manhole ring, determine the masonry height of the inspection manhole. Clean up the foundation pit before installing the steel frame. The surroundings of the manhole wall shall be leveled after pouring and compacting with low-grade strength concrete.
3) The steel frame should be processed into a square shape, and the installation should match the position of the manholehead, and a 4cm-thick protective layer should be ensured for the steel bars; the frame should be installed firmly, and no stepping on it should be avoided during concrete pouring.
4) The pre-embedded bolts can be installed at the same time as the manhole frame, or can be positioned by the mold, and installed when pouring the concrete in the first step; the bolts should be placed vertically; the nuts should be tightened before pouring the concrete in the second step. Make it effectively connected with the concrete and manhole frame reserved hole L.
5) Make a solid and applicable circular manholehead template. The formwork should be easy to install and dismantle to ensure that the manholehead size and the concrete surface are smooth and clean. During manholehead masonry, it should be considered to leave probe bricks as the fulcrum of the inner mold, and the top of the inner mold should be close to the manhole cover. To prevent grout leakage, remove the inner mold after all the concrete in step 2 is completed.
6) The manhole frame and manhole cover are used together. The installation of the manhole cover should ensure that the cross body is consistent with the driving direction; the manhole cover with the rotating shaft. The shaft should be welded to prevent damage to the asphalt at the shaft. The elevation of the manhole cover should be consistent with the elevation and slope of the road surface, and the elevation is determined according to the asphalt paving method and width, and the height of vertical (level) stone edges.
7) Rinse with water and fully wet the foundation tank before pouring concrete. Concrete pouring is carried out in 2 steps. The first step is pouring to the bottom of the upper steel bar. After the concrete is finally set, it is shaved and grouted, and three points are raised. After the bolts are fastened, the second step concrete is poured. Concrete needs to be compacted by vibration and closely combined with the excavated surface around the manhole. The reserved height above the concrete shall ensure that the asphalt around the manhole cover is greater than the design thickness of the upper layer.
8) Concrete should be cured for more than 7 days. Rolling is strictly prohibited during maintenance. Early strength agent or quick setting agent can be added appropriately according to the construction progress. To shorten the maintenance time.
The performance table of the inspection manhole, existing problems and construction improvement measures are introduced above. Customers in Pakistan and customers from other countries who want to buy inspection manhole can refer to the above information to determine what material inspection manhole they need. If customers need parameters, you can leave your contact information or contact us directly, and we will send you the most detailed parameters.
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