Road engineering has the characteristics of long line, changeable geological and hydrological conditions along the line and bare structure all the year round. The stability of subgrade is the key link of road life. Because there are various pipelines and underground facilities in urban roads, they need to be constructed at the same time; The need of urban traffic does not allow the construction period to be too long; Therefore, pipe trench backfilling and road construction in those years have become another feature of urban roads. At the same time, due to the three-dimensional distribution of pipelines, pavements, underpasses or overpasses, all kinds of urban public facilities, traffic facilities and road construction are built simultaneously, which increases the complexity of the project.

Second, the main quality problems existing in the current urban road engineering and preventive measures

(a) the junction of the rainwater well, the inspection well and the road surface collapses.

Because there are many auxiliary facilities in municipal road engineering, most rainwater wells are located in the driveway, and many main drainage pipes and inspection wells are also located in the driveway. Therefore, when the width of the well back is small, it is very difficult to backfill and compact, and it is also difficult to check the compactness. Negligence or lax supervision in construction will inevitably lead to quality problems in the project, leading to collapse defects at the joints between ordinary rainwater wells and inspection wells and the road surface, leading to bumps when vehicles are driving.

In this regard, special attention must be paid to backfill quality during construction, which requires the construction unit to take special measures to backfill. According to our experience, the gap behind the middle well (more than 50mm wide) can be filled with mortar, and the backfill thickness of each layer is ≤ 100mm, and compacted by layers. The back cracks of small wells (width less than 50mm) can be filled with masonry mortar, and the backfill thickness of each layer ≤ 100mm should also be compacted by layers.

In order to prevent negligence in construction, the supervisor should strengthen inspection. If necessary, supervision should be carried out at any time.

(2) The compactness of subgrade fill and trench backfill can not meet the standard requirements.

The strength and stability of subgrade are the basic conditions to ensure the strength and stability of pavement. Because all kinds of pipelines are laid in the underground part of urban roads, the compactness of trench backfill has great influence on road subgrade; In road subgrade construction, embankment filling and trench backfilling are the key parts of subgrade construction; The common quality defects of backfill compaction include ultra-thick backfill, inclined rolling, unqualified fill, etc., which will lead to backfill not meeting the standard requirements.

1, damage

(1) Not all the loose soil in the thickness of the pavement can meet the required compactness. If it is a road, it will cause the subgrade and pavement structure to sink; If it is a pipeline, it can't reach the density required by the chest, so the earth pressure on the chest is less than the top pressure and ground load of the pipeline, which may cause the upper part of the pipeline to rupture and the unreinforced pipeline may be squashed.

(2) The component loss caused by the compaction gravity of the roller makes the roller weight unable to exert its maximum compaction effect on the longitudinal slope. The greater the slope, the greater the lost compaction work.

(3) Blocks are entrained in the fill, which prevents the soil particles from squeezing each other and fails to achieve the overall compaction effect. On the other hand, the block supports the grinding wheel, resulting in accumulation, leaving gaps around the block, resulting in future subsidence.

(4) The soil layer backfilled with muddy water is saturated with water and cannot be compacted. The groundwater level drops and saturated water infiltrates, which will cause the fill to sink and endanger the safety of subgrade.

2. Governance methods

The construction unit shall make technical disclosure to the operators, so that the virtual paving thickness of subgrade fill and trench backfill shall not exceed the relevant provisions according to the model; Within the total width of subgrade, horizontal layered filling method should be adopted; When the transverse slope or longitudinal slope of subgrade ground is steeper than 1:5, steps shall be made; When backfilling the trench and filling the soil in sections, the steps should retreat by layers, the height of the steps should be greater than the compaction thickness, and the width of the steps should be greater than or equal to1m. Large stones in the fill should be removed, and hard clods larger than 10cm should be broken or removed.

(3) Repairing and rolling of soil roadbed.

1, damage

(1) Without compaction, the pavement structure is laid on the soft foundation, and there is a big gap in the soft foundation. After the infiltration of rain in rainy season and the accumulation of water in winter and spring, a large amount of water seeps into the soft soil foundation, which reduces the stability of the soil foundation, can not support the pavement structure, and the pavement is deformed and destroyed in the early stage.

(2) If we don't do the soil road bed technology, we can't find the soil layer with poor soil quality, weak soil foundation or excessive water content in time. As the upper structural layer, it will show the phenomenon of "spring", resulting in large-scale rework of the structural layer.

(3) Without controlling the elevation of vertical section and cross section of soil subgrade, only controlling the elevation of upper structural layer will not guarantee the design thickness of structural layer, and uneven thickness and weak parts will fail to meet the design requirements, leading to premature failure.

(4) The smoothness of dirt road bed is not controlled. Although it is rolled, the peak-valley length of the concave-convex part is smaller than the contact surface of the roller, that is, the surface where a pimple pit appears. In this way, the density will be uneven, the density of protruding parts will be high, and the density of low-lying parts will be poor, resulting in uneven density and strength of pavement structure layers.

2. Governance methods

(1) Train construction units or personnel with low technical quality, and make technical disclosure of working procedures during construction.

(2) According to the requirements of road bed technology, on the basis of controlling the center line elevation (+20mm), transverse elevation (+20mm, transverse slope less than or equal to +0.3%) and smoothness (10mm), the road bed in the filling section should be pressed down by 0 ~ 30 cm, and within this range, the road bed in the excavation section should be pressed down by 0 ~ 30.

(3) The compaction degree in the process of road bed is the main inspection item (i.e., the item with △), just like each structural layer of pavement. If the subgrade process is not done, the pass rate of compaction degree is zero, and it is judged as unqualified project according to the quality inspection evaluation standard. Therefore, it is necessary to strengthen the quality control of subgrade process.

(4) During the sidewalk construction, the blind slab is not installed firmly, and it is easy to fall off.

Because the blind road is downhill at the place leading to the crosswalk, the track slab here needs to be cut to protrude from the road surface. Once there are some problems in the installation quality, it is easy to cause the floor to fall off. This is also a common quality defect in municipal road engineering.

The supervisor shall put forward special requirements in the technical disclosure before construction. During construction, the construction unit shall be required to pay special attention to the construction quality here, and pay attention to the mortar label, dry humidity and mortar fullness. If necessary, the mortar used here can be required to be upgraded by one grade. We should also strengthen inspection during supervision.

(5) Cracks appear on the pavement crossing the groove.

In municipal road engineering, there are many pipelines that need to pass through the roadway, such as rainwater drainage pipelines, crossing power cables, communication cables, tap water pipelines, etc. These pipelines should be constructed before subgrade construction, so there is no problem of insufficient compaction. Special attention should be paid to this point to prevent pavement cracks caused by insufficient compaction.

When backfilling the bottom of the pipeline, the construction unit is required to fill the narrow part of the pipeline toe guard with gypsum, and then manually tamp it with a thickness of ≤200mm, and the tamping times shall not be less than 5 times. Above the pipeline, after two layers are backfilled by manual compaction, mechanical compaction is carried out. And put slopes on both sides to complete backfilling, so as to avoid vertical joints.

(6) The height difference between the cover plate of the street lamp manhole and the pavement of the sidewalk exceeds the standard, which is easy to cause mixed feet.

In sidewalk construction, because the manhole cover plate is large and difficult to install, the height difference between the manhole cover plate and the pavement is easy to exceed the standard, and the phenomenon of foot mixing may occur after delivery. Supervisors need to check and accept them one by one, and those who fail to meet the requirements persist in transformation until they meet the requirements.

Third, measures to improve the quality of urban road engineering management

(A) improve the quality management system of municipal engineering construction system

1. Establish and improve the engineering construction management system, standardize and guide the management of various departments and contractors in all stages and links of engineering construction projects from project initiation to completion acceptance.

2. Improve bidding management measures, further open the engineering construction market and avoid local monopoly. Optimize the bid evaluation method of construction bidding, so that enterprises with high engineering quality or good construction quality can win the bid more easily, or have more chances to win the bid, avoid vicious price competition of construction units, and make the bid return to rationality.

3. Establish and improve the work supervision and assessment methods for construction units, supervision units, design units, survey units and testing units, and form a rating optimization system for each unit.

4. Improve the reward and punishment system of project quality management.

5, improve the project construction management units and individuals integrity assessment and punishment management system.

6. Establish and improve the owner's project construction quality management outline, and define and standardize the contents, standards, procedures, methods and guidelines of quality management.

(two) to strengthen the supervision, assessment and rewards and punishments of the quality behavior of the construction unit.

1. Strengthen the monitoring and assessment of the on-site construction quality of the construction unit. By means of regular inspection and temporary spot check, the overall operation of project quality and the quality status of key parts are supervised and controlled. This kind of supervision and control should be jointly controlled by the owner, the supervisor and the quality inspection station. The contents of monitoring and evaluation should be discussed and studied in detail according to different engineering contents and requirements.

2. Check and assess the construction investment of the construction unit and the operation status of the project quality management system. Focus on the contractor's breach of contract, the contractor's organization and main person in charge in place, the investment of main construction equipment, the conformity of quality control procedures, the quality control of materials, the construction plan, the quality control of on-site entities, and the information in the industry. We should take two measures to grasp the results of inspection and evaluation: first, grasp the incentive measures; Pay attention to punish with one hand. Grasp with both hands, and both hands should be hard.

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