Introduction:

The municipal road drainage system is one of the critical infrastructures that ensure the proper functioning of urban municipal facilities, and guaranteeing the quality of its construction is of paramount importance. The most common quality issues fall into four categories: pipeline misalignment or water pooling; pipeline leakage and failure to pass the closed-water test; deformation or settlement of inspection wells; and poor-quality components and backfill settlement.

Problem 1: The pipeline is misaligned or water accumulates.

cause:

Measurement errors, construction distortions, and the inadvertent avoidance of existing structures have led to planar positional deviations, water accumulation, and even slope failures on the facade.

Precaution:

1. Measures to prevent diseases caused by measurement and construction mainly include:

(1) Prior to construction, re-test and protect the transfer piles in accordance with the construction survey specifications and regulations.

(2) Construction stakeout shall be conducted in conjunction with hydrogeological conditions, based on the embedment depth, design requirements, and relevant regulations, and must be retested to verify that the error complies with the specified requirements before construction can be handed over;

(3) Construction shall be carried out strictly in accordance with the sample piles, and the grooves and foundations shall be accurately surveyed and accepted with respect to alignment and longitudinal grade.

2. During construction, if an existing structure is encountered and must be avoided, a connecting well shall be provided at an appropriate location, with the connecting well aligned in a straight line. The rotation angle of the connecting well shall exceed 135°.

Problem 2: Water leakage in the pipeline, unqualified closed water test

cause:

Uneven foundation settlement, poor construction quality of pipes and their joints, inadequate sealing at the ends of closed water sections, and substandard well construction can all lead to water leakage.

Prevention:

1. Poor pipeline foundation conditions can lead to uneven settlement of the pipeline and its foundation, typically resulting in localized water accumulation. In severe cases, this may cause pipeline fractures or joint cracks.

The preventive measures are:

(1) Construct carefully in accordance with the design requirements to ensure the strength and stability of the pipeline foundation. When the local foundation’s geological and hydrological conditions are unfavorable, soil replacement and improvement measures shall be implemented to enhance the bearing capacity of the trench bottom.

(2) If the soil at the bottom of the trough is disturbed or saturated with water, the soft soil layer shall be excavated first, and the over-excavated area shall be backfilled with stable sandstone or gravel.

(3) When excavating earth below the groundwater level, effective measures should be taken to prevent drainage and precipitation at the bottom of the trench to ensure that the dry trench is excavated. If necessary, a 20cm thick soil layer can be reserved at the bottom of the trench. Dig and remove.

2. The pipe quality is poor, with cracks or loose local concrete, resulting in poor impermeability and leakage. Therefore, the following is required:

(1) The pipes used must be accompanied by a certificate and mechanical test report, as well as other relevant documentation, issued by the quality department;

(2) The pipe’s surface quality shall be smooth, with no loose particles or honeycomb-like defects.

(3) Conduct a thorough, section-by-section inspection prior to installation. If any defects are identified or if there are quality concerns, the item shall be ordered off-site or may only be used after effective remediation.

3. The pipe joint filler and construction quality are poor, and the pipe is damaged or joint cracked under the action of external force. Prevention:

(1) Select high-quality interface fillers and carry out construction in accordance with the trial mix proportions and appropriate construction techniques;

(2) During tape application, the joint seam must be kept clean; if necessary, it should be chiseled, and then the work should be carried out meticulously in accordance with the construction operation specifications.

4. The construction quality of the inspection well is poor, and the joint between the well wall and its connecting pipe is leaking. Preventive measures:

(1) The masonry mortar in the inspection well shall be fully packed, with no joints left unfilled; the surface shall be cleaned and moistened prior to wiping, the mortar shall be promptly troweled and finished during surface wiping, and proper curing shall be maintained. When groundwater is present, troweling and jointing must be completed in a timely manner in conjunction with the masonry work. Internal wiping or internal jointing shall not be carried out after backfilling.

(2) The outer surface of the pipe connected to the inspection well shall be moistened and evenly coated with a layer of cement paste, after which both the inner and outer surfaces shall be painted to prevent leakage.

5. Planned reserve branch pipes are not tightly sealed and are often overlooked because they are in the well. If a brick wall is used for blockage, the following points should be paid attention to:

(1) Clean the inner wall of the pipe within 0.5 m of the pipe mouth before plugging, and apply the cement paste while moistening the used bricks for later use;

(2) The grade of the grouting mortar shall not be lower than M7.5, and it shall exhibit good consistency;

(3) The grade of cement mortar used for jointing and plastering shall not be lower than M15. When the pipe diameter is large, the inner and outer sides should be smaller and only the outer single-face jointing or plastering shall be done. The plastering surface should be constructed according to the waterproof 5-layer construction method.

(4) In general, the inspection well shall be sealed prior to construction to ensure quality.

6. The closed-water test is a comprehensive inspection of the pipeline construction and material quality, during which it is inevitable that there will be three or two failures. At this time, you should mark the leaks one by one, and take care of them after draining the water in the pipe. For small gaps or pitted surface leakage, grout or waterproof coating can be used, and the more serious ones should be reworked. In addition to replacing pipes and refilling the joints, serious leakage can also be handled by professional and technical personnel. Do the test after the treatment, and repeat the process until the closed water is qualified.

Problem 3: The inspection well is deformed, sinking, and the quality of components is poor

cause:

The well exhibits deformation and settlement, the manhole cover is of poor quality, and the installation work is substandard; moreover, the ladder installed inside the well is mounted in a haphazard manner, all of which adversely affect both the aesthetic appearance and the functional performance.

Prevention:

1. Carefully inspect the well’s base layer and cushion, and break the pipe to create a flow trough to prevent the well casing from sinking.

2. The masonry quality of the inspection well should be well controlled to prevent the well body from deforming.

3. The inspection well cover and its frame must be properly matched; the grout filling must be complete during installation; the light and heavy models, as well as the bottom surface, must be in good condition; for iron ladder-type installations, the position of the first step up and down must be precisely controlled, with allowable deviation kept within acceptable limits, and the planar positioning must be accurate.

Problem 4: Backfill Soil Subsidence

cause:

Backfilling around the inspection well is not dense, not stratified and compacted as required, poor filler quality, poor water content control and other reasons affect the compaction effect and cause excessive settlement after construction.

Precaution:

(1) When backfilling the pipe trench, appropriate fill materials and compaction (tamping) equipment must be selected based on the backfill location and construction conditions. For example, the pits for drainage facilities beneath Nanning City’s main roads are backfilled with a mixture of sand and gravel. The trench should be filled from the top of the pipe down to 30 cm below the pipe crown, followed by water injection and vibration compaction until the relative density reaches or exceeds 0.7. Practical experience has demonstrated that this approach yields excellent results.

(2) When the trench is narrow, manual or frog-type rammer can be used to ram and fill. Different fillings and different filling thicknesses should choose different tamping tools to achieve the most economical compaction effect.

(3) Silt, tree roots, turf, and decayed vegetation in the fill material not only impair compaction but also shrink and decompose in the soil, creating voids. Such materials should not be used as fill to prevent settlement.

(4) The moisture content of the fill material shall be controlled to be greater than approximately 2% above the optimum moisture content; in the presence of groundwater or following rainfall, the water must be drained first, after which the fill material shall be placed in layers and compacted.

Treatment measures:

Take corresponding measures according to the degree of settlement damage:

(1) Minor settlement that does not affect other structures may be left untreated or require only surface treatment, such as partial patching of the asphalt pavement to prevent water accumulation;

(2) If the foundation of other structures is damaged, pump cement slurry can be used to fill;

(3) If the structure is damaged, the poor fillers should be excavated, replaced with materials with good stability, and restored to the damaged structure after compaction.

In summary, the pipeline project is a concealed undertaking; upon completion, only the inspection well remains accessible for inspection. Consequently, the construction quality of the inspection wells often plays a decisive role in assessing the overall project quality. The excellence of drainage pipeline engineering must be predicated on the excellence of the main structural works. During construction, it is imperative to address and overcome common issues, ensure that the overall project construction quality meets high standards, and further enhance the quality of the inspection well construction, thereby achieving the overarching goal of excellence.

Source | Pipe Gallery Construction