Tunnel lining construction is the key construction content of tunnel engineering, which is related to construction quality and construction safety. So what are the causes of common problems in tunnel lining construction? What preventive measures are there to ensure the quality of tunnel lining construction? Remember the following 15 points to easily avoid common problems in tunnel lining construction.
Quality issues and phenomena
1. There are voids behind the lining;
2. Obviously staggered lining, serious leakage, quicksand, and poor appearance quality;
3. The thickness of the lining does not meet the design requirements;
4. Water leakage in the lining;
5. The lining concrete is cracked;
6. The appearance quality of the water trench cable trough is poor;
7. Poor drainage of the drainage ditch.
Analysis of the cause of the cavity behind the lining
1. Construction and backfilling of over-excavation that is not in accordance with the specifications;
2. When lining the vault, the pouring concrete is not full and the vibration is not enough;
3. The pumped concrete creates a cavity at the far end of the conveying pipe due to pressure loss, slope and other reasons;
4. The slackness of the waterproof board is not well controlled.
Measures to prevent cavities behind the lining
1. The tunnel excavation surface is inevitably uneven. For the pits caused by over-excavation in a small area, the lining concrete is generally used for backfilling during the construction. Note that the waterproof board should be close to the rock surface and the tightness is suitable; for the collapse caused by landslides For deep sinking pits, use landslide treatment measures to backfill smoothly before the construction of the second lining;
2. The general lining formwork trolley has a reserved hole for pumping concrete at the front and rear of the arch top position. If the formwork trolley is longer, the reserved hole can be added in the middle to prevent the concrete from being poured out of place when the longitudinal slope of the tunnel is large. Backfill grouting after construction;
3. The new lining formwork trolley is equipped with attached vibrators on the side walls and the arch waist. At the same time, two plug-in vibrators are installed on both sides of the trolley during concrete pouring, and the separation is carried out from the reserved window of the trolley. Layer vibrating, these can effectively solve the problem of vibrating.
Analysis of the cause of poor apparent quality of lining
1. The rigidity of the lining trolley is not enough, and the template repair is not in place;
2. The workability of the lining concrete is not good, and the bleeding is serious;
3. No symmetrical pouring on both sides;
4. The pouring speed is too fast and the trolley floats;
5. The template is coated with too much oil, and a fish scale cloud will be formed after the mold is removed;
6. Part of the template is not cleaned up, and the phenomenon of “skinning” and lumps is formed after the mold is removed.
Preventive measures for poor apparent quality of lining
1. Lining trolleys are all processed by regular manufacturers, and the strength and stiffness are checked before processing. Check the calculation data when purchasing;
2. During lining construction, if the overlap of the lining formwork trolley does not exceed 0.5m, misalignment will generally not occur. Therefore, before the lining construction, plan the length of the trolley in place to avoid long overlap. At the same time, the surveying personnel must have certain construction experience, the lining center line and elevation are well controlled, and the offset control on both sides of the formwork trolley is appropriate to prevent the occurrence of too large or too small affecting the next set of trolleys in place;
3. The lining concrete shall be constructed in strict accordance with the designed mix ratio. When designing the mix ratio, the pumping concrete and workability requirements shall be considered. At the same time, the formwork trolley shall be coated with a mold release agent. The mold release agent is best to use a special mold release agent and apply evenly. Moderate dosage can improve the surface quality of the lining;
4. When the lining is poured, both sides should be layered and symmetrically poured, and the concrete falling height should be controlled within 2m to prevent segregation;
5. If there is some concrete sticking to the formwork trolley, clean it up before pouring next time, and then apply a release agent, otherwise it will affect the surface finish of the next set of linings;
6. The lining formwork trolley will float up due to the pressure of the cast-in-place concrete at the foot of the side wall and the end pressure will move longitudinally. Therefore, the formwork trolley is firmly reinforced before the lining construction. At the same time, the lining concrete is poured to the height of the center and the arch waist. The screw is re-reinforced to prevent the trolley from moving due to the loosening of the floating part of the screw.
The lining thickness is not enough, the cause analysis is enough
1. The contractor’s quality awareness is not strict, and the process monitoring is not in place;
2. Or the reserved settlement is insufficient;
3. The under-excavated parts are not processed.
Mmeasures to ensure the thickness of the lining
1. The thickness of the lining should be guaranteed, and the initial support section should be inspected before the construction of the lining. If there is any intrusion into the lining clearance, it should be treated according to the specifications;
2. For some tunnels with large settlements, pay attention to settlement observation. If the designed settlement does not meet the requirements, the reserved amount can be appropriately enlarged according to the actual situation, but it should not be too large to prevent artificial over-excavation. Waste lining concrete.
Analysis of Causes of Water Leakage in Lining
1. The lining is cracked;
2. Waterproof, drainage and water diversion facilities are not perfect;
3. There are quality defects in the treatment of circumferential construction joints and deformation joints, and the installation of water stop strips and water stop belts is not standardized;
4. The waterproof board is damaged, perforated, and the weld is not tight;
5. The lining is not compactly tamped, and there are holes or honeycombs;
6. Unqualified waterproof materials;
7. The number of drain holes is insufficient or the drainage is blocked.
Lining water seepage prevention measures
Lining seepage is generally caused by inadequate waterproof and drainage construction and imperfect lining. It is necessary to strengthen on-site management to ensure that the waterproof and drainage measures are in place, and the concrete lining is poured tightly. The following aspects should be done specifically:
1. Blind pipes are installed in place. Before the waterproof board is constructed, ensure that the blind pipes are installed according to the design requirements. The number of blind pipes should be increased if the water seepage in some sections is large. The blind pipes and the longitudinal drainage pipes are connected well to ensure the drainage effect;
2. Waterproof board construction is the key link of lining waterproofing. At present, there are many types of waterproof boards on the market, and the quality of the waterproof boards must be qualified; the waterproof board connection is best to be welded. During the construction process, quality supervisors will check on site and find problems in time deal with. Part of the uneven areas should be inspected to prevent leakage of welding; for reinforced concrete linings, the waterproof board should be prevented from being damaged during the construction of the steel bars. If there is any damage, the waterproof board construction personnel should be notified to repair; the waterproof board should be installed close to the rock surface , The degree of tightness is moderate to prevent the waterproof board from tearing due to pressure when the concrete is poured;
3. Treatment of construction joints and settlement joints: general construction joints and settlement joints are designed with embedded and embedded waterstops or waterstops, and some have back-attached waterstops, etc. The back-attached type is better for construction and close to The waterproof board can be fixed by the head plate; during the construction of the buried water stop strip, a corresponding size of the small size (half the thickness of the water stop strip) should be reserved in the middle of the lining end, and the water stop strip should be inlaid during the next set of construction. Into, firmly fixed. The construction of the buried waterstop requires the headboard to be constructed in layers, divided into two layers from the location of the waterstop to ensure that the waterstop is reserved and cannot be damaged, which seriously affects the construction of the headboard, so the construction is often not in place. Strengthen the management on site to ensure the construction of the buried waterstop is in place;
4. The horizontal drainage pipe should be reserved according to the design and adopt three-way connection to ensure that the drainage can flow into the ditch smoothly; the longitudinal drainage pipe is generally a perforated corrugated pipe, wrapped with geotextile to prevent the ingress of sediment and affect the drainage effect;
5. There should not be a long pause during the lining concrete pouring process, so the site materials, generators, etc. must be prepared to prevent mid-stop work, because the two pouring concrete is prone to cracks, causing water leakage in the lining; the only solution is to perforate grouting. Water, but the holes should be shallow to prevent damage to the waterproof board;
6. The lining concrete must have a waterproof effect. Generally, it is designed as a waterproof concrete. When designing with it, it must be considered from many aspects. It is necessary to ensure the workability and anti-seepage requirements, and the construction shall be carried out in strict accordance with the cooperation;
7. When pouring the lining concrete, control the concrete falling height to ensure layered pouring, layered vibrating in place, the formwork trolley window formwork is closed tightly to prevent mortar leakage, etc., to ensure the compactness of the concrete lining, and ensure that the construction concrete has a waterproof effect.
Analysis of the causes of lining cracking
1. Temperature difference and concrete shrinkage;
2. Alkali aggregate chemical reaction;
3. The side wall foundation sinks;
4. Hole body bias;
5. The joint part of the invert and the side wall is cracked due to stress concentration;
6. Cracking caused by difficulty in pouring concrete in the arch or interruption of pouring;
7. The demoulding time is too early, and the lining strength is not enough to support its own weight and cracks.
Preventive measures for lining cracking
1. The heat of hydration of high-grade concrete is increased. After construction, it must be sprinkled and maintained for no less than 14 days to prevent the surface from drying and causing cracks;
2. Select qualified materials for lining concrete materials, and construct in strict accordance with the mix ratio;
3. The lining generally does not crack. Generally, the lining is cracked due to bias pressure or terrain movement at the opening of the cave. Therefore, when backfilling the roof of the cave, pay attention to the symmetrical backfilling on both sides. For tunnels with biased pressure, strengthen the lining strength or reduce pressure;
4. The joint part of the invert and the side wall is prone to stress concentration. During construction, ensure that the side wall foot is excavated in place, and there should be no under-excavation, which will cause the lining to crack;
5. Control the demoulding time of the lining, and formulate the demoulding time and curing time according to the different tunnel temperatures in different seasons to prevent the concrete from falling off and cracking;
6. The lining concrete is guaranteed to be poured in place at one time and cannot be stopped halfway. It is not conducive to waterproofing and can easily cause cracks and reduce the strength of the lining. Therefore, the material reserves are sufficient before construction and the machinery and equipment are good; at the same time, the formwork trolley should be checked before the lining construction. There are deformations, loose bolts, welding off, etc., to prevent problems during the construction process, resulting in abnormal lining construction.
Analysis of Causes of Poor Appearance Quality of Cable Trenches
1. The mould is not meticulous and not firm, and the outer edge of the groove is not controlled according to the center line of the line;
2. The cover plate is prefabricated and has poor installation quality;
3. Other process construction, repeated lifting, moving and collision and damage.
Appearance quality control measures of water trench cable trough
The gutter cable trough is a tunnel surface project, and the surface construction quality affects the overall image of the tunnel. Therefore, it is necessary to ensure linearity and straightness, without dislocation and smooth surface.
1. The cable trough of the water ditch is controlled by measuring and laying out, the curve is controlled according to the radius, the height of the center line of 10m or 20m, and the straight line is controlled by 50m. The template adopts an integral steel template to ensure one-time pouring and molding. The template is coated with release agent to ensure the appearance quality. After the template is installed, the technician checks the installation of the template, whether the linearity meets the standard and whether the reinforcement is firm;
2. Cover plate prefabrication adopts centralized prefabrication in the prefabrication yard, adopts shaped steel-plastic template, with marks on the upper and lower sides, which is convenient for installation; the concrete requirements and workability of the cover plate are good, and the vibrating table is vibrated to ensure a smooth surface;
3. After the cover plate is prefabricated, it is stored in the prefabrication yard. After the tunnel trench construction is completed, it is placed in a centralized manner when no other processes are affected. The gap between the cover plate and the foundation is filled with mortar when placing, and the installation is required to be stable and not shake.
Analysis of Causes of Poor Drainage in Drainage Ditch
1. The vertical slope at the bottom of the ditch is not standardized, there are deviations, and the control is not accurate, and the bottom of the ditch is “wave”;
2. The slope of the longitudinal slope at the bottom of the ditch is small;
3. There are debris in the ditch and the flow path is blocked;
4. The bottom of the ditch is not smooth.
Preventive measures for poor drainage of drainage ditch
1. The trench is excavated in place, and the concrete is poured to ensure linearity and straightness, to ensure the smoothness of the trench and prevent water accumulation;
2. There are many sundries in the tunnel during working hours and it is easy to block the groove, so it should be cleaned regularly to facilitate drainage in the tunnel;
3. Drainage. Because the formwork is installed straight when ditching and pouring, the reinforcement is firm, and the concrete is tamped and compacted when pouring.