Failure Causes and Design of Waterproof Failure of Highway Culvert
Reasons and design for water-proof failure of highway culvert Jiang Hua, Zheng Chang-an (Hunan Provincial Transportation Research Institute, Changsha, Hunan The main parts of leakage and different waterproofing requirements put forward the selection of waterproof design and materials for various parts.
When roads cross the valleys, rivers, walkways, and farmland access roads, it is often necessary to build a variety of lateral drainage and pedestrian structures. The most common ones are round pipe culverts, cover culverts, box culverts, arch culverts, and inverted siphons. Divided by the use objects of generalized culverts, they can be divided into culverts and channels. The former is mainly used for drainage purposes, while the latter is mainly for horizontal passing, animals, and vehicles, taking into account seasonal drainage functions. Culvert waterproofing is a comprehensive and practical engineering technology. It plays a crucial role in the function of highway culverts. The waterproof performance determines the stability of the culvert structure, appearance quality, durability and platform backs. The stability of the roadbed. Obviously, the culverts with different functions have different waterproof requirements. The author elaborates the quality planning and control of culvert waterproofing from the design point of view.
1 Leakage forms and hazards It is not difficult to find from the use of culvert projects on roads that have been built, there are many problems in the waterproofing of culverts, and most of the culverts have different degrees of leakage soon after they are completed. The main manifestations are as follows: 1 From the external to the internal leakage This form is the water in the backfill outside the culvert to seep into the culvert, and the backfilling with water-permeable material is more serious. The seepage of water forms various solid crystals along the culvert walls or causes variegated color on the concrete surface, which seriously pollutes the appearance quality of the channel; if the top of the channel leaks, the long-term dripping in the hole continues, causing great complication to passing pedestrians or vehicles. It is inconvenient; if it is used for a long time, water seepage will erode the steel bars in the concrete, causing the steel bars to rust and expand, causing the concrete to peel off and even cause structural damage. The channel project should focus on preventing this type of leakage from the outside to the inside.
12 Leakage from the inside to the outside This form is commonly seen in pressure culverts and semi-pressure culverts, due to the higher water pressure in the culverts and the culverts have leaking channels that allow the water in the culverts to leak out of the culverts. After seepage into the roadbed, the water content of the subgrade soil becomes steeper, the strength decreases, uneven settlement occurs under the action of the vehicle load, and even the stability of the slope at the entrance is damaged; long-term occurrence of leakage can also cause corrosion of the steel in the concrete. , resulting in structural damage to the culvert. The inverted siphon project should focus on preventing this form of leakage.
13 The basement or cavern is paved with water Spilled water occurs in the basement paving or hole paving of culverts. Especially after precipitation, long-term water runoff will take away sediments laid on the basement or hole, hollow out the basement, and even cause culvert stability damage.
2Cause Analysis The reason for waterproof failure of culverts is not unilateral, but is due to a combination of factors. Technically, there are four main reasons for the design of waterproof solutions, the selection of waterproof materials, and the construction and maintenance of waterproof projects.
1 The reasons for the improper design of culverts are improper choices, such as the culpability of pressure culverts and non-pressure culverts, concrete strength, reinforcement configuration, etc., and the joints' waterproofing solutions cannot meet the requirements; culvert locations are located in high groundwater levels or springs The more abundant sites and the lack of effective substrate treatment solutions and measures can easily lead to flooding of the basement or the caverns; the waterproof design is too simple and general, and the waterproofing scheme is single. Most of the current waterproofing schemes use Zhejiang green flax and linoleum; culverts. The high filling capacity makes the culvert bear a large amount of earth pressure, and the strength of the designed reinforced concrete can not meet the actual requirements, resulting in concrete cracks forming leakage channels.
2 Material Reasons Culvert waterproofing materials are usually waterproof concrete, asphalt, linoleum and so on. Waterproof concrete materials do not meet the requirements, resulting in waterproof capacity. The seams discussed here mainly refer to pipe joints of round pipe culverts and round pipe inverted siphons. According to the joint form, it is divided into flat seams and the U1.u hole above the foundation of the foundation body and the end walls are painted with t* layers of heat. Each layer 4-20ChinacaaemiclOumalE decline; Zhejiang green high-temperature liquefied at low temperature brittle, poor adhesion, easy to fall off and aging; linoleum poor quality, low oil content, and its own poor adhesion, can not effectively prevent the occurrence of leakage.
3 Construction Reasons Clearly, waterproof construction is one of the key factors to ensure the waterproofing of culverts. Due to inaccurate waterproof concrete ratio or poor construction control, the waterproof capacity is reduced, especially the inverted siphon; the time of the twilighting of the Zhejiang-Chuqing bast is not enough to adhere the asphalt and the batting, or the temperature is too high. Aging dissipates the adhesive force; Zhejiang Qing and waterproof mortar infusion, Zhejiang green fluff packing is not dense; before construction, the adhesion of the base layer is not cleaned, so that the adhesion of the base layer and waterproof material can not be fully affixed, resulting in shedding.
4 Causes of conservation Concrete curing quality directly affects the waterproof performance of concrete, especially waterproof concrete, curing temperature, humidity, and time are the most important direct factors. In addition, another important factor that causes cracks in the surface of concrete is wind, which is the most easily neglected in concrete curing. In the course of using culverts, the occurrence of culvert leaks was not observed in time, and the leaked parts were not repaired in a timely manner. That is, there was no effective waterproof protection measures and they were left unchecked, leading to continuous expansion of culvert leaks. 3 Leakage source and leakage channel 1 Leakage source For pressure culverts and semi-pressure culverts, leakage occurs from the inside to the outside. Leakage is caused by flowing water in the culvert, especially the inverted siphon of long-term accumulated water. For other culverts, especially the passages, the main form of leakage occurs from the outside to the inside, and the source of seepage water is the water in the backfill of the culvert.
2 Leakage channel From the inside of the culvert, the main leakage points are concentrated in settlement joints, construction joints, support mold holes, and cracks. Cracks occur mainly in inverted siphons and high fill culverts.
4 waterproof design Culvert waterproof design is not for a fixed part, but the entire culvert all possible leakage parts of the waterproof design. Because the settlement joints, construction joints and other structural nodes are the weak links in waterproof design and construction, the waterproof design of these parts occupies an important position in the culvert waterproof design, so there should be no or less design in the design.
1 joints waterproof design joints, the former for ordinary pipe culvert, the latter for inverted siphon. Flat mouth seams are stuffed with hot Zushi hemp and then filled with hot Zheqing or filled with hot Zheqing batt, and finally coated with hot Zheqing as the adhesive, using three oil two felt or eight layers waterproof paper paste waterproof . When the waterproof requirement is high, the joints are also made of reinforced concrete hoop joints, which not only improves the waterproof performance of the joints, but also increases the longitudinal stiffness. Jikou joints are usually filled with Zhejiang green batting, and the joints are filled with waterproof cement paste (the amount of expansion agent can be added to reduce the amount of asbestos indentation, and it can also completely fill up with hot Zheqing batting. The seams are treated like a flat seam.
42 Settlement joint waterproof design The culvert settlement joint is a through joint that is disconnected from the top to the base. It is generally set at the construction joint and is the weakest position for waterproofing. The waterproof design of settlement joints is mainly divided into two parts: the foundation and the body. The foundation lining is filled with the insole wood board or the greening sand board. The clay can also be used to fill the tamping. The expansion agent is added at the edge of the water surface by 1:3. The cement mortar is packed about 15m deep, and the settlement joint in the basic part can also be filled with a 1:3 cement mortar mixed with expansive agent, and the hot Zheqing bast is packed within 5m at the top of the base. The water-repellent treatment of the settlement joint above the basement can be handled with reference to the construction joint.
43 Construction joints waterproof design Culvert construction joints are divided into longitudinal joints and transverse joints. The former is the joint between the prefabricated roof and the body, and the latter is the joint between the construction body and the prefabricated roof. The construction body of the culvert is filled with Zhejiang green batting. The waterproof mortar can be used on the inner side of the channel with higher appearance requirements. The depth of the joint is 5, and the top of the mortar is 1~2mm below the surface. That is, the inner side of the construction joint is treated as a concave joint, while the outer side can be waterproof. Three oil two felt or eight waterproof papers are used. Construction joints waterproofing can also be set to steel (rubber) water stop, the principle is to extend the water seepage line, which is equivalent to increase the thickness of the concrete to effectively waterproof, but the higher the requirement of waterproofing, the use of external waterproof and waterproof The use of buried steel (rubber) composites, in which the expansion of water swelling or putty and buried steel (rubber) composite best. The construction joints between the prefabricated panels and the wall and the prefabricated panels can be filled with waterproof mortar or green bamboo fleece, with three oil two felts or eight layers of waterproof paper on the outside. If the culvert is made of waterproof concrete rigid waterproof, the waterproof concrete can be poured at the same time with the waterproof layer, and independent waterproof design is not necessary. The support mold hole is left by the tie rod that penetrates the wall when supporting the template. The tie rod must be removed. Otherwise, the corrosion will expand and damage the wall. The support mold hole is usually filled with Zhejiang green batting. Since the support mold hole is small, it is easy to fill. Densified, the inside is filled with waterproof mortar, and three oils and two felts are laid on the outside with 10mX10c.
44 waterproof layer design Currently, there are two main types of culvert waterproof layer design, hot brushing and waterproof concrete rigid waterproof layer. Corrugated concrete culverts with a thickness of 1 to 1.5 m are required to have high water-resistance channels or clear culverts. 2m thick waterproof mortar or 4~6m waterproof concrete can be installed on the top of the culvert. The rigid waterproof layer is mainly composed of 50mm thick fine stone concrete on the top surface of the board, and a layer of M200 bidirectional reinforced mesh is placed in the waterproof layer. The appropriate amount of micro-expansive agent, water reducing agent and waterproof agent can be added to the concrete to improve its crack resistance. Impermeability. This kind of waterproof layer is relatively hard, can withstand a certain pressure, plays the role of protecting the roof, and makes the whole culvert prefabricated cover have better integrity. Because the waterproof layer is buried in the soil, the thermal expansion and contraction caused by the temperature change is very small, so it is not easy to produce cracks, and the service life is longer. It has a better waterproof effect than the brushing heat Zhejiang, but the cost is relatively high. Also pay attention to the failure of rigid waterproof due to irregular cracks caused by the overall deformation of the culvert. The culverts that are required for the construction period can also be waterproofed with flexible waterproof membranes. The construction speed is fast, but it is not suitable for waterproofing at the top of Ming culverts, and the cost is relatively high.
5 Selection of Waterproof Materials Waterproof concrete can be used for culverts with higher waterproof requirements, and the waterproof performance of concrete itself can be fully utilized, such as inverted siphon. Water-repellent concrete is usually doped with expansive agent because expansive concrete generates volumetric expansion during the hardening process, which causes pressure and strain within the concrete, compensates for various types of contraction deformation, cancels or partially cancels the corresponding tensile stress, thereby increasing the concrete's strength. Crack resistance. At the same time, due to the hydration of the cement binder, the microstructure of the concrete is effectively improved, thereby improving the impermeability of the concrete. The design of waterproof concrete for inverted siphons should not only consider the water pressure inside the pipe, but also fully consider the buried depth of the culvert and use this to determine the waterproof level. Waterproof mortar is generally used to fill various seams or hook seams, and also uses its micro-expansion principle to increase the packing density, thereby enhancing its waterproof performance. Waterproof concrete and rigid plaster cement mortar waterproof layer should adopt ordinary portland cement or expansive cement with strength no less than original No. 325, slag portland cement, sand crushed with good grading, and require gravel hard, Roughness and cleanliness; the mix ratio of cement paste and cement mortar should be determined according to the waterproof requirements, raw material properties and construction methods, and construction must be strictly controlled. The selected flexible outer waterproof material should have the characteristics of high temperature and non-liquefaction, low temperature non-brittleness, non-aging, strong adhesion, good waterproof effect, and easy construction.
5 Concluding remarks From the current status quo of the highway, it can be found that the highway construction and management units have not paid enough attention to the waterproof design, construction and maintenance of the culverts, and still believe that the culvert waterproofing is once and for all, that is, after the waterproof construction is completed, it will no longer require maintenance and management. thought of. It has been proved that the leakage of the existing road culvert is very serious. If it cannot be taken seriously, the service life of the culvert will be greatly shortened.
The concept of culvert waterproofing should be changed to raise the awareness of the importance of culvert waterproofing. Although other technical indicators and standards for road culverts have continued to increase, culvert waterproofing has still not received much attention. The cost of waterproofing projects accounts for only a very small part of the cost of culvert engineering, and usually only considers one-time waterproof investment.
Transform the existing single waterproof design concept. The existing road culverts still use relatively primitive waterproof technology, and rarely use new waterproof technologies and techniques. Underground waterproofing technology has been developing by leaps and bounds. Therefore, advanced advanced technologies for waterproofing of underground buildings should be actively consulted and optimized. Waterproof design, using reasonable and advanced construction techniques, in order to obtain the best waterproof effect.
Reasonable material selection is the key to achieving the comprehensive effect of technology and economy. The main principle is to select the waterproof grade, waterproof layer structure, waterproof part and detailed structure according to the importance of each part of the culvert and the degree of possible leakage; select the waterproof material according to the local climate characteristics; according to the performance of the waterproof material, Waterproof grade requirements, determine the thickness of the waterproof layer, and the right choice of high-quality waterproof material, to form a comprehensive waterproof design that is both economical and reasonable, but can fully play the effect.
It can be seen that the waterproof technology of road culverts is based on materials, the design is a prerequisite, the construction is a key, and maintenance is a comprehensive protection technology. The culvert must be provided with a defense system that prevents cracking, multi-channel fortification, and rigid-flexibility, and penetrates through the design and construction. The entire process of conservation and maintenance ensured the waterproof quality of the highway culvert works.
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