Damage Causes and Control About Reinforced Concrete Circular Pipe Culvert Under the High Fill Jun Zhang 1, a, Xiedong Zhang 2,b and Xiangyu Hu 3,c

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1 Applied Mechanics and Materials Vols (2013) pp Online available since 2012/Dec/13 at (2013) Trans Tech Publications, Switzerland doi: / Damage Causes and Control About Reinforced Concrete Circular Pipe Culvert Under the High Fill Jun Zhang 1, a, Xiedong Zhang 2,b and Xiangyu Hu 3,c 1 Inner Mongolia Communications Design & Research Institute. Hohhot. Inner Mongolia China 2 School of Transportation.Wuhan University of Technology.Wuhan.Huibei China 3 School of Transportation.Wuhan University of Technology.Wuhan.Huibei China a @126.com, b zhangxd@189.cn, c tospace@163.com Keywords: pipe culvert crack soil pressure structure analysis Abstract. The damages of reinforced concrete pipe culvert appeared in use process brought a lot of problems. Investigated the pipe culvert damage characteristics, analyzed the causes of damages from load, structure stress and production, give the corresponding control methods. Introduction In China's highway construction, highway levels increase and restricted by geologic and geomorphologic conditions, the design of the high fill subgrade is more and more, reinforced concrete pipe culvert as a indispensable supporting structure in highway engineering is used widely. Reinforced concrete pipe culvert in high embankment belongs to the superstratum pipe culvert, generally built in the surface or shallow ditch, and then in the pipe culvert top and sides fill compaction in layers, the original culvert top generally higher than the natural ground. This kind of pipe culvert characteristics are: holes in length, tube and tube between hinged, larger soil pressure on the top of the culvert, basic requirements are not high, the construction is simple but difficult to replace, etc. Reinforced Concrete Circular Pipe Culvert's Damage Characteristics Professor Anquan Gu investigated and analysed the damage of pipe culvert in the 1960 s, the survey of 303 culverts, pipe cracking destroyer accounted for 63.5%, of which 70% longitudinal cracks. The author also has did related practical research of Inner Mongolia Laoyemiao -Jining Highway and provincial channels, found that round pipe culvert the main damage form is cracking, the extrusion deformation, etc. Which pipe culvert cracking problems are the most common, according to the field construction personnel response,after the construction finished, pipe culvert top and bottom all appear different extent cracking, there were also cracks in the outer wall. Through the investigation and analysis, pipe culvert has the following damages:(a) the cracking position most in pipe roof, serious can produce through cracks, even have steel exposed;(b) along the pipe culvert direction, culvert pipe on both sides of the cave portal cracking is not very serious, but the central culvert pipe burst quite serious;(c) pipe diameter have compression deformation phenomenon appeared. Causes of the Pipe Culvert Damage Although ordinary cracking do not affect the using function of pipe culvert, but over time, such as water and air along the crack into concrete interior, bring about increasing rate of the corrosion of steel, alkali-aggregate reaction and the speed of carbonization, and thus cause the decline of durability, will directly affect the bearing capacity of culvert structure and use security eventually. Through the circular pipe culvert damage cause analysis, there are several possible reasons for pipe All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, (ID: , Pennsylvania State University, University Park, USA-03/02/15,16:00:55)

2 Applied Mechanics and Materials Vols culvert cracking: (a) the load on the influence of pipe culvert;(b) effects of culvert structure;(c) the influence of laying foundation;(d) the culvert pipe production materials, production process and the influence of the construction. The Load Factor. Culvert structure load including dead load(vertical earth pressure of filling,horizontal earth pressure and self weight,etc) and live load(vehicle load, impact load and braking force, etc).according the General Code for Design of Highway Bridges and Culverts, live load choose the corresponding vehicle load and load distribution width, according to the requirement of design value. Acting on the pipe culvert of dead load is soil pressure and self weight, at present, China's highway standard using "soil columns" method to calculate the soil pressure, this kind of method is to take the weight of the soil columns on the top of the culvert as soil pressure, assuming that the pipe top soil pressure and fill height into a linear relationship. But this kind of design has its defects, is not considering the difference of pipe-soil stiffness in the vertical pressure, and deny the stress redistribution of soil around the pipe, led to the soil pressure design value is small, this design miss is a cause of pipe culvert produces crack. In response to this situation, domestic and international scholars had been a large number of studies on the soil pressure calculation theory of culvert,and has obtained some achievements. Among them, the Anquan Gu formula with its innovative ideas, and line with the actual results, has been widely recognized in the industry. Professor Anquan Gu's research is based on Marston calculation assumptions, amendments to Marston formula. Marston formula has the following three assumptions: (a) the shear plane assumption, Along the pipe horizontal diameter two ends, draw two vertical lines towards the ground, intersect at a, b. Around the pipe soil is split into three parts by Vertical aa' and bb': inner soil column above the pipe, outer soil columns on both side of the pipe. In settlement process, inner and outer soil columns through its interface aa', bb'(namely slip plane) for relative motion, and generate shear force;(b) the limit equilibrium state assumption, the relative motion between the inner and outer soil columns represented by limit state;(c) vertical soil pressure distribution above the pipe according parabolic assumption. Marston calculation hypothesis is shown in Fig.1 Fig.1 Marston calculation hypothesis Professor Anquan Gu attributed various factors which affect top vertical soil pressure of pipe culvert to the differential settlement of inner and outer soil columns inside the culvert top plane. Due to the reinforced concrete circular pipe culvert stiffness is greater than soil body, settlement of inner soil column is less than outer soil column, outer soil column will produce a downward friction τ to inner soil column, culvert top not only assumed the self weight of inner soil column also a part of outer soil column load, and in pipe top appears soil pressure concentrated phenomenon, therefore soil pressure maximum at the culvert top midpoint, the actual value is much bigger than design value in fact, this is a main factor that culvert top produced cracks.

3 1084 Advances in Civil Engineering II Circle Pipe Culvert Structure Stress. Under the load circle pipe culvert will produce the action of bending moment, axial force and shear stress, it will appear cracks when the tensile stress exceed the tensile strength of concrete. Reinforced concrete circular pipe culvert section in the action of load and reaction force is a cubical statically indeterminate ring structure in the equilibrium state, the bending moment of pipe culvert is shown in Fig.2. On the culvert inner face, ring stress appear the largest tensile stress in pipe top A point, and then gradually decreases along the pipe around direction, in pipe side B point appear maximum pressure stress to pipe bottom C point again into large tensile stress; it is just the reverse on the culvert outer face. Fig.2 The bending moment diagram of pipe culvert According to the structural mechanics method to calculate the bending moment, the bending moment modification factor is 0.137,but Hongwei Wei thought that the highway standard calculation value is smaller than actual value by comparing the internal force derived formula, the calculation results and the experimental results, the proposal bending moment modification factor is 0.437, the bending moment value according with the standard design is the actual bending moment value partial small nearly two-thirds, design standard is too low, directly led to the structural strength is not enough, so it will appear crack at the maximum tension stress place. The Influence of the Circle Culvert Pipe Foundation. Culvert foundation will affect culvert stress, not only the pipe bottom internal force also the pipe top internal force. The greater the foundation stiffness, the settlement value of inner soil column will be smaller, cause the settlement difference between the inner and outer soil column increase, which will lead to culvert top stress increases. Through the pipe culvert foundation classification can be divided into: pipe without saddle(fig.3a), pipe culvert on the arc soil base (Fig.3b) and pipe culvert on the rigid base(fig.3c). Pipe without saddle is to laid the pipe on the basis, pipe bottom reaction force is obvious,it is a concentrated action at pipe bottom C piont. The contact area between round pipe and curved foundation increase, basic reaction will be dispersed, the reaction will reduce at the pipe bottom C point. Support reaction's distribution of curve pipe culvert on the rigid base is similar with it is on the arc soil base, because base's modulus of elasticity is the same as the culvert pipe's,in the condition of the same load and the same angle α, rigid support base pipe culvert inside and outside bending moment were less than arc soil base pipe culvert inside and outside bending moment. And the central angle 2α is bigger, the reaction of the support will be smaller at the same position. a b c Fig.3 Different circle culvert pipe foundation

4 Applied Mechanics and Materials Vols Culvert Pipe Production Technology and Construction. It's a long process the reinforcement concrete pipe culvert from production to completion, any miss will lead to the existence of the disease. At present, steel skeleton of the pipe culvert consist of helical cold-draw reinforcement and longitudinal bar. Yield strength of cold-draw reinforcement higher than the low carbon steel, but cold-draw reinforcement is more stiffer and brittler because of its lower ductility, it is very unfavorable when it bear impact load and periodic load. In the construction of roadbed, pipe will appear cracks on the surface when it bear impact load and periodic load. Culvert pipe produced by centrifugal casting usually. Steel skeleton will deviate to out when it under the action of the centrifugal force, the products will appear the inner protection course is too thick and the outer protection course is too thin or even the steel exposed. when the concrete protection course is too thin, especially the existence of microfracture in the concrete, the reinforcement will change into iron oxide when it rusting, the concrete will burst because rust volume expansion that extrusion concrete surround. And cement paste too thick very prone to produce shrinkage cracks. Reinforced concrete circular pipe culvert is widely used steam curing method, because lack of correct understanding and effective control, steam curing without necessary preliminary process of warm up, temperature change sharply, a large temperature difference between inside and outside wall of the concrete pipe culvert, it will produce larger temperature stress, concrete will craze. Poured concrete is still in a plastic state in hours, in the hot or gale weather, moisture on the concrete surface will evaporation too fast or concrete hydration heat up,concrete will produce plastic shrinkage cracks, the width of this kind of cracks small as hair or big up to several millimeters, the length and depth of the cracks also are various. Considering the shape of reinforced concrete circular pipe culvert, it is hard to stable and easy to rolling, the collision and tumble will cause round pipe culvert damage and destruction easily in lifting and transportation. It will cause cracks if not according the design and the job specifications,such as soil thick layer on both sides of the pipe are asymmetric, also do not balanced hierarchy filling and compaction, let large construction machinery pass through or use large vibratory in the state of small fill height above the pipe. Crack Control of Reinforced Concrete Pipe Culvert Through analysis the influence factors of reinforced concrete pipe culvert damage, we can see that the causes of damages are very complex, which is not only the result of on one hand, the various influencing factors related and influence each other. Sum up, the cracks of reinforced concrete pipe can be controlled from three aspects:(a) reduce loads around the pipe, especially the pipe roof;(b) structural form with the characteristic of reasonable stress;(c) optimizing the production process and standardize construction jobs. Culvert stress relieving measures is filling flexible material above the pipe to change differential settlement between inner and outer soil column, the downward friction that the outer soil column act on the inner soil column will decrease, and reduce the additional force on the pipe culvert, so as to improve the culvert top stress state, or even change settlement deformation characteristics of the fill completely, make the settlement of the inner soil column greater than the outer soil column, the outer soil column form a upward sliding trend, that the outer soil column act on the inner soil column a upward friction, so pipe culvert pipe top load will be less than the soil weight. Base on the structure mechanical characteristics of the circle culvert pipe, through enlarging the cross section of pipe's top and bottom where stress concentration to improve the normal section crack resistance. Adopting rigid foundation bed as much as possible, ensure the interface between foundation bed and pipe body large and closely, the bigger the center angle of contact surface between foundation bed and pipe, the better.

5 1086 Advances in Civil Engineering II Production of reinforced concrete pipe culvert selection should choose continuous set with clean coarse and fine aggregate, and ensure the strength and the appropriate water cement ratio, reinforcement skeleton using low carbon steel, welding the inner and outer rings steel with short bars which play a role of fixed erection. Using the centrifugal method to produce pipe must control the centrifugal speed, centrifugal time and feeding process, Centrifugal velocity is divided into fast, medium and slow three level, must control speed on time at all stages, it is better to choose secondary feeding process. Concrete steam curing should pass preliminary period,to heating period, to constant period, to cooling period four stages, forbidden large temperature changes. In the construction, transportation and installation should use fixtures to avoid collision damage, incorrect lifting way and roll the pipe is prohibited strictly. Should adopt correct filling method in the process of landfill, handle the culvert pipe foundation according to the request, the part where it's hard to construction should be tamped by small tamping machine, symmetric filling and tamping every layers on the both sides of the culvert pipe. Considering exciting force from vibratory roller and impact force from construction loads, construction mechanical load limit value for: it is allowed static roller or other construction machinery the weight within 20T access the state of fill height in 0.5m to 1m,vibratory roller or other construction machinery the weight within 25T access the state of fill height in 1m to 1.5m, vibratory roller or other construction machinery the weight in 40T to 50T access the state of fill height above 1.5m. Summary Reinforced concrete circular pipe culvert appear damage for many reasons, including material, section characteristics, filling characteristics, foundation soil characteristics and construction method etc, which affect and restrict each other, so the damage appear of reinforced concrete circular pipe culvert is a complex problem. As long as recognize the external affect and internal structure in theory, reduce artificial factors, the control on cracks of the circular pipe culvert will can be realized. References [1] Yongli Xie, Baojian Liu and Xiaohua Yang: Culvert in Highway Engineering (China Communication Press, Beijing 2009). [2] Hongwei Wei and Geli Wang: The Reason of Circle Culvert Pipe Crack and Control Countermeasures. China Concrete and Cement Products,No.4 (2001). [3] Xuesen Zhe and Anquan Gu: Analysis About Soil Pressure Under the High Fill. Xi'an University of Highway, volume 12 No.4 (1992). [4] Xiaomou Wang and Anquan Gu: The Vertical Soil Pressure Reduction Measures of Buried Pipe. Journal of Geotechnical Engineering, volume 12 No.3 (1990). [5] Marston, The Theory of Extends Loads on Closed Conduits in the Light of the Latest Experiments.Bulletin 96, Ames: Iowa Engineering Experiment Station,1930. [6] General Code for Design of Highway Bridges and Culverts.(JTG D )(In Chinese)

6 Advances in Civil Engineering II / Damage Causes and Control about Reinforced Concrete Circular Pipe Culvert under the High Fill /

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