See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/292977686 Repair and Strengthening of Underground Structures Article · December 2009 CITATION READS 1 4,658 1 author: Mohsen Shuaib Menoufia University 3 PUBLICATIONS 7 CITATIONS SEE PROFILE All content following this page was uploaded by Mohsen Shuaib on 04 February 2016. The user has requested enhancement of the downloaded file. Workshop of "Underground Structures in Hot Climate Conditions", 8-9 December 2009, Ministry of Transportation, Riyadh, Saudi Arabia REPAIR AND STRENGTHENING OF UNDERGROUND STRUCTURES Dr. Mohsen F. Shuaib Tech. Manager of Conclinic Arabia, Assoc. Prof. in Minofeya Univ. Eng. Hassan H. Ibrahim G. Manager of Shade Contracting Company Eng. Ahmad Abbass Manager of Road Dept., Al-Naim Office KEYWORDS: Maintenance, Repair Concepts, FRP, Decision Making ABSTRACT: In this paper, maintenance and inspection programs are presented briefly. This paper describes various methods for repairing specific deficiencies in structural elements within underground structures. Water infiltration is the most common cause of deterioration. However, deficiencies could be the result of substandard design or construction, or the result of unforeseen or changing geologic conditions in the ground that supports the tunnel. Another common reason for repairs is the fact that many tunnels have outlived their designed life expectancy and therefore the construction materials themselves are degrading. Due to the fact that there are different causes for the degradation, the method of repair could vary from one case to another. Some major structural deficiencies for underground structures are displayed. In addition, a detailed explanation of the different types of concrete deficiencies and methods for their repair is provided. Some practical case for underground structures repair are described including expansion joint leakage, and the use of advanced composite material or fiber reinforced polymer (FRP) for repair and strengthening. Finally, multi-criteria decision making tools for repair of tunnels are presented briefly. 1 INTRODUCTION Tunnel management system plays an essential role throughout the tunnel life including : design; construction; operation; planning for maintenance, repair and rehabilitation (MR&R); optimizing the allocation of financial resources, and increasing the tunnel safety. The first US national tunnel management system (TMS) stated in 2002, while the national bridge management systems (BMS) started early at mid of the 20th century. Structural deficiencies represent the greatest danger of all potential underground structures failures for disruption of community welfare and possibility of the loss of life. Maintenance programs aim to safeguard structural integrity; and to avoid deterioration which may lead to more costly work. In this paper, maintenance and inspection programs are presented briefly. Some major structural deficiencies for underground structures are displayed including leakage of water, steel rebar corrosion, cracking of the structure and design faults. The use of advanced composite material or fiber reinforced polymer (FRP) for repair and strengthening. Multi-criteria decision making tools are presented at end of the paper. 1 Workshop of "Underground Structures in Hot Climate Conditions", 8-9 December 2009, Ministry of Transportation, Riyadh, Saudi Arabia TUNNEL MAITENANCE PROGRAMS The maintenance program should be designed to include prevention of deterioration and damage; prompt detection of deficiencies; and early accomplishment of maintenance and repairs to prevent interruptions of transportations or limitation/restrictions of tunnel use as presented in Figure 1 (Chinh 2004). Figure 1. Effect of maintenance on structural condition of tunnels The main elements of tunnel maintenance programs are the inspection and the maintenance and Step by Step Inspection, analyzing, and recommendation for tunnels is shown in Figure 2 (ITA 1991). Inspection Inspections of tunnel are classified as follows (Shuaib 2006): initial inspection; routine inspection; damage inspection (emergency inspection); in-depth inspection; and special Inspection. Maintenance Maintenance of tunnels is the scheduled work that is required to preserve the tunnel condition. T h e maintenance is divided to routine maintenance like sealing concrete; preventive maintenance such as filling cracks; and major maintenance like water leakage and crack repair. Figure 2. Step by Step Inspection, analyzing, and recommendation for tunnels Preventive maintenance of structures system should include: washing/cleaning; inspection; maintenance; and testing of the following elements (Shuaib 2006a): Tunnel lining structures Tunnel finishers /claddings Ventilation tunnel emergency way 2 Anchors and mechanical supporting Drainage system in tunnel Roadway structures in road tunnel Structural system of railway Workshop of "Underground Structures in Hot Climate Conditions", 8-9 December 2009, Ministry of Transportation, Riyadh, Saudi Arabia Preventive maintenance of equipment systems in tunnels are subdivided into mechanical system and electrical system. The preventive maintenance of these systems must be complied with specialist rules and manufactures suggested preventive maintenance procedures. 3 TUNNEL INSPECTION PROGRAM Tunnel inspection program is a multi stage process, which may be categorized in the following different tasks which may occur during routine inspection works (US-DOT 2005). Inspection Management. Inspection and Condition Assessment. Reporting. Report Distribution and Archiving. 4 CAUSES OF TUNNEL DEGRADATION This section outlines major causes of deficiencies in structural elements within a tunnel. These defects must first be evaluated to determine the cause and the severity of the deterioration, in order to select the best repair method. Many concrete linings in highway tunnels have an additional tunnel finish which may hide the extent of the deterioration. Therefore, a repair analysis will need to account for the replacement or repair of the finish as well. Deterioration in tunnels may be caused by any of the various factors listed below (US-DOT 2004). Water Infiltration Cracked and separated joints Lack of tightness Design or construction mistakes Corrosion of embedded metals Thermal loads Effects Longitudinal spreading of foundations Longitudinal differential settlement Swelling soil and invert damage Spall of tunnel crown joints. Loss of support due to erosion Seismic load and shape distortion Ingress of dissolved gases Steep fill slopes above tunnels Changing of geologic conditions Poor Workmanship Deterioration of mortar Degradation in concrete strength Longitudinal loads on tunnels Chemical action on lining Damage to surface finishes Clogging drainage due to fines Cracks in track/road slab Inclined tension cracks at the base Differential movement at crown Damage in repair system Some defects in tunnels are presented in in Figures 3, 4, and 5 (Conclinic 2007). Figure 3. Water leakage in tunnels and underground structures 3 Workshop of "Underground Structures in Hot Climate Conditions", 8-9 December 2009, Ministry of Transportation, Riyadh, Saudi Arabia Figure 4. Concrete deterioration due to carbonation, alkali-aggregate reaction, and sulfate attack Figure 5. Longitudinal cracks in tunnels and underground structures REPAIR CONCEPTS OF TUNNELS Method of repair could vary due to the fact that there are different causes for the degradation. The applied repair methods must be durable, easy to install, capable of being performed quickly during non-operating hours, and cost-effective. Factors affecting the repair method are the deterioration severity, and the structural impact of the defect. The cause of the defect should be determined before and remedial works, otherwise the same problem may repeat itself. Repair priority definitions may be classified as follows (Chinh 2004); Critical: if it requires “immediate” action Priority: when interim or long-term repairs should be undertaken on a priority basis Routine: for that can be undertaken as part of a scheduled maintenance program. Repair of defect in a tunnel could be divided in the following steps (ACI 224.1R 2007): Evaluation of damage/defect Relating observation to causes Selecting appropriate methods and materials Preparation of drawing and specification Selection of a contractor Execution of the work Quality control and acceptance REPAIR FOR WATER INFLITERATION a- Cause of Water Infiltration Water infiltration is the main cause of deterioration of the tunnel structure. Tunnels can develop leaks due to inadequate connection/joint design, substandard construction, and deterioration of the 4 Workshop of "Underground Structures in Hot Climate Conditions", 8-9 December 2009, Ministry of Transportation, Riyadh, Saudi Arabia waterproof lining. Most tunnels are designed with drainage mechanisms around the exterior of the lining or embedded within the joints. As ground water flow patterns change over time a due to the accumulating effects of basements of surrounding buildings, drains become clogged with sediment, the water is bound to find its way into the tunnel through joints or structural cracks. Another scenario is that a tunnel which was designed to be above the water table, is subjected to hydrostatic forces that it is unable to resist and subsequently water infiltration becomes a problem. b- Repair of Water Infiltration Water infiltration repair must be investigated in the following zones (US-DOT 2005) : The surrounding ground Interface between ground and lining Tunnel Lining Structures The lining intrados Internal useful spaces of the tunnel Remedial works for water infiltration inside tunnels could be a short term solution, a long term solution and partial or full replacement of the tunnel lining. To determine the most cost efficient method of repair for a particular situation, a specific cost analysis should be performed that considers the costs over the life of the tunnel (ITA 1991). b.1 Short Term Repair This is a temporary or permanent solution by redirecting the infiltrated water to the drainage system until further investigation can be performed and a more long term solution implemented. This includes drainage toughs and using pipe network as shown in Figure 6 (Chinh 2004). Figure 6. Short term repair of water infiltration b.2 Long Term Repair Many factors are involved in determining which long-term method should be used. These factors are: site specific; cause of water infiltration, and water volume. A detailed study should be performed on major leaks to determine source, amount of water leakage, and exact location of the leak. Some of the long term repair methods are given below as shown in Figure 7 (Conclinic 2007), Insulated panels Waterproofing membrane Crack/joint injection Soil/rock grouting (back-wall grouting) Crack/joint repair (ACI 503.7 2007) Segmental joint repair 5 Workshop of "Underground Structures in Hot Climate Conditions", 8-9 December 2009, Ministry of Transportation, Riyadh, Saudi Arabia Figure 7. Long-term repair of water infiltration by waterproofing, and injection methods b.3 Structural Replacement Lining reconstruction has advanced to a point where repairing numerous localized areas of the liner becomes cost prohibitive. Reconstruction could include shotcrete or pumping plasticized concrete within a form liner. In addition, using an exterior drainage system in a tunnel below the ground water elevation is normally not effective over the long term because of the ability for water to penetrate very small cracks that develop between drains. Some of the available systems for extensive lining reconstruction are mentioned below as shown in Figure 8 (Watson 2003) and (Conclinic 2007). Shotcrete applications Joint control Water tight concrete Figure 8. Shotcrete , and joint control by re-injection system b.4 Joint Leakage Repair Existing Repair systems for water leakage repair includes the following items: (1) Types of Repair Materials (2) Types of Repair Methods Water-based epoxy Poly Urethane grout Cementit ious grout Acrylic grout Combined cementitious polymer grout Injection system (Epoxy, PU) Surface treatment system (cementitious) Surface filling systems (Polymer cementitious) (3) Problems of Repair Systems Low adhesion to the wet surface (epoxy, urethane) Improper hardening in a wet condition Water absorption (Urethane) Lack of movement of the substrate cracks by thermal change and vehicles (epoxy, cement) 6 Workshop of "Underground Structures in Hot Climate Conditions", 8-9 December 2009, Ministry of Transportation, Riyadh, Saudi Arabia Polyurethane fume has failed as injection material for case of sea water or high sulfate salts in the ground water (Kang et al. 2008), while acrylic grout is a durable leakage repair system as shown in Figure 9 (Conclinic 2007). Figure 9. Failure of polyurethane and success of acrylic for leakage repair system CONCRETE REPAIR OF TUNNELS Concrete deterioration in tunnels and concrete lining may be caused by various factors including: water Infiltration, corrosion from embedded metal, thermal effects, loading conditions, and poor workmanship. As concrete deteriorates, proper repairs shall help to avoid further degradation of the structure. a. Corrosion Protection of Concrete Concrete protection could be satisfied through construction areas and electrochemical/cathodic areas as shown below (ACI 224.1R 2007). Design improvement (increase of cover thickness) Material improvement (permeability using fly ash, slag, and silica fume) Material improvement (Inhibitor using anoding or cathodic protection) Concrete surface block (Painting, lining, sheet coating, and polymer mortar) Rebar surface block (Coatings using fusion bonded epoxy and zinc coating) Cathodic Protection - Sacrificial Anode Method (No impressed current, low initial cost and reliable) - Impressed Current Method Corrosion protection of concrete Cathodic protection by sacrificial anode method consists of the following items (Conclinic 2007) as shown in Figure 10.: Zinc mesh is used as a sacrificial anode Glass Fiber Reinforced Polymer (GFRP) jacket for structure rehabilitation Conductive mortar is used as a electrolyte solution Corrosion sensors is used as a corrosion potential monitoring Figure 10. Corrosion protection of concrete by sacrificial anode 7 Workshop of "Underground Structures in Hot Climate Conditions", 8-9 December 2009, Ministry of Transportation, Riyadh, Saudi Arabia b. Crack Repair of Concrete Concrete and reinforced concrete lining crack repair is classified (US-DOT 2004) as shown in Figure 11 (Conclinic 2007): Injection/grouting techniques Routing and sealing techniques Packing techniques The selection of techniques or any combination is based on: Dimension, condition of crack Condition of concrete area need to repair Required target Figure 11. Concrete crack repair by injection, sealant, and packing c- Spall Repair of Concrete Concrete and reinforced concrete lining crack repair is classified as shown in Figure 12 (Conclinic 2007) and (Newman 2001). Shallow spall with no reinforcement steel exposed Shallow spall with reinforcement steel exposed Deep Spall with reinforcement steel exposed c.1 Repair of shallow spall with no reinforcement exposed is given below (Emmons 1994). Removal of loose or deteriorated surfaces Clean the concrete surface Sawcut on a 20-degree angle around the spalled area Placing polymer repair mortar to original concrete depth c.2 Repair of shallow spall with reinforcement steel exposed is as follows (Newman 2001). Removal of loose or deteriorated surfaces Clean the concrete surface and the exposed steel rebar Sawcut on a 20-degree angle around the spalled area Coating rebars with anticorrosion agent compatible with the repair mortar Placing polymer repair mortar to original concrete depth Applying protective coat to the surface 8 Workshop of "Underground Structures in Hot Climate Conditions", 8-9 December 2009, Ministry of Transportation, Riyadh, Saudi Arabia Figure 12. Repair of shallow spall with reinforcement steel exposed c.3 Repair of deep spall with reinforcement steel exposed is as given below (Chinh 2004). Removal of loose or deteriorated surfaces Clean the concrete surface and the exposed steel rebar Sawcut on a 20-degree angle around the spalled area Coating rebars with anticorrosion agent compatible with the repair mortar Placing polymer repair mortar to original concrete depth Applying shotcrete with additional welded wire fabric mesh WWF. d- Seismic Strengthening of Tunnels Tunnels were considered the safest structures under earthquake loads, the recent studies have established that some damages have been observed in different tunnels and underground structures during and after ground shaking []. Deformation modes and behavior of circular and non-circular tunnels during earthquake are presented in Figure 13 (Hashash et al. 2001). Figure 13. Behavior of tunnels during earthquake 9 Workshop of "Underground Structures in Hot Climate Conditions", 8-9 December 2009, Ministry of Transportation, Riyadh, Saudi Arabia Seismic response of underground structures consists of three major steps as follows (El-Nahass et al. 2006). 1. Definition of the seismic environment and parameters 2. Evaluation of ground response to shaking 3. Assessment of structure behavior due to seismic loads Application of advanced composite material can help in strengthening and retrofit of tunnels for seismic resistance upgrade. Carbon and glass reinforced polymer (CFRP) and (GFRP) are used for such purposes for its high tensile strength with light weight. The application of theses material is shown in Figure 14 (Conclinic 2007). Figure 14. Application of fiber reinforced polymer for strengthening of culverts DECISION MAKING IN REPAIR Tunnel management system (BMS) should provide a Decision Support System (DSS) which helps in decision making for repair and rehabilitation of tunnels. Decision making is the study of identifying and choosing alternatives based on the values and preferences of the decision making to choose the one that best fits with our goals, objectives, desires, values, and so on. General decision making process is as follows (Shuaib 2009). Establish goals Identify alternatives Define criteria Assign decision matrix Establish priority score matrix Select a decision making tool Preference ranking of alternatives Sensitivity analysis Final recommendation Decision Matrix 10 Workshop of "Underground Structures in Hot Climate Conditions", 8-9 December 2009, Ministry of Transportation, Riyadh, Saudi Arabia Decision matrix combines both alternatives and criteria in one matrix to transfer the problem from practical field to mathematical field as shown in Figure 15 (Shuaib 2009). Criteria C1 C2 ………………. CN ( w1 w2 ……………wN) Alternatives ______________________________ A1 a11 a12 ………………. a1N A2 a21 a22 ………………. a2N . . . ………………. . AM aM1 aM2 ………………. AMN Figure 15. Decision matrix model where, (Ai) is the alternatives, such as; repair using: Carbon Fiber Reinforced Polymer (CFRP), Fiber Reinforced Polymer (FRP), Adding concrete element, adding steel plate and replacement of the tunnel or part of it. ( i) = 1,2,3,…. M and (M) is the total number of alternatives. (Cj) is the criterion on which a comparison is to be held between different alternatives such as; construction cost, construction duration; traffic detouring cost; maintenance cost; ease of construction; future flexibility and aesthetic appearance. (j) = 1,2,3,…… N; where (N) is the total number of criteria. (wj) is the weight and importance of each criterion, which is estimated by the decision maker group such as: the owner, the consultant office and public community representatives where ; N ∑ w j = 1.0 (1) j=1 (aij) is a measure or score of performance for each alternative subjected to each criteria. This measure could be a quantitative type or a qualitative type. Qualitative types should be transformed to an estimated quantity to handle decision making mathematically. Priority Score Matrix Each criterion has a different unit for measuring of (aij) such as US $, day,…elct. The decision matrix should be formalized by normalization of each column of the matrix to find the modified scores (bij) and to produce the dimensionless priority score matrix. Each column of the priority decision matrix should satisfy (Eq. 2 ) (Shuaib 2009). M ∑ (bij ) = 1.0 (2) i=1 Decision Making Methods There are several decision making methods such as: the weighted sum method (WSM); the weighted product method (WPM); the analytical hierarchy process (AHP); the ELECTRE method; and technique for order preference by similarity to ideal solution (TOPSIS) (Shuaib 2009). (I)- Weighted Sum Method (WSM) N Pi = ∑ (b ij ) * wj for i= 1,2,3… M (3) for i= 1,2,3… M (4) j=1 (II)- Weighted Products Method (WPM) N Pi = ∏ (100*b ij )wj j=1 11 Workshop of "Underground Structures in Hot Climate Conditions", 8-9 December 2009, Ministry of Transportation, Riyadh, Saudi Arabia CONCLUSION Tunnel management systems should be established carefully to increase the service life of tunnels. Degradation of new tunnels starts from the first day of service of tunnels. Scheduled maintenance of tunnels is required to preserve the tunnel condition. Water infiltration and water leakage represent the major reasons for deterioration of tunnels. Efficient drainage system and waterproof of the tunnel shall reserve tunnels. Regular repair of concrete and concrete lining are very essential for tunnels. Corrosion protection and corrosion protection system could retard deterioration of concrete in underground structures. The use of fiber reinforced material can help efficiently in strengthening and seismic upgrade of tunnels us. Decision making in repair and strengthening of tunnels is complicated issue but it could be modeled mathematically to use multi criteria decision methods for choosing the most preferable alternative for repair of tunnels and underground structures. REFERENCES American Concrete Institute (ACI) Committee 503.7. (2007). 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