Scholarly article on topic 'Stress Mitigation and Execution of Civil and Mechanical Works to Achieve the Definitive Alignment of Adduction Pipes of Ayurá WTP, Part of the Water Distribution System of Aburrá Valley'

Stress Mitigation and Execution of Civil and Mechanical Works to Achieve the Definitive Alignment of Adduction Pipes of Ayurá WTP, Part of the Water Distribution System of Aburrá Valley Academic research paper on "Agriculture, forestry, and fisheries"

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{"Adduction pipes" / "soil stress" / earthworks / "water distribution system"}

Abstract of research paper on Agriculture, forestry, and fisheries, author of scientific article — Johnny Andrés Bedoya Muñoz, Jorge Eduardo Guerra Londoño, Fernando Cálad Chica

Abstract The purpose of this article is to describe the diagnosis and execution procedure developed by many employees and contractors of EPM (Empresas Públicas de Medellín) in the alignment of two adduction pipes that transport near 65% of water supplied by the Aburrá Valley Distribution System (Antioquia, Colombia). Both pipes (of 800mm and 900mm) were installed 35 years and 43 years ago, respectively, and are part of the system that allows the water conduction from La Fe reservoir, in the El Retiro municipality, to La Aruyá Water Treatment Plant (WTP), in Envigado municipality. Over time and especially by the intensification of the harsh winter weather during the last four years, the soil has lost systematically its stability causing pipes to lose its original position. In accordance with the geological and geotechnical studies developed in 2011, was necessary mitigate the stress exerted on the pipe and to advance in works in order to protect pipes against the risk of new earthworks, earthquakes or other phenomena. The scheduling of activities started in July of 2011, beginning with the development of a drainage system to drain excess water and stabilize the soil. The alignment procedure did not require emptying pipes and was included the participation of about 100 people in each stage. This made possible the conception, adjustment and fabrication of realignment systems, brackets construction and fabrication of structures to support the machinery responsible for displace the pipes and dissipate the stress on pipes. The procedure developed did not require the service suspension due to the flexibility of the other two Water Treatment Plants: Manantiales and Villa Hermosa, which assumed the decreased flow in La Aruyá Water Treatment Plant [1–3].

Academic research paper on topic "Stress Mitigation and Execution of Civil and Mechanical Works to Achieve the Definitive Alignment of Adduction Pipes of Ayurá WTP, Part of the Water Distribution System of Aburrá Valley"

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ScienceDirect Procedía

Engineering

Procedía Engineering 186 (2017) 44 - 53 -

www.elsevier.com/locate/procedia

XVIII International Conference on Water Distribution Systems Analysis, WDSA2016

Stress mitigation and execution of civil and mechanical works to achieve the definitive alignment of adduction pipes of Ayurá WTP, part of the Water Distribution System of Aburrá Valley

Johnny Andrés Bedoya Muñoz1a *, Jorge Eduardo Guerra Londoño1b, Fernando Cálad

Chica1c

1Empresas Públicas de Medellín E.S.P. Medellín /Antioquia, (Colombia) aJohnny.bedoya@epm.com.co,bJorge.guerra@epm.com.com, cFernando.calad@epm.com.co

Abstract

The purpose of this article is to describe the diagnosis and execution procedure developed by many employees and contractors of EPM (Empresas Públicas de Medellín) in the alignment of two adduction pipes that transport near 65% of water supplied by the Aburrá Valley Distribution System (Antioquia, Colombia). Both pipes (of 800 mm and 900 mm) were installed 35 years and 43 years ago, respectively, and are part of the system that allows the water conduction from La Fe reservoir, in the El Retiro municipality, to La Aruyá Water Treatment Plant (WTP), in Envigado municipality. Over time and especially by the intensification of the harsh winter weather during the last four years, the soil has lost systematically its stability causing pipes to lose its original position.

In accordance with the geological and geotechnical studies developed in 2011, was necessary mitigate the stress exerted on the pipe and to advance in works in order to protect pipes against the risk of new earthworks, earthquakes or other phenomena. The scheduling of activities started in July of 2011, beginning with the development of a drainage system to drain excess water and stabilize the soil. The alignment procedure did not require emptying pipes and was included the participation of about 100 people in each stage. This made possible the conception, adjustment and fabrication of realignment systems, brackets construction and fabrication of structures to support the machinery responsible for displace the pipes and dissipate the stress on pipes. The procedure developed did not require the service suspension due to the flexibility of the other two Water Treatment Plants: Manantiales and Villa Hermosa, which assumed the decreased flow in La Aruyá Water Treatment Plant [1][2][3].

CrossMarl

* Corresponding author. Tel.: +4-574-380-7322 E-mail address: Johnny.bedoya@epm.com.co

1877-7058 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of the XVIII International Conference on Water Distribution Systems doi: 10. 1016/j .proeng .2017.03.206

© 2016 The Authors. PublishedbyElsevierLtd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of the XVIII International Conference on Water Distribution Systems Keywords: Adduction pipes, soil stress, earthworks, water distribution system.

1. Problem Description

In a complex procedure due to the high precision required and the size of the infrastructure intervened, a group of officials and contractors of EPM carried out the alignment of two parallel pipes that carry about 65% of the water supplied to the Water Distribution System of Aburrá Valley. Each pipe has a length of 120 m and diameters of 800 mm and 900 mm, connecting the La Fe Reservoir with La Ayurá Water Treatment Plant (WTP) in Envigado municipality. The process was carried out in two stages between 2012 and 2015. With time the soil in which these pipes lay, lost stability making the pipes move from its original position. This situation forced the execution of works in order to mitigate the stress generated on pipes.

1.1. Overview of the interconnected system of EPM Water Distribution System of Aburrá Valley

The EPM Water Distribution System covers 10 municipalities in the Aburrá Valley (see Fig. 1.) serving near 3.3 million of inhabitants. The main WTP are La Ayurá WTP, Manantiales WTP and Villa Hermosa WTP, they guarantee 95% of water service in the interconected distribution system. The system operation is mainly governed by La Ayurá WTP and Manantiales WTP, allowing the eventual reduction or extension of covered area depending on the system operational conditions.

The primary interconnected distribution system is compound by 260 km of pipes, valves and tanks, and has the particularity to be reconfigured depending the operational necessities. This flexibility is one of the great advantages of an interconnected distribution system, allowing an optimal operation based on the system hydraulics, pumping costs and production potable water costs.

Fig. 1. EPM Water Distribution System.

1.2. Overview of La Ayura system and problematic

La Ayur§ WTP is part of a robust and reliable system in hydrologic terms due to the base flow registered in its water sources located at East of Antioquia department.

The adduction system is compound by two pump stations, two reservoirs, three pressure pipelines, a channel, a tunnel, and in its final section, there are two steel pipes of 800 mm and 900 mm respectively, by which the WTP works depending on the system necessities. Under normal conditions, the WTP is able to treat between 4.5 to 6.0 m3/s, reducing or increasing the supply coverage to the storage tanks of the interconnected distribution system. Before entering the treatment process, there is a power generation plant that makes use of the potential energy available between La Fe reservoir and the WTP, which contributes to the interconnected electric system of the country.

Below, in Fig. 2. you can find a diagram of the system components.

1.3. Overview of La Aruya system

As consequence of the harsh winter weather in 2008 and 2011, transverse movements on pipes were generated underground; threatening the system stability due to the stress concentration in certain critic points on the pipes. In 2011, some studies of geology and geotechnics recommended some civil works in mitigation, analysis of critical points identified (see Fig.3.), as well as the activity design for the stress mitigation and realignment of pipes.

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Fig. 2. Diagram of La Ayurá system.

Fig. 3. Critical points detected in the system.

There is not only one main cause to the problem, but a combination of unfavorable conditions for the pipes, as the rainwater infiltration and the tendency to groundwater recharge in the zone. Additionally, some pipe saddles were found supported on low resistance materials, compressible and expansible, such as organic and/or volcanic ashes.

1.4. Geology and Geotechnics

Since the installation of pipes, in the late 1970s, the area in which the adduction pipes lay for La Ayur§ WTP, and principally in the section between two main anchorages, has been involved in a regional problematic associated with morphodynamic process as flow, activated by the general tendency of groundwater recharge in the zone.

1.4.1. Exploration and Instrumentation

To control and monitor the evolution of earthmoving and mainly the effectiveness of civil works performed to mitigate the problem, a set of inclinometers (to measure the terrain deformation) and piezometers (to measure the pore pressure and piezometric heights) was installed. With the progressive reading of equipment were made some analysis that become the basis for the study of problem and its feasible mitigation. The instrument results analysis allowed to determine the magnitude and depth of rotational mass that was generating deformations in the pipes. This made possible the design and sizing of civil works required for the stabilization of this morphodynamic process.

1.4.2. Drainage civil works

In order to reduce the amount of water in the ground and therefore the pores pressure, were constructed some filters of around 280 m per 6.0 m of depth. Then was monitored the process trough instruments and could be verified the correct and effective functioning of the drainage system. This was confirmed when was observed the decrease in speed of morphodynamic process.

2. Risk mitigation and pipes rehabilitation

2.1. Diagnosis and security factors

The consulting firm Integral S.A. developed the analysis and identification diagnosis study, in witch were identified the critical pipe points that required immediate attention. This because the stress generated by the deformations put in risk the conductions integrity. Once the general stress state was determined and located the critical points in the pipes, a detailed procedure for its definitive realignment was defined and the required equipment was designed and built. In this way was able to increase the security factors to admissible values (see Fig. 4.).

Fig. 4. Equipment to lift up and move the pipes.

2.2. Pipes movement

In January 20th of 2012 the critical points of 800 mm pipe were attended and on February 4th, 2012, the ones corresponding to the 900 mm pipe. The movement was performed with the pipes full but without flow, in order to decrease the dilations generated by temperature change and the probability of buckling by compression in the pipes' walls. The realignment process was always controlled by strain gauges located in each one of the supports and by high-precision surveying. The data obtained fed a mathematical model of finite elements which indicated the condition of the tensorial stresses state in order to determine the following actions to perform; this process implies an iterative process that took place in movements of a few millimeters at a time.

Below, in Fig. 5. is shown the partial state of 800 mm deformed pipe, which shows the initial and deformed state during the realigment process at different times of the work.

After the realignment activity was completed, it was possible to increase the safety factors to values greater than 1.5 throughout the intervened section, allowing to mitigate risks until the works of re-foundation and complete realignment of the pipes were made.

Fig. 5. Condición deformada de

tubería.

3. Risk of pipes failure

3.1. Flow management

In order to determine the flow velocity expected at the output the modeling and simulation of drained flow was performed during a possible breakage of the pipes, for different orifice sizes. This allowed to design and built transverse channels that convey water to La Sebastiana ravine in case of a potential breakage. La Sebastiana ravine is a natural stream located at north of the pipes (see Fig. 6).

Drainage structures that exist in the surrounding area to the conduction are stable and have the sufficient capacity to safely evacuate the flooding generated by a breakage.

La Sebastiana ravine, downstream of La Ayurá WTP, is able to drain a possible sudden discharge due to the breakage of the pipes, however the community could be surprised to see how in a typical day the normal flow of the stream is increased as if a moderate rainfall has presented.

Fig. 6. Location of the deviation works

3.2. Contingency and risk management

During the work planning, a set of activities aimed to identify and mitigate risks were implemented. Among them are the following:

• Review of the global and local buckling due to the compression generated by the stress state of the system, assuming full or empty pipe.

• Construction of three new derivation channels towards La Sebastiana ravine, to route the water from the pipes in case of breakage.

• Geotechnical and structural analysis of the pipe to determine actual safety factors and compare it with the design ones.

• Hydraulic modeling and simulation of the system to determine the maximum exceeding pressures on pipes from La Ayurá hydroelectric plant operation.

• Identification of water resources required to support a possible repairing work by the Equipment Maintenance Area of EPM.

• Calculation of the stresses to which the pipe was submitted and the stresses it would have at the intervention moment to compare with the admissible ones.

• Development of a contingency operation plan for the water distribution system in the case of a prolonged suspension of the WTP adduction system.

3.3. Contingency operation

Given the impact on WDS service in the Aburr§ Valley, a simulation of the operational plan was made during the suspension of each one of the pipes and considering the effect of work time duration longer than the estimated.

1st Scenario: Operational plans of the interconnected WDS with a 24 hours suspension of the adduction system during the lifting of the 800 and 900 mm pipes, each on different dates. This scenario require to have operational availability of the rest WTP in the interconnected system to offset the deficit generated by the suspension of one of the adduction pipes to La Ayur§ WTP, and did not involve rationing schemes in any circuit. The operative program for the suspension, pipe realignment and flow recovery in each pipe was estimated in 20 hours

2nd Scenario: Operational plans of the interconnected WDS with a 72 hours suspension of the adduction system during the lifting of 800 and 900 mm pipes, on different dates. Although it is unlikely to occur, if any of the identified risks happen, it implies to have the same scheme of operational availability of WTPs in 1st Scenario. This scenario did not involve full rationing in any circuit; however, it could require the implantation of partial and sectored rationing schemes in the Aburr§ Valley.

Finally, the work was carried out within the established time, which did not generate problems in the service at any sector of WDS.

4. Design of pipe's rehabilitation work and slope stabilization

Following the efforts that mitigates the stresses at critical points of both lines, was planed the construction of new containment and foundations works by EPM, as well as the implementation of a new mechanical supports' system that allow to absorb the displacements of pipe saddles and to realign them without having to perform additional work.

4.1. First stage: construction of a slurry Wall and culverts

In 2014 civil works identified as critical and to be intervened in the short term were implemented. These works included the construction of a slurry wall in piles, confinement of anchor 3 through the construction of piles and ditches on the north side of the pipes (see Fig. 7).

Fig. 7. (a) Detail of the slurry wall. (b) Ditches for water control and management.

4.2. Second stage: construction of new foundations between anchors 2 and 3, metal structures and final alignment of pipes

In 2015 the civil works to replace all the support points of both pipes between anchors 2 and 3 were executed, in order to assembly of metal structures that would enable to recover the initial position of both pipes. For the assembly of the metal structures it was necessary to demolish the original foundations of both pipelines and build new foundations which were in some cases supported on piles to ensure the proper transmission of stresses to the

stratigraphic profiles identified in the exploratory and design phase. To accomplish this, the project was divided into four phases of intervention and the pipe was supported on wooden blocks to avoid deformation of pipes.

Fig. 8. (a) Intervention phases. (b) Pipe support on wooden blocks

Simultaneously to the reconstruction of foundations, some specialized companies carried out the manufacture of prototypes that would serve as a base to the manufacture and assembly of all structures (see Fig. 9).

Fig. 9. (a) Structure model. (b) Installed prototype

Regarding to the monitoring, control and realignment of pipes, topographic surveys were continuously conducted to monitor and control the deformations that appeared in both pipes due to the demolition of original foundations. This information allowed to determine the recovery sequence of horizontal and vertical deformations to carry both pipes back to their original position. In the following figures the results and analysis of the topographic surveys are shown, including the results obtained once the final pipeline alignment was performed in January of 2016.

Fig. 10. (a) Vertical deformation - pipeline 2. (b) Horizontal deformation - pipeline 2

Fig. 11. (a) Vertical deformation - pipeline 3. (b) Horizontal deformation - pipeline 3.

5. Conclusions

The new suppor systems adduction pipes to La Ayurá WTP allowed to redistribute the loads and vertical reactions properly, causing a favorable effect on the induced stress on the pipes. For example, the vertical reaction on pipeline 2 went from being 18.7 ton to a maximum of 8 ton. Similarly, the vertical reaction on pipeline 3 was reduced from 19.8 ton to 11.7 ton. Additionally, the new metal gantries for the pipes worked in accordance to the design hypothesis, once the supporting conditions were improved and the pipelines were moved to their theoretical axes. These gantries will allow to perform future adjustments in the event of possible displacements that could take place in the ground on which the pipes of the intervened section is found.

References

[1] INTEINSA S.A. (2011). C-0800-11-2189 Informe Instrumentación Ayurá. Medellín, Colombia.

[2] E. Mejía (2003). Informe de los factores geológicos y/o geotécnicos que afectan la estabilidad de las conducciones que están entre el Portal Ayurá y la planta del mismo nombre, en el sector comprendido entre los Anclajes 1 y 3 y 7 y 8 en el sentido portal - planta de potabilización. Medellín, Colombia.

[3] INTEGRAL INGENIEROS CONSULTORES S.A. (2011) Diagnóstico geotécnico - Corredor de las tuberías, Documento I2214-ID-03. Medellín, Colombia.

[4] INTEGRAL INGENIEROS CONSULTORES S.A. (1973) Estudio sobre estabilidad del terreno- Tubería de presión La Ayurá. Medellín, Colombia.

[5] INTEGRAL INGENIEROS CONSULTORES S.A. (2012) Informe diseño geotécnico de apoyos definitivos, Documento I2214-ID-12. Medellín, Colombia.

[6] INTEGRAL INGENIEROS CONSULTORES S.A. (2013) Diseño de ingeniería detallado del soporte de la tubería de presión de la planta la Ayurá entre anclajes 2 y 3". Documento I-2339-ID-02_R1 Medellín, Colombia.

[7] INTEINSA S.A. (2011). Estudio geológico y geotécnico de la problemática presente en la conducción Ayurà entre los Anclajes principales 2 y 4, I-2189-Condución Ayura-01-Rev0. Medellín, Colombia.