The Philippines is an archipelago of 7641 islands in the western Pacific Ocean. The country belongs to Southeast Asia and is the fifth largest island state in the world in terms of area. The thirteenth largest country in the world has around 110 million inhabitants, consisting of dozens of different ethnic groups and cultures. The main city of the Philippines is Manila, located on the main island of Luzon in eastern Manila Bay. Together with 16 other cities and municipalities, Manila forms the 636 square kilometer Metro Manila region. The majority of Manila‘s inhabitants live in coastal areas that are less than 10 meters above sea level. This makes Manila the megacity most threatened by climate change in the world, as the sea level there has risen by 80 cm since 1967. This is due to the fact that the terrain is sinking sharply as a result of water extraction and building development. The city of Marikina is located in the north of the capital region. The city is characterized by the lowlands in the southeast and the mountainous foothills of the Sierra Madre, the longest mountain range in the Philippines, in the northeast.

Lowering the pipe into the trench

Natural Disasters: A constant threat
Geographically, the Philippines is part of the „Ring of Fire“, a belt running around the Pacific Ocean that is frequently affected by typhoons, earthquakes, tsunamis and volcanic eruptions. The country is located in a seismically active zone and the more than 36,000 km long coastline and the humid climate make it one of the most disaster-prone countries in the world. No other country in the world is exposed to tropical storms as often as the Philippines, which has cost thousands of people their lives in the past. According to the Joint Typhoon Warning Center (JTWC), around 80 typhoons develop over tropical waters every year, with around 19 of them reaching the region around the Philippine archipelago.

How can Krah help here?
According to Maplecroft (2015), the Philippines is one of the countries most at risk from climate change. The Heat Stress Index, one of 20 indices published as part of the 2016 Climate Change and Environmental Risk Analytics, shows that economies such as Singapore, Malaysia, Indonesia and the Philippines could be up to a quarter less productive than they are today within a generation. For these reasons, it is very important that drainage facilities are installed throughout the land to protect it from flooding.

The Marikina-Sumulong Drainage Project
A project to install new pipes for a drainage system is presented in this report. The project is being carried out by Krah Asia Inc., a company that manufactures large-diameter plastic pipes on Krah machines made in Germany. These pipes can be welded safely and 100% tightly using electrofusion thanks to the integration of a fusion wire. The Marikina-Sumulong Drainage Project aims to mitigate flooding and enhance stormwater management in the Marikina and Sumulong areas. By improving drainage systems, the project seeks to minimize flood risks, increase infrastructure resilience, and support sustainable urban development. The initiative aligns with goals of environmental protection, preventing soil erosion, and ensuring the safety of residents by reducing flood-related hazards. Through effective drainage solutions, the project contributes to a more resilient and sustainable community in the face of heavy rainfall and storm events. The project is now intended to compensate for the poor planning of previous years and provide a good solution for a flood-proof area. The goal is to create an intersection between the creek and the Marikina river and to redirect a big volume of water in case of heavy rain or floods, to protect the area. This project is unique to date and presented us with a number of challenges. One big one was that the rainy season starts in July, so there wasn‘t a lot of time from planning to production to implementation. Another difficulty was the location of the project, as the pipes had to be laid on one of Marikina‘s main roads, the „Sumulong Highway“.

Calculating the project needs
For the pipe design, ASTM F894 was used, but in metric dimensions. So, the pipes had a structural calculation based on ASTM F894, backed up with the German ATV-DVWK-A-127 approach, because the project conditions are not standard. The flow rate was set at: Q= 26 m³/sec (95% full, gradient 0.009 %). The entire project is to have a total length of 1 km - from the mouth (river) to Balanti/ Sapang baho creek. The spigot / socket is conical to facilitate the connection and create a better welding contact surface. At the beginning of the project, thoughts were given to which material and which way of laying the pipes would be the most appropriate and best solution. In the end, Krah plastic pipes were chosen because they have significant advantages over other materials. The alternatives were, for example, conventional, cast-in-place or prefabricated RCBC box culverts and concrete pipes. These were ruled out because pipes of this size are not available. Also, this would result in very slow installation, which would cause a traffic disaster as this is a very busy road. Another problem would be that a very wide space would be needed, which would also lead to traffic chaos. Another minus with this type of implementation would be that the hydraulic flow rate is much lower than with the method chosen at the end: the Krah pipes. In addition, the abrasion resistance of concrete pipes would be much lower than that of the Krah pipe, as a lot of scrap and hard components are expected. The cleaning aspect/maintenance costs were also a significant factor in deciding in favour of Krah pipes in the end.

Production and installation
After Krah Asia Inc. was awarded the contract for this project, the production of the pipes could begin. The pipes were produced on a Krah KR800-max machine at the plant in Cavite, Philippines. A special project-specific wall design was chosen for this project, as the standard profiles were not suitable for this application. The pipe weight per pipe was approx. 3.2 tons (length 5.8m plus socket and spigot end), the pipes were produced in multiple layers, co-extruded (for ease of inspection), with integrated electrofusion wire. If the core pipe 110 is available, the pipe weight can even be reduced by approx. 10%. The production time of one pipe was 4 hours and the material used was PE100 material BorSafe™ HE3490-LS. BorSafe™ HE3490-LS-HP is a bimodal polyethylene compound produced by the advanced Borstar technology. The product is a high-density polyethylene compound in pellet form and contains a combination of stabilizers and carbon black to ensure a reliable long-term stability and UV-resistance.

Overcoming installation challenges
Due to the low weight of the pipes, a small truck with a special trailer could be used to transport the pipes to the construction site. It was not planned to install any support rings to hold the diameter, so a virtue had to be made of necessity - the pre-bent pipes were installed with a 90° turn so that a negative deflection was achieved during installation. There were a few special features that had to be taken into account when installing the pipes. A narrow, short trench had to be dug with a maximum length of 15 meters due to the heavy traffic on the road. A bedding was then used to prepare the trench for laying the pipes. The maximum depth of the trench was allowed to be 7 meters and the partially low groundwater situation due to the proximity to the Marikina River caused some concerns in advance. Another problem was that the trench was very close to the foundations of mid-rise buildings, which meant that special care had to be taken when installing the pipes. Contrary to all concerns, however, the laying of the pipes went smoothly, so that work on joining the pipes could begin quickly. The pipes were welded together using the well-known and proven Krah jointing technology. For this purpose, electric wires were integrated into the pipe during production so that they could be heated on site using an e-box and joined with the other pipe. After many tests beforehand, two wire strings (top and bottom) were used. Two Krah E-Box23+ (230VAC) were used for electrofusion, powered by two diesel generators. Due to the narrow trench, welding was carried out from the inside of the pipe. It can be said that in the future it is being considered to perhaps carry out both from the inside - it is easier if the pre-bend of the pipe does not match the position of the e-welded joint - so correct positioning is particularly important here.

Eliminating gaps by special welding
Due to the special process, simultaneous welding was possible here. This can be explained by the fact that the main effect here is on the expansion forces and not on the compression forces. In retrospect, it can be said that it would have been much better to use 4 strings here. This is because less tension/energy could be used here due to the resistance of the wire - and the welding time would also be shorter (but neither of these is decisive in this project). According to the ASTM F894 standard, the socket and spigot tolerances for a PE pipe may only be 1%. In this case, that would be 35 mm. This would make welding impossible - so what could be done? In the end, the sum of the tolerances results in a gap at the apex or sides of the pipe. To eliminate the gap, the Chillang procedure was used here. To eliminate the gap, the correct time [t] and temperature [K] were used.) The figure shows the expansion force [FE] in red and the compression force [FC] in blue. From the outside, a strong flashlight was used to apply light and detect the gap. From the inside, the gaps were visually scanned and localized. Then the elimination of the gaps was started.

The tulip effect
Additional „bulges“ at the sleeve ends could create a false image. But how do these bulges occur? These are due to the behaviour of the pipe ends of „radially extruded“ (Krah pipe) as opposed to „axially extruded“ PE pipes. The main reason for this is the principle of cooling and the frozen stresses inside the pipe wall. This effect mainly occurs on the socket side (with Krah pipes), as the spigot end is conically machined. This can be irritating at first, as the gap looks very large when viewed from the outside. The German word for this is „Auftulpung“ - as the end looks like a „tulip flower“ / „tulip effect“.The local authority‘s regulation was that a manhole must be installed every 4 pipes. This should be arranged tangentially. The connection of the pipe to the fitting and the manhole (in height) was again secured by E-Fusion. Inside the manhole, a standard removable ladder was used - also to maintain the hydraulic capacity. The cover of the manhole is a concrete ring with standard parts, and the ring is placed not only on the „PE“-manhole but also on the surrounding soil, so that the load is also transferred to the soil. At the end, the manhole cover is embedded in the road with standard metal parts and a standard concrete ring. All parts of the manhole were produced using standard tools (mostly with wooden blades) and welded together using various extrusion welding machines. The rod (black and yellow) was made from the same material as the tube on a Krah welding rod production machine to ensure a homogeneous weld. The manhole is connected in the same way as all other pipes using the same electrofusion system. During the backfilling of the manhole, the customer wanted an 800 mm long inlet in the manhole. Due to the material properties, a DN/ID 800 mm inlet (solid wall pipe) was welded in within a very short time. Here, as always, the customer‘s wishes are the top priority. There were still some minor problems with the further installation of the pipes, but these were easily solved. For example, the first pipes, which had been stored for a long time and whose roundness was not supported, were now slightly bent. Here the pipes were turned 90° before installation so that the pre-bend could be used to our advantage.

Backfilling of the trench
The backfilling of the pipes began immediately after installation and welding. As the trench was very narrow, this was carried out using vibro-compaction. Vibroflotation, also known as vibrocompaction, is a soil improvement technique used to increase the density of loose, granular soils. Here‘s how it works: A vibroflot is inserted vertically into the soil. The Vibroflot generates vibrations that cause the surrounding soil particles to rearrange themselves and settle better. As the Vibroflot is gradually withdrawn, the aggregate particles settle and the soil becomes more compacted, reducing the voids between the particles.  After this, the sheet piles were removed. Generally, a layer of lean concrete is applied directly after backfilling before the asphalt is applied. The asphalt was then applied in order to reopen the road to traffic as soon as possible.

This project report is a good example of how Krah pipes can be laid and the problems that can arise. These are briefly summarized here to give a good overview. The first major problem was the pre-bending of the pipes (due to the lack of support rings) - the solution was to simply twist the pipes by 90°. Even with high pre-bending, the hydraulic power is correctly designed and therefore does not lead to any problems.

Chillang process and vibro-compaction
Then there was the problem with the tolerances in the pipe diameter - these were large enough to join the pipes and small enough to weld them together. The solution here was the Chillang process, which was explained earlier. The compaction of narrow trenches was carried out using vibro-compaction, which turned out to be the ideal solution. We were able to give our partner in the Philippines a few more suggestions for the next project. For example, we were able to provide solutions for joining concrete with plastic, as this has long been possible in Europe. Integrating HDPE sewer pipes with old sewer lines is a challenge due to the different material properties, joining methods and construction specifications.

Ensuring material compatibility is critical to prevent degradation, and adapting jointing methods to the transition between HDPE and the existing materials is necessary for a secure connection. To maintain structural integrity and prevent blockages, differences in pipe diameter and design must be addressed and well-supported transition areas created. To overcome these challenges and achieve successful and compliant integration of HDPE sewer pipes into older infrastructure, professional technical expertise is essential. In our opinion, the distance between the shafts can also be longer, which could save shafts in the next project. When designing the manhole, inlets should be planned earlier so that they can be better pre-constructed and do not have to be worked on at the construction site.

Summary
In summary, our Krah pipes convinced the local operator that they were the right choice for this project due to the availability of the pipe, ease of handling, reliability, long service life, low maintenance costs, quick installation and low overall investment costs. The long service life of the pipes will also reduce the total cost of ownership. Thanks to a good technical support team, Krah Asia Inc. has managed to complete a wonderful project that everyone is happy with. We can say with a clear conscience that with these plastic pipes we have once again contributed to making the world a better and more sustainable place.

Dr. Alexander Krah / CEO Krah GmbH
Jenny Krämer / Marketing Krah GmbH