Portrait

Trunk Line Design and Construction: The Relay Race Towards L.A.'s Critical Infrastructure

by Albert Rodriguez

Over the years, large diameter trunk line pipes being assembled or lowered into trenches have become iconic images of LADWP. From reports to websites and publications, each photo of a “stick” of pipe being installed symbolizes a stronger, more resilient Los Angeles with world class infrastructure. But there is so much more that goes on behind the scenes. That one segment of pipe depicted in a photo also represents a long process spanning months and sometimes years across different LADWP groups, other city agencies, and contractors. This process can be likened to a relay race, albeit a carefully measured one where each step, each proverbial passing of the baton, is meticulously planned and coordinated.

As the backbone of the water system, LADWP’s system of trunk line pipes are large enough to fit a person inside. They can transport large volumes of water from reservoirs to smaller diameter main pipes and service connections spanning the vast water distribution system around Los Angeles. Without regular monitoring, maintenance and scheduled replacement, our city would be cut off from the precious resource of water necessary to sustain life. The relay race that LADWP Trunk Line teams are engaged in is one against time and mother nature in the form of soil-caused deterioration, age, or the ever-present specter of a large earthquake.

“Our respective teams are all very aware of the critical role we play in ensuring a strong, resilient, and reliable water system. Being able to meet the water needs of our customers is what drives us. Whether it means exploring state-of-the-art technologies, innovative designs, or modern construction methods – we strive to improve the water infrastructure of the City of L.A.”
Priscilla Gonzalez, Manager of Trunk Line Design (TLD) Group

Trunkline Groups and their Duties

Water Engineering and Technical Services (WETS) Planning Group

  • Identify project

Trunkline Design (TLD)

  • Plan route
  • ID sub-structures
  • Underground radar
  • Digital modeling
  • Permits

Geotechnical Engineering and Geology

  • Geology
  • Geotechnical reports

Trunkline Construction Support

(referred to as TLCS for the purposes of this article only)

  • Permits
  • Community outreach
  • Legislative outreach
  • Project Management
  • Materials
  • Contracts

Trunkline Construction (TLC)

  • Excavation
  • Shoring
  • Installation

Trunk Line Design

It all starts with Water Engineering and Technical Services (WETS) planning groups identifying the need for a project to modernize existing, aging trunk lines or to support new infrastructure. Once identified, it then falls upon the Trunk Line Design (TLD) group to establish the size and scale of the work and the most appropriate location to install the pipe. This is no easy task when one considers the density of the population, traffic, and other infrastructure within one street alone. TLD engineers must consider various factors such as community impacts, construction safety, and changes to existing water operations.

The TLD group also factors in sensitive facilities such as hospitals and schools, or other city agency projects, into to its designs. Safety is also paramount for TLD as they have to look out for Trunk Line Construction (TLC) crews. They strive to ensure that proposed designs mitigate any possible hazards. Once a pipe route has been determined, TLD then goes through the painstaking process of identifying all the existing underground infrastructure, such as sewers, storm drains, gas lines, electrical conduits, and communication lines. This is done with state-of-the-art ground penetrating radar to fully understand what’s in the ground, so that crews can safely and efficiently perform the installation while also minimizing impacts to the neighborhoods they work in.

In addition, detailed geology and geotechnical reports have to be developed and carefully evaluated by LADWP’s Geotechnical Engineering Group and Geology group. The soil conditions of the proposed trunk line can have a huge impact on construction and installation methods.

The designs are created on sophisticated computer programs such as AutoCAD and Civil 3D. These software programs allow the TLD team to generate three dimensional designs and models of both the pipe and the surrounding environment, allowing them to identify, visualize and solve complex infrastructure challenges. Throughout the entire design process, TLD closely collaborates with Water Distribution Division’s Trunk Line Construction Support (TLCS) group and Trunk Line Construction (TLC) crews to incorporate other design considerations. Having close coordination between groups allows for useful feedback from crews on engineering designs. This helps identify any discrepancies or obstacles to help reduce costs, improve safety and efficiency, and streamline the overall delivery of each trunk line project.

“For me, it’s very exciting to work on designs and then see them come to fruition at a construction site. Knowing that our work leads to infrastructure that will serve the community for generations to come is very gratifying.”
Gilbert Fuentes, Civil Engineering Associate II - Trunk Line Design (TLD) Group

Trunk Line Construction Support

The next phase is setting the conditions for construction, which is the responsibility of Water Distribution Division’s Trunk Line Construction Support (TLCS) Group under the leadership of Genevieve Han. This group specifically supports LADWP’s in-house trunk line construction, large valve replacement, and regulator station manifold retrofit crews.

The first order of business is acquiring permits from various L.A. City departments, namely the Bureau of Engineering, Los Angeles Department of Transportation (LADOT), and Public Works. This is another area where TLD and TLCS must work closely together to coordinate with outside agencies in securing these important permits in a timely manner. Additionally, performing early outreach and obtaining concurrences from the L.A. City Council Offices, Neighborhood Councils, and key stakeholders are required prior to implementation of each work area. TLCS works closely with WETS Division’s Project Management Office, Legislative and Intergovernmental Affairs, and Communications and Community Affairs to perform these outreach efforts in advance.

Trunk line projects typically demand deep excavations in built up urban areas with heavy traffic. This demands an engineered design shoring plan to reinforce trench walls with beams and metal plates for the safety of the crews and the public. Other permits include sewer bypass plans, storm water prevention plans, peak hour exemptions, street closure approvals, and noise variance permits. All of these layers must be in place prior to work area mobilization.

In addition to permits, material procurement is also a critical task for all construction projects. TLCS relies on Water Distribution Division's various sub-groups to procure all materials needed for the project. Sub-groups involved are Contract Administration, Construction Support, and the Trunk Line Contracts group. Materials they procure include pipes, vaults, valves, and other pipe fixtures. Contract preparation, bid, award, and coordination of fabrication and deliveries are an arduous process that could take these sub-groups up to 18 months to accomplish. The procurement process typically begins when TLD transmits the 100 percent design drawings to TLCS. Due to the long lead times, all groups must work tirelessly and collaboratively to ensure everything is in place prior to groundbreaking.

“The needs of each project vary because of the location, traffic, and the complexity of the substructures within the pipe alignment. Although time consuming, early planning and being proactive on necessary permits and concurrences helps mitigate project delays. Our aim is to also ensure employee and public safety while keeping community disruption down to a minimum.”
Genevieve Han, Manager of Trunk Line Construction Support (TLCS) Group

Indeed, no matter how well you plan, both TLD and TLCS staff are ever wary of the unforeseen. This includes discovery of substructures such as gas, telecommunications and power lines, as well as storm drains, which can alter the design or scope of work. This can be mitigated somewhat with ground penetrating radar, but even then, crews still need to conduct potholing, where a small hole is placed in the ground through a process called vacuum excavation to confirm existence of a substructure. If there is a discrepancy, then this can be revised.

Soil conditions can also determine the rate of work and the type of shoring necessary to keep the site safe. Then there is the weather factor. Heavy rain can make working conditions difficult inside a trench and extreme heat may require monitoring of crews and regular breaks.

Construction Methods and Materials

Once conditions are met and everything is in place, Trunk Line Construction (TLC) field crews can begin construction using three different methods, depending on the work site. One useful method for dense urban areas is micro-tunneling, which bores a tunnel under infrastructure such as major intersections or freeway passes. Sections of pipe are then lowered and installed from an open pit. This reduces the footprint of the work area and avoids impact on existing infrastructure.

The next method is slip-lining, which is a trenchless, underground pipe technique that involves installing a pipe of a slightly smaller diameter into an existing larger “host” pipe. This process restores the structural integrity of the existing pipeline and reduces costs and construction time.

The last method is the more conventional open-trench installation, which requires digging a trench and the assembly of the trunk line with cranes. This method is the primary method used by LADWP’s in-house TLC crews. Crews ensure that trunk lines are installed properly and safely by rigorously pressure testing and checking for leaks before it goes into service. The majority of water utilities in the U.S. hire contractors to install their trunk lines, but LADWP takes pride in being the only water utility with its own in-house crews responsible for installing and replacing large diameter pipes and valves. As LADWP increases trunk line construction, TLC crews will continue to provide the needed in-house skills and expertise to ensure quality projects. TLC reached an important milestone this April with the 25th anniversary of their establishment as a working group.

“Our construction crews on the ground are dedicated to the work they do every day because they know it’s helping improve people’s lives and laying the groundwork for the future of the city. In addition, each project offers us new challenges and opportunities from which to learn from to improve our methods and techniques.”
Clemente Valdovinos, Civil Engineering Associate II - Trunk Line Construction Support Group

The Future is ERDIP

One of the most innovative developments in trunk line construction over the past decade is the increased availability of ERDIP (Earthquake Resistant Ductile Iron Pipe). Up until recently it had only been manufactured in smaller diameters for mainline pipe. Unlike conventional pipe that can snap and break during a seismic event, ERDIP is comprised of flexible pipe connections that can perform effectively against ground displacements. This type of technology is especially needed in parts of the city where trunk lines cross known fault zones and other geotechnical hazards such as liquefaction zones. In 2024, in-house crews began the replacement of City Trunk Line North Unit 1 (CTLN U1) and became the first in the world to install a new, more efficient earthquake-resistant joint assembly. It was developed based on feedback from crews to the pipe vendor during the installation of Foothill Trunk Line, the first, longest and largest ERDIP project in the nation. Construction on CTLN U1 is tentatively scheduled to be completed in 2030.

It is this race against time and aging infrastructure that keeps Priscilla Gonzalez, Genevieve Han and their respective teams working diligently towards their annual goals. For Genevieve, it is a passion punctuated by personal experience, having lived through a 7.8 magnitude earthquake as a child in the Philippines, and then later experiencing the 1994 Northridge Earthquake after she moved to the U.S. Priscilla also remembers the 1994 Northridge earthquake and saw the destruction it caused throughout the city. Both of these engineers have taken the baton passed on by their professional forebears and earthquake authorities Le Val Lund and Dr. Craig Davis, who helped pioneer the way LADWP approaches resilient infrastructure.

In the coming years, TLD, TLCS, and the many other groups involved with the trunk line process, will play a pivotal role in the historic Pure Water Los Angeles project, which will completely transform our relationship with our drinking water to one that is more self-reliant and sustainable.

Trunk Lines by the Numbers:

  • $500 million: total cost of projects in construction
  • $1.82 billion: total cost of projects in design phase
  • ­ Over 30 trunk line projects slated to begin within the next several years
  • 12.3 miles of total trunk line installed
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