Challenges and Lessons Learned of Horizontal Directional Drills in South Florida

Purpose:
CHA Consulting has been involved in the design and installation of water and sewer mains using the trenchless method of Horizontal Directional Drilling (HDD) in South Florida. A total of 30,000 LF of pipe has been installed using this technology and includes 21 separate projects in last 10 years. Pipe sizes for these projects vary from 8' to 54', including a world record of the longest 54' pipeline installed by HDD. The main purpose of this presentation is to share our experience and lessons learned with utility managers in other parts of the country.

Benefit of the Presentation:
This information will benefit all professionals involved in pipeline projects by providing in-depth analyses of the HDD method and its various applications, an overview of the technical design process, and a concise yet informative study of the challenges, both technical and non-technical, faced during the design, permitting, construction, and certification of pipelines installed with this technology. The goal is for professionals of all experience levels to gain a comprehensive understanding of the HDD method and its benefits, especially as it pertains to the use of this technology in South Florida. Design and Construction Challenges: Some of the critical design and construction challenges observed, are listed below.

Design Challenges:
- Entry and Exit Angles: These angles were generally kept between 8 and 12 degrees based on equipment limitations, ground conditions, and to facilitate breakover support during pipe pullback.
- Minimum Curvature Radius: For most projects, this was usually between 1,500' and 4,000' to minimize pulling forces during pipe installation. Bending radius outside the drill were between 40 to 50 times OD.
- Installation Loads: Pipes are subjected to tension, bending and external forces. HDD installation loads were determined during the design phase. A safety factor of 2 was used to determine pipe material and thickness.
- Pipe Material Selection: Pipe Material for HDD installation should be smooth, flexible, and must have sufficient strength to resist the installation, working tensions and any transients that may occur during operation. Types of pipes considered for these projects Included Fused Polyvinyl Chloride (FPVC), High Density Polyethylene (HDPE), and Steel.
- Utility information: Accurate utility information is critical for HDD projects. Subsurface Utility Engineering (SUE) was performed to confirm utility locations at critical areas of the project.
- Subaqueous installation: Installation under water bodies required maintaining clearances of 15' below the canal's cross section as well as minimum clearances from bridge piles.
- Connection to other type of pipe materials: HDD installation requires special pipe materials to connect to other types of pipe materials. Flange adapters, couplings, and restraints were used for these connections.

Construction Challenges:
- Staging: Staging Areas are typically 35' by 70'. Contractors needed to coordinate with property / business owners and reach agreements thru Public Relations Firms.
- MOT: Although HDD avoided the need for MOT along pipe alignment, traffic control around the entry and exit pits was required. The location of these pits determines the complexity of the traffic control required. This may be anywhere from simple lane closures/merges to entire intersection closures.
- Geological Conditions: Most of South Florida is characterized by sandy/clay conditions (medium to dense Brown Silty Sand, Gray Sand, and Silty Clays), medium to high density Brown Sandy Limestone area, and combinations of these conditions. These ground conditions were challenging for HDD installations.
- Existing Buried and Overhead Utilities: Detailed as-built records of the lines and other utilities in the areas were requested to avoid conflicts with designs and installations.
- Frac-out: The inadvertent return of drilling fluids to the surface during the drilling operation, frac-out can occur as a result of a variety of factors. This can be critical due to the proximity of environmentally sensitive areas. Frac-out plans were developed during the design phase and were part of the permit package.
- The projects included several canal crossings (Intracoastal Waterways, Miami River, Biscayne Canal, Biscayne Bay, etc). Close coordination with permitting agencies was required to obtain the approval of these crossings.

Permit Requirements:
Several environmental agencies have jurisdiction over the project locations; therefore, the permitting process has been very intense and challenging. Permits required for the HDD Installation in South Florida include: US Army Corps of Engineers (USACE), Florida Department of Environmental Protection (FDEP), South Florida Water Management District (SFWMD), Miami Dade County Department of Regulatory Environmental Resources (RER), Broward County Environmental Protection and Growth Management Department (BCEPGMD)

Status of Completion:
All of the 19 HDD installations covered in this presentation have been completed in the last 10 years in South Florida, mostly within the Miami-Dade County and Broward County. A summary of the most relevant projects of our experience is depicted below: 20' WM & 16' FM Las Olas Blvd, Ft Lauderdale, FL (4,300 LF, completed in 2017): Design/Build services for the design, permitting, and construction inspection of a 20-inch H.D.P.E. water main (2000 LF) and 16-inch H.D.P.E. force main (2300 LF). 54-inch HDPE/PCCP Force Main Miami Beach, FL (4,450 LF, completed in 2016): Design and installation of a 54-inch force main. 42' FM North Miami Avenue from NW 36th St. to NE 62nd St. (7,500 LF, completed in 2019): Design and installation of High-Density Polyethylene (H.D.P.E.) pipe, valves and fittings. 54' FM HDPE Redundant Bypass Line, FT Lauderdale, FL (8,400 LF, completed in 2020): Design-Build for the Installation of New Redundant 54' Bypass pipe. 12' FM on Brickell Key Drive, Miami FL (1,500 LF, completed in 2022): 14' H.D.P.E. F.M. Emergency Installation Underneath Brickell Key Bridge.

Conclusions:
A successful HDD project carefully considers the challenges described above and many other factors to ensure constructability, feasibility and project safety. Our experience during the last several years in the design of these pipelines has resulted in the adoption of several design characteristics as standards for effective designs. These include best entry and exit pit locations, optimum entry and exit angles, acceptable bending radii, and feasible pipe materials and dimension ratio (DR)s. In addition, installations in different jurisdictions and environmental locations have proven to create a robust repository of permitting information that has been useful when permitting and certifying these projects. The knowledge and information exhibited in this presentation is done so with the intention of communicating our experience and lessons learned designing HDDs in South Florida to our colleagues around the country.