CASE HISTORY: PILOT TUBE METHOD SOLVES BASEMENTS FLOODING PROBLEM

摘要

Improvements at Fenwick Road,Floyd Avenue and Essex Avenue in Fairfax County,Virginia,consisted of the design and construction of approximately 2000 feet of 10 and 12-inch I.D. vitrified clay sewer pipeline installed using Pilot Tube Microtunneling (PTMT) methods along two separate sites. The improvements were intended to alleviate basement backups and surcharging that have been experienced in the neighborhood homes during wet weather events. The proposed sewer lines will be connecting into existing lines and constructed parallel to these existing lines,in order to share or offload sewer capacity. Because the project is located in a congested urban environment; both open cut and PTMT were evaluated for installation of the relief sewer pipes. The two techniques were evaluated with regard to cost,risk,environmental impact,and construction schedule. Based on the evaluation criteria and the desire of the county to minimize the environmental impacts on the neighborhood,PTMT was selected.The paper discusses the selection methodology and advantages of the PTMT over open cut. The soils along the alignment were primarily residual soils extended beyond the pipe invert. The residual soils were generally medium stiff to hard brown or gray silt,sandy silt,and sand. Ground water was generally above the pipe with head between 4 and 6 feet above the pipe invert. During construction PTMT installation proceeded at a fast pace reaching 22-ft per hour at its peak. The PTMT installation technique proved to be flexible and able to adapt to unforeseen site conditions. The paper discusses unforeseen site conditions and the solution. The sewer lines were installed successfully and are helping to relieve the basements backup problems that have plagued the neighborhood homes for the past 10 years.This paper describes the evaluation methodology that was used to evaluate the PTMT vs. open cut including cost,risk,environmental impact,and construction schedule factors. Additionally,the paper presents that adaptability of the PTMT during construction to the challenge of unforeseen site conditions.