In an attempt to address aging cast iron infrastructure throughout San Diego, California, the City of San Diego initiated the replacement of a 30-inch potable water transmission main with a 24-inch PVC pipeline along Upas Street in historic Balboa Park, crossing under California State Route 163 (CSR 163). Horizontal directional drilling (HDD) installation methods were selected to minimize disturbance to the park and the critical highway. The California Department of Transportation (Caltrans) only required a casing for the segment crossing the highway. Therefore, a unique design for the HDD crossing was implemented, using a 30-inch, 700-foot-long, partial casing and a full 24-inch, 1,725-foot-long carrier pipe installed simultaneously. The casing length satisfied the Caltrans requirements by providing a casing under CSR 163, but limited the length of casing required for the entire installation. The installation included a specially designed pull-head, which allowed for simultaneous attachment to both the casing and carrier pipe ends and also allowed drilling slurry to flow between the two pipes. This provided an alternate form of ballasting for the casing while the carrier pipe was ballasted using a standard fill line arrangement.
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