Figure Eight Secant Shaft and Soil Mixing for a Sewer Lift Station

PPT Presentation

Pdf Summary

The presentation describes construction challenges and solutions for the Springfield Creek Lift Station project in Springfield, Nebraska, for the Sarpy County Wastewater Authority. It covers two phases: installation of figure-eight secant pile shafts in winter/spring 2024 and soil-mixing ground improvement in fall 2024.<br /><br />During sewer installation, actual ground conditions—including silty sand—created concerns about excavation stability. The team’s solution was to create a soil-cement block at least 12 feet wide, extending to elevation 990 feet, to support the work. An 8-foot-wide trench box was also incorporated into the approach.<br /><br />Laboratory testing examined how cement content and water-to-cement ratio affected soil-cement strength. Production involved 265 columns, 29 production shifts, and approximately 3,020 cubic yards of treated soil. Reported strength tests showed that higher cement factors generally produced greater compressive strength over time.<br /><br />The presentation also addresses uncemented or disturbed areas and the resulting grouting measures. Disturbed soil was treated with polyurethane grout injected from inside the shaft, while colloidal silica permeation grout was delivered into undisturbed soil through driven pipes. These treatments were used to improve system performance behind the secant wall.

Keywords

Springfield Creek Lift Station

Sarpy County Wastewater Authority

secant pile shafts

soil mixing

ground improvement

soil-cement block

excavation stability

cement content testing

polyurethane grout

colloidal silica grout