# 1.5 Years of Heavy Construction in 1.5 Hours Channel: Practical Engineering Source: https://www.youtube.com/watch?v=goWsVAE-JF0 Recap page: https://rapidrecap.app/video/goWsVAE-JF0 --- ## Quick Overview The new sewage lift station outside San Antonio, Texas, was constructed over 1.5 years to expand wastewater capacity and provide redundancy for a rapidly growing area, involving deep excavation, precast wet well installation, complex piping, and robust electrical infrastructure. **Key Points:** - The project constructed a new sewage lift station outside San Antonio, Texas, to increase wastewater capacity and provide redundancy for a rapidly developing area. - Construction began with excavating a 30-foot deep hole, requiring sloped sides for the first 10 feet and a slide rail shoring system for the remaining depth due to the narrow site. - The primary component, a precast concrete wet well, was assembled from 15-ton segments, sealed with gaskets and grout, and then leak-tested by filling it with water for several days. - Backfilling around the wet well and in pipe trenches utilized Controlled Low Strength Material (flowable fill), a self-compacting cement slurry, which allows for easier future excavation for pipes. - Three sewer lines were connected to the wet well, with holes core-drilled on-site for precise alignment, and flexible couplings installed to accommodate movement. - Doghouse manholes were installed over existing active sewer lines, and large plug valves were integrated into the system, requiring bypass pumping to divert wastewater during installation. - The site was graded with compacted select fill and native clay, and concrete slabs were poured for the electrical shelter and equipment, with rigorous quality control tests performed on the concrete. **Context:** Located outside San Antonio, Texas, a rapidly developing region, the construction of a new sewage lift station became essential to meet the increasing demand for utilities from new homes and businesses. This project, a collaboration with the San Antonio River Authority, aimed to expand the existing sewage system's capacity and introduce redundancy, ensuring continuous wastewater management even during maintenance periods. Lift stations are critical where gravity-fed sewers cannot reach treatment plants, requiring wastewater to be pumped to higher elevations. ## Detailed Analysis The construction of a new sewage lift station near San Antonio, Texas, spanned 1.5 years, addressing the critical need for expanded wastewater infrastructure in a rapidly growing area. The project commenced with excavating a 30-foot deep hole, utilizing sloped sides for initial safety and then a sophisticated slide rail shoring system to prevent collapse in the narrow, deep excavation. The native clay soil, unsuitable for backfill, was hauled away, and a remote-controlled compactor prepared the subgrade before a working "mud slab" was poured. The core of the station, a large concrete wet well, was constructed from multiple 15-ton precast segments, meticulously sealed with gaskets and grout, and then subjected to a multi-day leak test. Backfilling around the wet well and subsequent pipe trenches involved Controlled Low Strength Material (flowable fill), a self-compacting cement slurry that hardens but remains excavatable for future pipe installations. Three sewer lines were connected to the wet well, with their precise entry points core-drilled on-site after the wet well was in place, ensuring perfect alignment. These lines incorporated link seals for watertight connections and flexible couplings to absorb movement. Manholes, including "doghouse" designs that fit over existing active sewer lines, were installed, and critical plug valves were integrated to enable wastewater diversion and system redundancy. The installation of a large bypass plug valve on an active 24-inch sewer line necessitated temporary bypass pumping to maintain service. The site was meticulously graded, with select crushed rock fill used under concrete structures and native clay elsewhere, all compacted and tested for density using a nuclear gauge. Electrical conduits, marked with red concrete for safety, were laid underground, leading to a concrete pad for the control shelter. Concrete pours for various slabs, including the equipment pad and wet well cover, underwent rigorous quality control tests for slump, air content, and compressive strength. The project culminated in the installation of the wet well cover slab, which included numerous blockouts for pumps and other equipment, marking a significant step towards operational readiness. ### Initial Excavation & Shoring - Project began with a 30-foot deep excavation for the lift station's wet well - Native clay soil was hauled off-site, and a two-stage excavation process was used: sloped sides for the first 10 feet, followed by a slide rail shoring system for deeper sections due to site constraints - The shoring system involved precisely installing outer panels, corner rails, and sliding inner panels to prevent collapse and protect workers. ### Wet Well Construction - A remote-controlled compactor densified the subgrade at the bottom of the excavation, followed by the placement of a concrete "mud slab" as a working platform - The wet well, the primary component, was assembled from multiple 15-ton precast concrete segments, stacked like Lego - Each segment was sealed with compressible gaskets and lubricant, then grouted and coated internally, and finally underwent a multi-day leak test. ### Backfilling & Shoring Removal - Backfilling around the wet well was carefully coordinated with the removal of the shoring system - Controlled Low Strength Material (flowable fill), a self-compacting cement slurry, was used for backfill, chosen for its ability to harden without settling and its ease of excavation for future pipe installations - This process involved pouring batches of flowable fill and progressively removing shoring panels. ### Pipe & Manhole Installation - Three sewer lines were connected to the wet well, with their precise entry points core-drilled on-site after the wet well was in place to ensure alignment - Trenches for pipes required shoring boxes for worker safety and were bedded with gravel for support - Doghouse manholes were installed over existing active sewer lines, with their bottoms cast in place and precast tops added, and all joints were sealed and leak-tested. ### System Redundancy & Bypass - Plug valves were installed on sewer lines to allow diversion of wastewater, creating redundancy between the new and existing lift stations for maintenance - The installation of a large 24-inch plug valve on an active sewer line necessitated temporary bypass pumping, where wastewater was diverted around the construction area using hoses and an inflatable plug. ### Site Finishing & Infrastructure - The site was brought to final grade using compacted select fill (crushed rock) under concrete structures and native clay elsewhere, with density checked by a nuclear gauge - Underground electrical conduits, marked with red concrete, were laid for robust power connections to the pumps and controls - Concrete slabs were poured for the electrical shelter, equipment pad, and wet well cover, with rigorous quality control tests performed on all concrete batches.