Deep Foundation Design and Construction
Deep foundations are used when the surface soils are not adequate to support the structure loads and competent bearing strata are located at greater depths. The two main categories of deep foundations are driven piles and drilled shafts, each with specific advantages and limitations depending on the soil conditions, the loading requirements, and the project constraints. Driven piles are prefabricated elements made of steel, concrete, or timber that are driven into the ground using impact hammers, vibratory hammers, or hydraulic presses. The pile installation displaces the soil as it penetrates, increasing the density of the surrounding soil and developing load capacity through a combination of end bearing and skin friction. The pile capacity is verified during driving using the pile driving analyzer that measures the strain and acceleration at the pile top and computes the static capacity using wave equation analysis. The pile driving formula provides an estimate of the pile capacity based on the hammer energy and the penetration resistance, but the PDA testing provides more reliable capacity estimates.
Drilled shafts, also called drilled piers or caissons, are constructed by drilling a large diameter hole into the ground and filling it with reinforced concrete. The shaft diameter typically ranges from 24 to 72 inches, with depths of 30 to 150 feet depending on the soil and rock conditions. The drilling method depends on the soil and ground water conditions. The dry method is used in stable soils above the water table where the hole remains open during drilling. The casing method uses a steel casing that is advanced as the hole is drilled in unstable soils. The slurry method uses bentonite or polymer slurry to support the hole walls in water-bearing soils. The drilled shaft bottom must be cleaned of loose material before concrete placement to ensure adequate end bearing. The concrete is placed by the tremie method for wet shafts, with the concrete delivered through a pipe that extends to the shaft bottom to displace the drilling fluid upward.
The load testing of deep foundations verifies that the installed piles or shafts achieve the design capacity. Static load tests apply a controlled load to the foundation element and measure the resulting settlement. The test load is applied in increments using a hydraulic jack reacting against a weighted beam or anchor piles. The maximum test load is typically 200 percent of the design load to verify adequate safety margin. The interpretation of the load test results uses criteria such as the Davisson offset method that defines the failure load as the load at which the settlement exceeds the elastic compression of the pile plus a specified offset. The static load test provides the most reliable verification of foundation capacity but is expensive and time-consuming. The dynamic load test using the PDA provides a faster and less costly alternative for production pile testing after the static load test has established the capacity correlation for the site conditions.
Water and Wastewater Infrastructure Planning
Water infrastructure planning involves the development of strategies for meeting the current and future water supply needs of a community. The planning process begins with a demand forecast that projects the water consumption based on population growth, economic development, and conservation trends. The demand forecast considers the water use for residential, commercial, industrial, and public purposes, as well as the unaccounted-for water from system losses and unauthorized use. The water system capacity must be adequate to meet the maximum daily demand and the peak hour demand that occur during periods of highest use. The fire flow requirements add additional capacity requirements that often govern the design of water mains in commercial and industrial areas. pile driving analyzer for deep foundation capacity verification. tremie concrete placement method for drilled shaft construction. trenchless pipe rehabilitation methods for water infrastructure. The infrastructure planning identifies the improvements needed to maintain adequate capacity and pressure as the demand grows over the planning period.
Wastewater collection system planning addresses the conveyance of sewage from homes and businesses to the treatment facility. The system design is based on the projected wastewater flows from the service area, including the domestic flow from residences, the commercial and industrial flows, and the infiltration and inflow from groundwater and stormwater that enter the sewer system through defects and connections. The infiltration rate is typically 100 to 500 gallons per day per inch of pipe diameter per mile of sewer length for existing systems. The inflow from stormwater connections can significantly increase the peak flows during wet weather events. The capacity of the collection system must be adequate to convey the peak wet weather flow without surcharging that could cause basement flooding and sanitary sewer overflows. The separation of stormwater from the sanitary system through the construction of separate storm sewers reduces the wet weather flows in the sanitary system.
The rehabilitation of aging water and wastewater infrastructure is a growing challenge for communities with aging systems. The replacement of deteriorated water mains and sewer pipes is a major capital investment that must be prioritized based on the condition assessment results and the consequence of failure. Trenchless rehabilitation methods including pipe bursting, cured-in-place pipe lining, and slip lining replace or rehabilitate existing pipes without the disruption of open trench excavation. The water loss from leaking distribution systems in the United States averages 16 percent of the total water production, with some older systems losing more than 30 percent. The reduction of water losses through leak detection and repair programs conserves water resources and reduces the energy costs for water treatment and pumping.
Quality Control and Inspection
The quality control program for any construction activity includes the inspection of materials upon delivery, the observation of work in progress, and the testing of completed work. The inspector verifies that the materials meet the specifications and are stored properly to prevent damage before installation. The observation of the work during installation identifies any deviations from the contract documents that must be corrected before the work is concealed by subsequent construction. The testing of the completed work verifies that the installed materials achieve the specified performance requirements for strength, durability, and function. The documentation of the inspection and testing results provides the permanent record of quality for the project that is used for future maintenance and renovation. The non-conformance report documents any work that fails to meet the specifications and tracks the corrective action through to completion and verification.
The quality assurance program provides confidence that the quality control activities are being performed effectively. The QA program includes audits of the QC processes, review of the documentation, and independent verification of the test results. The QA manager reports to senior management independently of the project management to ensure objective evaluation of quality. The QA program also includes the training and qualification of the inspection and testing personnel. The corrective action process identifies the root cause of quality problems and implements changes to prevent recurrence. The continuous improvement of the quality program uses the feedback from the QC and QA activities to improve the processes and procedures for future projects.
Codes and Standards Compliance
The building code requirements for each type of construction are established by the International Codes and the applicable local amendments. The designer must review the code requirements for the specific occupancy and type of construction to ensure that the design complies with all applicable provisions. The fire resistance requirements, structural loading criteria, energy efficiency standards, and accessibility provisions must all be addressed in the design. The special inspections required by the building code for seismic and wind resistance must be performed by qualified inspectors. The documentation of code compliance includes the plans, specifications, calculations, and test reports that demonstrate that the construction meets the code requirements. The permit application review by the building department verifies that the design complies with the code before construction begins.
The industry standards published by ASTM, ANSI, ACI, AISC, and other organizations provide the material specifications and test methods referenced by the building codes. The ASTM standards cover the testing and specification of construction materials including concrete, steel, masonry, and wood. The ACI standards provide the code requirements and design guidance for concrete structures. The AISC specification governs the design of steel structures. The MSJC code provides the requirements for masonry structures. The reference to these standards in the contract documents ensures that the materials and workmanship meet the established industry benchmarks for quality and performance.
Environmental Considerations
The environmental impact of construction activities must be managed to comply with regulations and to minimize the effect on the surrounding community. The stormwater pollution prevention plan for construction sites controls erosion and sediment runoff during the construction period. The dust control measures including water spraying, wind barriers, and stabilizing exposed soils prevent air quality impacts. The noise control measures limit construction activities to permitted hours and use quieter equipment where feasible. The waste management plan diverts construction and demolition waste from landfills through recycling and reuse. The material storage and handling procedures prevent spills of fuels, oils, and other hazardous materials that could contaminate the soil and groundwater. The site restoration after construction includes revegetation, landscaping, and the removal of temporary facilities to return the site to its intended final condition.
The sustainable construction practices reduce the environmental footprint of the project through material selection, waste reduction, and energy-efficient construction methods. The use of locally sourced materials reduces transportation energy. The recycling of construction waste including concrete, steel, wood, and cardboard reduces landfill disposal. The construction of energy-efficient buildings reduces the operational energy consumption and greenhouse gas emissions over the building life. The indoor air quality during construction is protected by sequencing the work to avoid contamination and by ventilating the building before occupancy.