C+S March 2021 Vol. 7 Issue 3 (web)

When rigid inclusions are installed with displacement drilling tech- niques, the soil is displaced laterally, with virtually no vibration or spoil, eliminating the need to dispose of contaminated soil. The auger is screwed into the soil to the required depth increasing the density of the surrounding soil and increases its bearing capacity. During auger extraction, grout is injected under light pressure to build the column to stiffen and treat the surrounding soil. Driven casing methods are also sometimes used to install the elements. Rigid Inclusions are designed as a composite ground improvement system where the column rein- forcements and the surrounding soil share the loads. Rigid Inclusions have proven to be extremely versatile in treating a wide variety of soil conditions, including very soft, compressible lay- ers, very deep layers (rigid inclusions have been installed to depths of over 150 ft) and contaminated soils, since spoil generation is minimal. Unlike pile foundation systems, rigid inclusions are not typically con- nected to foundations. A layer of compacted stone referred to as a load transfer platform (LTP) is typically installed above the Rigid Inclusion elements to help distribute the load from the structure to the underlying soil and Rigid Inclusion elements. The LTP allows for shallow founda- tions to be designed and eliminates the need for pile caps, grade beams, and structural slabs. Conclusions While this article does not cover every ground improvement technique that is available, it highlights a wide range of techniques available to treat a variety of problematic soil conditions. Ground improvement systems are intended to be elegant in their simplicity, and are used to support any number of structure types including warehouses, buildings, storage tanks, equipment and machinery pads, highway embankments, retaining walls, earthen fills, berms, dikes, and levees. When comparing ground improvement to piling, it is important to understand that ground improvement may lead to savings related to foundation design and total construction costs, especially when not only the piling, but the associated pile caps, grade beams and structural slabs can be eliminated. An increasingly important benefit of ground improvement is environmental sustainability - in many cases less con- crete and steel is used in the foundation system. Menard Group USA is a design-build ground improvement contrac- tor with offices across the USA, offering solutions for a wide range of soil conditions and structure types. For more information or to discuss an upcoming project, pls contact info@menardgroupusa.com or call (412) 620-6000. MARTIN G. TAUBE, P.E., P.G. is Vice President of Business Development for Menard Group USA and works out of the Pittsburgh, PA office. He has more than 30 years of experience in geotechnical engineering, construction, and ground improvement. SONIA SORABELLA SWIFT, P.E. is Menard Group USA’s Design Manager and is based in Boston, MA. A registered Professional Engineer in eight states, she has more than 14 years of experience in ground improvement design and is responsible for the overall management of Menard’s design team and design protocols.

General range of applicable soil types for various ground improvement techniques

Where liquefaction is a potential risk, larger diameter drains know as Earthquake Drains can be installed. These drains are designed to alle- viate pore pressure build up during seismic events such as earthquakes, and reduce both the likelihood of liquefaction occurring and the amount of liquefaction-induced settlement that occurs. The drains are typically comprised of a 4-in-diameter slotted, flexible, corrugated pipe encased in a geotextile fabric. The drains are driven into the ground at spacings that typically range from 5 to 10 ft. Vibro Stone Columns/Aggregate Piers Vibro stone columns are continuous vertical columns of compacted aggregate that are formed using a vibratory probe to create vertical in- clusions with high stiffness and shear strength and improved drainage. Vibro stone columns typically range in diameter between 18 and 42 inches. When a vibratory probe is used to form the hole in which the stone column is constructed, then the elements are referred to as stone columns or vibratory stone columns. If separate drilling equipment is used to create the hole in which the stone is placed, then the elements are commonly referred to as aggregate piers. Stone columns are commonly used to reduce settlement and increase bearing capacity of soils for the support of structures. Because of their high shear strength, they are also commonly used to enhance slope stability and prevent lateral spreading. Stone columns can efficiently mitigate liquefaction resulting from the significant densification of granular layers that occurs during installation; enhanced drainage capacity is also a benefit for liquefaction mitigation. In spite of the versatility of stone columns, slower installation rates and subsequent higher cost of stone columns deeper than about 40 feet make their use for deeper soils less viable. Stone columns are also not applicable for very soft clays or organic soils where the columns would be prone to bulging which would lead to excessive settlement or even failure. Rigid Inclusions Rigid Inclusions are grouted vertical elements that typically range in diameter from approximately 12 to 18 inches. Rigid Inclusions are well adapted to high surface loading conditions and strict settlement requirements and are used to support slabs-on-grade, isolated footings, and embankments on compressible clays, fills and organic soils.



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