Oriented Jet Grouting 'M' Supports For Underpinning Historical Foundations-PPT Presentation

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The paper presents oriented jet grouting, particularly an “M” support configuration, as an underpinning method for historical foundations where conventional techniques are impractical because of fragile materials, limited access, or risks from excavation and dewatering.<br /><br />Jet grouting forms overlapping soil-cement columns and can be installed in small increments without excavation. However, the process temporarily liquefies the treated soil, so column size, spacing, and installation sequence must preserve support while grout sets. Wide foundations may also be difficult to reach without drilling through them.<br /><br />The M support arrangement uses angled columns from opposite sides to enclose and stabilize soil beneath the foundation’s center. This encapsulated soil is constrained against shear deformation and potential erosion, while the system can increase stiffness and bearing capacity, mitigate liquefaction, and act as part of the foundation. It may reduce the amount of grouting needed compared with complete underpinning.<br /><br />Design should establish the required improvement depth using bearing-capacity principles and verify performance with finite element modeling. Adequate encapsulation, column strength and thickness, overlap, and spacing are essential. Installation sequencing should limit interactions between unset columns and maintain continuous support.<br /><br />Construction controls include trial grouting, excavation or coring to verify column geometry, real-time structural monitoring, and recording jet-grouting parameters. Careful spacing of wet columns is also needed to avoid temporary loss of support.<br /><br />The authors conclude that M supports can provide an adaptable alternative to conventional underpinning, particularly in granular soils where sufficiently strong soil-cement can be produced.

Keywords

jet grouting

oriented jet grouting

M support

underpinning

historical foundations

soil-cement columns

bearing capacity

liquefaction mitigation

finite element modeling

construction monitoring