Micropile Retaining Wall Top-Down Construction
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Solution Overview
Problem
Conventional permanent earth retaining walls in mountainous terrain require large equipment for installing large-diameter soldier beams, leading to high costs, time consumption, and space requirements, often necessitating road closures due to limited space and unstable ground conditions.
Innovation Solution
The use of small-diameter micropile soldier beams formed by sectional casings that remain in the ground, connected to horizontal support members and tiebacks, allowing for a top-down construction method that reduces equipment size and space requirements, and eliminates the need for temporary lagging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If large-diameter drilled shafts are used for soldier beams, then the structural strength and stability of the retaining wall is improved, but the equipment size and space requirements increase significantly
Solution Approach 1:
The patent changes the diameter parameter of soldier beams from large (24-36 inches) to small (6-12 inches), transforming conventional large-diameter drilled shafts into micropiles. This parameter change maintains structural adequacy through increased number of piles and grouted bar reinforcement while dramatically reducing equipment footprint and installation space requirements.
Solution Approach 2:
The patent segments the structural load-bearing function from individual large soldier beams to multiple smaller micropiles arranged in rows. By distributing the retaining force across numerous closely-spaced micropiles (typically 6-12 inches on center), the system achieves comparable or superior structural performance with much smaller individual element sizes and reduced equipment requirements.
2Ease of manufacture
If large drilling equipment is used to install soldier beams, then the installation capability is improved, but the construction time and cost increase
Solution Approach 1:
The patent changes the installation equipment scale from large overburden percussion drilling rigs to small micropile drilling equipment. The reduced equipment size enables faster mobilization, quicker installation cycles, and the ability to work in confined spaces, thereby improving construction productivity and reducing overall project duration while maintaining adequate installation capability through proper micropile drilling techniques.
Solution Approach 2:
The patent employs temporary casing during micropile installation that is removed after grout placement, rather than permanent large-diameter casings. This temporary casing serves its purpose during installation and is then discarded, eliminating the need for expensive large equipment and extensive permanent casing materials, thereby reducing both equipment costs and construction time.
3Strength
If large equipment is used for soldier beam installation, then the structural capacity is improved, but the road closure requirement increases
Solution Approach 1:
The patent changes the spatial parameters of the retaining wall system by using multiple small-diameter micropiles in close spacing rather than fewer large-diameter beams. This allows installation equipment to operate in a much smaller footprint, enabling construction to proceed with minimal road closure or during off-peak hours, thereby reducing traffic disruption while maintaining adequate structural capacity through the collective strength of multiple micropiles.
Solution Approach 2:
The patent transitions from a horizontal spacing arrangement (fewer, widely-spaced large beams) to a closely-spaced array configuration (many small micropiles). This dimensional reorganization allows the installation equipment to work within a compact area, minimizing the road closure zone while achieving the same or greater structural capacity through the aggregated contribution of multiple closely-spaced elements.
4Reliability
If casing is removed after concrete placement, then the direct bond to ground is improved, but the construction complexity increases
Solution Approach 1:
The patent uses temporary removable casing during micropile installation that is discarded after serving its protective function. The casing is installed to maintain hole stability during drilling and grout placement, then removed to allow direct grout-to-ground bonding. This temporary casing approach simplifies construction by eliminating the need for permanent large casings while ensuring adequate bond development through direct grout contact with the ground.
Solution Approach 2:
The patent performs preliminary grout placement into the drilled hole before finalizing the micropile installation. The grout is placed while the hole is still accessible, ensuring complete filling and optimal bond development with the surrounding ground. This preliminary action sequence simplifies the overall construction process by establishing the bond interface early rather than requiring complex post-installation bonding procedures.
Data Source
AI summary
The present invention provides a permanent earth retaining wall having small diameter casings that remain in the ground to become vertical micropile soldier beams of the retaining wall, and a method for forming a retaining wall. The method includes a top-down method of constructing a retaining wall. The retaining wall may be constructed by placing a plurality of relatively small diameter micropile casings into the ground using overburden percussion drilling methods. The casings are configured to remain in the ground and form micropile soldier beams of the retaining walls. Tiebacks may be coupled to the micropiles via horizontal support wales that span multiple micropiles.