Anchoring Tendon Sequential Tensioning Load Transfer

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Solution Overview

Problem

Current ground anchoring technology is limited by the ability to transfer load to surrounding rock, with high stress loads leading to tendon corrosion and grout additives potentially being detrimental over time, and existing methods for increasing load transfer capacity either require harmful additives or provide only marginal improvements.

Innovation Solution

Sequential tensioning of different groups of tensile elements in a predetermined sequence to achieve initial and final displacement lengths, allowing for increased load transfer without de-bonding and avoiding the use of harmful grout additives.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Force

If higher stress loads are applied to increase anchoring capacity, then the load transfer capacity is improved, but the tendon becomes prone to corrosion due to grout cracking

Engineering Contradiction:

Improveload transfer capacityVSAvoidtendon corrosion resistance

Core Design Contradiction:

ForceVSReliability

Solution Approach 1:

The tendon is divided into multiple independent strands, each with its own corrugated sheath providing corrosion protection. This segmentation allows each strand to be protected individually while collectively providing the required load transfer capacity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A composite system is used combining steel strands with polyethylene corrugated sheathing and grout. The sheath acts as a protective barrier while the grout provides bond and load transfer, creating a multi-material system that addresses both strength and corrosion resistance requirements.

Inventive Principle:

Principle #40Composite materials

2Strength

If grout additives are used to increase grout strength, then the grout compressive strength is improved, but the long-term reliability of the anchor is compromised due to potential adverse effects of additives

Engineering Contradiction:

Improvegrout compressive strengthVSAvoidanchor long-term integrity

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The invention uses standard Portland cement grout without expensive proprietary additives. While the grout may not achieve ultra-high strengths, it provides sufficient performance for the application and avoids the long-term reliability concerns associated with unproven chemical additives.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

Instead of changing the chemical composition of the grout through additives, the invention achieves load transfer through mechanical means (corrugated sheath geometry and staggered bond lengths) while using standard grout parameters that ensure long-term stability.

Inventive Principle:

Principle #35Parameter changes

3Stress or pressure

If the diameter of the anchor/sheath is increased to reduce working stresses on the tendon, then the stress on individual strands is reduced, but the load transfer capacity only improves marginally

Engineering Contradiction:

Improveworking stress on tendonVSAvoidload transfer capacity

Core Design Contradiction:

Stress or pressureVSForce

Solution Approach 1:

By using multiple strands instead of a single large-diameter tendon, the load is distributed across many smaller elements. This segmentation allows for more efficient load transfer through the grout and sheath interface while maintaining acceptable stress levels in each strand.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention moves from increasing diameter (one dimension) to increasing the number of strands (another dimension). This dimensional shift allows for better load transfer efficiency without the diminishing returns associated with simply increasing the overall anchor size.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

4Reliability

If multi-strand tensioning is applied to minimize de-bonding risk, then the bond between tendon and ground is improved, but the complexity of the tensioning process increases

Engineering Contradiction:

Improvebond integrityVSAvoidtensioning process complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The tendon is segmented into multiple strands that can be tensioned independently or in groups. This segmentation allows for simplified tensioning procedures compared to tensioning a single large tendon, while still achieving the required bond integrity through controlled sequential tensioning.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The strands are tensioned in a predetermined sequence with preliminary tensioning stages before final tensioning. This preliminary action ensures proper bond development and minimizes de-bonding risks while organizing the complexity into manageable steps.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentEP2609258B1System for anchoring a load

Publication Date: 2017.04.12 SINCLAIR MARK RONALD

AI summary

The invention relates to a method for anchoring a load (26) to an anchorage (30) utilising at least one unitary anchoring tendon (10) including a plurality of tensile elements (12) each having a free length (14) and a bond length (18). The tendon is located lengthwise in a bore (34) formed through the load into the anchorage, and different groups (Gl, G2, G3) of the strands of the tendon are tensioned in a predetermined sequence to a respective initial displacement length prior to the different groups being collectively tensioned to a respective final displacement length to anchor the load.