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Soil stabilization - a network of underground rigid columns

A lecture on "A network of underground rigid columns - a method for soil stabilization", given by Eng. Moti Yuger as part of the 11th Construction and Infrastructure Conference on 11/21/2019.

* The lecture presents the progress in Israel and in the world, in a relatively new field of armor and land reclamation using a network of subterranean concrete columns drilled and cast using methods such as piles ("dry", CFA, bentonite) - in Israel, and cement mortar columns and others - abroad.

* The lecture on this topic was preceded by my lectures at the 6th Conference on Construction and Infrastructure 2009, the 3rd Conference on Buildings and Bridges 2013 and the 9th Conference on Construction and Infrastructure 2015.

* In the first stage, this technology was used to stabilize soil under railway embankments, roads and bridges, and gradually this solution was used for tanks, industrial buildings and ordinary buildings.

The foundation principle: it looks like a piling, but it's not!

The principle of foundation in this method is such that looks like Cullen, but in reality he is not.


Soil stabilization and improvement

As a result of the approach of referring to rigid columns and the ground, as a system of stabilized and reinforced soil, the following methods can be used to produce the columns (CMC, RI):

* Clean cement mortar columns, or mixed with soil
* Jet Grout columns
* Concrete columns drilled with the "dry" method/CFA/bentonite.

The columns in the above methods can include screwing, or without screwing, depending on the type of expected hassles, and their geometric location.

This method is not foundation piles and/or "restraint" piles. The elements are completely separated from the structure above, by a layer of granular substrate designed to distribute the loads from the structure above.


Methods for making hard pages

There are several methods for making rigid columns in a soil stabilization approach.

Comparison: stilts vs. concrete columns

Comparing piling foundations versus concrete columns.

Aspects of the method

* When the structure being treated is expected to horizontal forces due to the geometry of the site, earthquakes, etc., it is necessary to reinforce the columns with concrete which can be individual rods - with cement mortar columns and concrete cages - with drilled concrete columns.

* Not connecting the columns to the building allows for simpler behavior, and the reduction of seismic disturbances between the building and the ground.

* As a result, the foundation of the structure above is shallow and includes slabs and barges for the structures above and a layer of bedding to spread the burdens. In the case of dirt embankments, there is no need for plates and barges.

Improving geotechnical parameters

* Before installing the underground concrete columns, the existing soil has low values of E, k, and 𝜎, and therefore, has a high potential for failure and subsidence.

* After installing the hard posts the values of E, k, and 𝜎 improve greatly, and the potential subsidence decreases accordingly.

* The improvement achieved is a function of the diameter of the columns, the distances between them, the type of filling material (cement grout, concrete, other).

Behavior of rigid columns under uniform pressure

Development of the failure mechanism in the LTP bearing layer.

Deployment of the efforts at the main level of the concrete columns.

Negative friction enables the development of the arching phenomenon.


Software and methods for designing CMC/RI columns

Methods and software that help in column planningRI \ CMC.

*Finite element software (PLAXIS):
2D axisymmetric
2D plane strain

* Analysis for global stability (SLIDE, LARIX)

* Analysis for stability in earthquakes (LARIX, SHAKE)

* Dedicated software for CMC/RI

* Deterministic formulas


Examples from Israel
Development of the Ramot neighborhood in Jerusalem -   Stabilization of filling pits for the foundation of armored earth walls at a height of 20 meters

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