Stone Columns

Application of method

Reduce foundation settlements

Prevent soil liquefaction during earthquakes

Increase shear strength to improve slope stability

Increase water permeability to accelerate drainage

Suitability of method

Design steps

1.In cooperation with the architect, structural engineer, and the owner, define design objectives, such as max. admissible settlement, max. differential settlement, design earthquake (Mw and amax ), shear strength.

2.Perform a site investigation. Select the field sounding and lab testing program so that it later can answer all design and QA/QC questions.

3.Calculate with unimproved soil parameters (Es , phi’) to see what settlement (or stability against earthquake liquefaction, or slope stability) would result without treatment.

4.From 3. above derive a sensible definition of what soil parameters need improvement, how much, and in which zones of the project such improvement is needed. Keep in mind that small differences in specified improvement level can mean huge differences in cost.
Ask an expert to evaluate what level of improvement of in-situ soil parameters can be achieved in slightly silty to very silty sands and silts.

5.For proper QC conditions in the Technical Specifications, translate the target soil mechanical parameters (Es , phi’) into required sounding resistance values (NSPT, qc) that the contractor can work with.

6.A correct stone column design considers both, the improvement of the in-situ soil and the reinforcement effect of the granular column that interacts with the soil. For this composite material soil & column special calculation software is available. -> Ask for expert advice rather than use a too simple calculation approach or expect too much in-situ soil improvement where such improvement is a) not possible and b) due to the reinforcement effect not necessary.

7.Set up the QA/QC plan to supervise the ongoing installation works.

8.On large projects: Plan a test installation to allow the contractor to try out several column diameters and grid spacings for the local soil conditions.

Setting up the proper site investigation for a ground improvement project is of paramount importance. Since the end product is improved ground, one needs to know the BEFORE properties of this ground very well to a) establish the degree of improvement. -> Get expert advice already in this early phase.

Installation Process

Excavator based Stone Column Equipment

Komatsu PC400 excavator based rig for max. 6.5 m treatment depth of

Dry Bottom Feed Stone Columns (Muscat Airport, Oman)

Crawler Crane based Stone Column Equipment

Dry Bottom Feed Stone Columns rig for 60 ft (18 m) treatment depth. Here suspended from a

Manitowoc 4000 W crawler crane. (Tacoma, USA)