Soil improvement/reinforcement for wind turbine foundations


Hello everyone,


I have the task of suggesting a suitable ground improvement/reinforcement method for onshore wind turbine foundations with known dimensions according to a specific soil type and its properties. The methods I study are piles, micro-piles, rigid inclusions, stone columns, soil substitution and vibrocompaction. I have to make a software guide where the user must insert values as input and the output should be the suggested technique(s). My problem is that I am unsure of what input values should I look for and how to connect them to a specific technique. The soil properties are given from a pressuremeter test. During my research I found out that the grain size is important when it comes to selecting a technique. However, I am sure that the bearing capacity and maybe other parameters that I am unaware of are important too. I have read multiple geotechnical reports but the authors just give a method, they don't explain why they chose this method. I would be very grateful if some of you geotechnical engineers out there could help me because I feel a bit lost. 

Kind regards,

Boris

Soil Mechanics / Geotechnical Analysis Education Research Software Shallow Foundations Deep Foundations Ground Improvement

Asked 11/07/2018 12:22, updated: 03/01/2019 14:38
Boris Kasabov

4 Answers

Votes: 1

Salahudeen Bunyamin

Hello
Authors do not normally explain why they chose certain parameters for methods because the parameters themselves depend on the methods. Normally, the methods depend on parameters inclusive and having direct or indirect relationship with the method in question. To me, getting the methods and their associated parameters is enough to kick start your project. Knowing why parameters are chosen is explained expressly with the requirements of the method under consideration.

Votes: 1

SAMUEL MUSOBOZI RWAKIJUMA

Hi,

If you have pressuremeter test results, this is quite enough to provide a suitable solution. On the other hand, it is important to have soil classification information as basic data in the design process. If it is an onshore project, I would recommend that you employ screw/helical piles, as they are easy to install (aprox. rate of installation - 1.8m/min), then join them with a pile cap on top which would already have the needed anchors to receive the wind turbine. Another advantage with this technology is that the fabricant of the helicals will provide free of charge foundation design. You can send me an email, then I can send you photos of some case studies we have had in this regard.

All the best in your project!


Votes: 2

Foued Ben alaya

Hi,

Applicability of compaction techniques (Vibrocompaction, Dynamic Compaction, Rapid Impact Compaction, etc) will be mainly dependent on grain size distributions.

Applicability of reinforcement techniques with flexible inclusions (Stone Columns, Dynamic Replacement, etc) will mainly depend on depth of improvement, and lateral strenght of soil.

Applicability of reinforcement techniques with rigid inclusions (such as Controlled Modulus Columns) are frequently used for Wind Turbine foundations. Limitations could be related to significant uplifting forces, which may require to have armed rigid inclusisions linked to structure, i.e. piling solution.

Other than technical consideration, the economic aspect and availability of technique are key elements in the selection of the method.

Regards,


Votes: 2

Michael Joseph Byle

Having designed a variety of soil improvement and foundations for wind turbines in a wide range of soil conditions, I can tell you the right solution cannot easily be determined from simple soil properties.  Soil shear strength, soil density, degree of saturation, layer thicknesses, depth to firm stratum, soil chemistry/corrosivity, thermal resistivity, site location, and availability of matierials and equipment all have a roll to play in method selection.  Depth to rock or a stiff stratum can be a really important factor, especially for surface treatment methods such as RIC or DDC. You can get into a whole realm of solutions involving micropiles or anchors where soft soils are too deep for practical improvement and rock is too shallow to permit adequate uplift resistance.  Foundations over soft rock such as coal, can pose a whole different set of issues.  Each site can be very individual.  Many wind energy sites are not virgin ground and may have had prior industrial or minerals extraction activities that may have significantly altered the subsurface conditions increasing complexity of the sites.  

Ultimately it comes down to selecting the most economical and technically feasible method.  Unless you are dealing in a single geologic setting, you will have to assess the potential for geologic hazards including hydrocollapse, expansive clays, sinkholes, landslides, acid rock drainage, soluble minerals such as halite or gypsum, and other factors that can affect the selection of foundation support methods.  If working on contaminated sites, a whole additional set of factors comes into play related to safety, cross contamination and discposal of excavated soils.  Practical issues such as access for materials and equipment to remote locations and variability of conditions across sites can have a profound impact on the choice the method, since flexibility and applicabilty to a wide range of expected of conditions may be necessary.  I am not sure if any of this helps you, but at the very least, I hope it gives you some insight into the selection process to set appropriate limits for the applicability of your solution.  I suspect that trying to develop a universal approach would be problematic.  I would suggest that you should at the very least limit any programmed solution to a particular set of conditions or geoplogic setting.  Good luck.