Permeation Groutability Assessment on Volcani-Clastic -Sediments (Particularly on un Welded Tuff and Volcanic Breccia);A Case of Kesem Dam Foundation Grouting, in Afar Regional State, Ethiopia

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Addis Ababa Universty


Accurate prediction of groutability of a soil mass by permeation has always been complicated since the effective penetrability of grout in to voids is a function of several interrelated parameters contributed from the physical and mechanical properties of a medium to be grouted, the nature of grout used, efficiency of groutability assessment techniques adopted, and other factors related to grouting design and operation. Special concern on groutability sounds most relevant while dealing with grouting of medium with very fine fractures and/or porosity. Various researchers so far have developed relations or techniques by which the permeation groutability of a soil mass can be assessed. The present research has attempted application of those selected techniques for preliminary permeation groutability assessment on volcano-clastic sediments (particularly on unwelded tuff and volcanic-breccia deposits). The study was conducted as a case study at Kesem dam and irrigation project located in Afar regional state of Ethiopia. The proposed dam site abutments geology comprises of thin to thickly bedded, pervious and very weak un-welded tuff and volcanic breccia deposits which occur sandwiched in between competent rock units. Though intensive permeation grouting was implemented at both the abutments, it did not bring satisfactory result on those layers. The present research therefore has dealt about permeation groutability evaluation of un-welded tuff and volcanic breccia deposits composing abutments of the Kesem dam project. The research has followed two basic approaches for evaluation of permeation groutability: one is applying soil permeation groutability assessment techniques, and second is based on insitu condition manifestations. For the former approach, grain size distribution, permeability and porosity of media were studied and used in the analysis. In the later case, the actual foundation permeation grouting response was examined on the basis of evaluation of project records kept for previous actual and test grouting that were conducted in the study area. Besides, indications of an in-situ chemical permeation grouting test (attempted during the present research using sodium silicate grout) were used. The evaluations have led to identification of suitable grout types viable for effective permeation in to porespaces in unwelded tuff and volcanic breccia deposits studied. Effective permeation range of the deposits has fallen within chemical grout zone, colloidal (silicate) solution or any less viscous solutions. Moreover, the dependability of the current research approach, for use on preliminary permeation groutability assessment on Volcanoclastic sediments, was verified since results from both approaches end up with good agreement. Finally, on the basis of findings of the research, recommendations are forwarded to help on the on going efforts to look for solutions against encountered geotechnical problems of the site.



Volcani-Clastic -Sediments