Effect of Cementation on Cone Resistance in Sands: A Calibration Chamber Study.

An understanding of the effect of cementation on geotechnical properties of soil deposits is gaining increasing atten tion in the profession. When low levels of cemen­ tation in sands are neglected, pile capacity and slope stability are underestimated and liquefaction is overestimated. The recent Loma, P r ie ta earthquake led to fail­ ures along the northern Daly City bluffs causing catastrophic failures in residences scattered on these slopes. These failures were not anticipated, possibly due to (he confidence felt in constructing on bluffs of cemented deposits. It is essential to devise schemes to identify cementation in soil investigations and develop methods in eval­ uating engineering characteristics of cemented deposits. The objective of this study is to develop a method to identify cementation in sands and assess the engineering characteristics of cemented sand deposits using the cone penetration testing scheme. The scope of the study includes evaluation of the effect of cementation on cone penetration testing (experimental model) and comparison of these ex])erimental re­ sults with theoretical models of penetration mechanism in cemented sands. Existing models based upon the bearing capacity theories and cavity expansion models are utilized in theoretical modeling. A constitutive model is developed for strengthdeformation behavior of cemented sands and is used in theoretical modeling. .Artificially cemented Monterey No. 0/30 is used in the calibration chamber study. A total of 30 tests are conducted at, three ranges of relative density ( 'h5-nü, 65-75 and above 85 %), three confining pressures (100, 200 and 300 kPa) and three different cement content (0, I and 2 %). Pluviation method is used for specimen preparation. Specimens are cured for 7 days, transferred into the flexible wall cal­ ibration chamber and then consolidated under R'o conditions. Penetration testing was conducted with a 1.27c??? diam eter m iniature cone which reduced the chamber size effects on the results significantly. Separate drained triaxial tests provided the necessary parameters for strength-deformation modeling of cemented sands. xviii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The experimental model results coupled with the theoretical model predictions provide a semi-empirical and empirical schemes for evaluating engineering character­ istics of cemented sand deposits. An assessment of the applicability of these models in prediction of cementation in such deposits is also provided. The results indicate th a t tip resistance and sleeve friction in cone penetration testing provide a reason­ able assessment of cementation. The charts and the analysis method provided can be used to estim ate the engineering characteristics of such deposits. It is found essential th a t reliability and accuracy of the proposed methods of analysis be evaluated by insitu tests in a well-documented, naturally cemented sand deposit.