The Influence of Cementation of the Static and Dynamic Behavior of Sands

Cementation in sands is known to have a significant effect on the performance of slopes and liquefaction resistance. However, little has been done in the past to quantify this influence probably because of the difficulties in sampling these materials. Cemented sands are found in many geological environments around the world. They are held together by various types of cementing agents or by welding at the points of contact. The unconfined compressive strength of cemented sands can range from slightly greater than zero up to a few thousand kN/sm. Where they are found in natural slopes they characteristically stand at angles of 45 degrees or more and in heights of up to 100 m.

This investigation is directed primarily towards the behavior of cemented sands when subjected to dynamic loading under undrained conditions. The main objective is to quantify the influence of small levels of cementation on liquefaction resistance. However, in order to accomplish this goal, studies also have to be made into the drained response of cemented sands and the mechanisms of the cementation effects. Behavior of both naturally and artificially cemented sands were investigated, with the artificially prepared samples used to provide a cemented material where density and cementation-level could be controlled.

Before actually performing the load-test program, a number of issues pertaining to the methods of experimentation had to be resolved. This involved developing procedures for:

1. Manufacturing homogeneous samples of very weakly cemented sand with a range of density levels.
2. Saturating cemented sand samples at low back-pressures.
3. Automatically recording volume changes which occurred during drained shear testing.

Techniques to deal with each of these problems were successfully developed.

With the basic procedures in hand, a testing program was begun which consisted of more than 60 static and dynamic tests on samples of naturally occurring cemented sands and more than 250 tests on artificially cemented sands. The static testing results show that in all cases the cementation causes the sand to exhibit a cohesion intercept, but the friction angle of the soil remains essentially at the level of an uncemented sand.

From the undrained dynamic tests, cementation is found to increase the resistance of a sand to liquefaction. Curves are developed to illustrate the interaction of the influences of cementation as well as density of the sand. The results are believed to help explain anomalous behavior which has been observed in the field, and should be useful in practice in regard to important issues related to the potential for liquefaction of cemented sands.