Studies on Artificial Soils (II)

Kneading Effects on the Penetration Resistance of Artificial soil

Abstract

No descriptions have been made about the methods of manufacturing artificial soils in most of the reports concerning with them.
In the preceding tests with artificial soils, the authors noticed that the touch of them was changing while we mixed and stirred a mixture of sand, bentonite and oil in a vessel with hands and that kneading effects would occur in an artificial soil as well as in natural soils by machanical manipulations, We thought that in ordinary soil bin tests, it would be better to use artificial soils beyond their “saturation point of kneading effect”, that is to say, artificial soils should be kneaded to such an extent that no further effects occur. That was the aim of this study.
A certain strength of an artificial soil can be expressed in equation (1). Cone and plate penetration resistances were selected as Q. Temperature was controlled within 24±2°C. The kneading action given to the mixtures examined in this test covered broad ranges when compared with soil mixing action given in ordinary soil bin tests.
The following conclusions obtained by this small scale test, in which rather a simple soil preparation method was adopted, suggest the necessity of reinvestigation in the preparation processes in usual soil bin tests at the use of artificial soils
1) Three kinds artificial soils were manufactured consisting of mould sand, bentonite and cylinder oil 90W. At first, equal quantities of sand and bentonite were mixed in the stirring vessel and after a minute, oil was added, namely, soil A; 9.91%, soil B; 16.12% and soil C; 20.00% in weight ratio. The grades of kneading time were determined by the observation of the test materials while they were being kneaded and are shown in Table 1.
2) Kneading effects and saturation points were recognized in two kinds of the test artificial soils (Figure g), Penetration resistances decreased (soil A) or increased (soil B) as the soils were kneaded and reached a constant value respectively within about 20 minutes, But, a steady tendency was not obtained in soil C.
3) A reproducibility of the artificial soil was examined (Table 2), The reproducibility at the surface layer was inferior to those of deeper zones. Though the numbers of repetition of tests were small, we dare to make a statement that in a similitude studies or studies on dynamic behaviours of soil machine system dealing with several percentages of differences of forces, elaborate soil preparing techniques will be necessary before tests. The problems concerning with soil preparation remain particularly in soil C as well as in natural cohesive soils.
4) Sufficient strength was found in the artificial soils to simulate natural soils covering from sandy barns to cohesive clay concerning with cone index.