Test Procedures 



Following the soil preparation, as described in Appendix A, the 

 model footings were placed on the soil surface in specified patterns 

 designed to minimize mutual interference. The descent rate of the 

 footings was controlled to give the water trapped between the footing 

 and soil surface sufficient time to escape and to minimize disturbance 

 of the soil. Initial measurements for settlement records were taken 

 as soon as the soil was supporting the weight of the submerged footing. 



The subsequent treatment of each footing was a function of the 

 tests scheduled for it. Some non-preconsolidated footings were tested 

 for immediate bearing capacity and lateral load resistance, usually 

 within 60 minutes of the time the footing was placed on the soil. The 

 remaining non-preconsolidated footings were allowed to reach complete 

 primary consolidation settlement, indicated by cessation of measurable 

 displacement, under the dead load of the footing prior to further 

 testing. The footings to be preconsolidated were connected to a common 

 vacuum manifold and vacuum was applied within 24 hours after the foot- 

 ings were emplaced. These footings were also allowed to reach complete 

 primary consolidation settlement prior to testing. Figure 3 shows a 

 typical laboratory test arrangement. Three 2-inch and two 6-inch diam- 

 eter footings are connected to the vacuum manifold ready for preconsol- 

 idation, and one 2-inch and one 6- inch diameter footing are settling 

 under their own dead load. The settlement of the footings was measured 

 with the simple rod-and-scale device shown in Figure 3, and with a dial 

 gage system not shown. With the rod-and-scale device, settlement 

 readings could be estimated to the nearest 1/64 inch. The dial gage 

 system was an order of magnitude more accurate than the rod-and-scale 

 system but was not as versatile since the dial-gage spring force fre- 

 quently caused extra movement of the small footings, particularly in 

 the Rogers Lake clay. 



When several of the non-preconsolidated and preconsolidated model 

 footings had ceased settling, they were subjected to an added "design 

 loading" which amount to \ pound for the 2- inch footings, 3 1/3 pounds 

 for the 6-inch footings, and 13 1/3 pounds for the 12-inch footing. 

 These design loadings applied a pressure increase of about 0.12 psi to 

 the soil surface. (The footings themselves applied about 0.06 psi.) 

 The total design settlement loading; i.e., footing dead load plus 

 design load, had a factor of safety of about two with respect to the 

 experimentally determined bearing capacity of the non-preconsolidated 

 footings . 



MODEL PERFORMANCE 



Settlement 



The effect of preconsolidation alone on the model footings is 

 shown in Figures 4 and 5. Figure 4 illustrates typical performance of 



