Many piles with various lengths and plates were tested in Khon Kaen loess. The critical depth of driven and bored piles was found to be 9.5 and 7.5 times that of pile size respectively. The pile friction was the effective stress multiplied by 0.5 and 0.3 for driven and bored piles respectively. Plate bearing tests and the tests run on the piles without friction confirmed the validity of the Terzhagi bearing capacity equation. Since the SPT-N value taken in the loose to medium dense loess has a low accuracy, the foundation design methods based on SPT are not recommended. The CPT-based methods are suggested to be employed. The moisture content in the soil should be taken into consideration because it affects the foundation bearing capacity. Only a 7 % increase in moisture content could reduce by about 50 % of driven pile and plate bearing capacity. The bored pile installed in loess is not recommended because its bearing capacity is strongly affected by moisture content. Plate bearing and double consolidation test results show that if the soil under pressure was saturated for about two hour, the great settlement occurred. The water table should be checked carefully and any drainage system should be strictly prevented to interfere with the soil supporting foundation.
Khon Kaen Province is located in Northeast Thailand. The loess deposits exist above the water table in abundance in Khon Kaen. The thickness normally ranges from a few to more than 6 m. The soil characteristic is non-plastic red sandy silt or silty sand (ML or SM). Almost all the soil is 0.005 to 0.042 mm in size. The research presented in this paper is to find out the suitable parameters and some criteria such as critical depth for the foundation design in Khon Kaen area.