showed that the frictional resistance reduced substantially. A disparity 

 in threshold frictional resistance, therefore, exists due to the sparsity 

 of data and inconsistent testing procedures. End bearing is even less 

 studied and very little data on end bearing capacity are reported. 

 Figure 1 shows a plot of q determined from field pile tests in chalk and 

 weak cemented calcareous soils versus standard penetration test (SPT) 

 resistance value, N. The figure shows a wide scatter of data, indicating 

 that the SPT, a popular in-situ test device, may not be a good tool for 

 determining the q value for piles in calcareous soils as the CPT. 



Pile Design Methods 



The design of pile foundations is far more uncertain in calcareous 

 soils than in terrigenous soils. Unfortunately the information available 

 cannot be fully explained by conventional theory and does not aid in 

 making necessary judgments. Where important facilities are planned, it 

 is a normal practice to conduct pile load tests to confirm load predic- 

 tions. These tests are costly, time-consuming, and impractical for most 

 projects. Instead, large factors of safety are normally introduced to 

 account for design uncertainty. However, this approach leads to costly 

 over-design in many cases and unsafe designs in other cases. 



Design practice for determining the ultimate axial capacity of piles 

 in calcareous sediments can be divided into the following categories: 



1. Use of conventional theory with modifications to account for 

 certain aspects of calcareous soils. 



2. Empirical correlation with penetration resistance during 

 driving. 



3. Correlation with in-situ tests. 



4. Correlation with full scale pile load tests. 

 The features of these methods are summarized in Table 2. 



Conventional Theory . The conventional theory for predicting axial 

 capacity of piles in terrigenous soils is used with modifications to 

 account for various engineering aspects of calcareous soils. Table 3 

 shows design parameters presently used for estimating axial capacity of 

 driven piles in calcareous sands; parameters for silica sands are also 

 shown for comparison. The parameters can be used to show that predicted 

 pile capacity for calcareous sands is only about one-third of that for 

 silica sands for similar conditions. Similarly, for piles subjected to 

 tensile loading, the capacity predicted for calcareous soils may be only 

 20% of that predicted for silica sands. Unfortunately, the design param- 

 eters in Table 3 do not relate the degree of cementation to measurable 

 soil properties. 



Agarwal et al. (1977) recommended design parameters based on carbon- 

 ate content that are significantly higher than those in Table 3. The 

 use of these parameters would lead to higher predicted capacities. Datta 

 et al. (1980) recommended coefficients of lateral pressure for calculating 



