# Complex Method of Airfield Pavement Condition Evaluation Based on APCI Index
## 5 Results
### Natural Airfield Pavement Condition Indicator  
The assessment of the condition of natural airfields pavements by APCI method is based on the results of field research, which include:  
1. Tests of turf layer strength to 0.3 m depth,
2. Test of the load bearing capacity of natural pavement to 0.85 m depth. The basis for the developed methodology is to evaluate individual input parameters based on the results and conducted measurements. Research performed in the fields are input data for process analysis, as a result of which the output data describes the condition of the natural airfield pavements. The evaluation procedure is presented in Figure 5.  
Data delivered to the model of developed method come from measurements and field tests and are the results of the turf layer strength and the load bearing capacity of the natural pavement, carried out in accordance with the requirements of the Polish military standard NO-17-A503:2017 [46]. The method was also described in [47]. The turf layer test is performed using a turf penetrometer to a depth of 0.3 m. For each measurement point, the average strength of the evaluated layer \(\sigma\) is calculated. On the other hand, testing of the load capacity of natural pavement is performed using a dynamic cone penetrometer to a depth of 0.85 m. The load capacity parameter of the airfield pavement is expressed by the California Bearing Ratio. Figure 5: Procedure for assessing the technical condition of the natural airfield’s functional element pavements using the APCI method. The pavement parameters collected during field studies are input data for analysis. The developed model of the APCI\({}_{\text{NN}}\) for natural airfield pavements presents the following dependence (15). \[APCI_{NN}=100-\frac{(w_{\sigma}\sigma+w_{CBR}W_{CBR})}{\sum w_{i}}, \tag{15}\]  
where: \(w_{\sigma}\) is a weight for the strength of a turf layer of a natural pavement; \(\sigma\) is the strength of the turf layer of natural pavement; \(w_{CBR}\) is a weight for the load capacity of the natural pavement; the \(W_{CBR}\) is a load capacity indicator of the average airfield's functional element natural pavement; and \(\sum w_{i}\) is the sum of weights. The average load capacity indicator of natural pavement is based on individual results of California Bearing Ratio values designated in an intermediate layer in between \(0\div 15\) cm and in a layer in between \(15\div 85\) cm. It is calculated on the basis of the geometrical average of the partial load capacity of load capacity for intermediate layer \(0\div 15\) cm indicator and the partial load capacity of load capacity for intermediate layer \(15\div 85\) cm indicator according to dependence (16). \[W_{CBR}=\frac{1}{n}\sum_{i=1}^{n}\sqrt{W_{CBR15i}\times W_{CBR85i}}, \tag{16}\]  
where: \(W_{CBR15i}\) is a partial indicator of natural pavement load capacity for intermediate layer \(0\div 15\) cm in \(i\) point of tests; \(W_{CBR85i}\) is a partial indicator of natural pavement load capacity for intermediate layer \(15\div 85\) cm in \(i\) point of tests; and \(n\) is a number of tests points. Partial load-bearing indicators are determined using the nomogram presented in Figure 6. The nomogram was created based on rich experience in diagnosing the airfield pavements. For each California Bearing Ratio value, the value of the corresponding indicator is read from the vertical axis, depending on the consumed intermediate layer of natural pavement. The nomogram can vary your character depending on the safety coefficient (\(W_{B}\)) that was adopted. The safety coefficient of 1.2 is assumed as standard. Increasing its values causes lower partial indicators, and thus, tightening the requirements. California Bearing Ratio results in the range of (\(15W_{B},+\infty\)) each time it gives a partial indicator of 1.0. Comprehensive assessment of the technical condition of natural airfield's functional element pavements includes the sum of the above-mentioned parameters, suggested according to standardization and loaded with specific weights.