# Experimental Evaluation of Load Distribution between Piles in Case of Block Failure
## 2 Test system and Properties of the Materials Used in Tests
### Experimental Procedure  
The soil used in the pile raft foundation tests was prepared at a water content of 33% (\(w=1.5\)xw\({}_{\rm L}\)), filled into tanks. The purpose of preparing the test soil with a water content of 33% was to form the mixture homogeneously and to obtain a slurry (fluid) consistency and place it in the test tanks without air bubbles. Then, the soils placed in the tanks were consolidated under pressure of 100, 200, 300 kPa. Thus, 3 soils with different strength parameters were obtained. The consolidation process was carried out by  
Figure 4: Piled raft foundation (**a**) and loading of a piled raft (**b**).  
Figure 3: Pile foundations used in experiments.  
transferring the air pressure to the inner tube and expanding the inner tube with the effect of pressure. As shown in Figure 5, this inner tube, placed between the lid of the test tank and the consolidation piston, consolidates the soil by creating pressure. As a result of the consolidation, the pressure of the inner tubes began to decrease due to the settlement on the soil. In order to prevent this situation, the pressure of the inner tube was kept constant with the air regulator.  
In field applications, piles are driven into the soil using diesel hammers, vibro hammers that apply vibration or pistons that apply hydraulic pressure, depending on the diameter or cross-section shape of the pile. In the experimental study, the piles were pushed into the soil at a rate of 1.5 mm/min as shown in Figure 6.  
In order to determine the load distribution between piles, strain gauge was installed on each pile and half Wheatstone bridge was used to connect to the datalogger. Strain gauges were fixed on the piles as shown in Figure 7a and calibrated in the unconfined compression  
Figure 5: Piled raft foundation and loading of a piled raft.  
Figure 6: The process of driving the pile into the soil.  
test equipment. The loads on the piles were measured and recorded using 6 strain gauges in all experimental stages. The placement of strain gauges on the foundations can be seen in Figure 7b. As can be seen in Figure 7b, strain gauges were installed on all piles in symmetrical condition and the load carried by each pile was measured. The loads obtained from these strain gauges were compared with the total load measured with the s-type load cell and the proportional load carried by each pile was determined as in Equation (1).  
\[\text{Total Load}\ \text{ }_{\text{(measured by S--type load cell)}}=\text{S1}+\text{S2}+\text{S3}+\text{S4}+\text{S5}+\text{S6}+\text{S2}^{ \prime}+\text{S3}^{\prime}+\text{S4}^{\prime} \tag{1}\]  
Here, S1, S2... S6 are the loads measured with strain gauges as seen in Figure 7b, and since S2\({}^{\prime}\), S3\({}^{\prime}\), S4\({}^{\prime}\) are symmetrical to S2, S3, S4, these values are considered the same.  
After the piles were driven, the leveling condition of the model foundation was checked so that the vertical loads would not affect the foundation eccentrically, and the load distribution between the piles was determined by applying static vertical loads to the foundation. During the experiment, data obtained from 6 strain gauges, 2 LVDTs and 1 S-type load ring were recorded via data logger. During the loading tests, LVDTs were used in order to measure the settlements occurring on the pile raft foundation. Pile loading speed was applied as 1.5 mm/min in all experiments.