## 3 Results and Discussion  
Based on laboratory tests results, the graphs of dependence of shear stresses on linear displacement \(\tau=f(d)\) were plotted. Figure 9 shows the results of testing of very stiff clay according to the schemes \"soil-soil\" and \"soil-concrete\". The ultimate shear resistance values obtained in the \"soil-soil\" test change from 100 to 165 kPa, while in the \"soil-concrete\" test, the ultimate shear resistance values range from 55 kPa to 80 kPa. Figure 8: Materials for laboratory tests: (**a**) direct shear apparatus; (**b**) concrete plates. Figure 9: Graphs of dependence of shear stresses on linear displacement for soil–soil and soil–concrete schemes for clay. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Soil**} & **Plastic Limit** & **Liquid Limit** & **Plasticity Index** & **Shear Rate \(V\),** \\  & \(W_{P}\)**, \%** & \(W_{L}\)**, \%** & \(I_{P}\) & **mm/min** \\ \hline Very stiff clay & 45 & 90 & 0.45 & 0.005 \\ Very stiff foam & 28 & 44 & 0.16 & 0.05 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Physical characteristics of the soils and shear rate. During the testing of very stiff loans on the scheme \"soil-soil\", the ultimate shear stress ranged between 100 and 160 kPa; during the testing with concrete plates, the values of shear stresses ranged between 50 and 80 kPa. Graphs of the dependence of shear stresses on linear displacement \(\tau=\) f(d) for very stiff loans are presented in Figure 10.  
The strength reduction at the soil-structure contact can be characterised by the friction coefficient or the strength reduction factor \(R_{inter}\), which is defined as the ratio of the strength at the contact point to the strength of the soil. The shear resistance, angle of internal friction, or specific cohesion can be taken as the strength. The obtained average values of the strength reduction factor at the contact point of the soil with concrete are equal to the following:  
* For clays, 0.53;
* For loans, 0.44. The greatest influence on the convergence of the graph-analytical solution with the numerical solution, as well as on the value of settlement, was the influence of the load distribution along the length of the pile. Experimental studies of piles [14; 15; 16] have shown that the pile tip accounts for 0-30% of the applied load, and the lateral surface of the pile about 70-100%. However, often, the pile is embedded in several layers of soil, whose strength and stiffness are not equal; accordingly, the load will not be distributed uniformly on the lateral surface. In the graph-analytical method, it is assumed that the pile tip accounts for 10-15% of the applied load and the lateral surface for 85-90%, with the load distribution along the lateral surface distributed according to the stiffness of the soil. Such relations allowed for good convergence to be obtained with the numerical solution. Figure 11 shows the characteristics of the appearance and distribution of zones of plastic failure of soil during growth of a vertical load on a pile, which, in general, confirm the accepted assumptions and preconditions for solving the problem using the graph-analytical method. At first, plastic zones appeared in the head zone; then, in the weak middle layer; and further, gradually until full exhaustion of the bearing capacity of the soil occurs along the entire length of the pile. However, it should be noted that the active growth of plastic points under the pile tip occurs, among other things, due to the presence of stress concentrators in the corner zone of the pile. Figure 10: Graphs of dependence of shear stresses on linear displacement for soil–soil and soil– concrete schemes for loam. Figure 12 shows the calculation diagram of the problem for calculating the settlement of the pile using the graph-analytical method at the stage when a load equal to 2200 kN is applied.