# Design of Conical Foundations with Increased Bearing Capacity in Areas of Undermined Soils
## 2 Materials and Methods
### Laboratory Testing  
An expanding box, consisting of steel channels and a sealing of thick rubber is bolted together (Figure 5). Unscrewing the bolts leads to the expansion of the rubber spacer between the channel sections and, accordingly, extension of the box in length. This design of a sliding box allows you to simulate soil deformation caused by horizontal tension mentioned in Figure 2.  
Handmade soils were compacted by 5 cm layers with a 10 kg roller into the volumetric expandable box. During the compaction process, the density of the material was controlled by its specific weight. The soil used was an artificial soil selected using the equivalent materials method [18], which considers the processes of destruction and deformation of rock masses. The equivalent material was the replication of natural soils of the Karaganda region and made by mixing 97% fine sand and 3% spindle oil to increase viscosity and cohesion in the range of 0.5-1 kPa. The main physical and mechanical characteristics are presented in Table 2.  
Figure 5: Volumetric expandable box: (**a**) general view; (**b**) top view, 1—individual channel sections, 2—compressed elastic gaskets, 3—bolted connections, 4—side walls, 5—height-adjustable supports, 6—support frame. For given values of cohesion for natural soil and equivalent material, the modeling scale is:  
\[m_{l}=1/L=C_{m}/C_{n}\cdot\gamma_{m}/\gamma_{n} \tag{6}\]  
where \(l/L=m_{l}\)--linear scale;  
\(\gamma_{m}\), \(\gamma_{n}\)--specific gravity of model and natural materials;  
\(C_{m}\), \(C_{n}\)--cohesion of model material and soil in real conditions on the site (natural condition);  
Thus, \(m_{l}=0.9/40\times 20.5/17.0=1/40\). The modeling scale in the experiments was taken to be 1/40. Models of conical foundations with a diameter of D = 80 mm and a height of H = 40 mm were made of aluminum alloy with an aperture (apex) angle of 90\({}^{\circ}\), a diameter of D = 78 mm and a height of H = 46 mm with an aperture (apex) angle 80\({}^{\circ}\) and conical models with stand pile (Figure 6). The conical model foundation from aluminum alloy and concrete were placed on the compacted soil immersed 0.75 height into the ground. Laboratory tests of conical and isolated shallow foundation models are presented in Figure 7. The load on the foundation models was transferred statically in steps of 0.001 MPa and is maintained until the settlement is conditionally stabilized, which is taken to be a settlement of less than 0.01 mm in 15 min. The foundation model was loaded with surcharges weight until the specific pressure under the footing reached P = 16.7 kN/m\({}^{2}\). The settlement of the cone model foundations was measured with vertical dial gauges with reading accuracy up to 0.01 mm. The maximum load was taken to be the load from which the model lost its load-bearing capacity, and its settlement/movement became continuous. Horizontal tensile strains were achieved by unscrewing the joint between the channel sections and extending the box length by 3, 6, 9 mm/m. This caused horizontal soil movement and the displacement of the foundation models, which were monitored both vertically and horizontally. \begin{table}
\begin{tabular}{c c c c} \hline
**Soil Characteristics** & **Units** & **Natural Soils** & **Equivalent Material** \\ \hline bulk unit weight, \(\gamma\) & kN/m\({}^{3}\) & 20.5 & 17 \\ cohesion, \(c\) & kPa & 40.0 & 0.9 \\ angle of internal friction, \(\varphi\) & degree & 29 & 37 \\ modulus of deformation, \(E\) & MPa & - & 0.24 \\ Poisson ratio, \(\
u\) & - & - & 0.25 \\ \hline \end{tabular}
\end{table} 
Table 2: Physical and mechanical characteristics of the testing soils. Figure 6: Cone foundation model. The experiment area was located on the field of the Kostenko mine, Karaganda region (Kazakhstan).