SPREAD FOUNDATION CALCULATION ACCORDING TO PREDETERMINED SETTLEMENT

Purpose: The aim of this work is to improve the functioning conditions for building superstructures due to non-uniformity minimization of spread foundation settlements down to its ultimate value. Design technique: The main conditions and assumptions of the proposed design technique for shallow spread foundation calculation according to a given settlement are based on the analytical method. Settlement correction indices for the nonlinear stage of soil deformation are obtained experimentally in trough plate bearing tests. Findings: The reduction in the settlement non-uniformity of shallow spread foundations is provided by the proposed design technique which involves rather accurate analysis of foundation settlements. At the initial design stage of sizing the settlement, the non-linear soil deformation is used to provide the extension of the settlement value range. A nonlinearity factor of the elasto-plastic foundation is used to determine its settlement at a given stage of soil deformation. This factor is obtained from the volume change trajectory of the yielding area calculated with the following assumptions. For the linearly deformed half-space, the boundary of applicability is 1.1 of the initial critical soil pressure; when the foundation achieves the ultimate pressure (according to Coulomb's wedge theory), the yielding area volume also achieves a certain ultimate value; the foundation transition to the ultimate limit state is a complex, random process. Examination of the physical nature in the soil deformation analysis is improved by a transition from a piece-wise approximation of the dependence between the foundation base pressure and yielding area volume to the continuous function and the initial critical soil pressure introduced as a phase transformation criterion instead of the estimated resistance. The account for these conditions and deformation processes of different-density soils requires the improvement of design formulas. Therefore, we carry out trough plate bearing tests and introduce correction factors based on the results obtained. Their careful comparison with calculations of other authors and numerical simulation with the Mohr – Coulomb model, shows good agreement and proves the assumption correctness. Results: The proposed technique allows designing foundations using the predetermined settlement via its non-uniformity reduction down to the minimum allowable value, thereby avoiding the main weakness of the foundation design approach, i.e. the pressure balance under the foundation base using the design resistance. This pressure balance contributes to the different volume of foundation soils involved in work beneath, thereby causing the settlement non-uniformity. Calculations based on the settlement restriction prevent superstructures from crack propagation and provide the quality change in design of shallow spread foundations. Practical implications: Allowing for the non-linear soil deformation, the foundation base pressure can be increased relative to the soil design resistance. Hence, the foundation calculation will be less material-intensive due to the reduction in its size and labor costs during the construction. The developed BRNL-FT software package allows simplifying the proposed method which will be rather resource-efficient for foundation engineering. The proposed method can be used in spread foundation design, the safety factor for bearing capacity being ensured. Originality/value: Research results show good agreement between experimental data and theoretical calculations obtained by the proposed method. So does the comparison with results of other authors obtained within the pressure ranging between 1.1 of initial critical and 0.7 of ultimate at different values of soil density.

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