Determination of the optimal row distance for double row piles and the calculation method for earth pressure between piles

The double-row pile system without a connecting beam is challenging to implement in practical engineering because of its complex load characteristics and the lack of a standardized model for soil pressure between piles. To better understand the stress characteristics of double-row piles and to efficiently calculate the inter-pile soil pressure, this study used the numerical simulation software GEO5 to investigate the impact of pile row spacing on the stress of piles. In addition, a new method based on the theory of limit equilibrium of rigid bodies was proposed to calculate the soil pressure between piles easily. This method calculated the residual sliding forces of the front and back rows of piles separately, and then sequentially removed the front and back rows to calculate the remaining single-row pile residual sliding forces, which are used to calculate the soil pressure between the double-row piles. The results showed that when the spacing of pile rows is between 2b and 6b (b is the length of the short side of the pile section), the residual sliding force of the front and rear row piles is almost equal. However, the difference between the maximum internal force of the front and rear row piles increases gradually. As the pile row spacing increases, the sum of the pile thrust of the double-row piles initially increases and then decreases, while the thrust behind the front row of piles remains almost unchanged. This variation is primarily influenced by changes in the thrust behind the back row of piles. The optimal spacing for the double-row piles should be between 2b and 4b. When the spacing of pile rows is between 2b and 6b, the front pile rear thrust in double-row piles is equal to half of the sum of the single-row pile rear thrust and pile front resistance at the same position. Similarly, the rear pile front resistance is equal to half of the sum of the single row pile rear thrust and pile front resistance at the same position, with a maximal error of only 0.07%. Comparison with the original scheme and the existing studies shows that the results are consistent with previous findings, validating the reliability of the calculation method presented in this study. In conclusion, this study provides a valuable insight for rapidly determining the optimal spacing of double-row piles and calculating the soil pressure between piles.