Maximum permissible slope for interlocking concrete block paving for residential roads

Abstract

Concrete Block Paving (CBP) is a popular surfacing method currently used for rural roads in Sri Lanka, primarily due to its cost-effectiveness, ease of construction, and suitability for medium- to low-traffic conditions. Nowadays, CBP is applied not only on flat terrains but also on steep slopes. Determining the maximum permissible slope for block paving is critical to ensuring the durability, stability, and functionality of the pavement system. Empirical studies and field observations show that gradients exceeding permissible limits can lead to problems such as erosion, block displacement, and reduced skid resistance, especially over unsealed subgrades. While several studies have examined the influence of block shape, laying pattern, laying angle, joint width, and block thickness on CBP performance in flat terrain, these factors may behave differently on sloped surfaces due to additional forces acting on the blocks. Therefore, the aim of this research is to investigate the maximum permissible slope for CBP under medium- to low-traffic conditions. As part of the study, a 90-meter road segment with slopes ranging from 0° to 10° was constructed. Paving was done at 10-meter intervals using Uni-style blocks, while varying the block patterns, laying angles, and cross beam intervals. Field data were used to calculate relative vertical deflections. A Finite Element Model (FEM) was also developed in ANSYS software to simulate the behavior of the pavement system by varying slope, laying pattern, laying angle, and cross beam spacing. The results indicate that as slope increases, horizontal deflection tends to increase while vertical deflection decreases. However, when cross beams are placed at optimal intervals, both horizontal and vertical deflections become negligible. Under such conditions, the effects of slope, laying pattern, and laying angle on pavement performance are significantly reduced, making CBP a viable option for rural roads even on sloped terrains