Which test would be best for assessing soil bearing capacity?

The California Bearing Ratio (CBR) test is specifically designed to assess the strength of soil and its bearing capacity, which is critical for determining how much weight the soil can support without experiencing deformation or failure. This test involves measuring the pressure required to penetrate a soil sample with a standard-sized piston. The results provide a ratio of the soil's strength compared to a standard base material, which is essential for applications such as pavement design and other structural applications where the soil's load-bearing capabilities must be evaluated.

The other options, while important in their own right, do not provide direct measurements of soil bearing capacity. The Standard Proctor test focuses on determining the optimal moisture content and maximum dry density of soil, which helps in compaction analysis but does not assess bearing capacity directly. Grain size analysis identifies the distribution of different particle sizes within a soil sample, which informs on drainage characteristics and soil behavior but does not directly evaluate how much load the soil can support. The Atterberg limits test measures the plasticity characteristics of fine-grained soils, which offers insight into the soil's behavior under varying moisture conditions but is not a direct indicator of its bearing capacity.

Thus, the CBR test is the most appropriate choice for assessing soil bearing capacity.