The correct answer is D. Compaction.
Compaction is the process of reducing the void space in a soil by applying pressure. This can be done by using a variety of methods, such as rolling, vibrating, or tamping. Compaction increases the density of the soil, which makes it stronger and more able to support loads.
Grouting is the process of injecting a fluid into the ground to fill voids and cracks. This can be done to improve the stability of the ground or to seal off water leaks. Grouting does not improve the bearing capacity of the soil.
Chemical action is the process of using chemicals to change the properties of the soil. This can be done to improve the drainage of the soil or to make it more resistant to erosion. Chemical action does not improve the bearing capacity of the soil.
Drainage is the process of removing water from the soil. This can be done by installing drainage pipes or by using surface drainage methods, such as ditches or swales. Drainage improves the bearing capacity of the soil by reducing the amount of water that is present in the soil.