When building your horse arena, you will need to start with the sub-base. The sub-base is your native soil. The characteristics of your soil determine how to set up your base, or if your soil is suitable, a base as is. Why is this important? Not all soils are created equal, and neither should your arena.
If you have:
Clay Soil is very sticky and rolls when wet. It can hold more total water than most other soil types and, although only about half of this is available to dry out. It swells when wet and shrinks when dry, so movement can take place in these soils depending on weather conditions. Clay is very late to warm up.
Sandy Soil is light, warm, dry and light. These soils have quick water drainage and are easy to work with. They are quicker to warm up in spring than clay soils but tend to dry out in summer and are easily washed away by rain.
Silt Soil is a light and moisture retentive soil type that drain and hold moisture well. As the particles are fine, they can be easily compacted and are prone to washing away with rain.
Granite Soil can resemble sand. It is like gravel, but finer and more stable. Often called Decomposed Granite, this soil, once compacted well, will be fairly hard, very permeable and handles water extremely well.
Bottom line: You will never have a good arena without an adequate base. Hire a soil consultant and get it done right the first time. Soil consultants are engineers who understand all the ins and outs of working with soil. They are the ones called in to advise facilities such as baseball fields, golf courses and parking lots. Look for a soil consultant under listings for engineering consultants. Your soil consultant will help determine your base requirements and if the soil will form a stable base.