How to calculate the template area of drainage ditch

When the elevation of the lower skin of the drainage layer is higher than the floor, the number of formwork areas is the sum of the outer area of the trench wall plus the inner lateral area, plus the area below the floor. When the elevation of the top surface of the ditch wall is equal to the elevation of the floor drain, only the surface area of the inner side wall is calculated for the formwork quantities. When the ground elevation is located in the middle of the drainage ditch wall, the number of templates is (surface area of inner wall+surface area of side wall above the ground elevation).