When creating surfaces, based on the default setting of surface creation, flat triangles may be created. This happens a a lot when adding contours to a model or if not enough data is defined/given to form the desired grade.
A fix to this problem is found within the properties of each surface being created.
Within the first group of the surface properties, named Surface, you will see an option named Adjust 'flat' triangles set to No.
Setting the Adjust 'flat' triangles to Yes will adjust how the surface projects the triangles. Dependent on how the model breaklines and contours are given, breaklines may still need to be added to the model to achieve desired grade.
Refer to the pictures below to observe how the triangles are formed by changing that setting and, lastly, adding a breakline.
Before Adjusting Flat Triangles:
After Adjusting Flat Triangles:
Lastly, Adding a Breakline: