When using explosives you want to dig out underneath, mix fuel oil and amonium nitrate in a bucket, pour it in the hole, add a couple sticks of dynamite and blast them right out. I like to use enough to really rip them and blow the hole into a clean crater. I have blasted pieces 300 ft, ha. You can directinal blow depending on charge placement and size, smaller blast they want to go sideways, the bigger the straighter up. They blast better in solid ground, poorly in soft sponge or sand. As for trench, drill hole every 18 inches and drop in sticks. They are close enough together one sets the next off.