Obtain all shovel handle upgrades. There are 6 in total. 5 are given to you as you level up and the 6th and final one can be bought from Ivors store.
Note: The 6th Shovel (the one you buy) is not required for the achievement.
Here is the breakdown:
1. Broken Handle (Level 1)
2. Iron Handle (Level 6)
3. Bronze Handle (Level 13)
4. Silver Handle (Level 23)
5. Gold Handle (Level 28)
6. Platinum Handle (Buy from Ivor for 11,250 coins)