Planning approval means the developer has been given permission for a building with the basic attributes of height, overall size (floorspace), setbacks from the property line, and usage (i,e. residential, commercial, mixed use, etc.). In order to actually proceed with the building, building permits are required - the developer has to submit the detailed construction drawings and specifications to be reviewed by the city for adherence to the all the applicable building codes. Once the review has been completed, including addressing any questions or concerns raised by the permit inspectors, and making any changes or corrections as required, the construction permits are issued, and the building can be built.
In order to save some time, it is possible to submit an application for partial permits - in this case for shoring (and I would suspect excavation), which once the permit was issued, would allow the shoring and excavation activities to proceed while the balance of the permit review process is ongoing.
One example - 621 King Street West (Thompson Residences) - the developer filed for shoring and excavation permits while appealing to the OMB to add additional floors to the building. Construction activities started based on the shoring and excavation permits (I believe the footings and foundation as well) before the final planning approvals for the additional floors were received from the OMB.