distances of 1 to 20 ft (0.3 to 6.1 m) from the face of the shoring walls, creating a concern that the installation of the caissons could cause disturbances within the sand layer that could result in excessive movement of the shoring and in the overloading at higher bracing levels. At the heritage structure, the structural caissons were located as close as 10 ft (3.0 m) from the supporting king piles. Vibration transmission through the king piles into the sensitive structure above was a concern as well as limiting the vibration transmission through the shoring into adjacent structures to less than the vibration limit of 0.2 in/sec (5 mm/sec) mandated by the City of Toronto. Real-Time Risk Management Driving 10 ft (3.0 m) diameter casing at subgrade using APE 400 vibrator 1.5 m) to be installed from grade prior to excavation using a BG40 and BG55 with temporary segmental casing. The smaller diameter caissons located in the center of the site to advance the installation of the tower crane footing - which was used to place drilling equipment into the base of the excavation for the installation of the caissons - were also installed from grade. Due to low headroom beneath the heritage building and support structure, a modified BG24 low headroom rig was used to install both the lower secant pile cutoff 90 * DEEP FOUNDATIONS * JAN/FEB 2020 wall and the structural caissons. The large diameter caissons were installed using an APE 400 vibrator to drive the casing to rock before drilling the soil inside the casing using a BG55 rotary drill. Using the vibratory driver installation method for the large diameter caissons involved a balance between an efficient installation methodology and the risks to adjacent structures, including the actively loaded excavation shoring, heritage façade and other surrounding structures. The structural caissons were located at To manage the risk from the installation of the large diameter caissons, an installation sequence was adopted along with monitoring of the shoring performance to converge on areas of largest risk. This installation monitoring plan involved installing the first caisson at a test location to confirm the installation methodology and then to evaluate the impact of the installation on the shoring at each new group of caissons as they were installed closer to the shoring wall. The SAA was relocated to each location using the tower crane to monitor real-time shoring performance. If large movements occurred, modifications to installation methodology could be made or additional bracing could be added to the remainder of the shoring wall prior to continuing the installation of caissons. The performance of the shoring remained within acceptable levels at each location and no additional bracing was required. Another concern was that the calculated natural frequency of the support king piles for the façade of the heritage building (10 to 15 Hz) was within the operating range of the APE 400 vibratory driver (6.7 to 23 Hz). To control this risk, real-time vibration monitoring was installed onto the king piles between the lateral brace elevation and base of excavation. During proximal caisson installation, vibration was closely monitored for amplification of readings at the king piles and overall vibration within the heritage façade.