Building Expansion Joint for Underground Parking Structures

Underground parking structures are subject to hydrostatic water pressure from the surrounding soil and groundwater, as well as chemical attack from deicing salts tracked in by vehicles. Expansion joints in these structures must provide reliable waterproofing under pressure while accommodating the thermal movement of the structure. Hydrostatic pressure at underground parking joints depends on the depth of the structure below the groundwater table. For a structure 5 meters below the water table, the hydrostatic pressure at the base is 50 kPa (0.5 bar). The expansion joint must be designed to withstand this pressure without leakage. Pressure-rated waterstop systems are required for joints subject to hydrostatic pressure. Waterstop selection for underground parking joints must consider the movement range, the hydrostatic pressure, and the chemical exposure. PVC waterstops are the most common choice for moderate conditions, providing good flexibility and chemical resistance at low cost. EPDM waterstops provide better chemical resistance and are preferred for joints exposed to deicing chemicals. Swelling rubber waterstops are used for joints where the movement range is small and the primary concern is waterproofing. Chemical resistance of joint materials to deicing chemicals is critical for underground parking structures in cold climates. Calcium chloride and magnesium chloride deicing chemicals are more aggressive than sodium chloride and can attack PVC waterstops and concrete. EPDM waterstops and polyurethane sealants provide better resistance to these chemicals. Drainage design for underground parking joints must prevent water accumulation at the joint location. A drainage channel adjacent to the joint collects any water that seeps through the joint and discharges it to the drainage system. The drainage channel must be designed to handle the peak water flow during heavy rainfall or snowmelt events. Maintenance of underground parking joints requires annual inspection for leakage, sealant deterioration, and waterstop damage. Any leakage must be repaired promptly to prevent water infiltration into the structure. Injection grouting can be used to seal leaks in existing joints without removing the joint assembly.