Bridge Expansion Joint for Bridges with Expansion Joints in Deck Slabs on Vibroflotation

Vibroflotation is a ground improvement technique that densifies loose granular soils by vibrating a probe into the ground. The vibration liquefies the soil temporarily, allowing the particles to rearrange into a denser configuration. Vibroflotation near existing expansion joints requires careful planning to minimize the effects on the joints. Vibroflotation process involves vibrating a probe (vibroflot) into the ground using a crane. The probe vibrates at a frequency of 30-50 Hz, which liquefies the surrounding granular soil. As the probe is withdrawn, the liquefied soil densifies around the probe. The process is repeated at multiple probe locations to treat the full area of loose soil. Vibration from vibroflotation can affect adjacent expansion joints. The vibration level depends on the probe frequency, the probe size, and the distance from the probe to the joint. Vibration monitoring is recommended during vibroflotation near existing joints. Ground settlement from vibroflotation occurs as the loose soil densifies. The settlement depends on the initial density of the soil and the degree of improvement achieved. Settlement monitoring is recommended during vibroflotation near existing joints. Post-vibroflotation inspection of existing expansion joints must verify that the vibroflotation has not caused any damage. The inspection should check the joint gap width, the concrete edge beam condition, and the anchor bolt torque. Any damage must be repaired before the bridge is returned to service. Vibroflotation effectiveness is verified by comparing the soil properties before and after treatment. Standard penetration tests (SPT) or cone penetration tests (CPT) are performed before and after treatment to measure the improvement in soil density. The test results are compared with the design requirements to verify that the treatment has achieved the required improvement.