Field investigation on the characteristic of clayey soil close to diaphragm walls-PPT Presentation

PPT Presentation

Pdf Summary

The study investigated how diaphragm-wall construction affects nearby clay, particularly undrained shear strength and potential shaft friction. Researchers took field measurements during excavation at two HS2 sites: Victoria Road Crossover Box in London Clay and the Bromford Tunnel eastern portal in reworked and weathered Mercia Mudstone. Soil close to the walls was assessed using pocket-penetrometer resistance and water-content measurements. Results were compared across wall panels with different construction times and with bored-pile load-test findings.<br /><br />Measurements showed increased water content and reduced penetration resistance near the walls, indicating soil softening associated with unloading during excavation. The reduction was greater for panels with longer construction times. At approximately 2.5 cm from the wall, normalized penetration resistance ranged from 0.29 to 0.61 across the panels, with lower values generally associated with longer construction periods. The observed trends were consistent with bored-pile load-test data relating construction time to adhesion, and numerical simulations also supported the findings.<br /><br />The results suggest that excavation-related softening can reduce undrained shear strength and, consequently, skin friction along diaphragm walls. Construction duration may therefore be an important consideration when estimating shaft resistance in cohesive soils.

Keywords

diaphragm-wall construction

undrained shear strength

skin friction

clay softening

excavation unloading

pocket penetrometer

water content

HS2 sites

shaft resistance

construction duration