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

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The study investigates whether diaphragm-wall construction softens clay adjacent to the wall, potentially reducing soil–wall shear transfer and the wall’s earth-pressure and bearing-capacity performance. During excavation, support-fluid pressure may be lower than the soil’s initial stress, causing deformation and pore-pressure changes. Water uptake and clay–fluid interactions may further soften the soil while the trench remains open.<br /><br />Field measurements were conducted at two construction sites in overconsolidated clay. At each site, two wall panels with different opening times were examined. Researchers measured soil penetration resistance at varying distances from the wall and collected samples to determine water content.<br /><br />At both sites, penetration resistance was lower close to the wall and increased with distance. At Site 1, water content was also higher near the wall. The reductions in resistance were more pronounced for panels with longer opening times: normalized resistance within 2.5 cm of the wall ranged from 0.29 to 0.61 across the four panels. Site 2 also showed a thin, discontinuous layer of very soft clay on the wall, though its formation could not be established.<br /><br />The results indicate that excavation can soften nearby clay and that the effect becomes more substantial as opening time increases. The authors used the measured strength reductions to estimate adhesion factors, which were consistent with trends reported from bored-pile load tests: adhesion tends to decrease with longer construction times.<br /><br />The findings offer field evidence of near-wall clay softening, a phenomenon with potential implications for diaphragm-wall design. However, the investigation covered only four panels, and the proposed adhesion factors are estimates derived from penetration-resistance measurements.

Keywords

diaphragm wall

clay softening

soil-wall shear transfer

earth pressure

bearing capacity

excavation

penetration resistance

water content

adhesion factor

overconsolidated clay