Case studies of composite soil-nailing walls and movement estimate

The displacement evaluation method for composite soil-nailing walls has not been discovered due to the complicated properties of soils and various retaining structures although composite walls have been widely applied. 26 typical case histories of composite soil-nailing walls in deep excavations are presented. The maximum lateral displacements and settlements are analyzed in these cases to find out the relationships between geology and retaining structures. The statistical results show that the maximum lateral displacements and settlements for composite soil-nailing walls are 0.4% and 0.2% of excavation depths, respectively. The former is about twice that for piles and diaphragms. The maximum lateral displacements are reduced slightly for the composite soil-nailing walls with prestressed anchors and micro-piles. The new concept, the unit shear strength of soil, is proposed based on the Mohr-Coulomb failure criterion to quantify the whole shear strength of soil. The maximum displacements are found to decrease significantly as the unit shear strength for the main strata increases.