Allowable Bearing Stress to be confirmed

[maxwolf]

For the design of a residential cellar extension using new CIP retaining walls down to 10ft below grade, the allowable bearing is tentatively assumed to be 1500 psf. There is no geotech report available. The cellar will be an extension of an existing rowhouse cellar. At a minimum, a test pit will be required in the construction documents to confirm bearing capacity, and I would like to hear comments on what the requirements for testing should be and any other thoughts. The new cellar is ~18ft square in plan, with one side abutting a prop line, which will trigger a few feet of underpinning on site and possibly for the neighbor. Existing cellar wall (rubble) is not in the water table and shows no signs of settlement damage, nor does the superstructure. Existing is ca. 1880, Manhattan. Viele map shows the area to be originally sloped meadow with some small outcropping in the area, so there may be some fill since the area is now quite flat.