How high can a house be built on such a foundation?

If the cement mortar is a cushion (in fact, it should be concrete), we will not look for piles, and generally speaking, most buildings in Beijing do not need piling, and the foundation bearing capacity is basically sufficient.

If the depth is this, you can build a house with about fifteen floors. If it is six meters, you can have a basement. My home is in Tongzhou, and it's on the tenth floor without a basement.

Last time I suggested that you ask the construction workers, they knew that Beijing dug more than six meters. We have a three-story basement with 15 or 16 meters, but there are only 17 floors above ground. Some buildings have only two floors underground, but there may be 30 floors above ground. This is hard to say. As long as the surveyed structure meets the design requirements, it can be built. Generally, the basement level of more than ten floors is enough. There used to be a saying that 1: 10, underground 10 floor, now underground 15 floor. More than four meters is enough for a single basement, and with the floor, it is almost six meters.

You'd better ask the construction workers what they do, or ask the property. They have an obligation to tell you. I still think it might be a vertical parking lot on the ground or something. If the whole pit area is not large, it may also be a fire pit.

Look at its width. Is it enough for a family?