11.3.3 Ground settlement and building settlement
The simplest method to measure ground settlement is marking the ground surface with steel nails（called settlement nails），to make a foresight to a fixed point and backsight to the nails using a level to obtain the ground settlement at the points where the nails are driven in.The fixed point is the datum point outside the influence range of excavation.A certain position of a building with the pile foundation can be assumed to be a fixed point.If there are not any buildings with pile foundations nearby，a marking object in the distance or outside the influence range of settlement has to be adopted.If necessary，a permanent benchmark has to be set to serve as a fixed point.
The surrounding ground of an excavation may be soil，asphalt pavement，or concrete pavement.The asphalt pavement and concrete pavement have relatively high rigidities.That is，even though the soil below them has settled，the pavements do not necessarily show signs of settlement.Thus，the settlement nails have to be driven through the pavements so that the settlement of the nails can represent the real settlement of the soil.Figure 11.10 illustrates a possible way of setting the settlement nails.
Figure 11.10 Schematic diagram of the installation of a settlement nail
The measurement of the settlement of buildings is the same as that of ground settlement except that the settlement nails are to be set on the buildings themselves，on the wall or on the columns，for example.