6.7 Example：Excavation in Sand
PLAXIS is a finite element package intended for the two⁃dimensional or three⁃dimensional analysis of deformation，stability and groundwater flow in geotechnical engineering.Geotechnical applications require advanced constitutive models for the simulation of the non⁃linear，time⁃dependent and anisotropic behaviour of soils and／or rock.In addition，since soil is a multi⁃phase material，special procedures are required to deal with pore pressures and（partial）saturation in the soil.Although the modelling of the soil itself is an important issue，many geotechnical projects involve the modelling of structures and the interaction between the structures and the soil.PLAXIS is equipped with features to deal with various aspects of complex geotechnical structures.
This part describes the construction of an excavation pit in soft clay and sand layers by using the software PLAXIS 3D.The pit is a relatively small excavation of 12 by 20 m，excavated to a depth of 6.5 m below the surface.Struts，waling and ground anchors are used to prevent the pit from collapsing.After the full excavation，an additional surface load is added on one side of the excavation.
The proposed geometry for this exercise is 80 m wide and 50 m long，as shown in Figure 6.18.The excavation pit is placed in the center of the geometry.Figure 6.19 shows a cross section of the excavation pit with the soil layers.The clay layer is considered to be impermeable.
Figure 6.18 Top view of the excavation pit
Figure 6.19 Cross section of the excavation pit with the soil layers