# The Effect of the Water Table on the Bearing Capacity of a Shallow Foundation
## 3 Influence of Immersion on the Bearing Capacity of Shallow Buried Foundation
### Depth of Safety Impact of Rising Groundwater Level on Building Foundation Stability  
According to the test and analysis of the influence of different saturation degrees on soil mechanical properties, it can be seen that the bearing capacity and strength characteristics of clay foundations with a low liquid limit are highly correlated with their moisture content. After the groundwater rises into the foundation bearing layer, it will impact the bearing capacity and deformation stability of the building foundation, and its degree will gradually become serious with the rise of the groundwater level. Therefore, it is necessary to conduct an in-depth analysis of the depth of the safety impact of the rise of the groundwater level on the stability of the low liquid limit clay foundation to provide a basis for the definition of the immersion affected area. According to the analysis of the immersion mechanism of buildings in Section 3.1, combined with the physical and mechanical properties test of low liquid limit clay in typical immersion areas in Section 2, when the distance from the groundwater level to the bottom of the foundation is at a certain value, the bearing capacity of the foundation is equal to the sum of the additional stress of the building and the self-weight stress of the soil. This value is the safe depth affected by the rise of the groundwater level, as shown in Figure 4. The following will detail the method to obtain the foundation bearing capacity of the soil layer at the groundwater level and the additional stress of the building there.  
According to article 5.2.7 of the _Code for Design of Building Foundations (GB50007-2011)_[43], the sum of additional stress and self-weight stress at the groundwater table should satisfy the following formula:  
\[P_{\rm k}=\left((F_{\rm k}+G_{\rm k})/\rm A\right)\leq f_{\rm ac} \tag{1}\]  
where \(F_{\rm k}\) is the vertical force value transmitted from the superstructure to the top surface of the foundation corresponding to the standard combination of the load-open effect. \(G_{\rm k}\) is  
Figure 4: Safe depth for the impact of groundwater level rise.  
the sum of the foundation and the soil self-weight on the foundation. A is the foundation bottom area. \(f_{\text{ac}}\) is the corrected eigenvalues of foundation bearing capacity.  
The \(P_{\text{z}}\) value in the figure can be solved by the corner point method according to the additional stress under the corner points of the rectangular uniform load, that is, \(P_{\text{z}}=4\alpha\cdot p_{0}\), which \(\alpha\) is the additional stress coefficient of the corner point of the \(1/4\) rectangle of the foundation bottom. The value in the table in Appendix K.0.1-1 of _Code for Design of Building Foundations (GB50007-2011)_[43], and \(p_{0}\) is the additional stress of the base.  
Different groundwater levels are set along the base. The additional stress, self-weight stress, and foundation bearing capacity are calculated according to the methods in the _Code for Design of Building Foundations (GB50007-2011)_[43]. Generally speaking, when the size and burial depth of the foundation are constant, the additional stress below the bottom surface of the foundation gradually decreases, the self-weight stress gradually increases, and the bearing capacity of the foundation increases gradually. When the sum of the self-weight stress and additional stress at the groundwater level is equal to the bearing capacity of the foundation, the distance from the groundwater level to the basement at this time is the safe depth affected by the rise of the groundwater level.