code: def get_v_eff_stress_at_depth(self, y_c):
          
          sigma_v_c = self.get_v_total_stress_at_depth(y_c)
          pp = self.get_hydrostatic_pressure_at_depth(y_c)
          sigma_veff_c = sigma_v_c - pp
          return sigma_veff_c
docs: Determine the vertical effective stress at a single depth z_c.
  
          :param y_c: float, depth from surface