**4.4 Settlement sensitive structure on a geological fault**

The soil investigation for the science and congress center Darmstadtium in Darmstadt, Germany, showed that the planned settlement-sensitive structure is situated above the eastern fault of the Rhine Valley. The construction was finished in 2007 and is shown in **Figure 16**.

The eastern fault of the Rhine valley crosses the project area as shown in **Figure 17**. In the northern and western areas unconsolidated sediments of the Rhine Valley fault were found. In the eastern and southern area, rocks of the Odenwald crystalline were identified (granodiorite). The tectonic activities along the fault zone have not finished *Reducing Carbon Emissions by Combined Pile-Raft Foundations for High-Rise Structures DOI: http://dx.doi.org/10.5772/intechopen.104559*

#### **Figure 15.**

*FE-mesh of the numerical model and calculated settlements.*

**Figure 16.** *Science and congress center Darmstadtium, Germany.*

up to now. The area of Darmstadt that is located west of the Rhine Valley fault has an annual settlement of about 0.5 mm. These tectonic displacements hand to be considered for the design of the foundation system and the rising structure. In the area of the rock, the foundation was constructed as a spread foundation and a CPRF was constructed in the area of the Rhine Valley (**Figure 18**).

### **4.5 Horizontal loads on a CPRF**

The Exhibition Hall 3 in Frankfurt am Main, Germany, was finished in 2001 and is one of the biggest exhibition halls in Europe. Its length is about 210 m and its width is about 130 m. The height is about 45 m. The roof is a double-curved, threedimensional, load-bearing structure consisting of five arched compression trusses and

**Figure 17.** *Excavation pit and gradient of fault.*

**Figures 18.** *Foundation system.*

six arched tension trusses with a free span of 165 m [16, 17]. **Figure 19** shows a crosssection of the realized project and the subsoil conditions. Twelve A-frames, six on each side, carry the horizontal and vertical loads of the roof. These A-frames, with a height of 24 m, are constructed of two steel tubes (**Figure 20**). According to [6] the project belongs to the Geotechnical Category GC 3.

*Reducing Carbon Emissions by Combined Pile-Raft Foundations for High-Rise Structures DOI: http://dx.doi.org/10.5772/intechopen.104559*

#### **Figure 19.**

*Cross-section and subsoil conditions.*

The soil investigation showed, that the conditions are not equal all over the project area. Under the surface is a 5–9 m thick layer of fillings and quaternary soil. Below this follows a layer of tertiary sediments. The project area is crossed diagonally by a layer of tertiary sand and gravel. The settlement active Frankfurt Clay follows until bigger depth.

A strong limitation of the displacements of the foundation is necessary due to the strong interaction between the superstructure, the foundation, and the subsoil. Threedimensional numerical analyses were used for the design of the horizontal loaded CPRF. On each end of the hall is a CPRF which consists of a raft and 14 bored piles. The raft has a thickness of 1.4 m, a length of 127.5 m, and a width of 22.15 m. The bored piles have a diameter of 1.5 m and a length of 15 m.

According to the observational method, a geotechnical and a geodetic measurement program was installed. By four inclinometers the horizontal displacements of the CPRF were observed at a depth of 50 m under the surface. For the measurement of the vertical displacements, four extensometers were installed. In addition. pressure cells in the soil under the raft, strain gauges at A-frames, and geodetic measurement points were installed. The measurements showed horizontal displacement up to 1 cm and vertical displacements between 1.0 cm and 3.5 cm.

The example shows that the CPRF can be used for a settlement-reduced transfer of horizontal loads into the subsoil. Compared to a classic file foundation or a massive block foundation the CO2 emission was reduced significantly.

#### **4.6 High-rise building on cavernous subsoil conditions**

The project Moscow City contains several high-rise building for business in Moscow, Russia, on an area of more than one square kilometer [18]. In this project, the Federation Tower is a complex of two single towers (**Figure 21**). Tower A is about 374 m high, or 450 m high when including the spire on the roof. The height of Tower B is about 243 m. At the start of the construction in 2003, the high-rise double-towers were planned as the highest high-rise buildings in Russia and Europe. The two towers are founded on a foundation raft, which is 4.6 m thick and has a length of 140 m and a width of 80 m. The foundation level is about 20 m below the surface.

**Figure 20.** *Schematic visualization of the A-frames and the CPRF.*

Tower A has a total load of about 3000 MN and Tower B has a total load of about 2000 MN. Including loads of about 1000 MN for adjacent buildings and the basement floors and a load of about 1300 MN for the foundation raft itself, the total load results in 7300 MN.

The project area of Moscow City is located on the left bank of the River Moskva in the west of the central district. The anthropogenic artificial fillings are followed by the quaternary accumulation of the river terrace. Below this, an alternating sequence of carbon follows. The foundation level of the Federation Tower is in a complex alternating sequence of variably intensively fissured, cavernous and porous limestone and variably hard, more or less watertight clay/marl. The thickness of the layers varies between 3 m and 10 m. The project area is located in a territory where potentially dangerous karst-suffusion processes occur.

*Reducing Carbon Emissions by Combined Pile-Raft Foundations for High-Rise Structures DOI: http://dx.doi.org/10.5772/intechopen.104559*

**Figure 21.** *Federation Tower in Moscow City, Russia.*

In the project, area exists several groundwater horizons carrying confined water which are not or just moderately corresponding with each other due to the sealing effect of the clay/marl. The pressure of the confined groundwater is up to 12 m. The groundwater mainly circulates in the fissured and karst-suffusion-affected limestone.

For the determination of the load-bearing behavior of deep foundation elements, two pile load tests have been carried out on the construction site. The test piles TP-15-1 and TP-15-2 had a diameter of 1.2 m and were instrumented with O-Cells. The pile segments in total were 6.9 m and 13.35 m long. The empty drill hole was filled with sand. The piles are completely positioned in the limestone (**Figure 22**).

The test piles had two segments with an O-cell in between. The displacements of the segments were measured with displacement transducers.

The maximum load of pile load test TP-15-1 was about 33 MN with an unloadingphase at 15 MN back to zero and a reloading-phase as shown in **Figure 23**. The upper

**Figure 22.** *Test piles TP-15-1 and TP-15-2 with O-Cells.*

**Figure 23.** *Load-displacement diagram of test pile TP-15-1.*

pile segment has a final displacement of 0.6 cm and the lower pile segment has a final displacement of 0.4 cm. No failure was seen and the empirically defined limit in [4, 6] of the settlement s = 0.1, D = 12 cm was not reached. The results of the pile load test TP-15-1 gives skin friction of qs = 1140 kN/m<sup>2</sup> and base resistance of qb = 5380 kN/m<sup>2</sup> . Both values are not ultimate ones because failure criteria was not reached.

The maximum load of pile load test TP-15-2 was about 33 MN with three unloading-phases back to zero as shown in **Figure 24**. The upper pile segment has a final displacement of 4.3 cm and the lower pile segment has a final displacement of 2.2 cm. Again, no failure was seen and the empirically defined limit of the settlements of s = 0.1, D = 12 cm was not reached. The results of the pile load test TP-15-2 gives

*Reducing Carbon Emissions by Combined Pile-Raft Foundations for High-Rise Structures DOI: http://dx.doi.org/10.5772/intechopen.104559*

#### **Figure 24.**

*Load-displacement diagram of test pile TP-15-2.*

skin friction of qs = 2310 kN/m2 and base resistance of qb = 5630 kN/m<sup>2</sup> . Both values are not ultimate ones because failure criteria was not reached.
