**3.1. Engineering geology**

Based upon the preliminary geological investigation [36], the ground for Case A is generally consisted of a 1.5-m-thick surface backfill, a 4.5-m-thick low plasticity clay, a 4-m-thick silty sand and a successive very soft silty clay, as shown in **Figure 1**. The blow count N value for the clays varies from 1 to 4, whereas for the sands it varies from 5 to 10. The groundwater level is close to the ground surface. The soft soil deposits can thus easily get softened once disturbed or even washed away as subjected to significant hydraulic gradients.

The geological profile at the worksite of Case B is consisted of a 4-m-thick alluvial loam, a 7-m-thick very soft silty clay and an underlying soft silty clay, as shown in **Figure 2**. The static groundwater level in the vicinity of the worksite is some 2 m below the surface. The N value varies from 1 to 2 for the very soft silty clay, whereas for the soft silty clay, it varies from 2 to 3. The soft clays thus can behave as a fluid once subjected to construction disturbances.

#### **3.2. Grouting programme**

In the Case A, the eight-storey reinforced concrete building with one-storey basement was seated on the silty sand. The nonuniform consolidation of the successive silty clay led to the tilting of the eight-storey building afterwards. Since the tilting of the eight-storey building was amplified along with time, jacking the tilted eight-storey building back to the acceptable range of tilting was urgently needed. After considering all the possible alternatives to level up the tilted eight-storey building, grouting method was chosen due to the two reasons, that

**Figure 1.** Geological profile of worksite and properties of soft soil deposits (Case A).

**Figure 2.** Geological profile of worksite and properties of soft soil deposits (Case B).

is, (1) the concentrated grouting pressure during injection was distributed over the rigid mat foundation and would not damage the integrity of the tilted building, and (2) the unoccupied basement provided free and easy access to install grouting pipes and associated grout injection facilities. A reaction block right below the foundation soil should be given prior to the implementation of the jacking-up grouting. In this regard, the first stage of sleeve grouting (the stabilisation grouting) with the mild setting grout was carried out at a depth range of 9–16 m below the ground surface using a series of sleeve pipes (known as TAM). The pipe spacing varied from 3 to 4 m, and the layout of the 35 sleeve pipes is shown in **Figure 3**. The grout began intruding the soils upwards from the bottom of each sleeve pipe through one rubber sleeve at a period of time for a total of 15 rubber sleeves. As the building tilted to the southwest, the grout intake per sleeve pipe for the three different grouted zones depicted in red, black and green in **Figure 3** was 16.8, 14.7 and 6.3 m<sup>3</sup> , respectively, and was distributed evenly to 14 ports for 8 cycles of injection. The grout mix adopted in this stage is shown in **Table 1**.

double tube. Thus, the grouting mode (penetration or fracturing) could be chosen by varying the cycle time which is defined by the summation of injection time for each grouting pipe in the simultaneous injection operations. The grout due to the cycle time shorter than the setting time would penetrate through the yet-to-be hardened zone from previous injection to create a reaction block. In the event that the cycle time is longer than the setting time, the grout was injected repeatedly into the region where the grout from previous injection had already been hardened to level tilted building. With this simultaneous injection system, the travel of grouts was effectively limited, and the heave of ground was successfully initiated, jacking up the tilted building. Since performing injection in clay easily promotes hydrofracturing of soil due to its low permeability. During grouting works at the Case B, the soft clay deposits right below the mat foundation of this eight-storey building, thus ruled out any other ground improvement methods other than fracturing grouting. Because the final compensation efficiency could

Clay Grouting Mechanisms and Applications http://dx.doi.org/10.5772/intechopen.74091 109

**Cement Calcium oxide Water**

Weight (kg) 400 20 866

**Figure 3.** Layout of 35 sleeve pipes (Case A).

Volume (L) 1000

**Table 1.** Grout mixture for the stabilisation grouting (Case A).

Once the successive silty clay was strong enough to serve as a reaction block, the second stage of JOG grouting (the jacking-up grouting) was carried out where the quick setting grout was injected into the silty sand right below the mat foundation at a depth range of 7–9 m below the surface to level the tilted building. Each JOG grouting pipe was 20 cm offset from the sleeve pipe installed previously. To achieve the purpose of simultaneous injection, a multiple injection system involved with 18 JOG grouting pipes and a central controlling unit were introduced in grouting operations, as shown in **Figure 4**. The daily monitoring records from SB 1 to SB 7 were used for determining the grouting duration at each JOG grouting pipe and grouting order of each injection cycle. The injection of the extremely short setting grouts (**Table 2**) was achieved using the double tube, thereby preventing premature solidification and limiting the travel of grouts. Two types of grouts separately injected were mixed and solidified at the outlet of the

**Figure 3.** Layout of 35 sleeve pipes (Case A).

is, (1) the concentrated grouting pressure during injection was distributed over the rigid mat foundation and would not damage the integrity of the tilted building, and (2) the unoccupied basement provided free and easy access to install grouting pipes and associated grout injection facilities. A reaction block right below the foundation soil should be given prior to the implementation of the jacking-up grouting. In this regard, the first stage of sleeve grouting (the stabilisation grouting) with the mild setting grout was carried out at a depth range of 9–16 m below the ground surface using a series of sleeve pipes (known as TAM). The pipe spacing varied from 3 to 4 m, and the layout of the 35 sleeve pipes is shown in **Figure 3**. The grout began intruding the soils upwards from the bottom of each sleeve pipe through one rubber sleeve at a period of time for a total of 15 rubber sleeves. As the building tilted to the southwest, the grout intake per sleeve pipe for the three different grouted zones depicted in red,

to 14 ports for 8 cycles of injection. The grout mix adopted in this stage is shown in **Table 1**.

Once the successive silty clay was strong enough to serve as a reaction block, the second stage of JOG grouting (the jacking-up grouting) was carried out where the quick setting grout was injected into the silty sand right below the mat foundation at a depth range of 7–9 m below the surface to level the tilted building. Each JOG grouting pipe was 20 cm offset from the sleeve pipe installed previously. To achieve the purpose of simultaneous injection, a multiple injection system involved with 18 JOG grouting pipes and a central controlling unit were introduced in grouting operations, as shown in **Figure 4**. The daily monitoring records from SB 1 to SB 7 were used for determining the grouting duration at each JOG grouting pipe and grouting order of each injection cycle. The injection of the extremely short setting grouts (**Table 2**) was achieved using the double tube, thereby preventing premature solidification and limiting the travel of grouts. Two types of grouts separately injected were mixed and solidified at the outlet of the

, respectively, and was distributed evenly

black and green in **Figure 3** was 16.8, 14.7 and 6.3 m<sup>3</sup>

**Figure 2.** Geological profile of worksite and properties of soft soil deposits (Case B).

108 Current Topics in the Utilization of Clay in Industrial and Medical Applications

double tube. Thus, the grouting mode (penetration or fracturing) could be chosen by varying the cycle time which is defined by the summation of injection time for each grouting pipe in the simultaneous injection operations. The grout due to the cycle time shorter than the setting time would penetrate through the yet-to-be hardened zone from previous injection to create a reaction block. In the event that the cycle time is longer than the setting time, the grout was injected repeatedly into the region where the grout from previous injection had already been hardened to level tilted building. With this simultaneous injection system, the travel of grouts was effectively limited, and the heave of ground was successfully initiated, jacking up the tilted building.

Since performing injection in clay easily promotes hydrofracturing of soil due to its low permeability. During grouting works at the Case B, the soft clay deposits right below the mat foundation of this eight-storey building, thus ruled out any other ground improvement methods other than fracturing grouting. Because the final compensation efficiency could


**Table 1.** Grout mixture for the stabilisation grouting (Case A).

grouting (the stabilisation grouting) with a maximum grouting pressure of 20 kg/cm<sup>2</sup>

Weight (kg) 400 300 90 325

mixture used in the jacking-up grouting is shown in **Table 4**.

**Na2**

Volume (L) 250 250

**Table 4.** Grout mixture with 20-s setting time for the jacking-up grouting (Case B).

**4. Analysis and discussions**

**A liquid (500 L)**

**B liquid (500 L)**

**4.1. Multiple and simultaneous grouting results**

to stabilise the soft clays in the depth range of 5–9 m to provide the reaction required in the next jacking-up stage, and the second stage of sleeve grouting (the jacking-up grouting) was to intrude the clays ranging from 4 to 6 m depth to level up the tilted building. The grout

**O-3SiO2 Water**

**Cement Pulverised coal CaO Water**

The effectiveness of the proposed multiple and simultaneous grouting programme for the Case A was demonstrated using the measured column elevations from SB 1 to SB 7. The column elevation before each day grouting and the change in the column elevation after grouting were measured. **Figure 5** shows the relationship between the grout take and the change in the column elevation for this simultaneous and multiple jacking-up grouting. Most of grouts were injected into the southwest corner (SB 7), and the associated change in the column elevation measured 15.6 cm at the end of the grouting, as shown in **Figure 5**. Only a few grouts were injected into the northeast corner (SB3) and resulted in a nearly unchanged column elevation. The elevation change contour lines of the mat foundation were also prepared based upon the monitoring results of the column elevation change. The volume between the mat foundation contour lines before grouting and those after grouting represented the elevated volume of tilted building at the end of each day. Additionally, the volume between the mat foundation contour lines after grouting and those before next day grouting corresponded to the overnight settled volume of tilted building caused by the dissipation of excess porewater pressure resulting from previous grouting. Thus, both the elevated efficiencies defined by the ratio of the elevated volume to the injected grout volume and the settled efficiency defined by

the ratio of the settled volume to the injected grout volume can be derived.

**Figure 6** shows the cumulative elevated, settled and injected grout volumes, respectively, against each grouting day of this jacking-up grouting. From day one, the elevated volumes were greater than the settled volumes for each grouting day, which indicated a benefit from the reaction block, resulting from the stabilisation grouting. In the event that the soils subjected to the stabilisation grouting are not satisfactorily strengthened and showed an inability of

was

111

Clay Grouting Mechanisms and Applications http://dx.doi.org/10.5772/intechopen.74091

**Figure 4.** Illustration of the proposed multiple and simultaneous grouting system.


**Table 2.** Grout mixture with 2-s setting time for the jacking-up grouting (Case A).


**Table 3.** Grout mixture with 25-s setting time for the stabilisation grouting (Case B).

be largely improved with the repetitive injection procedure, a total of 49 sleeve pipes were installed 5 m beyond the mat foundation. Their locations are depicted by solid grey circle in **Figures 7a** and **8a**. The spacing between the sleeve pipes was 2 m. The grout hose system of 1.5 shot with a quick setting grout (**Table 3**) was introduced to ensuring the compensation efficiency. Similarly, two stages of grouting were implemented; the first stage of sleeve


**Table 4.** Grout mixture with 20-s setting time for the jacking-up grouting (Case B).

grouting (the stabilisation grouting) with a maximum grouting pressure of 20 kg/cm<sup>2</sup> was to stabilise the soft clays in the depth range of 5–9 m to provide the reaction required in the next jacking-up stage, and the second stage of sleeve grouting (the jacking-up grouting) was to intrude the clays ranging from 4 to 6 m depth to level up the tilted building. The grout mixture used in the jacking-up grouting is shown in **Table 4**.
