**1. Introduction**

Foundation soil bearing capacity for Taipei basin is usually inadequate, where a 40–55-m-thick alluvial formation (the Sungshan formation) of alternating soft clay and silty sand layers is deposited, followed by a gravel formation (the Chingmei gravel formation) [1, 2]. The shear strength of the soft soil deposits due to the water contents close to their liquid limits is very low, leading to an inability of supporting upper buildings and/or structures [3–7]. To tackle this key engineering issue, grouting technologies have been widely adopted to improve the mechanical properties of the soft soil deposits [8–23]. Notwithstanding that, the effectiveness of grouting in such geological conditions can be significantly affected by the configuration of

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

grouting programme. The differential settlement or tilting of building, for instance, can be contributed not only by the soil right below the building foundation but by the successive soils. Thus, a grouting programme aimed to first stabilise the successive soils by 'stabilisation' grouting and then to lift the tilted building by 'jacking-up' grouting in the foundation soil is proved to be effective [24]. In the event that the grouting programme is designed to improve the properties of the foundation soil only, the jacking of the tilted building would not be effectively implemented due to a lack of the sufficient reaction forces given by the successive soils. Additionally, the intrusion of grouts may swell the cohesive soil and generate the positive excess porewater pressure. As long as the porewater pressure dissipates along with time, the associated settlement could override the heave generated during grout intrusion and thus result in a negative final compensation efficiency which is defined as a ratio of the total heaved volume to the injected volume of grouts [25–29]. Since the fracturing grouting due to easy travelling of the low viscosity grouts could generate higher porewater pressure than compaction grouting, regrouting at the same injection point is deemed to be necessary in order to change the stress state of cohesive soil to the overconsolidated state from its ordinary state [24, 30]. Any further grouting activity would only generate negative excess porewater pressure, and resettlement would not be occurred, thereby improving the final compensation efficiency. If both closer spacing between grout injection points and simultaneous injection are introduced, the final compensation efficiency can be further improved [27]. The above indicates that configuration and design parameters of the grouting programme play a leading role in the success of project.

were found to be nearly horizontal, indicating that the ground is overconsolidated, with

It is reported by Au et al. that for normally consolidated or slightly overconsolidated clays, the significant decrease in the grouting efficiency with time was due to the dissipation of

 value greater than unity [31]. The sand proppant was thicker at locations where soils were relatively weak, but there was no strong evidence that soil stratigraphy at this worksite controlled the orientation of the fractures. Murdoch and Slack reported similar results in sand-propped hydraulic fractures [32]. Additionally, the horizontal fractures imply that the shallow soil strata should be overconsolidated. Moreover, the elevated volume would be considerably smaller than the injected volume in the event the hydraulic fractures vented to the ground surface. Liu and Yuan established an in situ slurry fracturing apparatus to analyse the slurry fracturing and fracture propagation phenomena [33]. It was observed that the fracturing pressure was highly related to the soil and slurry properties and that slurry with large bulk density and high viscosity was beneficial in preventing slurry fracture propagation. Conducting grouting in clay due to its low permeability rules out any other grouting techniques other than fracturing grouting. The excess porewater pressure generated during grout injection is greater than the in situ effective stress, leading to fractures in the surrounding clay. Existence of fractures accelerates the consolidation process and shortens the strength increase time due to consolidation. During injection, the fractures provide a channel for exchangeable cations, which make the strength increase due to chemical reactions much more quickly than anticipated. Additionally, the compensation efficiency may not be governed by clay type but by the setting time of grout, soil stress history, injection volume of grout and so on. However, the high mobility and low viscosity of the grout can lead to an inability of limiting the travel of grout, thereby resulting in a lower soil-heaved volume to injected volume of grout ratio also known as the grouting efficiency. The grouting efficiency is generally smaller than 1 due to the loss of fluid, resulting from the bleeding effect of grout and escape of the grout from the designated area by migration along fractures, and the ground settlement caused by the dissipation of excess porewater pressure generated in injection [31]. Marchi et al. carried out a comprehensive case study in Venice where a rather unique soil fracturing intervention was implemented to improve the mechanical properties of the soft silty clay underlying the ancient Frari bell tower [34]. For soils with negative values of liquidity index, the gradients from the plots of fracturing pressure against initial confining pressure are approximately 2, which indicated the fracture initiated by tensile failure in these cases, while for soils with positive values of liquidity index, the gradients are approximately 1, indicating that the fracture was triggered by shear failure. Komiya et al. conducted a field trial of shield tunnelling in a deep soft clay deposit to investigate the long-term consolidation effect on grouting efficiency [25]. The grouting programme was consisted of the tail void grouting and grout jacking. In both cases, the monitoring results indicate that the upward displacement owing to grout injection was negated by the consolidation settlement resulting in a net settlement. The considerable consolidation of clay after grout injection due to the dissipation of the excess porewater pressure generated as the grout intruded the sensitive and compressible clay contributed to this phenomenon. This also indicates that the grouting

Clay Grouting Mechanisms and Applications http://dx.doi.org/10.5772/intechopen.74091 105

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efficiency in soft clay may be negative.

The objectives of this study are (i) to present the results of an application of this proposed simultaneous and multiple grouting technique for levelling two tilted buildings seated on soft soil deposits in Taipei basin, (ii) to verify the effectiveness of introducing a grouting programme consisting of the stabilisation grouting of first stage and jacking-up grouting of the second stage by analysing the elevated and settled efficiencies and (iii) to outline the lessons learnt from the case studies.
