Mechanical Properties of Cement-Treated Soil Mixed with Cellulose Nanofibre

Cellulose nanofibre (CNF), a material composed of ultrafine fibres of wood cellulose fibrillated to nano-order level, is expected to be widely used because of its excellent properties. However, in the field of geotechnical engineering, almost no progress has been made in the development of techniques for using CNFs. The authors have focused on the use of CNF as an additive in cement treatment for soft ground, where cement is added to solidify the ground, because CNF can reduce the problems associated with cement-treated soil. This paper presents the results of a study on the method of mixing CNF, the strength and its variation obtained by adding CNF, and the change in permeability. CNF had the effect of mixing the cement evenly and reducing the variation in the strength of the treated soil. The CNF mixture increased the strength at the initial age but reduced the strength development in the long term. The addition of CNF also increased the flexural strength, although it hardly changed the permeability.

1D Compressibility of High Moisture Content Clays Solidified with Small Cement Dosages

Soft soil is normally associated with high moisture content and fine content which result in high compressibility and low strength. However, a proper treatment such as solidification by means of hydraulic binders is required in order to be usable for beneficial purposes (e.i backfilling). This paper experiments the effects of cement treatment on the one-dimensional (1D) consolidation behavior of a high moisture content (MC) soil (twice liquid limit), based incremental loading test. The effects of Portland cement addition are evaluated for dosages ranging from 0 % to 15% by dry mass of soil. After curing, it was found that 10 % cement was required to make meaningful reduction in MC for kaolin while no major difference was noted between after mixing and after curing for DMS. In kaolin the moisture content decreased by 6.5 % for each 5 % increment of cement. Similarly, the MC of DMS reduced by 10 % for each 5 % increment. Thus, the reduction, immediately after mixing, in DMS was higher by 3.5 % compared to kaolin. The most evident effect of the treatment feasibility is the development of a cementation-induced yield stress after 7 days of curing: the bigger the cement dosage, the greater the yield stress and the greater the vertical effective stress that can be sustained at any void ratio. The maximum yield stress at 15 % cement content was found 30 kPa and 70 kPa for DMS and kaolin respectively. The highest void ratio values were found in the control specimens (3.77) in kaolin and DMS (5.66) whereas the lowest void ratio was corresponded to 15 % cement 3.35 and 4.65 for kaolin and DMS respectively. The control specimens decreased dramatically from 38.93 m2 / KN - 0.13 m2 / KN and 36.03 m2 / KN - 0.19 m2 / KN for kaolin and DMS specimens respectively. The results correspondingly provide a consistent depiction of the effects of cement treatment on MC, void ratio and coefficient of volume compressibility. The effectiveness of the treatment is obvious compared to the untreated soil.

Site Measurement and Study of Vertical Freezing Wall Temperatures of a Large-Diameter Shield Tunnel

When a large-diameter shield tunnel boring machine enters or exits a tunnel, the newly exposed tunnel face is prone to instability and water seepage. In order to prevent collapse of the tunnel face, local ground improvement can be used until the permanent tunnel lining can be installed. The tunnel launching project of the Nanjing Metro Line 10 cross-river tunnel had a high stability requirement for the entry and exit phases. To this end, this project used a combination of cement treatment and ground freezing methods. In this project, field measurement of the vertical freezing improvement of the large-diameter shield tunnel was carried out. The temperature distribution and ground surface deformation of the vertical frozen soil wall at the end of the tunnel during the active freezing and maintenance freezing periods were analyzed in detail. The result shows that the surface settlement and seepage were successfully controlled by the combined cement treatment and ground freezing. On the other hand, the combination of cement treatment and ground freezing helps to control the freezing-induced heaving. The hydration heat in improved ground leads to an increase in ground temperature and this leads to additional freezing duration. It was examined that the frozen soil wall and the enclosure structure were in a good cementation condition. These measured values provide guidance on the timing of the shield departure. The project results confirmed that instability and water permeation did not occur in the tunnel face during the subsequent excavation.