Existing structures can deform and damage due to newly constructed underground structures, which induces surrounding soil deformation due to ground loss and stress relief. Compensation grouting is an active control method widely used in practice due to its advantages of using readily accessible material, a convenient construction process, and the ability to make real-time adjustments compared with passive control methods. However, in current studies, consolidation settlement is commonly considered the primary factor causing the gradual loss of the grouting effect. In this study, a numerical model exhibiting an elastic viscoplastic behavior was established using the finite-difference method to investigate the influence of creep on grout efficiency. The model parameters were first calibrated by comparing them with the measured and computed results of the grouting tests conducted in a consolidometer. Then, the model was used to perform parametric studies, to investigate the influences of initial overconsolidation ratio (OCR) and grout volume. The results show that the grout efficiency, defined as the ratio between total displacement and ideally anticipated heave displacement after grouting, is lower than that when only consolidation is considered. It can decrease up to 2.5 times over 3 years when the OCR is set to 1.00 and the grout volume is 1 mL. This implies that neglecting creep behavior may lead to a nonconservative design for compensation grouting in the long term. The creep control efficiency, defined as the ratio between the settlement induced by creep and that induced by consolidation, has been newly proposed to evaluate the influence of soil creep. It is found that the creep control efficiency of OCR = 1.00 serves as an upper limit under different OCRs because of the significant consolidation settlement in underconsolidated soil and the small creep settlement in overconsolidated soil. Therefore, the creep control efficiency value of OCR = 1.00 can be recommended for conservative design estimates when determining the final grout efficiency.

This paper presents a case study for soil improvement using a combined vacuum and fill sur-charge preloading method for the 3rd runway of the Suvarnabhumi International Airport in Bangkok, Thailand. Prefabricated vertical drains of 10 m long was used. The preloading consisted of an average of 86 kPa of vacuum pressure plus a 22 kPa of fill sur-charge due to the granular fill and drainage layer. The vacuum preloading system adopted is described. Monitored settlements and pore water pressures are presented. The average ground settled monitored is around 70 cm and the average degree of consolidation as estimated using settlement data is higher than 90%. Degree of consolidation is also calculated using pores water pressure distribution monitored along the depth which gave a good verification of the degree of consolidation achieved.

In the reconstruction and expansion of expressways in soft soil areas, controlling the differential settlement between the new and existing subgrades is of vital importance. To investigate the settlement and deformation characteristics of both the new and existing subgrades, piezocone penetration test (CPTU) and dissipation tests were conducted on these subgrades. The CPTU dissipation data was utilized to determine the soil's degree of consolidation, and settlement calculations for the new and existing road subgrades were based on the CPTU test results. Subsequently, a finite element model was developed using the CPTU test findings to analyze the horizontal displacements, vertical settlements, and differential settlements of the new and existing subgrades before and after the reconstruction and expansion. Based on the measured settlement results, the new and old subgrade settlement calculation results are verified. The outcomes revealed that the degree of consolidation for the existing road subgrade of the Lianhuai Expressway ranged between 42 % and 96 %. The maximum horizontal displacement of the subgrade pre- and post-expansion occurred at the slope toe. Before expansion, the maximum vertical settlement was observed along the road's centerline, while after expansion, it was located in the centerline of the widened section. The maximum additional settlement amounted to 274.77 mm. During the new road construction phase, the differential settlement between the new and existing road subgrades increased rapidly over time, peaking at its maximum value. However, during the operational phase of the new road, this differential settlement tapered off as time progressed.