Post-pressure grouting is an effective method to improve bearing capacity of ordinary bored cast-in-situ piles. The migration of the grout along the pile side is regarded as an important mechanism responsible for the improvement of the pile capacity. Research into the penetration height of the grout is of great important in evaluating the behavior of base grouted piles. In this paper, a prediction method of grouting penetration height along the shaft of the base grouted pile was proposed. Considering the balance and losses of the grout pressure during grouting, an iterative procedure was given to determine the penetration height of the grout in layered soils. Field test results were also provided to indicate the validity of the proposed method.

A rational approach of predicting the response of the grouted shaft has been developed in this paper. The mechanisms of how base grouting affects the end bearing and side friction are analyzed in detail. Based on this analysis, four improvement factors are introduced into the hyperbolic load transfer function to account for the improvement of the shaft performance due to base grouting. The rational ranges of these factors have been determined by statistical analyses of a large group of in-situ testing results. The improvement load-transfer function was used to predict the behavior of the grouted shaft and the results show that the measured response of the shaft lies between the predicted upper and lower bound, which indicates the validity of the approach.

The surrounding rock control is a tough issue in the roadway with the swelling soft rock. The steel set is an important material for the control of swelling soft rock roadways. However, traditional steel sets failed to prevent the expansive pressure of the soft rock. Based on traditional steel sets, this paper developed a new steel set through both theoretical analysis and numerical simulation. The results showed that the new steel set was the set with the roof beam 1000 mm from the top of the set and the floor beam 400 mm from the bottom end of the set. The maximum deformations of the roof-floor and two sides of the ventilation roadway controlled by the best-improved set at the observation point were 147 mm and 108 mm, respectively. So, the best-improved set can effectively control the surrounding rock of the ventilation roadway. This provides an effective method for the surrounding rock control in extremely soft rock roadways.

Constant stiffness confining condition seems more reasonable than constant stress confining condition to simulate the actual confining stress environment of in situ rock which varies with the lateral strain. Compression tests of sandstone samples with two different confining conditions were conducted to study the energy evolution characteristics of rock under constant stress confining condition and constant stiffness confining condition. Except for the conventional triaxial compression tests, CFRP-confined rock samples were also used to simulate the constant stiffness confinement of the rock specimen in the laboratory. The stress–strain curve and failure mode of the samples under different confining conditions were compared. The influence of confining condition on the characteristics of rock energy evolution was investigated. The results show that the stress–strain curves under the confining conditions of constant stress and constant stiffness exhibited strain softening and strain hardening, respectively. Under constant stress confining condition, the specimen failed in the ductile mode while the specimen exhibited a sudden and brittle failure behavior under constant stiffness confining condition. The evolution trend of the elastic strain energy was greatly affected by the magnitude of confining stiffness. The elastic strain energy of the specimen under low stiffness confining condition decreased slightly after reaching its peak. As the confining stiffness increased, the elastic strain energy would not decrease but continued to increase until the failure of the specimen. The maximum elastic strain energy under the confining condition of the high confining stiffness is greater than that of constant stress. Considering the influence of confining stiffness on the storage and release of the strain energy, to obtain the true mechanical behavior of the rock mass under confining conditions, stiffness confining conditions should be taken into consideration in the laboratory.

A special double-row support structure used for braced excavation was modeled numerically using finite element method. The performance of the braced excavation depends on the interaction between the two walls of the support structure. Comprehensive parametric studies were carried out to investigate the influence factors on the performance. It was ascertained that the support structure behavior was largely influenced by overlapping length of two support walls, embedment ratio of inner support wall and spacing between two support walls. Appropriate parameters should be chosen to limit wall deflection and to maintain the stability of the support structure.

An inner support structure is usually adopted when the installed support wall is failure to satisfy the requirement of stability and control of ground movement. The influence of excavation on surrounding environment especially the underground pipelines, which is controlled by the parameters of inner structure, is a major concern for design. Numerical analyses were performed to study the pipeline deformation caused by the double-row supported excavation. Comprehensive parametric studies were carried out to investigate the influence factors for deformation control. It is concluded that the deformation of pipelines is largely influenced by the interaction between the two walls. In addition, design recommendations are given according to the tolerated stress of the pipeline.