Shaorui Sun

Effect of the combination characteristics of rock structural plane on the stability of a rock-mass slope

The structural planes play an important role in rock mass slope stability. In this paper, a series of triaxial tests on the rock mass samples with different dip angles, plane numbers and plane spacing of structural surfaces were carried out to study the effect of the combination characteristics of the rock structural plane on rock mass mechanic parameters. Based on the test results and the combination characteristics of the field structural plane, the rock mechanics parameters for the spillway lock chamber slope of the Liyuan hydroelectric station were forecast. The stability of the slope was rationally evaluated based on the forecasted rock mass mechanical parameters. Finally, the safety factor was obtained based on the shear strength reduction method.

Improvement Effect of Water-Based Organic Polymer on the Strength Properties of Fiber Glass Reinforced Sand

The mechanical properties of sandy soil can be effectively improved by the incorporation of water-based polymer and glass fibers. In order to study the reinforcement effects of a type of water-based organic polymer and fiber glass on sand, three strength tests (unconfined compression test, direct shear test and tensile test) and scanning electron microscopy were carried out. A series of polymer content, fiber content and dry density were selected for the tests. The results revealed that the composite reinforcement of water-based organic polymer and fiber glass can improve the strength. With an increase in polymer content and fiber content, the unconfined compression strength, the cohesion, and the tensile strength increase. The internal friction angles maintain a relatively stable state. All three strength properties increase with an increase in dry density. The results can be considered as the reference for sand reinforced engineering.

Experimental Study on 3D Roughness and Shear Failure Mechanism of Rock Mass Discontinuity

A set of systematic experimental methods, including 3D accuracy scanning and identification of discontinuous surface topography, physical model construction, and laboratory direct shear experiment under different directions and normal stresses, was proposed to research the influence of discontinuity roughness on strength and deformation of discontinuity. During physical model construction of discontinuity, three types of discontinuity and rough natural rock joint surface models were constructed and moulded. Meanwhile, many influence factors of discontinuity surface topography, such as asperity inclination angle (AIA), asperity height (AH), normal stress (NS), and shear direction (SD), were considered during the direct shear experiment. On the basis of the experimental results, it can be found that there were two types of failure modes under different loading conditions, which were named “failure by shearing through the asperities” and “failure by sliding over the asperities”. The obvious stress concentration phenomenon, climbing, and cutting effects appeared in the process of the direct shear experiment. In addition, the accurate identification of surface topography of natural rough rock joint surface was carried out using three-dimensional sensing system (3DSS) and self-programming software before and after the experiment. The subsamples with the same surface topography as the original samples were moulded using a self-developed instrument. Then, the mechanical behavior of the original samples and subsamples for the natural rough rock joint surface under different shear directions and normal stresses was studied. The results show that the shear displacement under different shear directions and normal stresses is very large before it reaches the failure state. And the residual strength of the original samples is higher than that of the subsamples. In addition, failure modes of the subsamples are main failure by shearing through the asperities due to the significant difference between peak shear strength and residual strength. The failure modes for parts of the original samples are failure by sliding over the asperities. The change ratio of area for the discontinuity after the experiment depends on surface topography, strength of heave on the surface of discontinuity, and particle size of minerals on the surface of discontinuity.

Case Study on Influence of Step Blast-Excavation on Support Systems of Existing Service Tunnel with Small Interval

During the construction of newly built tunnel (NBT) adjacent to the existing service tunnel (EST), stability of the EST with small interval is affected by vibration waves which are caused by blasting load. The support structures of the EST will be cracked and damaged, while the unreasonable blast-excavation methods are adopted. Presently, the studies on behavior of support structure in the EST under blasting load are not totally clear, especially for the bolts system. Besides, the responses of support structure on blasting load are lacking comprehensive research. In this paper, New Zuofang tunnel is taken as a study case to study the influence of step blast-excavation in NBT on support structures of the EST through field experiment and numerical simulation. Some data, such as blasting vibration velocity (BVV) and frequency of support structures, are obtained through field measurement. Based on these data, the formula of BVVs is obtained. Research on stability of tunnel support structures affected by step blast-excavation is conducted using numerical simulation method. The dynamic-plastic constitutive model is adopted in the software ABAQUS to assess safety of support structures. The range and degree of damage for the support structures are obtained. In addition, change laws of axial force and stress with time for the bolts are analyzed.

Ground Settlement Model for Excavation of a Non-Partial Pressure and Shallow Buried Double-Arch Tunnel

The ground settlement model due to tunnel’s excavation was summarized in this paper. Firstly, the geological characteristics of a double-arch tunnel in Jinliwen Expressway are investigated and analyzed, which mainly act as discontinuity. Especially, settlement pattern during excavation of such a double-arch tunnel with non-partial pressure and shallow bury was taken out by data analysis from those monitoring information. After ground settlement model and its increment model following the each step of tunnel’s excavation were built, the difference of forecasting between single tunnel and double-arch tunnel was shown. Secondly, the ground settlement model was testified by comparing between forecasting and field data. Thus, theoretical basic to avoid overmuch settlement during excavation of such a double-arch tunnel was provided.

Research on the engineering geological conditions and stability evaluation of the B2 talus slide at the Jin’an Bridge hydropower station, China

The B2 talus slide at the Jin’an Bridge hydropower station is located on the left bank of the Jinsha River and very close to the left abutment of the dam. The stability of the dam is directly influenced by the engineering geological properties, formation mechanisms, and failure modes of the B2 talus slide. This paper highlights the investigation and analysis of the in situ engineering geological conditions of the slide area. The results indicate that the B2 talus slide is composed of three parts: the talus deposits consisting of a soil-rock mixture (SRM) in the upper part, unloaded and relaxed rock mass in the middle part, and bedrock with several tuff interlayers in the lower part. Based on topographic and geomorphologic analyses, the structure of the rock and soil, distribution characteristics, formation mechanisms, and influencing factors, the strength of the SRM in the upper part and the properties of the tuff interlayer in the lower part are the main factors affecting the stability of the slide. Additionally, the failure modes of the slide are likely to be circular in nature in the talus deposits, broken line sliding along the interface between the unloaded and relaxed rock and the upper boundary of the tuff and broken line sliding along the tuff interlayer. The strength parameters of the SRM and the tuff interlayer were obtained through laboratory experiments and theoretical inverse analyses. Additionally, a three-dimensional geological model of the slide was created using the aforementioned results and the software GoCAD. Limit equilibrium and finite element methods were used to evaluate the stability of the slide using two-dimensional and three-dimensional models. The results indicate that the slope is stable under natural conditions. However, the slope may be unstable, under special conditions, such as artificial excavation, flood discharge atomization, rainstorms, and earthquakes.

Effect on the Resistance of Concrete Acid Corrosion in Superficial Soil Layers

To understand the effect and mechanism of urban heat island (UHI) and the acid corrosion of concrete on the strength of concrete in superficial soil layers from Nanjing area, both laboratory and field tests of accelerated corrosion of concrete were carried out and analyzed. The laboratory test results indicate that the concrete corrosion depends on acid concentration, tested time, and also on the temperature. The maximum corrosion coefficient (K-value) of 45.86%, as observed at 10% of acid concentration, 40°C of tested temperature, and 90 days of tested time, was about 2 times that of specimens with 10% of acid concentration, 5°C tested temperature, and tested after 90 days. The field test showed that the compressive strength of specimens in urban station was lower than that of specimens in rural station. The K-value of specimens with same acid concentration observed at urban area was higher than that of specimens at rural area. Both the laboratory and field tests showed that the temperature has an increasingly powerful influence on the concrete corrosion under acid environment. Therefore, the UHI effect will accelerate the acid corrosion in concrete construction and may affect the stability and durability of buildings in urban areas. The safety and life assessment of concrete buildings therefore require great attention.

Numerical Tests Research on Mechanical Parameters of Rockmass considering Structural Plane Combination Characteristics

It is essential to determine rockmass mechanical parameters in stability assessment. The structural z is the main factor in this regard, and we know little about the relationship between mechanical parameters and multiple structure planes. In this paper, we have conducted a series of numerical tests to obtain mechanical parameters for a dam foundation in Southwest China. The biaxial numerical test was performed based on the discrete element method. This numerical test considers the spacing, types, dip angles, and size effect. We established a relationship of mechanical parameters between small size lab samples and large size field samples. We forecasted the strength parameters for a spillway slope in Southwest China. The dip angle has a significant effect on the slope strength and stability. In this case, the rockmass fracture stress-dip angle curve forms a U-shaped distribution. The X-shaped double structure plane demonstrates severe strength weakening relative to a single structure plane. As structure plane spacing reaches a certain level, its influence on rockmass strength diminishes. The elementary volume of the rockmass for dam foundation analysis is about 4 m × 4 m × 4 m.

Research on crack initiation mechanism and fracture criterion of rock-type materials under compression–shear stress:

With the focus on the failure of single-cracked rocks under compression–shear stress, the form and the critical conditions of crack initiation by adopting theoretical derivation and numerical experiments methods are researched in this article. Maximum circumferential stress criterion and modified Griffith’s criterion are utilized to derive the expressions for crack initiation angle and fracture criterion. Moreover, the PFC3D, numerical simulation software, is used to verify the results of theoretical research and the research on the generation process of shear fracture zone and the number of microcracks and their distribution law. The results show that the crack initiation angle θ0 and critical conditions of crack initiation correlate with some factors, such as crack inclination angle β, coefficient of friction μ, and the ratio of normal stress to shear stress σ1/τx. When β is less than or equal to 90°, the deviation between the theoretical result of crack initiation angle and actual result is small; when the value of Mode I fracture toughness KIC is accurate, the crack criterion derived is reliable when β is less than or equal to 120°. The friction between cracks restricts the compression–shear failure on the surface of crack. The ratio of shear stress required for crack initiation to peak shear stress in the model decreases with the normal stress increased. At the crack initiation stage, when the increase in microcracks is relatively slow, the shear fracture zone is thin and when the increase in microcracks becomes rapid, shear fracture zone becomes thick at the peak stage. The shear strength is proportional to the number of microcracks in the model.

Mechanical and failure characteristics of rock-like material with multiple crossed joint sets under uniaxial compression

The strength and deformation of rock masses transected by persistent joints are controlled by the fracture network. In this work, bonded particle model modeled by particle flow code in three dimensions was used to study the effect of geometry parameters on the strength and behavior of jointed rock masses under uniaxial compression. The effect of the number of crossed joint sets, joint orientation, and joint spacing on the uniaxial compressive strength was investigated, and this article presents the results of the numerical simulations. Rigorous validation process had done before the numerical experiments. Four types of blocks (Series A, B, C, and D) with different numbers of joint sets were considered in this article. Then, a sensitivity study is undertaken to investigate the effects of joint set numbers and joint geometry configuration on the failure mode, unconfined compressive strength, and Young’s modulus of jointed rock mass. The interaction among the crossed joint sets was found to have marked effects on the mechanical properties and failure modes. A study about the effects of joint spacing on the failure modes, unconfined compressive strength, and Young’s modulus was also conducted. Joint spacing was found to have no significant effect on the failure modes of jointed rock masses in a certain range. It is also shown that the range and variance of unconfined compressive strength are affected principally by joint set numbers and decreased slightly with the decrease in joint spacing. The effect of crossed joint sets on the stress field was carried out. Stress concentration was found to be the reason for relatively lower strength of blocks with crossed joint sets compared to the block with the same weakest single joint set. The result in this article is of great help to reveal the mechanism of damage and fracture of jointed rocks under uniaxial compression.