The subgrade soil is generally in saturated or unsaturated condition. To analyze complex thermo-hydro-mechanical-chemical (THMC) behaviors of subgrade, it is essential to determine the soil–water characteristic curve...The subgrade soil is generally in saturated or unsaturated condition. To analyze complex thermo-hydro-mechanical-chemical (THMC) behaviors of subgrade, it is essential to determine the soil–water characteristic curve (SWCC) that represents the relationship between matric suction and moisture content. In this study, a full-automatic rapid stress-dependent SWCC pressure-plate extractor was developed. Then, the influences of overburden stress and degree of compaction on the SWCC of subgrade soil such as high liquid limit silt (MH) and low liquid limit clay (CL) were analyzed. Accordingly, a new model taking into account the influences of overburden stress and degree of compaction based on the well-known Van Genuchten (VG) SWCC fitting model was presented and validated. The results show that with the increase of the degree of compaction and overburden stress, the saturated moisture content of subgrade soil decreases, while the air-entry value increases and the transition section curve becomes flat. The influences of the degree of compaction and overburden stress on the SWCC of MH is greater than that of CL. Meanwhile, there was a satisfactory agreement between the prediction and measurement, indicating a good performance of the new model for predicting the SWCC.展开更多
The cut-off wall in a clay-core rockfill dam built on a thick overburden layer is subjected to a large compressive pressure under the action of the loads such as the dead weight of both the dam and the overburden laye...The cut-off wall in a clay-core rockfill dam built on a thick overburden layer is subjected to a large compressive pressure under the action of the loads such as the dead weight of both the dam and the overburden layer, the frictional force induced by the differential settlement between the cut-off wall and surrounding soils, and the water pressure. Thus, reduction of the stress of the cut-off wall has become one of the main problems for consideration in engineering design. In this paper, numerical analysis of a core rockfill dam built on a thick overburden layer was conducted and some factors influencing the stress-strain behaviors of the cut-off wall were investigated. The factors include the improvement of the overburden layer, the modeling approach for interfacial contact between the cut-off wall and surrounding soils, the modulus of the cut-off wall concrete, and the connected pattern between the cut-off wall and the clay core. The result shows that improving the overburden layer,selecting plastic concrete with a low modulus and high strength, and optimizing the connection between the cut-off wall and the clay core of the dam are effective measures of reducing the deformations and compressive stresses of the cut-off wall. In addition, both the Goodman element and the mud-layer element are suitable for simulating the interfacial contact between the cut-off wall and surrounding soils.展开更多
This paper describes a field and numerical investigation of the overburden strata response to underground longwall mining, focusing on overburden strata movements and stress concentrations.Subsidence related high stre...This paper describes a field and numerical investigation of the overburden strata response to underground longwall mining, focusing on overburden strata movements and stress concentrations.Subsidence related high stress concentrations are believed to have caused damage to river beds in the Illawarra region, Australia. In the field study, extensometers, stressmeters and piezometers were installed in the overburden strata of a longwall panel at West Cliff Colliery. During longwall mining, a total of1000 mm tensile deformation was recorded in the overburden strata and as a result bed separation and gaps were formed. Bed separation was observed to start in the roof of the mining seam and gradually propagate toward the surface as the longwall face advanced. A substantial increase in the near-surface horizontal stresses was recorded before the longwall face reached the monitored locations. The stresses continued to increase as mining advanced and they reached a peak at about 200 m behind the longwall face. A numerical modelling study identified that the angle of breakage(i.e., the angle of the boundary of caved zone) behind the longwall face and over the goaf was 22–25° from vertical direction. This is consistent with the monitoring results showing the high gradient of stresses and strains on the surface150–320 m behind the mining face.展开更多
To ensure the stability of a tunnel during construction, rock bolts are usually installed, which affects the stress distribution around the tunnel. Therefore, it is necessary to study the effects of rock bolting on th...To ensure the stability of a tunnel during construction, rock bolts are usually installed, which affects the stress distribution around the tunnel. Therefore, it is necessary to study the effects of rock bolting on the stress distribution around the tunnel. In this article, the effects of rock bolting on the stress distribution around the tunnel, including the pesition and orientation of bolts, the overburden depths, and the bolt lengths, are simulated using the ANSYS software with an elnstoplastic model. The effect of multiple bolts of 2 m and 1 m lengths on the stress distribution in the roof and on the lateral sides of a tunnel and at different overburden depths is considered. An important finding is that the tensile stress region that is very dangerous for rock in the bottom of the tunnel grows rapidly with increasing overburden depths when rock bolts are installed only in the roof or on the lateral sides of a tunnel. The determination of the length of the rock bolt used around a tunnel is dependent on the loads and the integrity of the rock mass around the tunnel. In addition, rock bolting around the tunnel can obviously reduce the coefficients and the size of the region of stress concentration, especially when installed in high-stress areas. This fact is very important and essential for the design of tunnels and ensures engineering safety in tunnel engineering.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.52208419)Science and Technology Innovation Program of Hunan Province,China(Grant No.2022RC1030)Project of Scientific Research of Hunan Provincial Department of Education,China(Grant No.21C0187).
文摘The subgrade soil is generally in saturated or unsaturated condition. To analyze complex thermo-hydro-mechanical-chemical (THMC) behaviors of subgrade, it is essential to determine the soil–water characteristic curve (SWCC) that represents the relationship between matric suction and moisture content. In this study, a full-automatic rapid stress-dependent SWCC pressure-plate extractor was developed. Then, the influences of overburden stress and degree of compaction on the SWCC of subgrade soil such as high liquid limit silt (MH) and low liquid limit clay (CL) were analyzed. Accordingly, a new model taking into account the influences of overburden stress and degree of compaction based on the well-known Van Genuchten (VG) SWCC fitting model was presented and validated. The results show that with the increase of the degree of compaction and overburden stress, the saturated moisture content of subgrade soil decreases, while the air-entry value increases and the transition section curve becomes flat. The influences of the degree of compaction and overburden stress on the SWCC of MH is greater than that of CL. Meanwhile, there was a satisfactory agreement between the prediction and measurement, indicating a good performance of the new model for predicting the SWCC.
基金the National Natural Science Foundation of China (Grant No.51379066)the Fundamental Research Funds for the Central Universities (Grant No.2016B03514)+1 种基金the National Key Technology Support Program (Grant No.2015BAB07B05)the Key Laboratory of Earth-Rock Dam Failure Mechanism and Safety Control Techniques (Grant No.YK913007).
文摘The cut-off wall in a clay-core rockfill dam built on a thick overburden layer is subjected to a large compressive pressure under the action of the loads such as the dead weight of both the dam and the overburden layer, the frictional force induced by the differential settlement between the cut-off wall and surrounding soils, and the water pressure. Thus, reduction of the stress of the cut-off wall has become one of the main problems for consideration in engineering design. In this paper, numerical analysis of a core rockfill dam built on a thick overburden layer was conducted and some factors influencing the stress-strain behaviors of the cut-off wall were investigated. The factors include the improvement of the overburden layer, the modeling approach for interfacial contact between the cut-off wall and surrounding soils, the modulus of the cut-off wall concrete, and the connected pattern between the cut-off wall and the clay core. The result shows that improving the overburden layer,selecting plastic concrete with a low modulus and high strength, and optimizing the connection between the cut-off wall and the clay core of the dam are effective measures of reducing the deformations and compressive stresses of the cut-off wall. In addition, both the Goodman element and the mud-layer element are suitable for simulating the interfacial contact between the cut-off wall and surrounding soils.
基金sponsored by ACARP, BHP Billiton Illawarra Coal and CSIRO
文摘This paper describes a field and numerical investigation of the overburden strata response to underground longwall mining, focusing on overburden strata movements and stress concentrations.Subsidence related high stress concentrations are believed to have caused damage to river beds in the Illawarra region, Australia. In the field study, extensometers, stressmeters and piezometers were installed in the overburden strata of a longwall panel at West Cliff Colliery. During longwall mining, a total of1000 mm tensile deformation was recorded in the overburden strata and as a result bed separation and gaps were formed. Bed separation was observed to start in the roof of the mining seam and gradually propagate toward the surface as the longwall face advanced. A substantial increase in the near-surface horizontal stresses was recorded before the longwall face reached the monitored locations. The stresses continued to increase as mining advanced and they reached a peak at about 200 m behind the longwall face. A numerical modelling study identified that the angle of breakage(i.e., the angle of the boundary of caved zone) behind the longwall face and over the goaf was 22–25° from vertical direction. This is consistent with the monitoring results showing the high gradient of stresses and strains on the surface150–320 m behind the mining face.
基金Acknowledgments The program was supported by the National Natural Science Foundation of China （51427804） and the Open Found of State Key Laboratory of Deep Coal Mining ＆ Environment Protection.
文摘To ensure the stability of a tunnel during construction, rock bolts are usually installed, which affects the stress distribution around the tunnel. Therefore, it is necessary to study the effects of rock bolting on the stress distribution around the tunnel. In this article, the effects of rock bolting on the stress distribution around the tunnel, including the pesition and orientation of bolts, the overburden depths, and the bolt lengths, are simulated using the ANSYS software with an elnstoplastic model. The effect of multiple bolts of 2 m and 1 m lengths on the stress distribution in the roof and on the lateral sides of a tunnel and at different overburden depths is considered. An important finding is that the tensile stress region that is very dangerous for rock in the bottom of the tunnel grows rapidly with increasing overburden depths when rock bolts are installed only in the roof or on the lateral sides of a tunnel. The determination of the length of the rock bolt used around a tunnel is dependent on the loads and the integrity of the rock mass around the tunnel. In addition, rock bolting around the tunnel can obviously reduce the coefficients and the size of the region of stress concentration, especially when installed in high-stress areas. This fact is very important and essential for the design of tunnels and ensures engineering safety in tunnel engineering.
