Design and performance evaluation of vertical shafts: rational shaft design method and verification of design method

1988 ◽  
Vol 25 (2) ◽  
pp. 320-337 ◽  
Author(s):  
R. C. K. Wong ◽  
P. K. Kaiser
Keyword(s):  
Design Method ◽  
Three Dimensional ◽  
Earth Pressure ◽  
In Situ Stress ◽  
Cohesive Soils ◽  
Strength Parameters ◽  
Yield Zone ◽  
Ground Deformations ◽  
And Performance

Ground deformations around axisymmetric shafts cannot be determined with the design approaches currently available, which are mostly based on plasticity methods. The convergence–confinement method (usually applied to tunnels), with consideration of gravitational effects and the three-dimensional conditions near a shaft, is proposed as a tool to predict formation pressure on a shaft and radial ground displacements. It is shown that the behaviour of a shaft is governed by (1) the mode of yield initiation dominated by the in situ stress state and the soil strength parameters and (2) the extent of the yield zone that develops if wall displacements are allowed to occur during construction.Closed-form solutions are presented to approximate the pressure–displacement relationship for cohesionless and cohesive soils. Results from this approach compare well with those obtained by finite element analyses. The conventional design methods that provide the minimum support pressures required to maintain stability are not conservative. These pressures are generally less than those actually encountered if ground movements during construction are restricted with good ground control. Key words: shaft, design method, support, interaction, yielding, stress, displacement, earth pressure, arching.

scholarly journals The Influence of Bedding Planes and Permeability Coefficient on Fracture Propagation of Horizontal Wells in Stratification Shale Reservoirs

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-19
Author(s):  
Yuepeng Wang ◽  
Xiangjun Liu ◽  
Lixi Liang ◽  
Jian Xiong
Keyword(s):  
Permeability Coefficient ◽  
In Situ Stress ◽  
Stress Difference ◽  
Strength Parameters ◽  
Breakdown Pressure ◽  
Permeability Coefficients ◽  
Bedding Planes ◽  
Initiation Pressure ◽  
Shale Reservoirs

The complexity of hydraulic fractures (HF) significantly affects the success of reservoir reconstruction. The existence of a bedding plane (BP) in shale impacts the extension of a fracture. For shale reservoirs, in order to investigate the interaction mechanisms of HF and BPs under the action of coupled stress-flow, we simulate the processes of hydraulic fracturing under different conditions, such as the stress difference, permeability coefficients, BP angles, BP spacing, and BP mechanical properties using the rock failure process analysis code (RFPA2D-Flow). Simulation results showed that HF spread outward around the borehole, while the permeability coefficient is uniformly distributed at the model without a BP or stress difference. The HF of the formation without a BP presented a pinnate distribution pattern, and the main direction of the extension is affected by both the ground stress and the permeability coefficient. When there is no stress difference in the model, the fracture extends along the direction of the larger permeability coefficient. In this study, the in situ stress has a greater influence on the extension direction of the main fracture when using the model with stress differences of 6 MPa. As the BP angle increases, the propagation of fractures gradually deviates from the BP direction. The initiation pressure and total breakdown pressure of the models at low permeability coefficients are higher than those under high permeability coefficients. In addition, the initiation pressure and total breakdown pressure of the models are also different. The larger the BP spacing, the higher the compressive strength of the BP, and a larger reduction ratio (the ratio of the strength parameters of the BP to the strength parameters of the matrix) leads to a smaller impact of the BP on fracture initiation and propagation. The elastic modulus has no effect on the failure mode of the model. When HF make contact with the BP, they tend to extend along the BP. Under the same in situ stress condition, the presence of a BP makes the morphology of HF more complex during the process of propagation, which makes it easier to achieve the purpose of stimulated reservoir volume (SRV) fracturing and increased production.

scholarly journals Damage Adaptive Titanium Alloy by In-Situ Elastic Gradual Mechanism

Materials ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 406
Author(s):  
Siqian Zhang ◽  
Jing Liu ◽  
Haoyu Zhang ◽  
Jie Sun ◽  
Lijia Chen
Keyword(s):  
Titanium Alloy ◽  
Damage Tolerance ◽  
Three Dimensional ◽  
Crack Tip ◽  
In Situ Stress ◽  
Crack Deflection ◽  
Adaptive Mechanism ◽  
Ultrafine Grained ◽  
Elastic Gradient

Natural materials are generally damage adaptive through their multilevel architectures, with the characteristics of compositional and mechanical gradients. This study demonstrated that the desired elastic gradient can be in-situ stress-induced in a titanium alloy, and that the alloy showed extreme fatigue-damage tolerance through the crack deflection and branch due to the formation of a three-dimensional elastically graded zone surrounding the crack tip. This looks like a perceptive and adaptive mechanism to retard the crack: the higher stress concentrated at the tip and the larger elastic gradient to be induced. The retardation is so strong that a gradient nano-grained layer with a thickness of less than 2 μm formed at the crack tip due to the highly localized and accumulated plasticity. Furthermore, the ultrafine-grained alloy with the nano-sized precipitation also exhibited good damage tolerance.

scholarly journals Exploring Deep-Rock Mechanics through Mechanical Analysis of Hard-Rock In Situ Coring System

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Jianan Li ◽  
Heping Xie ◽  
Ling Chen ◽  
Cong Li ◽  
Zhiqiang He
Keyword(s):  
Rock Mechanics ◽  
Hard Rock ◽  
Design Method ◽  
Drill Pipe ◽  
In Situ Stress ◽  
Drilling Depth ◽  
Innovative Design ◽  
The Core ◽  
Deep Rock

Exploration of deep-rock mechanics has a significant influence on the techniques of mining and rock mechanics. Rock coring technique is the basic method for all rock mechanics study. With the increase of the drilling depth and increasing strength of the hard rock, how to obtain high-quality rock core through various coring techniques is an eternal work. Here an innovative method is applied to design the new coring system to maximize the efficiency of operation. The stress conditions or parameters of rock core in the coring are analyzed, and the mechanism of the core with in situ stress is shown in this paper. The conflict of the core and coring tool chamber is proposed for the innovative design. The innovative design method is fulfilled by the theory of inventive problem solving (TRIZ). An improved coring system for the full-length core with in situ stress was obtained with the solutions of improved coring mechanism, cutting mechanism, and spiral drill pipe.

scholarly journals Experimental Study of Volumetric Fracturing Properties for Shale under Different Stress States

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Hongjian Wang ◽  
Jin Li ◽  
Fei Zhao ◽  
Jinyu Dong ◽  
Yanzong Cui ◽  
...  
Keyword(s):  
Crack Initiation ◽  
Shale Gas ◽  
Three Dimensional ◽  
In Situ Stress ◽  
Failure Strength ◽  
Constant Loading ◽  
One Dimensional ◽  
Shale Rock ◽  
Volumetric Fracturing

Shale gas can be commercially produced using the stimulated reservoir volume (SRV) with multistage fracturing or multiwell synchronous fracturing. These fracturing technologies can produce additional stress fields that significantly influence the crack initiation pressure and the formation of an effective fracture network. Therefore, this study primarily investigated the evolution of crack initiation and propagation in a hydraulic rock mass under various stress conditions. Combining the in situ stress characteristics of a shale reservoir and fracturing technology, three types of true triaxial volumetric fracturing simulation experiments were designed and performed on shale, including three-dimensional constant loading, one-dimensional pressurization disturbance, and one-dimensional depressurization disturbance. The results indicate that the critical failure strength of the shale rock increases as the three-dimensional constant loads are increased. The rupture surface is always parallel to the maximum principal stress plane in both the simulated vertical and horizontal wells. Under the same in situ stress conditions in the wellbore direction, if the lateral pressure becomes larger, the critical failure strength of shale rock would increase. Additionally, when the lateral in situ stress difference coefficient is smaller, the rock specimen has an evident trend to form more complex cracks. When the shale rock was subjected to lateral disturbance loads, the critical failure strength was approximately 10 MPa less than that in the state of constant loading, indicating that the specimen with disturbance loads is more likely to be fractured. Moreover, shale rock under the depressurization disturbance load is more easily fractured compared with the pressurization disturbance. These findings could provide a theoretical basis and technical support for multistage or multiwell synchronous fracturing in shale gas production.

In situ stress states and lateral deformations of soil–bentonite cutoff walls during consolidation process

2020 ◽  
Vol 57 (1) ◽  
pp. 139-148
Author(s):  
Xing Tong ◽  
Yu-Chao Li ◽  
Han Ke ◽  
Ying Li ◽  
Qian Pan
Keyword(s):  
Earth Pressure ◽  
Lateral Wall ◽  
In Situ Stress ◽  
Depth Range ◽  
Consolidation Process ◽  
Pressure Distributions ◽  
Cutoff Walls ◽  
Horizontal Strain ◽  
Stress States

A long-term in situ test was performed on two soil–bentonite (SB) cutoff walls with different dimensions. The total stresses and pore pressures in the walls were monitored for 8 months, and the lateral wall deformations were monitored for 15 months. The monitoring results revealed that the primary consolidation of the presented SB cutoff walls took approximately 8 months. In the first 5 days, the stress states of the walls were nearly isotropic. The total stresses were less than the geostatic stress, and the lateral wall deformations were negligible. As the consolidation developed, the total horizontal stresses in the walls decreased and then remained unchanged at most depths after 1 month, while the stresses at the bottoms continued decreasing. The nonlinear profiles of the horizontal effective stresses in the cutoff walls were similar to the active earth pressure distributions behind the retaining walls moving in translation mode. The trench sidewall movements were found in translation mode within a specific depth range. Obvious dependencies of the horizontal effective stress and the horizontal strain on the wall height were observed. Comparison with the literature illustrates the influence of backfill properties on the consolidation behavior of the SB cutoff walls.

scholarly journals Design and Performance Analysis of Contra-rotating Pumpjet Propulsor under Condition of Torque Unbalance

2018 ◽  
Vol 167 ◽  
pp. 03006
Author(s):  
Xiao-er Wang ◽  
Zhen-shan Zhang ◽  
Meng Zhang
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Design Method ◽  
Three Dimensional ◽  
Underwater Vehicle ◽  
Inverse Design ◽  
Parameter Design ◽  
Power Difference ◽  
Inverse Design Method ◽  
And Performance

In order to balance the torque of front rotor and rear rotor of underwater vehicle, the analysis of the speed triangles at the inlet and outlet of the front and rear rotor has been done. Then, the thought of using contra-rotating pumpjet to achieve the objective was raised. The stator is installed behind the rear rotor so as to ensure the overall torque of the propulsor balance, at the same time, the stator can also support the shroud of the propulsor. the parameter design of the rotor and the stator has been carried out by using the three dimensional inverse design method. At last, the performance of the designed pumpjet propulsor is obtained when it is installed on the underwater vehicle By using computational fluid dynamics. The results show that the total torque of the propulsor is reduced to 1.8 N * m on the design point although the power difference ratio of the front rotor and the rear rotor is 20%. The torque ratio is also reduced from 4.6% to 0.4%, which is good to meet the propulsor balance requirement and verifies the 3-D design method of pumpjet is effective.

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