scholarly journals Constraint Embankment Construction to Prevent the Collapse of Underground Caves

2019 ◽  
Vol 2019 ◽  
pp. 1-18
Author(s):  
Zhen Zhang ◽  
Zhongda Chen
Keyword(s):  
Tensile Strength ◽  
Rock Mass ◽  
Numerical Solutions ◽  
Geological Strength Index ◽  
Concrete Slabs ◽  
Construction Specifications ◽  
Reinforced Concrete Slabs ◽  
Local Construction ◽  
Embankment Height ◽  
The Stability

Dozens of underground karst caves were found before constructing the Changli highway. The thickness-to-span ratio of nearly half of the caves is less than 0.05, and the greatest ratio is only 0.35, far less than the value demanded by local construction specifications (0.8). The caves located at K50 + 700 and K178 + 800 are by far the only two caves that have become unstable. Only one passive measure was taken when constructing the highway, i.e., building 0.5 m thick continuous reinforced concrete slabs above the embankment; this measure did not contribute to the improvement of the stability of the underground caves. Numerical solutions based on strength reduction and analytical solutions based on the beam hypothesis are used to assess the stability of underground caves. The capacity of an underground cave to bear embankment construction is observed to be proportional to the tensile strength of the rock mass and the square of the thickness-to-span ratio of the cave roof. The tensile strength of the rock mass is ψ times lower than that of the intact rock. The value of ψ is mainly determined by the geological strength index (GSI). To prevent instability of underground caves, the embankment height should be reasonably controlled. However, local construction specifications requiring that the thickness-to-span ratio of underground cave be greater than 0.8 are conservative.

scholarly journals STUDY OF A STRUCTURE SUSPENDED FROM A SYSTEM OF STEEL COLUMNS AND TRUSSES (SYSTEM AND STABILITY)

2020 ◽  
Vol 9 (9) ◽  
pp. 43-54
Keyword(s):  
Reinforced Concrete ◽  
Lateral Force ◽  
Concrete Slabs ◽  
Structural Constraints ◽  
Steel Columns ◽  
Force Method ◽  
Reinforced Concrete Slabs ◽  
The Stability

Throughout history, men always wanted to build structures that are each more impressive than the next, while rising higher in the air. In this process, men were not satisfied with making sure that these structures were beautiful, impressive and majestic, but that they could also be very useful, that they fulfilled a function, and that they were able to resist the various structural constraints that will be imposed on it, or that could be imposed on it. With this in mind, we thought of creating a structure that could both inspire this side of wonder and structural beauty, while being useful and resistant to the loads imposed on it. In this work, we are going to talk about a building suspended to its foundation, in the sense that the building does not rest directly on the ground, but is suspended nearly eight meters from the ground by each of the three columns which support the said building by a system of trusses. The structure is made of steel with reinforced concrete slabs, which gives it a significant advantage in terms of weight. Another advantage is that it reacts quite well to earthquakes, showing only very small deflections using the equivalent lateral force method. In this work we will focus on the stability of the members of the system that carries the building and the stability of the building in general.

scholarly journals Analysis of Fiber-Reinforced Concrete Slabs under Centric and Eccentric Load

Materials ◽  
2021 ◽  
Vol 14 (23) ◽  
pp. 7152
Author(s):  
Zuzana Marcalikova ◽  
Vlastimil Bilek ◽  
Oldrich Sucharda ◽  
Radim Cajka
Keyword(s):  
Tensile Strength ◽  
Reinforced Concrete ◽  
Concrete Slab ◽  
Fiber Reinforced Concrete ◽  
Experimental Program ◽  
Concrete Slabs ◽  
Detailed Knowledge ◽  
Fiber Reinforced ◽  
Reinforced Concrete Slabs ◽  
3D Deformation

Research on the interaction between slabs and subsoil involves the field of materials engineering, concrete structures, and geotechnics. In the vast majority of cases, research focuses on only one of these areas, whereas for advanced study and computer simulations, detailed knowledge of the whole task is required. Among the new knowledge and information upon which this article focuses is the evaluation of subsoil stress using specialized pressure cells, along with detailed measurements of the deformation of a fiber-reinforced concrete slab. From a design point of view, this research is focused on the issue of the center of the cross section and the influence of eccentricity. Knowledge in this area is not yet comprehensively available for fiber-reinforced concrete slabs, where 2D deformation sections of the slab and 3D deformation surfaces of the slab are used in experiments. The experimental program includes a centrically and eccentrically loaded slab. These are structural elements that were tested on a specialized device. Both slabs had the same concrete recipe, with a dispersed reinforcement content of 25 kg/m3. The dimensions of the slab were 2000 × 2000 × 150 mm. Laboratory tests assessed compressive strength, the modulus of elasticity, splitting tensile strength, and bending tensile strength. Based on approximate data from the 3D deformation surfaces, an evaluation of the load-displacement diagrams for the center of the slab and for the center of eccentricity was performed. In conclusion, an overall evaluation and discussion of the results relies on experiments and the mechanical properties of fiber-reinforced concrete.

scholarly journals A novel solution for ground reaction curve of tunnels in elastoplastic strain softening rock masses

2017 ◽  
Vol 23 (6) ◽  
pp. 773-786 ◽  
Author(s):  
Ali GHORBANI ◽  
Hadi HASANZADEHSHOOIILI
Keyword(s):  
Rock Mass ◽  
Strain Softening ◽  
Numerical Solutions ◽  
Polynomial Regression ◽  
Parameter Determination ◽  
Geological Strength Index ◽  
Support Pressure ◽  
Rock Masses ◽  
Reaction Curve ◽  
Ground Reaction Curve

Ground Reaction Curve (GRC) is one of the most important elements of convergence-confinement method generally used to design tunnels. Realistic presentation of GRC is usually assessed based on the advanced rock strength criteria, also, rock mass behavior (including plasticity and softening treatments). Since taking these parameters into ac­count is not simply possible for practitioners and needs complicated coupled theoretical-numerical solutions, this paper presents a simple novel approach based on Evolutionary Polynomial Regression to determine GRC of rock masses obeying both Mohr-Coulomb and Hoek-Brown criteria and strain softening behaviors. The proposed models accurately present support pressures based on radial displacement, rock mass strength and softening parameter (determination coefficient of 97.98% and 94.2% respectively for Mohr-Coulomb and Hoek-Brown strain softening materials). The ac­curacy of the proposed equations are approved through comparing the EPR developed GRCs with the ground reaction curves available in the literature. Besides, the sensitivity analysis is carried out and in-situ stress, residual Hoek-Brown’s m constant and residual dilation angle are introduced as parameters with the most influence on the support pressure in Hoek-Brown and peak and residual geological strength index are the most affective parameters on the support pressure of tunnels in the strain softening Mohr-Coulomb rock mass.

scholarly journals Analysis of rock mass behavior with Empirical and Numerical method for the construction of diversion tunnel, Laos

2022 ◽  
Vol 1212 (1) ◽  
pp. 012028
Author(s):  
D J W Mboussa ◽  
S Sun
Keyword(s):  
Numerical Modeling ◽  
Rock Mass ◽  
Field Investigation ◽  
Geological Strength Index ◽  
Rock Masses ◽  
Mountain Area ◽  
Diversion Tunnel ◽  
The Stability ◽  
The Cost ◽  
The Impact

Abstract Tunneling construction in the mountain area is a challenge for engineers and geotechnicians because of instability due to the presence of discontinuities. The objective of this paper is the modeling of surrounding rock masses for the stability of the diversion tunnel to predict the behavior of rock masses during the excavation process for the Nam Phoun hydropower station project in Laos. Field investigation and laboratories test was realized; Empirical methods as Rock mass designation and Geological Strength Index were performed, rock masses were classified in three categories (RM-1, RM-2, and RM-3); in situ stresses were obtained from existing equations, numerical modeling was performed by the 2D plane strain finite element code Phase2 developed by Rocscience, using Generalized Hoek-Brown criterion for each type of rock masses. The results of numerical modeling show the strength zones of stresses and deformations around the tunnel and predict the instabilities around the tunnel during excavations processes. Thus, for all rock’s masses, it will be necessary to consider an analysis for the supports design before the excavation’s process. The findings of this study allow a clearer understanding of the importance to assess a predictive analysis of slope stability during the feasibility phase of a project by engineers to have an idea of instabilities and its significant in preventing the impact on the cost of the project.

scholarly journals Experimental and Numerical Investigations on Flexural Behaviour of Prestressed Textile Reinforced Concrete Slabs

2021 ◽  
Vol 7 (6) ◽  
pp. 1084-1097
Author(s):  
Dang Quang Ngo ◽  
Huy Cuong Nguyen
Keyword(s):  
Tensile Strength ◽  
Reinforced Concrete ◽  
Three Dimensional ◽  
Concrete Slabs ◽  
High Tensile Strength ◽  
Flexural Behaviour ◽  
Textile Reinforced Concrete ◽  
Prestressing Steel ◽  
Reinforced Concrete Slabs ◽  
Three Dimensional Finite Element

Nowadays, concrete is mostly prestressed with steel. But the application of prestressing steel is restricted in a highly corrosive environment area due to corrosion of prestressing steel, leading to a reduction in strength and may cause sudden failure. Carbon textile is considered an alternate material due to its corrosive resistance property, high tensile strength, and perfectly elastic. Prestressing is also the only realistic way to utilize fully ultra-high tensile strength in carbon textile material. In this study, experimental and numerical analyses were carried out for the flexural behaviour of prestressed and non-prestressed carbon textile reinforced concrete slabs. This study also focuses on the influences of textile reinforcement ratios, prestressing grades on the flexural behaviour of carbon textile reinforced concrete (TRC). Fifteen precast TRC slabs were tested, of which six were prestressed to various levels with carbon textile. The obtained results show that prestressing textile reinforcement results in a higher load-bearing capacity, stiffness, and crack resistance for TRC slabs. The first-crack load of the prestressed specimens increased by about 85% compared with those of non-prestressed slabs. Three-dimensional finite element models were developed to provide a reliable estimation of global and local response. The modeling techniques accurately reproduced the experimental behaviour. Doi: 10.28991/cej-2021-03091712 Full Text: PDF

scholarly journals Structural analysis and design of irregular shaped reinforced concrete slabs using a simplified design method

2020 ◽  
Vol 3 (4) ◽  
pp. 276-288
Author(s):  
Mohammed Salem Al-Ansari ◽  
Muhammad Shekaib Afzal
Keyword(s):  
Reinforced Concrete ◽  
Numerical Solutions ◽  
Design Method ◽  
Structural Safety ◽  
Concrete Slabs ◽  
Analysis And Design ◽  
Finite Element Software ◽  
Reinforced Concrete Slabs ◽  
Simplified Method ◽  
Simplified Design Method

This paper presents a simplified method to analyze and design the irregular reinforced concrete slabs based on structural safety and economy. The triangular, trapezoidal, and curved slab sections are selected in this study to be analyzed and designed using a simplified design method approach (SDM) as these sections are the most common type of irregular slab sections used in the construction industry. Flexural design formulas for triangular and curved slabs are derived based on the theoretical principles of plate and yield line theories and ACI building code of design constraints. Numerical examples are presented in this study to illustrate the method capability of designing the most commonly used irregular slabs sections. The complete design of four triangular slabs (TS-1 to TS-4) and four curved slabs (CS-1 to CS-4) is provided in this study. Besides, the required equivalent (triangular and rectangular) shaped sections are provided to deal with irregular trapezoidal slab section. The selected irregular slab sections (triangular and curved slab sections) are also analyzed and designed using the computer software (SAFE) and the results obtained are compared with the numerical solutions. The percentage difference of the simplified method with the finite element software (SAFE) ranges from 4% to 12%. The results obtained for all the selected irregular shaped slab sections indicates that the SDM is a good and quick approach to design irregular (triangular and curved) slab sections.

scholarly journals Stability Assessment of Rock Mass System under Multiple Adjacent Structures

Systems ◽  
2022 ◽  
Vol 10 (1) ◽  
pp. 5
Author(s):  
Bo Sung Kim ◽  
Joon Kyu Lee
Keyword(s):  
Rock Mass ◽  
Numerical Solutions ◽  
Algebraic Expression ◽  
Mass System ◽  
Adjacent Structures ◽  
Mass Properties ◽  
Real Performance ◽  
The Stability ◽  
Strip Footings ◽  
Complicated Task

Numerical modeling is important for exploring the fundamental processes occurring in rock and for evaluating the real performance of structures built on and in rock mass system, and thus for supporting the design of rock engineering problems. Estimating the stability of rock mass foundation systems entirely based on a theoretical approach is a complicated task if there exists overlapping of their potential collapse modes. This paper applies finite element limit analysis to evaluate the bearing capacity of equally spaced multiple strip footings resting on rock mass obeying the modified non-linear Hoek–Brown failure criterion. Numerical solutions are expressed in terms of the efficiency factor that is dependent on the spacing between footings, as well as the rock mass properties. In addition, the effects of surface surcharge and footing roughness are quantified. The maximum spacing at which the interfering effect of adjacent footings becomes disappeared is evaluated and an algebraic expression for approximating the maximum spacing is proposed. Failure mechanisms for a few cases of rock mass under multiple strip footings are examined.

scholarly journals Seismic stability analysis of rock slopes by yield design theory using the generalized Hoek-Brown criterion

2018 ◽  
Vol 149 ◽  
pp. 02026
Author(s):  
Mounir Belghali ◽  
Zied Saada
Keyword(s):  
Rock Mass ◽  
Stability Analysis ◽  
Design Theory ◽  
Rock Slope ◽  
Numerical Solutions ◽  
Stability Study ◽  
Seismic Stability ◽  
Rock Slopes ◽  
The Stability ◽  
Kinematic Approach

The stability of rock slope is studied using the kinematic approach of yield design theory, under the condition of plane strain and by considering the last version of the Hoek-Brown failure criterion. This criterion, which is suitable to intact rock or rock mass highly fractured regarded as isotropic and homogeneous, is widely accepted by the rock mechanics community and has been applied in numerous projects around the world. The failure mechanism used to implement the kinematic approach is a log-spiral rotational mechanism. The stability analysis is carried out under the effects of gravity forces and a surcharge applied along the upper plateau of the slope. To take account of the effects of forces developed in the rock mass during the passage of a seismic wave, the conventional pseudo-static method is adopted. This method is often used in slope stability study for its simplicity and efficiency to simulate the seismic forces. The results found are compared with published numerical solutions obtained from other approaches. The comparison showed that the results are almost equal. The maximum error found is less than 1%, indicating that this approach is effective for analyzing the stability of rock slopes. The relevance of the approach demonstrated, investigations are undertaken to study the influence of some parameters on the stability of the slope. These parameters relate to the mechanical strength of the rock, slope geometry and loading.

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