STRENGTHENING THE FOUNDATIONS OF PHYSICALLY OBSOLETE BUILDINGS

The problems and prospects of existing methods of strengthening the foundations of physically obsolete buildings are outlined, which is relevant for the preservation of buildings of architectural and historical value, as well as for mass renovation in large cities in cramped conditions with a high density of existing buildings. Method of calculation of hollow rectangular and round sections filled with concrete during bending is considered. In this article the dependence of compacted zone radius on initial characteristic of soil density and diameter of pressed pipe concrete element is analyzed. The conclusion is formed that the method of arrangement of the pipe-concrete horizontal distributor for simultaneous reinforcement of soil of the base and foundations chosen for the study allows to regulate the process of leveling the building settlement as a whole, and is also the most environmentally safe and does not negatively affect the surrounding buildings and structures.

Optimization of the Plastic Area of a Borehole Based on the Gas Extraction Effect and Its Engineering Application

Gas extraction is most commonly used to control gas disasters in coal mines. The distribution of the plastic zone around a borehole and the sealing quality are key factors affecting gas extraction. In this paper, the plastic zone was simulated by COMSOL, and a theoretical equation of the plastic zone radius was derived. In addition, an antispray hole equipment and the “two plugging and one injection” sealing technology were proposed. The results show that a larger borehole pore size corresponds to a larger plastic zone and larger range of pressure relief of the borehole. The error between the calculated and simulated plastic zone radii is within 1%, and the modified equation is applicable to Puxi mine. The loss and harm caused by borehole spraying are reduced by applying antispray hole equipment. By applying the “two plugging and one injection” sealing technology and phosphogypsum-based self-produced gas expansion paste material to block the borehole, the sealing quality is improved and an accurate gas mixing flow, pure flow, and concentration were obtained. As the plastic zone enlarges, the gas extraction flow gradually increases with, but the relative variation of flow first increases and subsequently decreases. Considering the safety and economy of construction, the optimal radius of the plastic zone is 64.9 mm.

Elastoplastic Analysis for Circular Tunnel Based on Modified Lade Criterion considering Strain Softening and Dilatancy

Modified Lade criterion can not only describe the strength properties of many kinds of rocks well but also has simple and practical parameters. Although the elastoplastic solution of circular tunnel has been extensively investigated, the method based on modified Lade criterion considering the effect of the intermediate principal stress, strain-softening behavior, and dilatancy has not yet been studied. In this paper, a new numerical procedure based on modified Lade criterion is proposed to calculate the elastoplastic solutions for surrounding rock of the circular tunnel. The comparisons of stress, displacement, and plastic zone radius are carried out between the presented method and published literatures under axisymmetric and nonaxisymmetric original in situ stress field. Finally, a series of parametric analyses are executed and discussed. It can be concluded that the lateral pressure coefficient, λ, influences both the size of plastic zone and the development direction. The plastic zone radius shows a negative power function change with increasing critical deviatoric plastic strain and increases slightly with increasing dilation angle, ψ.

Improving the tensile property calculations with plastic zone radius measurements in depth-sensing spherical indentation tests

Depth-sensing spherical indentation tests (SITs) have been widely used in tensile property calculations, but the accuracy and reproducibility of calculations may be significantly influenced by displacement measurement errors. Taking two representative tensile property calculation methods as examples, namely the analytical and numerical methods, the rationale as to why accurate and reproducible tensile property calculations cannot be expected from the depth-sensing SITs was discussed in detail. Subsequently, the proportional limit σ0 calculation from plastic zone radius rp measurements, which was analytically developed in the expanding cavity model (ECM) and experimentally measured by digital image correlation (DIC), was introduced to enhance the accuracy and reproducibility of the two representative methods. Principles for setting the strain threshold εth were established, and factors influencing the σ0 calculation from rp measurements were investigated through the optical system, the friction condition, the hardening behaviors of specimen materials, and the indentation depth. Through finite element calculations, it was proven that tensile property calculations at the existence of displacement measurement errors, particularly the constant error from the origin correction, can be significantly improved with the introduction of rp measurements. Similar findings were also observed in experiments on four metals that exhibited different hardening behaviors.

Mechanical Characteristic and Length Optimization of System Anchor in Loess Tunnel Based on Field Measurement and Analytical Solution

In this paper, field measurement is used to obtain the force of system anchor in its actual working condition and stress situation of system anchors in different parts of loess tunnel is analyzed based on field test results, indicating the reasons why values of measured axial force of system anchor are different in different parts of loess tunnel. Based on the displacement solution of Mindlin problem, this paper deduces the analytical solution to stress distribution of system anchors in the sidewall of loess tunnel under the pull-out force, analyzes the distribution forms and influencing factors of shear stress and axial force. At the same time, analytical solutions to system anchor stress and surrounding rock plastic zone radius are tentatively applied to the analysis of stress characteristics and length optimization of system anchor in loess tunnel. The research results are of great significance to understand the mechanical characteristics of anchors in loess tunnel and to optimize the design of anchors in the primary support system of loess tunnel, which leads to accelerated construction progress and low economically cost, especially in loess tunnels with large cross section and long span.

Unified Analytical Solutions of Circular Tunnel Excavated in an Elastic-Brittle-Plastic Rock Mass considering Blast-Induced Damage and Dead Weight Loading

Stress and deformation around circular tunnel are crucial for optimizing the support system and evaluating the tunnel stability. The damage zone induced by blasting or mechanical excavation can dramatically influence the support design and methods because the self-weight of broken rock mass at the roof of the tunnel can exert a high pressure on the support system, leading to the support system instability due to the overload. This paper presents a new closed-form solution for analyzing the stress and deformation of deep circular tunnel excavated in elastic-brittle rock mass with the consideration of the rock gravity and damage zone by using the unified strength criterion. A new modified equilibrium equation in the fracture zone is used to determine the stress and the radius of fracture zone. The correctness of the solution is also verified by comparison with the numerical simulation results. The results illustrate that the rock gravity, damage zone radius, and intermediate principal stress have an extremely important influence on the ground response. The tunnel surface convergence and damage zone radius with the consideration of the gravity are obviously larger than those without consideration of the gravity. The rock gravity effect under the high intermediate principal stress gradually weakens, illustrating that the intermediate principal stress is beneficial to tunnel stability. Large deformation instability of the tunnel is dependent on the extension of damage zone. The larger the radius of damage zone, the larger both fracture range and tunnel surface deformation. The proposed solution in this study is novel and can be used to assess the ground convergence for different scenarios and to optimize the support system during the early design stage of the tunnel.

Determining an optimum zone radius for zone routing protocol (ZRP) based on node mobility

Mobility is one of the important issues in Mobile Ad hoc Networks (MANET). By definition, MANET nodes are free to move around and this may cause difficulty in routing. MANET routing protocols must consider this factor when making routing decision. Zone Routing Protocol (ZRP) is a hybrid routing protocol, which utilizes the proactive and reactive routing protocols advantages. ZRP proactively maintains routing information within a routing zone, while reactively discovering routes to destinations beyond the routing zone. Since ZRP is based on the concept of routing zone, determining an optimum routing zone radius has the major impact on the performance of that protocol. In this research, we studied the effect of zone radius on the performance of ZRP with different levels of node mobility. Node mobility is defined using two different parameters: node speed and pause time. Based on the simulation results, ZRP protocol using zone radius of two provides the best packet delivery fraction, throughput and normalized routing load. However, a larger zone radius will provide a lower delay.

Evolution regularity of temperature field of active heat insulation roadway considering thermal insulation spraying and grouting: A case study of Zhujidong Coal Mine, China

To study the active heat insulation roadways of high-temperature mines considering thermal insulation and injection, a high-temperature −965 m return air roadway of Zhujidong Coal Mine (Anhui Province, China) is selected as a prototype. The ANSYS numerical simulation method is used for the sensitivity analysis of heat insulation grouting layers with different thermal conductivities and zone ranges and heat insulation spray layers with different thermal conductivities and thicknesses; thus, their effects on the heat-adjusting zone radius, surrounding rock temperature field, and wall temperature are studied. The results show that the tunneling head temperature of the Zhujidong Mine is >27°C all year round, consequently causing serious heat damage. The heat insulation circle formed by thermal insulation spraying and grouting can effectively alleviate the disturbance of roadway airflow to the surrounding rock temperature field, thereby significantly reducing the heat-adjusting zone radius and wall temperature. The decrease in the thermal conductivities of the grouting and spray layers, expansion of the grouting layer zone, and increase in the spray layer thickness help effectively reduce the heat-adjusting zone radius and wall temperature. This trend decreases significantly with the ventilation time. A sensitivity analysis shows that the use of spraying and grouting materials of low thermal conductivity for thermal insulation is a primary factor in determining the temperature field distribution, while the range of the grouting layer zone and the spray layer thickness are secondary factors. The influence of the increased surrounding rock radial depth and ventilation time is negligible. Thus, the application of thermal insulation spraying and grouting is essential for the thermal environment control of mine roadways. Furthermore, the research and development of new spraying and grouting materials with good thermal insulation capabilities should be considered.

Mathematical interpretation of avian egg shapes

The general principles of ovoid shapes and their mathematical interpretation were considered concerning previous data and experience. Previously, bird egg description was carried out using the composite ovoid model. According to this model, an ovoid is considered as a set of arcs with a smooth transition between them. The studied group of eggs was named true ovoid. They differ from other forms in size of their infundibular zone radius (thick end) that is almost equal to half of the diameter (0.5D ± 0.01 ˂ ri = 0.5D).We suggested that this commonality, a priori, implies the presence of an abstract geometric model, which is a satisfactory solution and logical approach for analyzing the diversity of natural ovoids. Such a model is a system of circles passing into each other. This allows, within a single system, to assign a vendor code to each form, which involves the name, geometric shape, and quantitative parameters that can be implemented in bird taxonomy.Early, 0.01 D was chosen as the model difference value and the ratio of symmetrical eggs in the analyzed database was 1.1%. In this research, we extended the difference value to 0.05 D and this covered 6.0% of the egg shapes. This is the maximum interval at which the curvature of the polar zones does not visually differ. We revealed that the variability in the egg shapes depends on the radii of curvature of the lateral and polar arcs. The larger the radius of the lateral arches, the greater the degree of freedom for variation of the lateral arches. We supposed that our data could associate any form of bird egg with its biological content. In turn, many ovoid features relevant to other natural objects can be used in bird taxonomical study.

The effect of network size and density to the choice of zone radius in ZRP

<span>Mobile Ad hoc Network (MANET) is a network that consists of several nodes that connect without using a permanent infrastructure. Each node in MANET moves inside and outside of the network freely and randomly. The free and random movements of nodes may cause the topology of the network to change constantly. Therefore, the task of finding routes between nodes is a big challenge. Routing protocols in MANET can be divided into three categories, namely, proactive, reactive and hybrid routing protocols. Hybrid routing protocols such as the Zone Routing Protocol (ZRP) combines the advantages of both proactive and reactive routing protocols by dividing the network area into many overlapping zones. Data transmission to nodes within the zone is done using a proactive routing mechanism, while data transmission to nodes outside the zone is done using a reactive routing mechanism. The zone radius in ZRP determines how much proactive and reactive routing is used, and therefore plays a key role in determining the performance of the network. In this paper, the performance of the ZRP routing protocol is evaluated using the NS2.33 network simulator. The focus of the research is to evaluate the ZRP performance concerning the network size and density to identify an optimum ZRP zone size that will provide good performance. The performance is evaluated by using four performance metrics which are normalized routing load, average end-to-end delay, throughput, and packet delivery fraction. The results show that ZRP produces the best performance when the zone radius size is equal to two hops.</span>