建筑节能与岩棉外墙外保温技术分析

通过概述我国的能源形势,论述建筑节能的意义,并就岩棉外墙外保温技术的优缺点及性能进行了分析。     

Responses of jointed rock masses subjected to impact loading

Impact-induced damage to jointed rock masses has important consequences in various mining and civil engineering applications. This paper reports a numerical investigation to address the responses of jointed rock masses subjected to impact loading. It also focuses on the static and dynamic properties of an intact rock derived from a series of laboratory tests on meta-sandstone samples from a quarry in Nova Scotia, Canada. A distinct element code (PFC2D) was used to generate a bonded particle model (BPM) to simulate both the static and dynamic properties of the intact rock. The calibrated BPM was then used to construct large-scale jointed rock mass samples by incorporating discrete joint networks of multiple joint intensities into the intact rock matrix represented by the BPM. Finally, the impact-induced damage inflicted by a rigid projectile particle on the jointed rock mass samples was determined through the use of the numerical model. The simulation results show that joints play an important role in the impact-induced rock mass damage where higher joint intensity results in more damage to the rock mass. This is mainly attributed to variations of stress wave propagation in jointed rock masses as compared to intact rock devoid of joints.     

Reply to Discussion on “Empirical methods for determining shaft bearing capacity of semi-deep foundations socketed in rocks”

Semi-deep foundations socketed in rocks are considered to be a viable option for the foundations in the presence of heavy loads imposed by high-rise buildings and special structures, due to the low settlement and high bearing capacity. In this study, the unconfined compressive strength (UCS) and rock mass cuttability index (RMCI) have been applied to investigating the shaft bearing capacity. For this purpose, a comprehensive database of 178 full-scale load tests is compiled by adding a data set (n = 72) collected by Arioglu et al. (2007) to the data set (n = 106) presented in Rezazadeh and Eslami (2017). Using the database, the applicability and accuracy of the existing empirical methods are evaluated and new relations are derived between the shaft bearing capacity and UCS/RMCI. Moreover, a general equation in case of unknown rock types is proposed and it is verified by another set of data (series 3 in Rezazadeh and Eslami (2017)). Since rock-socketed shafts are supported by rock mass (not intact rock), a reduction factor for the compressive strength is suggested and verified in which the effect of discontinuities is considered using the modified UCS, based upon RMR and RQD to consider the effect of the rock mass properties.     

Shear strength criteria for rock,rock joints,rockfill and rock masses: Problems and some solutions

Although many intact rock types can be very strong, a critical confining pressure can eventually be reached in triaxial testing, such that the Mohr shear strength envelope becomes horizontal. This critical state has recently been better defined, and correct curvature or correct deviation from linear Mohr–Coulomb (M-C) has finally been found. Standard shear testing procedures for rock joints, using multiple testing of the same sample, in case of insufficient samples, can be shown to exaggerate apparent cohesion. Even rough joints do not have any cohesion, but instead have very high friction angles at low stress, due to strong dilation. Rock masses, implying problems of large-scale interaction with engineering structures, may have both cohesive and frictional strength components. However, it is not correct to add these, following linear M-C or nonlinear Hoek–Brown (H-B) standard routines. Cohesion is broken at small strain, while friction is mobilized at larger strain and remains to the end of the shear deformation. The criterion ‘c then σ_n tan φ’ should replace ‘c plus σ_ntan φ’ for improved fit to reality. Transformation of principal stresses to a shear plane seems to ignore mobilized dilation, and caused great experimental difficulties until understood. There seems to be plenty of room for continued research, so that errors of judgement of the last 50 years can be corrected.     

Numerical study on failure mechanism of tunnel in jointed rock mass

During underground excavation many surrounding rock failures have close relationship with joints. The stability study on tunnel in jointed rock mass is of importance to rock engineering, especially tunneling and underground space development. In this paper, a numerical code called RFPA was used to study the influence of different dip angle of layered joints and the lateral pressure coefficient on the stability of tunnel in jointed rock mass. Numerical analysis indicated that both the dip angle of joints and the lateral pressure coefficient have significant impacts on the failure mode and displacement characters of tunnel. The progressive failure processes of tunnel in jointed rock mass were presented and the mechanisms were discussed. The applicable condition of geographical method by Goodman is also discussed. These results offer a guideline in support design.     

A novel image-based approach for interactive characterization of rock fracture spacing in a tunnel face

This paper presents a novel integrated method for interactive characterization of fracture spacing in rock tunnel sections. The main procedure includes four steps:(1) Automatic extraction of fracture traces,(2)digitization of trace maps,(3) disconnection and grouping of traces, and(4) interactive measurement of fracture set spacing, total spacing, and surface rock quality designation(S-RQD) value. To evaluate the performance of the proposed method, sample images were obtained by employing a phot...     

Comparison and discussion on fragmentation behavior of soft rock in multi-indentation tests by a single TBM disc cutter

This paper is to investigate the mechanical responses and failure characteristics of soft rock in multi-indentation tests by a single TBM constant cross section (CCS) disc cutter. Different pre-set penetration depths and totally three cycles of indentation processes were employed in the repeated indentation tests conducted on the cubic cement mortar specimens. The load-penetration depth curve, penetration load, peak-load penetration depth, rock breakage work and compacted zone depth for the three indentation processes were analyzed. The strength and deformation properties and failure behavior of soft rock under different indentation conditions were revealed. The rock breakage behavior after several indentation processes still presents brittle failure characteristic with small pre-set penetration depths, but the specimens with large pre-set penetration depths appear obvious plastic failure mode. Approximately equal leap loads are obtained from both the intact specimen in direct indentation failure test and the weakened specimens after several indentation processes with different pre-set penetration depths, but the peak-load penetration depths for specimens with different pre-set penetration depths are varying. Curves of the cumulative penetration depth and cumulative rock breakage work both reach the corresponding peak values for one certain pre-set penetration depth. Along with this most unfavourable pre-set penetration depth, rock breakage efficiency is the lowest and energy consumption is the highest.     

Identification of structural domains considering the size effect of rock mass discontinuities: A case study of an underground excavation in Baihetan Dam,China

This study used a case study of an underground excavation in Baihetan Dam, China to identify structural domains, which are highly affected by size effects. The magnification and reduction methods involving nonparametric hypothesis tests of the KS, T-, and F-tests were proposed for the identification of structural domains. This process considers the fracture properties of orientation, trace length, position, and density. An ideal fractured rock mass model, whose structural domain identification reliability can easily be assessed, was generated and the size effect was proved to be significant. A sampling window with 159 stochastic fractures along an underground excavation was then presented. Calculations showed that different calculation sizes produce apparently different identification results. Given the objective of the analysis and further calculations, reliable results for the magnification and reduction methods were obtained.