Attenuation of rock blasting induced ground vibration in rock-soil interface

Blasting has been widely used in mining and construction industries for rock breaking.This paper presents the results of a series of field tests conducted to investigate the ground wave propagation through mixed geological media.The tests were conducted at a site in the northwestern part of Singapore composed of residual soil and granitic rock.The field test aims to provide measurement data to better understand the stress wave propagation in soil/rock and along their interface.Triaxial accelerometers were used for the free field vibration monitoring.The measured results are presented and discussed,and empirical formulae for predicting peak particle velocity(PPV)attenuation along the ground surface and in soil/rock were derived from the measured data.Also,the ground vibration attenuation across the soil-rock interface was carefully examined,and it was found that the PPV of ground vibration was decreased by 37.2% when it travels from rock to soil in the vertical direction.     

Non-linear superposition models of blast vibration

Current waveform models of blast vibration typically consider a linear superposition of characteristic (seed) waveforms. However, blasting produces large strains in the surrounding medium, which, in turn, implies a non-linear response of the material. It is therefore questionable to use a linear superposition scheme to add the contributions of individual charge masses. These individual charge masses could be the elements of charge within a single blasthole, or the separate charge masses associated with each blasthole within a full-scale blast. Within a single blasthole, each charge element is necessarily in the very-near-field of its neighbour. In this case, a simple non-linear superposition scheme can be devised such that the vibration due to the entire explosive column is consistent with charge weight scaling. If A is the traditional scaling constant, then non-linear superposition predicts that the vibration is less than that obtained using linear superposition provided A<1. However, if A>1, then non-linear superposition predicts a vibration greater than that predicted by linear superposition, which is in conflict with accepted theories of large strain non-linear attenuation. For a full-scale blast, each charge mass is clearly separated, which complicates the situation. In this case, two non-linear superposition approaches are given—one based solely on charge weight scaling, the other based on the distinct notion of blast damage. In principle, the damage model is more realistic than the charge weight scaling model, and this is also consistent with the predictions based on these two schemes when compared with measured results.     

Blasting vibration criterion for a rock-anchored beam in an underground powerhouse

The design approach for a rock-anchored beam (RAB) in an underground powerhouse is briefly introduced, and the dynamic response characteristics of an RAB under blasting vibration are presented. It is found that the key to ensure the safety of RAB under blasting vibration is to prevent the split of the bonding interface between the RAB and a vertical rock wall, and to control the horizontal peak particle velocity (PPV). On the basis of the practices at Longtan hydropower station and other projects, and taking into account the comprehensive factors such as the structure characteristics of RAB, the age of concrete and the strength of bonding interface, the safe PPV for an RAB in a large underground powerhouse are thoroughly studied. It is concluded that a PPV of 7 cm/s for an RAB with an age older than 28 d would be of some safety. The safe PPV for young concrete proposed by GB6722-2003 could be adopted as those for an RAB with an age no older than 28 d, i.e., a safe PPV of 3–7 cm/s for an RAB at an age range from 3 d to 7 d, and 2–3 cm/s for an RAB at age range from 0 d to 3 d.     

Impact of orientation of blast initiation on ground vibrations

The blast-induced ground vibrations can be significantly controlled by varying the location and orientation of point of interest from blast site. The blast waves generated due to individual holes get superimposed and resultant peak particle velocity (PPV) generates. With the orientation sequence of holes blasts on site, the superimposition angle of wave changes and hence results in significant variation in resultant PPV. The orientation with respect to the initiation of blasts resulting in lowest PPV needs to be identified for any site. By knowing the PPV contour of vibration waves in mine sites, it is possible to reduce the vibration on the structures by changing the initiation sequence. In this paper, experimental blasts were conducted at two different mine sites and the PPV values were recorded at different orientations from the blast site and its initiation sequence. The PPV contours were drawn to identify the orientation with least and highest PPV generation line. It was found that by merely changing the initiation sequence of blasts with respect to the sensitive structure or point of interest, the PPV values can be reduced significantly up to 76.9%.     

《爆破安全规程》(GB 6722—2014)边坡岩体爆破振动速度安全允许值的理论探讨

开挖爆破诱发的地震波对岩质边坡有显著影响,我国《爆破安全规程》(GB 6722—2014)给出了边坡岩体的爆破振动速度允许值,但未明确说明取值的理论依据。为此,分析露天开挖爆破条件下邻近边坡岩体的附加动应力和质点振动速度场分布特征,推导以坡表质点振动速度表征的岩体附加动应力表达式。以边坡岩体不发生剪切和张拉破坏为控制要求,考虑边坡岩体分级特征和坡体结构特征,提出基于简单边坡模型的浅层岩体的爆破振动速度允许值。分析表明,岩体强度、边坡坡度、滑动面深度和地震波频率等均对边坡岩体的允许振动速度存在显著影响。其次,无剪切破坏条件下计算的爆破振动速度允许值与《爆破安全规程》(GB 6722—2014)的控制标准在量级上较接近,而无张拉破坏时各级岩体的爆破振动速度允许值差别不大,《爆破安全规程》(GB 6722—2014)中岩质边坡爆破振动控制标准应在理论分析和工程实践基础上进一步细化。     

Modified scaled distance regression analysis approach for prediction of blast-induced ground vibration in multi-hole blasting

The blast-induced ground vibration prediction using scaled distance regression analysis is one of the most popular methods employed by engineers for many decades. It uses the maximum charge per delay and distance of monitoring as the major factors for predicting the peak particle velocity (PPV). It is established that the PPV is caused by the maximum charge per delay which varies with the distance of monitoring and site geology. While conducting a production blasting, the waves induced by blasting of different holes interfere destructively with each other, which may result in higher PPV than the predicted value with scaled distance regression analysis. This phenomenon of interference/superimposition of waves is not considered while using scaled distance regression analysis. In this paper, an attempt has been made to compare the predicted values of blast-induced ground vibration using multi-hole trial blasting with single-hole blasting in an opencast coal mine under the same geological condition. Further, the modified prediction equation for the multi-hole trial blasting was obtained using single-hole regression analysis. The error between predicted and actual values of multi-hole blast-induced ground vibration was found to be reduced by 8.5%.     

Effects of blast induced vibrations on the fresh concrete lining of a shaft

During shaft excavation, blast induced vibrations can cause micro-cracks in the fresh concrete lining and decrease its strength. The traditional method to reduce the vibration effect is to control the scale of blasting and apply temporary support to protect the fresh concrete. Recent research was conducted to study the effects of the blast induced vibration on the fresh concrete. Shaft sinking operations (drilling, blasting and concrete lining) were simulated in a laboratory model. Additives of triethanolamine – TEA (N(C₂H₄OH)₃) and sodium chloride (NaCL) in varying proportions were added to the concrete lining to increase the early strength. Vibration was generated by small scale blasting. The experimental results show that the blast induced vibration has negative and positive effects on the strength of the fresh concrete depending on the curing time at blasting. Vibration can increase the strength within the first 1–2 days. After that period, vibration can cause cracks in the fresh concrete and reduce the strength. Still later, it has no more effect. The time windows vary with the magnitude of vibration and the strength of the concrete at the time of blasting. It was also found that both additives increased the early strength of concrete lining and expanded the time windows. These results indicate that proper timing of blasting and use of additives can change the negative effect of the blast induced vibration into a positive effect and increase the strength of a concrete lining.     

Prediction of blast-induced ground vibration using artificial neural network

An attempt has been made to evaluate and predict the blast-induced ground vibration and frequency by incorporating rock properties, blast design and explosive parameters using the artificial neural network (ANN) technique. A three-layer, feed-forward back-propagation neural network having 15 hidden neurons, 10 input parameters and two output parameters were trained using 154 experimental and monitored blast records from one of the major producing surface coal mines in India. Twenty new blast data sets were used for the validation and comparison of the peak particle velocity (PPV) and frequency by ANN and other predictors. To develop more confidence in the proposed method, same data sets have also been used for the prediction of PPV by commonly used vibration predictors as well as by multivariate regression analysis (MVRA). Results were compared based on correlation and mean absolute error (MAE) between monitored and predicted values of PPV and frequency.     

振动测试在监测强夯地基施工中的应用

介绍了强夯振动测试的原理和方法,通过测试强夯振动的速度与距离的关系分析了强夯对建筑物的影响,确定了强夯振动的衰减规律,从而为类似工程施工提供依据。     

地下洞室连续围岩岩爆定量预测模型

根据能量平衡理论,推导了岩爆能量公式,定量分析了地下洞室连续围岩岩爆区位置、面积及碎块弹射速度的影响因素。研究结果表明,围岩水平应力与竖向应力比值小于1,岩爆区面积和碎块平均弹射速度随侧压力系数增大而减小,否则反之。岩爆区面积随岩体峰值荷载前后模量比率系数、岩石颗粒直径、裂隙密度和岩石断裂韧度增大而减小,随泊松比增大而增大。碎块平均弹射速度随颗粒直径、泊松比和岩体峰值荷载前后模量比率系数的增大而减小,随岩石断裂韧度的增大而增大,随裂纹密度的增加先增加后减小最终趋于稳定值。     

Advances in statistical mechanics of rock masses and its engineering applications

To efficiently link the continuum mechanics for rocks with the structural statistics of rock masses,a theoretical and methodological system called the statistical mechanics of rock masses(SMRM)was developed in the past three decades.In SMRM,equivalent continuum models of stressestrain relationship,strength and failure probability for jointed rock masses were established,which were based on the geometric probability models characterising the rock mass structure.This follows the statistical physics,the continuum mechanics,the fracture mechanics and the weakest link hypothesis.A general constitutive model and complete stressestrain models under compressive and shear conditions were also developed as the derivatives of the SMRM theory.An SMRM calculation system was then developed to provide fast and precise solutions for parameter estimations of rock masses,such as full-direction rock quality designation(RQD),elastic modulus,Coulomb compressive strength,rock mass quality rating,and Poisson’s ratio and shear strength.The constitutive equations involved in SMRM were integrated into a FLAC3D based numerical module to apply for engineering rock masses.It is also capable of analysing the complete deformation of rock masses and active reinforcement of engineering rock masses.Examples of engineering applications of SMRM were presented,including a rock mass at QBT hydropower station in northwestern China,a dam slope of Zongo II hydropower station in D.R.Congo,an open-pit mine in Dexing,China,an underground powerhouse of Jinping I hydropower station in southwestern China,and a typical circular tunnel in Lanzhou-Chongqing railway,China.These applications verified the reliability of the SMRM and demonstrated its applicability to broad engineering issues associated with jointed rock masses.     

核电站爆破挤淤对在建楼基础的振动影响

基于福建宁德核电站西部陆域形成及软基处理工程爆破挤淤振动监测结果,初步分析了爆破挤淤产生的振动对在建办公楼基础新浇混凝土的影响,提出了保护在建办公楼基础的具体措施。     

构造振速函数近似回归计算爆破振速的方法研究

介绍了构造振速函数近似回归地面质点振速的计算方法,它可以根据多个振速函数关系式的计算结果与实测数据进行对比分析,优选出与实际最接近的关系式作为振速预报的依据,克服了萨氏等常用公式对任何场地条件和爆破条件都采用一种固定模式的缺点,能够有效提高地面质点振速预估的精度.该方法在预测爆破振速、确定爆破安全药量和安全距离时,取得了更好的预测效果.     

Determination of the ground vibration attenuation law from a single blast: A particular case of trench blasting

The general transmissivity law of ground vibrations was studied, and a user-friendly methodology for determining the behavior of vibrations generated in any rock mass is proposed. The study was based on a single blast in a trench excavation, analyzing the vibration components recorded from two fixed locations. The attenuation law and the main variables according to the legal requirements, frequency and peak particle velocity (PPV), are defined with this novel method, achieving a high confidence level in a simple manner. The proposed approach can also have an important impact in terms of reducing the potential consequences of vibrations for the surrounding construction and achieving the required definition of rock mass. Reducing the cost and time in many projects where blasting techniques are applied is particularly useful for the design of future blasts.     

广州地铁东站南站厅竖井石方爆破震动控制

针对爆破震动产生的原因，在设计及施工中按分层分步法采用微震动控制和光面爆破技术，通过对爆破进行跟踪、监测、指导施工，将爆破震动控制在允许范围内，实现了安全爆破。     

Nonlinear hydroelastic vibration of a cylindrical tank with an elastic bottom containing liquid-analysis using harmonic balance method

Theoretical analyses and experimental studies have been carried out on the non-linear hydroelastic vibration of a cylindrical tank with an elastic bottom. In this paper, nonlinear axisymmetric free vibration analysis of the bottom plate of the tank, coupled with that of the liquid contained within it, is presented by means of the harmonic balance method. In the analysis, the effect of an in-plane force in the plate due to static liquid pressure is taken into account. The effect of the liquid on the non-linearity of the backbone curve of the super-harmonic and the sub-harmonic resonances as well as the principal resonance of both sloshing- and bulging-type responses was clarified, and it was found that with an increase of liquid height, the non-linearity with a hard-spring type of the bottom plate decreased in degree, and became close to linear characteristics. The influence of the bottom plate motions on the free surface response amplitude in the first bulging-type resonance region was also investigated.     

Reduction of blast-induced vibration in the direction of tunneling using an air-deck at the bottom of a blasthole

The present study proposed an air-deck method for reducing blast-induced vibration in the direction of tunneling. The air-deck method involves the use of a thin paper-tube at the bottom of a blasthole. The vibration-reduction effect and excavation efficiency of the air-deck method were quantitatively investigated through numerical and experimental studies. The parameter considered in the numerical and experimental studies was the length of the air-deck at the bottom of a blasthole. The numerical and experimental results agreed well with each other. It was revealed that the air-deck at the bottom of a blasthole reduced blast-induced vibration in the direction of tunneling. The air-deck method was also found to be more effective than the conventional method of reducing the advance per round. Finally, design conditions for reducing blast-induced vibration in the direction of tunneling were proposed by introducing the concept of factor of safety.     

Experimental and numerical analyses of an opening in a jointed rock mass under biaxial compression

Tunnel construction in a rock mass produces damage around the tunnel by concentration of in situ stress and by construction activity such as blasting. The generated damage changes the mechanical and hydraulic properties of the rock mass. In this study, the rock fracture and joint sliding behaviors of jointed rock masses with an opening under biaxial compression are investigated through experimental and numerical analyses. The tested rock models have a persistent joint set with dip angles of 30°, 45°, and 60° to the horizontal. Under the applied biaxial compression, tensile crack initiation and propagation are the dominant fracture behaviors around the hole in a low joint dip angle rock model (i.e., 30° to the horizontal). The propagation direction of the tensile cracks is roughly normal to the joint surface, and with propagation of tensile cracks, removable rock blocks are generated. The experimental results are simulated using a discrete element code. The numerical analysis simulates several aspects of rock mass cracking and the joint sliding processes around an opening: progressive fracture behaviors in a low joint angle rock model, abrupt initiation and propagation of tensile cracks and joint sliding in a high joint angle rock model (i.e., 60° to the horizontal), propagation of tensile cracks normal to the joint surface, generation of removable blocks in rock segments, an increase of lower hoop stress threshold inducing tensile fractures with a decrease in the joint angle, and an increase of the damage zone around the hole with a decrease in the joint angle.     

萨道夫斯基公式在隧道中夹岩爆破振速分析中的适用性研究

以福建浦南高速与南平城区连接线狮子山隧道为工程依托,通过大量的现场振速测试和基于MIDAS/GTS软件进行的有限元数值模拟,运用萨道夫斯基公式对狮子山隧道中夹岩的振速回归分析进行了研究。得出运用萨道夫斯基公式对中夹岩内在同一测线并在同一方向上的测点振速进行回归分析是可行的,但采用萨道夫斯基公式对于在隧道现场不同位置或不...