Grout Holes Research Articles

Failure Analysis on Galvanized Steel-tube Pole Used for Supporting Electrical Equipment in 500 kV Substation

Electrical equipment in substation plays a key role in power transmission and distribution, which is usually supported by the steel-tube pole. In recent years, more and more crack defects were found in steel-tube pole used for supporting electrical equipment in substations, thus the safety and stability of power grids is severely affected. In this paper, the cracked steel-tube support of electrical equipment in a 500kV substation was investigated by means of macro-morphology inspection, chemical composition analysis, mechanical properties test, microstructure analysis, water sample analysis and fireworks experiment. The result showed that there was a grouting hole with poor sealing in the top of the steel-tube pole, so the rainwater and snowmelt could flow into the tube through the gaps. Once the temperature dropped abruptly, the water inside the tube would freeze and expand, led to the bursting of the steel-tube pole. Finally, effective suggestions were put forward, which could ensure the electrical equipment operating safely and stably.

Drill Monitoring for Rock Mass Grouting: Case Study at the Stockholm Bypass

In tunneling, rock mass grouting is a method applied to reduce water ingress. Grouting is influenced by rock mass conditions, especially apertures, frequency, and continuation of fracturing. These rock mass conditions can partly be determined by rock mass classification systems. At the Stockholm bypass, the Measurement While Drilling (MWD) Fracturing Index was applied to characterize the rock mass for grouting purposes, with a focus on adjusting the grout hole drill plan to minimize environmental impact. This study divided the rock mass in a 1.9 km tunnel into six categories based on rock mass conditions, identifying rock mass quality, apparent fracturing, and grout consumption. These categories were then compared with the mean fracturing index based on the coefficients of penetration rate and rotation pressure variations, as well as grout consumption at each grout umbrella. The fracturing index was 93% successful in assessing favorable and unfavorable rock mass conditions in the studied tunnel and 85% successful in determining grout consumption. Finally, a conceptual method was developed to reduce the grouting activities using the MWD fracturing index and water loss tests. The introduction of this conceptual method for grouting decisions could potentially reduce 59% of the umbrellas found in the case study.

Ultrasound Study of the Quality of Consolidation Grouting Works for Retaining Rocks in Underground Structures

The effectiveness of consolidation grouting for retaining surrounding rocks of the turbine hall at the Rogun hydro power plant (HPP) on the Vakhsh River in southern Tajikistan is evaluated. The ultrasonic method is used to examine samples, informing the choice of a test site in the aleurolite zone, as well as a drilled grout and test hole scheme. The results of processing and analysis of the ultrasonic study results are presented.

Rock Mass Characterization for the Underground Surge Pool Cavern – A Case Study, India

Abstract Underground surge pool cavern for the storage and lifting of water is being constructed in the part of Telangana State of India. For better rock mass characterization and support design, 3D engineering geological mapping was carried for the heading portion of the surge pool. 3D geologic mapping of heading portion is very important for large underground cavern to know about the cavern behavior during benching down. The direction of the longest axis of the cavern was finalized based on the in-situ hydrofracturing testing inside the deep borehole. The assessment of tunnel quality index ‘Q’ for the exposed granitic rock mass was done based on the information available of the rock joints and their nature, 3D geological mapping and in-situ stress measurement. Roof support and wall support pressure was estimatedbased on Q-values, and in this case applicable for the non-squeezing ground condition. For structural stability of crown and walls, rock support arrangement was recommended based on NMT technology and geological conditions of site, which includes steel fibre reinforced shotcrete, grouting, rock bolt and drainage hole provisions. The capacity of support system is determined to evaluate the efficacy of the proposed support system.

Study on Fracturing and Diffusion Mechanism of Nonslab Fracturing Grouting

The coupling effect of a slurry and the fractured rock layer controls a spatial attenuation of the fracture channel width and grouting pressure from a grouting hole to the slurry top of fracture diffusion. This paper comprehensively considers the influencing factors such as the mechanical properties of the injected rock mass and the time-varying characteristics of the serous viscosity and introduces the control equation of the fracture channel width to establish a single-fracture nonslab fracturing grouting model. Combining the motion law of the slurry with the extension form of fracture, the equation of slurry diffusion motion, considering the fracture geometry and the time-varying characteristics of the serous viscosity, is derived. Comparing this equation with the existing theories and experiments, the validity and reliability of the theory are verified. In this paper, the effects of rock elastic modulus, slurry viscosity, and grouting rate on the fracturing grouting diffusion law of rock mass are analyzed. It is pointed out that when fracturing grouting in deep rock layers, a larger initial grouting rate and grouting pressure should be selected in the early stages of grouting to generate or penetrate fractures in the rock layer. Also, when the grouting pressure is stable, it is appropriate to increase the viscosity so that the slurry can quickly gel in the fractures thus sealing the fractures.

Analysis on the crown convergence deformation of surrounding rock for double-shield TBM tunnel based on advance borehole monitoring and inversion analysis

The surrounding rock deformation during tunnelling is difficult to be measured or calculated accurately, especially in tunnels constructed by double-shield TBM. A method for prediction of the crown convergence deformation of surrounding rock based on advance borehole monitoring and numerical inversion analysis is proposed. Combined with the field deformation monitoring and numerical simulation, the final crown convergence deformation of surrounding rock is obtained. When TBM advances to the test section, the horizontal directional drilling machine is used to drill an advance borehole at the top of tunnel and 1.6 m away from the tunnel face, and the measuring tube with fiber Bragg grating (FBG) sensors has been installed in the borehole to conduct the deformation monitoring. Then, based on the numerical simulation with the viscoplastic creep constitutive model, the final crown deformation of surrounding rock during TBM tunneling process has been predicted, in which the parameters of surrounding rock are obtained through the inversion analysis of deformation data and the error caused by the displacement of reference point has been corrected. The surrounding rock crown convergence deformation was also estimated by using a scaled instrument in the grout hole of lining segment and is approximately the same with the above predicted value, which show that the proposed method can well analyze the surrounding rock crown convergence deformation during tunneling for double-shield TBM tunnels.

Improved filtering and normalizing of Measurement-While-Drilling (MWD) data in tunnel excavation

Measurement-While-Drilling (MWD) data are complex because of the drilling process and drilling system. Swift and accurate normalization and filtration processes are required if MWD data are to be used for rock mass characterization. The current method for MWD data filtration does not consider all the effects of the drilling process, e.g., collaring or extension rod coupling. This paper presents a new method for MWD data filtration and normalization. The new method filters the operational parameters and normalizes the data on a stepwise algorithm, including production factors (collaring drill hole and rod extension coupling) and rock drill settings. It shows reliable results for the normalization and filtration of MWD data gathered for drill hole collaring and coupled extension drill rods at grout holes and for different rock drills.

Design of grout curtain for temporary embankments on rock foundation

ABSTRACT The design of curtain grouting for dams on rock foundations and the importance of finite element seepage analysis is reported by highlighting a case study of the upstream cofferdam of Gulpur Hydropower Project, Pakistan. Results from seepage analysis decreased the scope of curtain grouting by almost 3 times as compared to initial scope based on results from empirical correlations and water pressure tests. The total grouting holes were decreased from 185 to only 66 and this meant a decrease of construction time by 72% and saved a huge amount of capital and resources as well. The performance of the grout curtain is concluded to be satisfactory, for an operation phase of 3 years which includes two major floods as well and during this period, no visible erosion, quick condition or saturation was found on the downstream end. The paper concludes that if the safety criteria are satisfied, even with high inflows of the river, the scope of curtain grouting can be partially reduced or completely eliminated for temporary dams having an operational life of 1–5 years.

Extension of grouting-induced splitting fractures in materials similar to coal rocks containing prefabricated fractures

Abstract To reveal the influence of prefabricated fractures (PFs) with different parameters on the extension of grouting-induced splitting fractures, a combination of numerical simulation and physical experiments were used to carry out grouting trials on similar materials to coal rock. The RFPA software was used to simulate the whole process of fracture initiation and expansion of coal rock with PFs during grouting. In the experiment, acoustic emission (AE) technology was used to monitor the extension process of grouting-induced splitting fractures. The results demonstrated that when the PFs do not intersect with the grouting holes, the extension of grouting-induced splitting fractures in rocks containing PFs experienced four stages: splitting and penetrating, slurry filling, fracture splitting and splitting extension. PFs have an orienting effect on the direction of grouting fracture extension and the size of the PFs influenced the extension of the grouting-induced splitting fractures: the larger the size, the easier the surrounding rocks were ruptured, the easier the connection was formed of channels between the grouting-induced splitting fractures and the PFs were formed, and the more complex the secondary splitting pattern in the PFs. This indicated that the angle of PFs played a decisive role in determining the extension direction of grouting-induced splitting fractures. The extension of grouting-induced splitting fractures during grouting of rock mass with different parameters is revealed by numerical simulation and experimental results.

Alignment of Vertical and Inclined Jet Grout Columns for Waterproofing

Abstract Good overlapping among jet grout columns is crucial for the success of waterproofing in the ground. Drilling alignment, column spacing, and diameter of jet grout columns are the controlling factors of good column overlapping. This study evaluated the drilling alignment of vertical and inclined jet grout columns using field-measured alignment data and statistical analysis. A three-dimensional (3-D) image of a jet-grouted mass was established by combining the measurement results of drilling alignment and jet grout column diameter from the trial test. The 3-D image was used to examine the overlapping of the jet grout columns and identify possible locations of windows (non-grouted zones) in the jet-grouted mass. Vertically drilled jet grout holes maintained excellent alignment, with an average estimated inclination angle of 0.43° and standard deviations of 0.11°. However, to avoid underground obstacles, inclined drilling is often required. An inclined drill jet grout hole can easily deviate from its designed drilling alignment because of gravity and result in poor overlapping and potential windows. The average estimated inclination angle and standard deviation of inclined drilling were approximately three times those of vertical drilling.

Stability Evaluation of Concrete Structure Considering the Local Damage Using Nondestructive Detection and Numerical Analysis

Shield tunneling is one of the most important technologies for building of underground engineering. Many grouting holes were prefabricated for the requirement of backfill grouting, which is easy to induce local damages and potential disasters, such as leakage and cracking. Accordingly, an integrated workflow for damage detection and stability evaluation was performed based on nondestructive testing (NDT) and numerical simulation. As a case study, this method was applied to an underwater shield tunnel. Firstly, Ground Penetrating Radar (GPR) was used to detect the conditions in grouting holes. Then, the infrared camera was used to determine the damaged positions induced by grouting holes. According to NDT results, the numerical models were developed to analyze the mechanical behaviors of structure. It indicated the geophysical inversion results are consistent with field conditions. The influence area increases with a significant value of water pressure, and stress magnitude would increase to 45KPa if the increment of water pressure reaches to 10KPa. As a promising application, structure stability was evaluated in the light of analytical results.

Simultaneous Operations of Pregrouting and Shaft Drilling in Shaft Construction

In shaft construction, conducting shaft drilling and pregrouting simultaneously is expected to speed up the sinking rate and save the cost. Reasonable determination of the spatial locations of the drilled shaft and grouting holes and proper defining of the start time of each construction work are the crucial techniques. To smoothly execute the simultaneous operations, the bedrock to be grouted is divided into two sections. The upper bedrock is injected first using straight grouting holes to act as a tight cover to protect shaft drilling. Then, the lower formations are grouted using S‐shaped grouting holes, which are performed simultaneously with shaft drilling. The construction time of simultaneous operations of pregrouting for the lower bedrock using S‐shaped holes and shaft drilling is the saved time. The main technical challenges include the stability of grouting holes and safety of shaft walls, as well as the disposal of the contaminative waste drilling mud. The stability of grouting holes which might affect by the shaft drilling‐induced ground vibration could be evaluated according to the penetration of ground vibration caused by TBM tunnelling. If the grouting hole is in the range of ground vibration, protective measures including casing and ground improvement should be utilized to ensure the stability of grouting holes. The stability of unlined walls of the drilled shaft caused by the increased groundwater pressure can be achieved by a tight cover between the drilled shaft and pregrouting holes. The thickness of the cover is actually the length of the straight holes. The cover should have sufficient thickness and impermeability, which can considerably reduce or even completely stop the increased groundwater pressure in vicinity of the drilled shaft. The thickness and permeability of the cover could be determined using Maag’s solution for penetration of grouts in porous media. On the other hand, the waste drilling mud with proper modifications can be reutilized to prepare clay‐cement‐like grouts, which could provide an eco‐friendly and cheap solution to harmlessly treat the huge volume of waste drilling mud. The properties of waste drilling mud and behaviors of grouts prepared using the waste mud should be experimentally investigated before reutilization, owing to uncertainties of geology in various cases. The construction time using the simultaneous operation method is just about 60% of that of the traditional excavation method, and the low value of measured residual water inflow shows the reliability of reusing the waste drilling mud as grouting materials. The proposed method could virtually improve the shaft sinking rate and save the construction cost. The principles developed for these technical challenges have been proved to be applicable in practices, which are believed to strongly support the applicability of this new method in other cases.

Application of Measurement While Drilling Technology to Predict Rock Mass Quality and Rock Support for Tunnelling

A tunnelling project is normally initiated with a site investigation to determine the in situ rock mass conditions and to generate the basis for the tunnel design and rock support. However, since site investigations often are based on limited information (surface mapping, geophysical profiles, few bore holes, etc.), the estimation of the rock mass conditions may contain inaccuracies, resulting in underestimating the required rock support. The study hypothesised that these inaccuracies could be reduced using Measurement While Drilling (MWD) technology to assist in the decision-making process. A case study of two tunnels in the Stockholm bypass found the rock mass quality was severely overestimated by the site investigation; more than 45% of the investigated sections had a lower rock mass quality than expected. MWD data were recorded in 25 m grout holes and 6 m blast holes. The MWD data were normalised so that the long grout holes with larger hole diameters and the shorter blast holes with smaller hole diameters gave similar results. With normalised MWD data, it was possible to mimic the tunnel contour mapping; results showed good correlation with mapped Q-value and installed rock support. MWD technology can improve the accuracy of forecasting the rock mass ahead of the face. It can bridge the information gap between the early, somewhat uncertain geotechnical site investigation and the geological mapping done after excavation to optimise rock support.

The significance of hydraulic jacking for grout consumption during high pressure pre-grouting in Norwegian tunnelling

Pre-grouting is a common measure for reducing water ingress into tunnels. This study has investigated parameters which are expected to have an impact on grout consumption during high pressure pre-grouting of rock mass in Norwegian tunnelling, with special attention to the occurrence of hydraulic jacking of fractures. A significant positive correlation between grout consumption and hydraulic jacking was found, especially when grouting with microfine cement, but it was not established to what extent hydraulic jacking contributes to the total grout consumption. Also, there was found to be a general increase in time consumption for grout holes where hydraulic jacking was indicated. It was concluded that hydraulic jacking does not tend to be a good choice for the economy of the projects, because it involves longer grouting time and higher grout consumption, particularly when using microfine cement.

DDA based grouting prediction and linkage between fracture aperture distribution and grouting characteristics

Apertures of rock fractures is frequently considered as one of the most important factors affecting grouting characteristics. The real fracture distribution, however, is inaccessible due to its complex intrinsic properties, making it cumbersome to directly assess its impact on on-site grouting. In this paper, we argued that investigation of the grouting characteristics of a fracture network with a priori aperture distribution is promising to be an alternative approach for understanding the linkage between fracture distribution and grouting characteristics. A grouting module based on the Discontinuous Deformation Analysis (DDA) was developed to explore the linkage, with transient flow of grout studied. It is found that the grout consumed by the preset fracture networks exhibits a lognormal distribution, in agreement with the statistics of grouting data from 1361 grout holes at the Jurong Rock Cavern (Singapore). The observed agreement can be treated as an indirect verification of the robustness of our proposed grouting module. As anticipated, the grouting characteristics are significantly affected by the distribution of fracture apertures and connectivity among fractures around an injection hole, which are controlled by the distribution parameters. The grouting features of some dominant fractures could represent that of an entire fracture network.

Grouting Defect Detection of Lapped Bar Connections Based on Impact‐Echo Method

Grouted lap‐splice connections are widely used for connecting precast concrete components. Grouting defects in the connections significantly influence the structural performance of the whole connection, which leads to the need for grouting defect detection. In this study, the impact‐echo (IE) method was used for detecting defects in grouted lap‐splice connections. Grouted connections with different levels of artificial grout defects were prepared in a shear wall, and the IE method was used to measure the frequency response. In addition, finite element (FE) analysis based on ABAQUS was conducted to simulate the tests. Based on the validated FE model, a parametric study was conducted to investigate the effect of the depth of the grout hole on the amplitude spectrum. The results indicated that (1) the IE method offered a good potential for grouting defect detection in grouted lap‐splice connections; (2) the proposed FE model could well predict the frequency response of the grouting hole; and (3) the measured frequency and amplitude of the grouting hole in an impact‐echo test would be considerably influenced by the hole depth.

The behavior of synchronous grouting in a quasi-rectangular shield tunnel based on a large visualized model test

A quasi-rectangular shield tunnel can increase the effective usage area and decrease the degree of adverse impact from the surrounding environment relative to that of a circular shield tunnel. Synchronous grouting in a quasi-rectangular shield tunnel plays an important role in construction. This experiment used an integrated simulative experimental platform in the form of a large-sized quasi-rectangular shield tunneling machine to simulate the synchronous grouting process. Different grouting cases were implemented in this test to identify the best grouting approach in a quasi-rectangular tunnel. By installing 190 miniature soil pressure gauges in the surface of a designated organic glass segment and arranging four cameras inside the organic glass segment, the short-term and long-term grouting pressure, grouting flowing path and toroidal grouting pressure distribution were visually and accurately measured and analyzed. Moreover, settlement of each soil layer was measured to observe the influence of grouting on the ground settlement. After testing, the covering soil was removed to ensure that the final grout shape could be visibly surveyed. The results demonstrate that the key parameters of synchronous grouting in a quasi-rectangular tunnel are the grouting ratio and the position of the grouting holes. Finally, a cosine function grouting pressure formula is proposed.

Experimental Investigation on the Law of Grout Diffusion in Fractured Porous Rock Mass and Its Application

Because of the limitation of mining techniques and economic conditions, large amounts of residual coal resources have been left in underground coal mines around the world. Currently, with mining technology gradually developing, residual coal can possibly be remined. However, when residual coal is remined, caving areas might form, which can seriously affect the safety of coal mining. Hence, grouting technology is put forward as one of the most effective technologies to solve this problem. To study the grouting diffusion in fractured rock mass, this paper developed a visualization platform of grouting diffusion and a three-dimensional grouting experimental system that can monitor the grout diffusion range, diffusion time and grout pressure; then, a grouting experiment is conducted based on this system. After that, the pattern of the grouting pressure variation, grout flow and grout diffusion surface are analyzed. The relationship among some factors, such as the grouting diffusion radius, compressive strength of the grouted gravel, porosity, water-cement ratio, grouting pressure, grouting time, permeability coefficient and level of grout, is quantitatively analyzed by using MATLAB. The study results show that the flow pattern of the grout in fractured porous rock mass has a parabolic shape from the grouting hole to the bottom. The lower the level is, the larger the diffusion range of the grout is. The grouting pressure has the greatest influence on the grouting diffusion radius, followed by the grouting horizon and water-cement ratio. The grouting permeability coefficient has the least influence on the grouting diffusion radius. The grout water-cement ratio has the greatest influence on the strength of the grouted gravel, followed by the grouting permeability. The grouting pressure coefficient has the least amount of influence on the grouting diffusion radius. According to the results, the grouting parameters are designed, and a layered progressive grouting method is proposed. Finally, borehole observation and a core mechanical property test are conducted to verify the application effect. This grouting technology can contribute to the redevelopment and efficient utilization of wasted underground coal resources.

Analysis and engineering application investigation of multiple-hole grouting injections into porous media considering filtration effects

The arrangement parameters of multiple grouting holes are important issues in soil sealing and in guaranteeing the grouting effectiveness. To better understand the effects of the arrangement parameters of multiple grouting holes, including the arrangement of the pass and space between the holes (the effective range of slurry diffusion and effective porosity of the injected media), on the effectiveness of grouting reinforcement, diffusion models of single-hole grouting and multiple-hole grouting are constructed based on fractal geometry and filtration effects. Then, the parameters of the grouting hole obtained by the present model are applied to the site. After grouting, the effect of grouting reinforcement under the corresponding parameters of the hole is obtained by analysing ground-penetrating radar data for the design profile and the porosity of each observation hole. The theoretical and engineering test results show the following responses: (1) The predictions from the proposed model show good consistency with the literature data and application results. For instance, in the case with filtration, the porosity increases faster at nearer distances, beyond which there is approximately no change in porosity with increasing distance. However, in the case without filtration, there is approximately no change in porosity with increasing distance during the whole process of grouting. (2) In the case without filtration, the effective diffusion range of the slurry depends only on the diffusion pressure of each test point. However, in the case with filtration, the effective diffusion range of the slurry depends not only on the diffusion pressure of each test point but also on the porosity of the injected media. (3) Under identical parameters of grouting hole and engineering geological conditions, the grouting expense of a triangular pass is less than that of a rectangular pass to achieve the same grouting effect.

Destabilizing Disaster Mechanism of Stope & Its Advanced Governance Control

In order to study the problem of surrounding rock control excavation caused by complex environmental conditions under the stop instability mechanism and its scope of influence. Based on the real rupture process numerical analysis software, the collapse mechanism of the collapse zone and its dynamic catastrophe process were revealed and its impact of the collapse of the instability was identified, the study of grouting pre-reinforcement and its effective monitoring in the unstable collapse area was carried out. The results show that the hidden area formed after the collapse of the stop is type V, the slip surface of the collapse is determined, grouting prereinforcement of the program and steps are presented, and the three-dimensional visualization model of the grouting hole is drawn. The results show that the integrity of the ore body and the filling body is better after grouting. While the water pressure test showed a significant reduction in the value of Live, That is, the slurry is filled and compacted between the ore body and the filling body between the holes and cracks. According to the research results of the mining environment ahead of governance, the safety problems faced by the mining hazards in the mine are effectively solved.