Grouting Conditions Research Articles

Development of a Rock Groutability Index Based on the Rock Engineering Systems (RES): A Case Study

Penetration grouting is used to improve rock conditions under dams and foundations. So far no comprehensive ranking has been presented for the rock groutability assessment. However, a need for an index is tangible to classify the jointed rock masses from cement-based grouting conditions point of view. In this paper an attempt has been made to propose a rock groutability index (RGI) based on the rock engineering systems (RES). RES is an approach to evaluate the interrelationship between the factors affecting rock engineering activities. After discussing the rock grouting mechanism and identifying all the effective factors, an interaction matrix is introduced to study the groutability of rock masses. Thereafter, the interaction intensity and dominance of each factor in the system is determined to classify these factors. As a result, an index is presented to predict the groutability potential of rock masses. Bakhtiari Dam of Iran was selected as a case study and the proposed index was used to rank the seven geological units of Sarvak formation in this dam. It was observed that the rock groutability index could suitably predict rock masses condition from grouting point of view. For the purpose of evaluation, cross correlations was carried out between the Lugeon values with RGI. It was showed that with increasing Lugeon values the RGI decreases linearly with good correlation coefficients.

GPR signal analysis of post-tensioned prestressed concrete girder defects

The accurate inspection of the duct condition in post-tensioned prestressed concrete (PPC) is an essential part of GPR concrete inspection. The purpose is to inspect the grouting condition of the ducts where the strands are located, to find out if there is a void in the ducts, and if any water exists. In order to investigate the radar image characteristics of different PPC duct defects, a number of model girders were manufactured. Three major ducts are included in our study: (1) well grouted and no void (normal condition); (2) the duct is half filled, and the void is filled by water or air; and (3) the duct is not filled at all, and the duct is water or air filled. The data corresponding to seven different situations are acquired and processed. It is found that the radar can detect the first interface in the duct, and the detailed structure inside the duct cannot be ‘seen’ from the images directly. Characteristic curves greatly help the interpretation. A completely void duct is the easiest to differentiate from the others. The signature for this situation is characterized by a strong and clear reflection interface which becomes weaker as the void is water filled. The normal condition shows the weakest reflection interface. As for the half void situation, the front scan shows a similar result to the normal condition whether it is water or air filled, and the back scan shows similar features to the completely void situation. The experiment and analysis is helpful and instructive for practical engineering inspection.

S7-13 Detecting Voids in Tendon Ducts of Post-Tensioned Bridge Girders

The tendon ducts in post-tensioned bridge girders must be grouted fully so as to prevent water and oil stain from entering the ducts, which will decrease the durability and load-carrying capacity of post-tensioned bridges badly. This paper describes the motivations for and recent history of Impact-Echo (IE) scanning applications to internal grout condition evaluation of tendon ducts in post-tensioned girders. The tendon ducts’ internal injection quality of a railway bridge in Yichang city was evaluated using IE technology. During the in-situ testing, the IE signals were collected firstly, then the transformation from the time to the frequency domain was carried out using the principles of the fast Fourier transform, data interpretation was much simpler and quicker in the frequency domain. The grout condition of tendon ducts could be determined according to the frequency analysis, poorly grouted sections can be differentiated from the well-grouted sections within the tendon ducts. Results show that the IE method can be employed to detect voids in the grouted tendon ducts of many types of post-tensioned structures.

Inspection of Grouting Quality for Grouted Tendon Ducts Using Ground Penetrating Radar Technique

With the wide applications of post-tensioned concrete structures, the grouting conditions of tendon ducts are paid more attentions. In order to accurately assess the internal grouting quality of the grouted tendon ducts and certainly guarantee the lifetime of prestressed concrete structures Ground Penetrating Radar (GPR), which is a kind of nondestructive testing (NDT) method, has been applied to inspect and evaluate qualitatively and quantitatively on the grouting defects, respectively. A series of in-house tests were carried out for simulating the defects of tendon ducts by foams with different sizes. The results show that the GPR technic was one of the optimal methods for inspecting the internal grouting quality of grouted tendon ducts for post-tensioned concrete structures.

Nongrouted Ratio Evaluation of Rock Bolts by Reflection of Guided Ultrasonic Waves

The objective of this study is to develop and apply reflection methods for guided ultrasonic waves used in evaluating the grout condition of rock bolts installed in a rock mass. Three types of rock bolts with different grouting ratios are prepared. First, piezoelectric disk elements are used as the source of guided ultrasonic waves to investigate grouted nonembedded rock bolts. Second, reflection methods with piezo disk elements and hammer impacts are used with rock bolts embedded in concrete columns. Third, a hammer impact with a center punch is applied for investigating rock bolts embedded in a rock mass in the field. The measured guided waves were analyzed using wavelet transforms. The peak magnitudes of the wavelet transform are used for group velocity calculations. Although piezo disk elements are sufficient as sources for nonembedded rock bolts and rock bolts installed in concrete columns, they do not provide sufficient energy in the field. However, a hammer impact with a center punch can generate guided ultrasonic waves with enough energy to evaluate the nongrouted ratio in rock bolts embedded in a rock mass. The group velocities of the guided ultrasonic waves increase with increasing nongrouted ratio. This study demonstrates that the suggested hammer impact method is effective for evaluating the nongrouted ratio of rock bolts in the field.

Corrosion under Simulated Grout Conditions for Prestressed Concrete

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Grout and bentonite flow around a TBM: Computational modeling and simulation-based assessment of influence on surface settlements

Adequate consideration of the various interactions between the Tunnel Boring Machine (TBM) and the surrounding underground is a pre-requisite for reliable prognoses in shield supported tunneling based upon numerical analysis. In addition to face support and the grouting of the annular gap the contact conditions along the shield skin between the moving TBM and the surrounding, deforming soil constitute the most relevant component of TBM–soil interactions in mechanized tunneling. This paper is concerned with the analysis of the interface conditions between the shield skin and the soil and its adequate numerical representation in the context of a process-oriented numerical simulation model for mechanized tunneling. The situation around the shield skin is influenced by the design of the Tunnel Boring Machine, the deformational behavior of the surrounding underground and by a possible inflow of process liquids into the steering gap. A novel simulation method is proposed which allows to model the viscous flow of the process liquids into the steering gap and its interactions with the face support, the tail void grouting, the deforming soil and the moving TBM. The proposed numerical model for the TBM–soil interaction is part of a recently developed three-dimensional, process-oriented finite element model for shield tunneling ( Nagel et al., 2010). It allows to investigate the effects of the inflow of process liquids into the steering gap during TBM advance considering realistic machine-related and geological conditions. It is, in particular, capable to compute the pressure distribution within the developing liquid film in association with the face support and grouting conditions and to predict its influence on the surface settlements and the overall TBM–soil interaction affecting, e.g. the hydraulic jack forces or shield deformations.

Static Testing of Pile-Base Post-Grouting Piles of the Suramadu Bridge

Abstract Pile-base post-grouting is a method in which solidifiable cement slurry is injected into the base of the pile through grouting pipes after the strength of the concrete reaches a certain value to strengthen the loose sediment at the hole base and the soil around the pile. The roles of grouting are to eliminate the influence of the technological defects of bored piles, to recover the bearing capacities of strata, and to improve the bearing capacities of piles. Pile-base post-grouting piles technology and Osterberg Cell load testing were applied to some test piles of the Suramadu Bridge. Based on test results of the bearing capacity, side frictional resistance, and base resistance of piles before and after grouting, post-grouting was found to have an obvious role in improving the quality, bearing capacity, and load transfer characteristics of the piles. An equation for calculating post-grouting piles under specific grouting conditions was obtained based on the statistical analysis of more than 50 test piles. The ranges of the improvement coefficients of side frictional and pile-base resistance for different soils are given. Key technologies and parameters of post-grouting are also suggested. The results of this research can be applied to designing bridge pile foundations, which may tap the bearing potential of the piles and result in notable economic benefits.

Impact-Echo Based Nondestructive Evaluation of Grout Condition in Post-Tensioned Bridge Ducts

The field of Nondestructive Evaluation (NDE) is a very broad, interdisciplinary field that plays a critical role in civil engineering for controlling new structures (quality control) as well as for assessing the internal grout condition of prestressed pipes in post-tensioned concrete structures. Because it allows voids in grouted tendon ducts to be inspected and measured without damaging them, impact-echo based NDE provides an excellent balance between quality control and cost-effectiveness. This paper focuses on the nondestructive evaluation of internal injection quality in post-tensioned bridge ducts, and the developments in civil engineering NDE in China are also introduced.

Experimental study on pile-end post-grouting piles for superlarge bridge pile foundations

The application of pile-end post-grouting piles for super-large bridge pile foundations in some important projects was introduced in this paper. There are totally 21 test piles. The maximum pile diameter varies from 2.5 m to 3 m, and the maximum length is 125 m; the bearing capacity of the post-grouting piles is over ten thousands tons. Based on the test results, the bearing capacity, displacement, and bearing characteristics before and after grouting were analyzed. The results show that the bearing capacity of the piles is increased in different degrees after grouting although the technical parameters, including the patterns of grouting pipes, pressure, dosages of cement, duration of grouting lasting time, are different. However, the obtained values are very discrete. In addition, the calculation formula for the post-grouting piles under specified grouting condition was deduced based on the statistics analysis results of 57 test piles. The research results have been applied in the design of bridge foundation.

Chloride-Induced Corrosion in Insufficiently Grouted Posttensioned Concrete Beams

An experimental program was carried out to clarify the effect of chloride-induced corrosion on posttensioned concrete (PC) beams under different grout conditions using the electrically accelerated corrosion testing method. A series of accelerated corrosion tests were performed to evaluate the influence of insufficient grout condition on corrosion of sheath and prestressing tendon. The radial pressure surrounding the sheath during the corrosion process was also investigated. After a period of accelerated corrosion, the mechanical behavior of the deteriorated PC beams was clarified through loading tests. Prestressing tendon corrosion and its correlation with beam load-carrying capacity was also investigated. The results of the experiments demonstrate a significant influence of corrosion of sheath and prestressing tendon on load-carrying capacity of PC beams. The width of the corrosion crack in PC beams increases with grout filling level inside the sheath. The presence of water inside the sheath leads to increased rates of corrosion of the sheath and prestressing tendon, resulting in an earlier deterioration in the load-carrying capacity of PC beams.

Applications and Limitations of Impact Echo Scanning for Void Detection in Posttensioned Bridge Ducts

Findings are summarized from an internal research study to determine applications and limitations of the impact echo scanning (IES) system for void detection in posttensioned bridge ducts. The nominal thickness of the test panels ranged from 0.2 to 0.7 m with plastic and steel ducts inside. The diameter of the ducts ranged from 50 to 120 mm. One tapered section (with wall thicknesses between 0.2 to 0.7 m) had draped ducts, with the rest being straight ducts. Impact echo (IE) testing was performed using the IE scanner system. This system, as rolled, automatically performs an IE test at 25-mm (1-in.) intervals. All IE scans in this investigation were performed on lines perpendicular to the general posttensioned duct direction. The maximum frequency of excitation of the impactor in the scanner used in research is 25 kHz. This internal research is an expanded study from a previous research project funded by the NCHRP-IDEA program titled Nondestructive Evaluation Method for Determination of Internal Grout Conditions Inside Bridge Posttensioning Ducts Using Rolling Stress Waves for Continuous Scanning. The purpose of the study was to better understand the nominal thickness limitation of the structures for IE tests, using a scanner with a maximum excitation of 25 kHz to correctly identified voids in posttensioned bridge ducts.

Imaging Concrete Structures Using Air-Coupled Impact-Echo

In this paper, air-coupled impact-echo is successfully applied for nondestructive evaluation of concrete. The air-coupled sensor is a small (6.3mm diameter) measurement microphone located several centimeters above the top surface of the concrete being evaluated. Unwanted ambient acoustic noise is attenuated by a specially designed sound insulation enclosure. Test results show that air-coupled sensors are effective for impact-echo when appropriate impactors are used. Impact-echo data obtained by air-coupled sensors are equivalent to those obtained by conventional contact sensors. Test results from concrete slabs containing artificial delaminations and voids are reported, where an air-coupled impact-echo scan is conducted over the entire slab area. Defects are located in the generated two-dimensional contour image. The areal size of defects are accurately determined when the measurement point spacing in the scan is smaller than half of the expected defect size. Test results from air-coupled impact-echo scans carried out over internal metal and plastic ducts within another concrete slab are also reported. The goal of the experiment is to investigate the grouting condition inside the ducts. Impact-echo line scan images differentiate poorly grouted sections from the well-grouted sections within the metal duct.

A new parameter to assess hydromechanical effects in single-hole hydraulic testing and grouting

Grouting or filling of the open voids in fractured rock is done by introducing a fluid (grout) through boreholes under pressure. The grout may be either a Newtonian fluid or a Bingham fluid. The penetration of the grout and the resulting pressure profile may give rise to hydromechanical effects, which depend on factors such as the fracture aperture, the pressure at the borehole, and the rheological properties of the grout. In this paper, we postulate that a new parameter, Å, which is the areal integral of the fluid pressure change over the fracture plane, is an appropriate measure to describe the change in fracture aperture volume due to a change in effective stress. In many cases, analytic expressions are available to calculate pressure profiles and the Å parameter. The approach is verified using a fully coupled hydromechanical simulator for the case of a Newtonian fluid. Results of the verification exercise show that the new approach is reasonable and that the Å parameter is a good measure for the fracture volume change: i.e., the larger the Å parameter, the larger the fracture volume change, in an almost linear fashion. To demonstrate the application of the approach, short duration hydraulic tests and constant pressure grouting are studied. It is concluded that using analytic expressions for penetration lengths and pressure profiles to calculate the Å parameter provides a possibility to describe a complex situation and compare, discuss and weigh the impact of hydromechanical couplings for different alternative grouting strategies. Further, the analyses identify an effect of high-pressure grouting, that of uncontrolled grouting of larger fractures and insufficient (or less-than-expected) sealing of finer fractures under certain grouting conditions.

Sensitivity Studies of Grout Defects in Posttensioned Bridge Ducts Using Impact Echo Scanning Method

Findings are presented from an NCHRP Innovations Deserving Exploratory Analysis Program project, Nondestructive Evaluation Method for Determination of Internal Grout Conditions Inside Bridge Posttensioning Ducts Using Rolling Stress Waves for Continuous Scanning. The study involved a defect sensitivity study of an impact echo scanner to detect and image discontinuities in posttensioned ducts of a mock-up U-shaped bridge girder and a mock-up slab. Various sizes of ducts were included in this study as well as various sizes of void defects. A detailed sensitivity study of nondestructive grout defect detection with impact echo scanning of eight ducts 4 in. in diameter with constructed defects was the main focus in the study. Comparisons of the impact echo defect interpretation and the actual design conditions of the ducts inside the bridge girder or slab are presented. The impact echo results are presented three-dimensionally by using thickness surface plots to provide improved visualization and interpretation of the internal grout to void defect conditions inside the ducts of the girder. The impact echo tests were performed with a scanner, which greatly facilitates the impact echo test process by allowing for rapid, near continuous testing and true scanning capabilities to test concrete structures. The general background of the impact echo technique and the impact echo scanner is summarized. Descriptions of two mock-up specimens used in the experiment and the discussion of the results from the impact echo scanner are presented.

Detection and evaluation of failures in high-strength tendon of prestressed concrete bridges by acoustic emission

Failures in high-strength steel tendons of prestressed concrete structures are becoming a serious problem, as the deterioration of structures progresses due to aging. The failure is mainly attributed to the corrosion induced in severe environment as salt attack. Intensive studies were made in a laboratory and fields to investigate an applicability of acoustic emission (AE) technique to detect and locate the corrosion-induced failure. Three types of beams post-tensioned by steel bar, strand, and parallel wire cable with three different grout conditions (unbonded, partially grouted and fully grouted) were prepared in the laboratory tests. Failure was introduced by artificial corrosion, charging anodic current to the tendon. It was found that significant AE signals with extremely high amplitudes were produced by failures of steel wires and bars. Linear source location of the events was performed by three AE sensors placed in the center and the two ends of the beams. Reliability was shown to be 82–86% in terms of delectability of the failures. Continuous AE monitoring was carried out in two high-way bridges in service for 24 days. Eighteen AE sensors were placed at strategically selected positions on the post-tensioned beams of these bridges. Artificial AE signals were indirectly detected from the beams due to artificial failures by corrosion in small post-tensioned specimens bonded to the beams. Intensive analysis of the detected AE signals showed that meaningful AE events from the failures are clearly discernable from other sources as traffic noises and hammering. It has been proven that AE is a very useful technique to detect and evaluate failures of high-strength steel tendons in prestressed concrete bridges.

Influence of grouting condition on crack and load-carrying capacity of post-tensioned concrete beam due to chloride-induced corrosion

Chloride-induced corrosions of a sheath and a prestressing tendon in post-tensioned concrete (PC) beams are investigated under different grouting conditions. Two series PC beams were tested by the electrically accelerated corrosion. The first series of accelerated corrosion tests were performed to determine the influence of grouted ratios in a straight sheath on the corrosion of the sheath and the prestressing tendon. In the second series of tests, the influence of the length of grout filling was investigated in a curved sheath on the corrosion process. After the accelerated corrosion tests, the mechanical behavior of the deteriorated PC beams was investigated under flexural loading. The results of the experiments show that corrosion of the sheath and the prestressing tendon significantly decreases the load-carrying capacity of PC beams. As the grouted ratios in the straight sheath and the length of grout filling in the curved sheath increase, the cracks due to corrosion of the sheath propagate earlier along the prestressing tendon and the width of the cracks increases. From the view point of load-carrying capacity, it is verified that proper grouting can protect a prestressing tendon from corrosion despite the wider cracks due to corrosion of the sheath. The presence of water inside the sheath leads to increased corrosion of both the sheath and the prestressing tendon, resulting in the decrease in the load-carrying capacity of the PC beam.

Physical Model Testing of Compaction Grouting in Cohesionless Soil

Preliminary results of small-scale model compaction grouting tests performed in a geotechnical centrifuge are presented. The soil response to a one-stage grout bulb injection in dry uniform sand was examined at various prototype depths, and the effects of grout composition on grout bulb development and shape and on soil response are evaluated. Preliminary results indicate that the shape of the injected grout bulb is a function of overburden pressure. For specific grouting conditions, there is a maximum size that the grout bulb will achieve. Observed soil deformations were similar to those observed in models of deep uplift anchors. The addition of either clay or flyash to the grout mix reduced the ability to sustain high injection pressures.

RELATIONSHIPS BETWEEN PERFORMANCE CONDITIONS OF PREPACKED CONCRETE AND GRADIENT OF MORTAR SURFACE

In order to produce the prepacked concrete of high quality, it is important to fill up the voids of preplaced coarse aggregate with mortar perfectly.The author had proposed a theoretical method for predicting the process that the voids of the coarse aggregate were grouted.As an example of practical application of the theory, relationships between the maximum gradient of mortar surface and performance conditions were calculated, and further, a procedure to decide the adequate grouting conditions was offered.

MIXED INTEGER PROGRAMMING FOR THE OPTIMAL (LEAST COST) DESIGN OF ECCENTRICALLY LOADED MASONRY BEARING WALLS: PART I. LOW ECCENTRICITIES

A mixed integer approach for the least cost design of structural masonry walls with high eccentricities is developed. The integer variables in the approach are used to select the optimum values from a range of discrete block sizes, discrete grouting conditions, and discrete reinforcement levels. The structural constraints in the model are based upon the requirements of the Transformed Section type of analysis for masonry walls. The non-linear functions representing the relationships for determining the resisting capacities of the masonry element are approximated by linear functions which come very close in form and results to the original curves. Application of the model to an example problem demonstrates that in spite of the integer requirements, the approach is easily and efficiently solved using a standard software package.