Jet Grout Columns Research Articles

Geotechnical and structural remediation of residential building damaged by pit excavation

AbstractResidential building in town Pula in Croatia sustained structural damage through differential settlement, which occurred as a result of works in the nearby pit for sewage construction. Although no horizontal deflection was observed on the retaining structure of the pit, excessive vibration during installation caused consolidation of marine sediment soil on which the building rests. Building, which is more than 100 years old masonry structure, developed vertical and diagonal cracks on the outer bearing as well as inner walls, which widened from the ground floor to the top. Since differential settlements and tilting of the building continued after filling of excavation pit, remediation of the building was needed. Reinforced concrete beams were constructed under the masonry foundation strips as well as the jet grouting columns which transferred foundation loads to bedrock. Structural strengthening was done simultaneously. After the remediation, settlements and tilting soon subsided and stopped, while the monitoring equipment was left permanently on the building.

Design, construction and performance of single bore multiple anchored diaphragm wall in Turkey

AbstractThis paper presents the design, construction and performance of an anchored diaphragm wall utilizing high capacity Single Bore Multiple Anchor (SBMA) technology which is a proprietary product of Kasktaş in Turkey to support one of the largest and deepest basement excavations in very soft soil conditions of Kağıthane region in İstanbul for the first time. A 60cm thick diaphragm wall, with a total depth of 20m, was designed incorporating one level of temporary ground anchors in order to perform the excavation in dry condition without causing any hazard to surrounding structures and roads, within a heavily urbanized location. Additionally, 7 rows of jet grout columns were executed in order to improve the soil at the toe of the diaphragm wall. Within the scope of the prestigious on‐going Ferko Line Project, a shoring system consisting of 12,500m2 of diaphragm wall, 8,900m of Single Bore Multiple Anchor (SBMA) and 62,400m of jet grout columns and a piled‐raft foundation system consisting of 33,150m of 100cm bored piles socketed into rock by 5 m were completed.

Design procedure for the modelling of jet-grout column slabs supporting deep excavations

Overlapping jet-grout columns are often used to form a grout slab at the bottom of deep excavations to support the retaining structures. Columnar geometrical imperfections, spatially varying strength and stiffness and the post-peak behaviour of the grout, render the simulation of the jet-grout column slab a very complex issue. In practice, these aspects are not taken into account and simplified models are commonly used, in conjunction with the application of a strength reduction factor. With the aim to improve the existing design process and extend its applicability to serviceability limit state analysis, a consistent design procedure is presented.

A case study on the application of destructive and non-destructive methods for evaluating jet-grouting column integrity for bridge-pier scour protection (Cuneo, NW Italy)

A case study on the use of direct and indirect investigations for the effectiveness evaluation of jet-grouting interventions for bridge scour protection is presented. The major concern of this scour countermeasure is that a reliable verification and imaging of the exact dimensions and shape of the grouted elements and their related strength and integrity are difficult to obtain. An integrated cost-effective and slightly invasive approach, by means of indirect surveys, is proposed in this work to limit re-drilling and core sampling of jet columns. Tests are performed on a bridge located in the Province of Cuneo (NW Italy). On site, active fluvial activity was scouring four of the 19 bridge piers and jet-grouting interventions were designed to prevent bridge collapse. A dual approach was consequently applied to evaluate the goodness of jet-grouting treatments: results of direct tests (visual and mechanical characterization of core drillings, with Point Load and Uniaxial Compressive Strength tests) have been compared to indirect investigations (seismic down-hole tests and 2-D cross-hole tomography, laboratory Ultrasonic Pulse Velocity measurements). All the techniques showed potentiality in identifying variations of the jet-grouting properties within the columns. Generally, worsening in jet-grouting properties was coherently identified by a decrease in the seismic velocities and in the mechanical parameters and confirmed by visual inspection of core drillings. Local anomalies and discrepancies between the adopted method were however highlighted and critically discussed as a function of the limitations, disturbances and investigated volumes of each method.

Simple Method to Predict Ground Displacements Caused by Installing Horizontal Jet-Grouting Columns

During the horizontal jet grouting in soft ground, injection of large volumes of water and grout into the soil can lead to significant ground displacements. A simple method is proposed in this paper to predict the ground displacements caused by installing horizontal jet-grouting columns. The process of installing a horizontal column is simplified as the expansion of a cylindrical cavity with a uniform radial stress applied at plastic-elastic interface in a half plane. In this study, the analytical solution is adopted to calculate the deformation induced by the expansion of a cylindrical cavity. Considering the main jetting parameters (jetting pressure of the fluid, flow rate of the fluid, and withdrawal rate of the rod) and the soil properties (stiffness of the surrounding soil), an empirical equation to estimate the radius of plastic zone is developed. Two field tests are carried out in Shanghai, China, to verify the correctness and applicability of the proposed method. Comparisons between the predicted and measured values indicate that the proposed method can provide a reasonable prediction. The proposed simple method can be recommended as a useful tool for the design of ground improvement by means of horizontal jet grouting.

Evaluation of jet grout column diameters by acoustic monitoring

To evaluate the diameter of jet grout columns actually formed under the ground, several methods had been developed over the past years. Nevertheless, uncertainty still exists in different methods mostly due to the variations of ground and grouting conditions. This study proposes an acoustic monitoring system capable of directly recording the jet grouting sounds detected at different distances from the jet nozzle. To correlate the actual diameter of the jet grout column with the monitored sound prints, a field test was conducted in an interlayered sandy and gravelly soil and the jet grout column was excavated for dimension measurement. The recorded sounds show that the distribution of the threshold peak amplitudes at different distances can be represented by the curve of the normal distribution function. In addition, the standard deviation and mean of the normally distributed threshold peak amplitudes can be used as indicators to determine the effective diameter of the jet grout column for a specific jet grouting project. Although this acoustic monitoring method would be costly and time-consuming if used to examine all jet grout columns, it is suitable for frequent use in trial tests for finding reasonable grouting parameters when forming jet grout columns with design diameters.

Strength of cement-stabilised clay by hardness testing

This paper presents an investigation of the evaluation of the unconfined compressive strength (UCS) of cement-stabilised Shanghai clay by hardness testing. Laboratory tests including the hardness test and the unconfined compression test were carried out. An innovative decision was taken to use the Shore-A durometer to measure the hardness of cement-stabilised clay. Based on the regression analysis of laboratory test results, an exponential equation is proposed to express the unique relationship between the UCS and the degree of hardness. By measuring the hardness of jet grout columns installed in Shanghai clay, the proposed exponential equation was applied as a trial for predicting their UCS. Comparison results suggested that the exponential equation proposed in this study may be used to produce a quick prediction of the UCS by measuring the hardness of samples in the field.

Probabilistic investigations on the watertightness of jet-grouted ground considering geometric imperfections in diameter and position

The effect of geometric imperfections in both diameter and position of jet-grouted columns on the watertightness of an underground cement-treated slab is investigated in this study. A three-dimensional discretized algorithm is proposed to facilitate the detection and measurement of untreated zones that penetrate the treated slab. The normalized flow rate of a cement-treated slab is then evaluated by calculating the harmonic average area of the penetrated defect. Statistical evaluation of the gross flow rate through the penetrated defects is carried out via Monte Carlo simulations. The results show that a more economic design is obtainable if intracolumn variation of diameter is considered or multi-shaft jet-grouting is used. Based on the statistical results, a reliability-based design method is proposed for designers to strike a balance among various design parameters, including slab thickness, depth, column diameter, and column spacing.

Recent Advances in Horizontal Jet Grouting (HJG): An Overview

This paper discusses recent advances in the implementation of horizontal jet grouting (HJG) for the ground improvement of soft soil. Field trials of HJG were undertaken in soft soils in Shanghai, and the research is reported and discussed in this paper. Particular emphasis was placed to study the hardening process in non-cohesive soils. The recent innovations in HJG were found to arise principally from challenges in implementing jet grouting in sandy soil and also from the harmful effects on the surrounding caused by the traditional implementation process. Accordingly, the recently developed composite jet pipe, pressure-control jet grouting and control discharge horizontal jet grouting methods have been successfully implemented to mitigate the ground upheaval and displacements. Moreover, the characteristics of the jet grout columns obtained with these methods were found as a rule to perform beyond expectations. It was also found that the newly developed horizontal twin-jet grouting technology, underpinned by an instant-solidification mechanism, overcame challenging issues such as mixing uniformity, loss of admixture and hardening. The characteristics of hardening in particular have initiated new perspectives, given that a better acquaintance of the mechanisms of hardening and ground displacements is bound to play an important role in the future practice and the development of the jet grouting process. Interestingly, smoothed particle hydrodynamics technique was found to be suited for modeling jet grouting mechanisms.

The characteristic strength of jet-grouted material

In spite of being one of the most popular ground improvement techniques, jet grouting is often viewed with suspicion, its properties underestimated and its role downgraded to provisional or subsidiary, mostly because of the lack of reliable methods to manage uncertainty. The random composition and scattered properties of the material observed at the small scale of laboratory tests lead designers to assume arbitrarily unjustified over-conservative strength. A methodology is herein introduced to quantify uncertainty, characterising the different factors of variability in the jet-grouted material and simulating their effects on representative structural elements. An experimental database representative of a broad range of situations, consisting of laboratory tests on samples cored from jet-grouted columns and sonic tomography scans performed on large blocks, is first examined to characterise the mechanical response of the jet-grouted material and its variability. Probabilistic and autocorrelation functions are then introduced to simulate the stochastic and spatially correlated variability and virtually reproduce realistic populations of samples. The virtual simulation of uniaxial compression tests on these samples with a three-dimensional finite-element method code leads to the statistical distribution of the strength being obtained and the mean and variance being computed. Repeating systematically this process for the variable parameters of the original functions and for different shapes and dimensions of the samples leads to general formulas expressing the statistical distribution of the uniaxial compressive strength. The inferred relations are finally combined to calculate correcting factors giving the characteristic strength of prismatic jet-grouted elements with variable dimensions and slenderness, starting from the distribution observed at the laboratory scale.

Geotechnical investigations and remediation design for failure of tunnel portal section: a case study in northern Turkey

Mass movements are very common problems in the eastern Black Sea region of Turkey due to its climate conditions, geological, and geomorphological characteristics. High slope angle, weathering, dense rainfalls, and anthropogenic impacts are generally reported as the most important triggering factors in the region. Following the portal slope excavations in the entrance section of Cankurtaran tunnel, located in the region, where the highly weathered andesitic tuff crops out, a circular toe failure occurred. The main target of the present study is to investigate the causes and occurrence mechanism of this failure and to determine the feasible remedial measures against it using finite element method (FEM) in four stages. These stages are slope stability analyses for pre- and postexcavation cases, and remediation design assessments for slope and tunnel. The results of the FEM-SSR analyses indicated that the insufficient initial support design and weathering of the andesitic tuffs are the main factors that caused the portal failure. After installing a rock retaining wall with jet grout columns and reinforced slope benching applications, the factor of safety increased from 0.83 to 2.80. In addition to slope stability evaluation, the Rock Mass Rating (RMR), Rock Mass Quality (Q) and New Austrian Tunneling Method (NATM) systems were also utilized as empirical methods to characterize the tunnel ground and to determine the tunnel support design. The performance of the suggested empirical support design, induced stress distributions and deformations were analyzed by means of numerical modelling. Finally, it was concluded that the recommended stabilization technique was essential for the dynamic long-term stability and prevents the effects of failure. Additionally, the FEM method gives useful and reasonably reliable results in evaluating the stability of cut slopes and tunnels excavated both in continuous and discontinuous rock masses.

Optimised design of jet-grouted rafts subjected to nonuniform vertical loading

A parametric study based on three dimensional finite element (3D FE) simulations of jet-grouted rafts (JGRs) subjected to nonuniform vertical loading has been conducted to investigate the interactions of JGR elements that are raft, jet-grouted columns (JGCs), granular interlayer mat and subsoil. The presented initial 3D FE simulation of a single JGC which is geometrically approximated with the rotated sinusoidal functional representation accounting for the actual variation of JGC diameter with depth is validated performing the back-analysis of the developed 3D FE models with the well-known experimental results reported in the literature. The image processing technique allowing the 3D FE modelling of complex irregular geometries has been employed and the extension of simulation to the complete JGR system is accomplished. Considering the design strategies previously defined for JGR systems, Paper resolves how the independent variables of interlayer thickness, JGC spacing and length under the core and edge areas of raft affect the design responses of settlements, bending moments and vertical stresses. The multi objective optimization analysis has been performed using Response Surface Method (RSM) to achieve the most economical design solution that satisfies the presented design constraints for JGRs. The effects of design constraints on the optimised design are presented graphically. Paper concludes the coupling of design strategies defined separately for JGC and piled raft provides opportunity to achieve the optimised design of complete JGR systems using 3D FE simulation with the image processing technique and RSM.

A new prediction method for the rheological behavior of grout with bottom ash for jet grouting columns

Among the many variables involved in jet grout technology, dealing with the complex phenomena of grout flow, specifically related to the pumping pressure (shear stress), the pumping rate (shear rate) and the viscosity, mostly becomes a difficult task for grouting in practice. Thus, this study presents the capability of a new methodology in soft computing techniques, called gene expression programming (GEP), to predict the rheological behavior (i.e., the shear stress versus the shear rate and the viscosity versus the shear rate) of grout with bottom ash for jet grouting columns, as an alternative approach to traditional methods. For this purpose, shear stress and viscosity formulas, including the main input variables of the shear rate and bottom ash proportion, are derived using GEP modeling through the stages of production and testing. Then, the performances of the GEP formulas are compared with the measured data and the regression and conventional rheological models (De Kee and Robertson-Stiff) for use in practice. The results indicate that the GEP formulas are able to yield estimations with good precision resulting in better predictions (R≥0.96) compared to the regression model. A successful description of the pseudoplastic response of rheological behavior is given, and a response consistent with conventional rheological models is obtained. Moreover, the measured data (shear stress and viscosity) generally follow the GEP modeling well, but the level of satisfaction is more favorable at high proportions of bottom ash. In conclusion, the study reveals that the derived GEP formulas are relatively promising for estimating the pumping pressure, the viscosity and the pumping rate of grout with bottom ash for jet grouting columns, at least in assisting conventional methods for preliminary designs.

High pressure jet-grouting column installation effect in soft soil: Theoretical model and field application

This paper presents a theoretical model for investigating the installation effect of high pressure jet grouting column in soft clay. The model is formulated by assuming the installation process as a series of pressure-controlled spherical cavity expansion in semi-infinite soil, of which the approximate solutions are derived by combining use of two fundamental solutions of spherical cavity expansion in finite spherical symmetry soil and displacement-controlled spherical cavity expansion in semi-infinite soil. The approximate solutions are then validated by comparing the predictions with FEM results as well as published results. The comparison results show that the presented approximate solutions are suitable for the problem of pressure-controlled spherical cavity expansion in semi-infinite soil, particularly in evaluating the limit expansion pressure as well as the expansion pressure-ground surface displacement relation. Subsequently, the proposed approximately solutions are applied to interpret the limit injection pressure and the grouting pressure-ground surface displacement during the installation process of HPJ-GC. Some parametric studies are also conducted. Furthermore, an instrumented field test study of HPJ-GC is conducted in the thick soft soils comprising quaternary alluvial and marine deposits of the Lianyungang-Yancheng Highway located in Jiangsu Province, China. The measured ground heave is compared with the analytical predictions using the proposed theoretical model. Reasonable agreement is achieved.

Observed deformation characteristics of a deep excavation for the spring area in Jinan, China

The observed deflections and internal forces of pile-anchor retaining excavation were studied in spring area in Jinan city of China. Based on field measured data, the ground surface settlement, deflection of retaining piles and wall, internal force analysis of concrete piles, axial anchoring forces, groundwater table, and the deformation of surround building and pipelines were investigated. The results indicates that the combining application of concrete piles, jet grouting columns and anchors support system can effectively control excavation-induced surface ground settlements. The field maximum lateral wall deflections are between 0.02% and 0.19% of the excavation depth due to the competitive site conditions. The bending moment-depth relationship curve is S-type. Groundwater leakage results in the sharp drop in groundwater level, which is part of the reasons for the adjacent building settlement. The axial anchoring forces of the upper layer of anchors increase gradually during the excavation, but those of the lower layer of anchors slightly reduced firstly and then tend to be stable during the excavation procedure. In comparison with the histories of excavation cases, the small lateral wall deflection in this study results from the favorable site condition and the relative rigidity of the retaining structure system.

Numerical approach to predict ground displacement caused by installing a horizontal jet grout column

ABSTRACTWhen horizontal jet grouting is conducted in fine-grained soils, the injection of large volumes of fluid with high injection pressure into the ground may cause ground surface upheaval and the lateral movement of subsoil. This paper provides a numerical approach to calculate the ground displacement caused by installing a horizontal column based on determination of the influencing radius of injection pressure and the volumetric expansion strain caused by fluid injection. During the course of this study, the relationship between the influencing radius, column radius, volumetric expansion strain, and jetting parameters is established. The proposed numerical approach is applied to analyze a case history conducted in Shanghai soft soil deposits, which include the monitoring of vertical displacement of the ground surface and lateral displacement of the subsoil during construction. A comparison of the results between the simulated values with the Mohr Coulomb model and field data demonstrates that the numerical approach can yield a reasonable prediction of these field measurements when the influencing radius is six times the radius of the column. The influence range of the horizontal jet grouting activity is also discussed by numerical analysis with respect to two soil models (the Mohr Coulomb model and the hardening soil model).

Estimation of lateral displacement induced by jet grouting in clayey soils

The installation of jet-grouted columns in soft ground can induce lateral displacement resulting from injection of a great amount of water and grout into the ground, which may then lead on to further significant effects. This paper presents an approach to estimate the lateral displacement due to the installation of a jet-grouted column in clayey soils. Assuming that the installation of a jet-grouted column is represented by the expansion of a cylindrical cavity with a uniform radial stress applied at the plastic–elastic interface in a half-plane, the analytical solution developed by Verruijt is adopted in this study to calculate the lateral displacements attributable to the expansion of the cylindrical cavity. An empirical equation that accounts for the jetting parameters (jetting pressure, flow rate of the fluid and rod withdrawal rate) and soil properties (soil type and its undrained shear strength) has been developed to determine the radius of the plastic zone. Three case histories analysed in this paper demonstrate that the proposed method can be used for estimation of the lateral displacement caused by installing jet-grouted columns in clayey soils, despite minor discrepancies from the group column installation case between the predicted and measured values. These minor discrepancies can most likely be attributed to the omission of the effect of installation sequence and rheological properties of the grout in the calculation.

Extending chemo-thermal quality assessment for jet grouting

Today quality assessment of jet grouting focuses on the determination of the diameter of the column and the cement content of the improved soil exploiting the exothermal nature of the hydration of cement. This is accomplished by in situ temperature measurement followed by a back-calculation employing a simplified one-dimensional chemo-thermal finite-element simulation model. The underlying assumptions, such as simple geometric properties and disregarding the construction process, lead to the questions of the range of applicability of the existing quality-assessment tool and, in what cases a more refined simulation approach becomes necessary. By means of a two-dimensional simulation, the influence of the geometric properties (height/radius ratio) of jet-grouted columns and of adjacent columns on temperature development is investigated. Finally, the simulation results are compared with the measurements from a construction site, showing the benefit of the proposed model and the simulation approach in the case of complex jet-grouting applications.

Crosshole and downhole seismics: a new quality assurance tool for jet grout columns

ABSTRACTSealing and strengthening of the subsoil by grout injection is a major issue in the field of geotechnical engineering. One commonly applied method is jet grouting, which allows creating columns of grouted soil by eroding and mixing the in‐situ soil with a thin cement suspension. A general difficulty linked with this method is in predicting the resulting column diameter and its material strength. In this paper, we illustrate the application of a newly developed non‐destructive quality assurance tool used to determine the diameter of jet grout columns. This approach incorporates standard crosshole and downhole seismic measurements. To demonstrate its effectiveness, we tested the new approach within two‐dimensional finite‐difference numerical simulations. Additional field tests showed that this tool is also applicable in real site conditions. For this purpose, three jet grout columns were produced with different process parameters in a depth between 3 and 10 m. The evaluated diameters were within 1 and 1.5 m, slightly deviating from the previously predicted range by the jet grouting contractor. Moreover, we were able to detect the base of the columns at a 10‐m depth with no significant difficulties. On the other hand, unsaturated, less compacted sands between the groundwater level and surface considerably affected the seismic data, hence complicating the detection of the top of the columns.

Effect of Jet-Grout Columns on the Seismic Response of Layered Soil Deposits

AbstractGround-improvement techniques, such as jet-grout columns, may have positive effects on structures founded on soft soil when subjected to earthquake loading. The main objectives of this paper are first to evaluate the effects of soil-improvement width and depth on the ground response of a layered soil and, second, to define critical zones in which cemented columns might crack. A series of numerical calculations are performed by means of the finite-element method, considering a linear viscoelastic model for soil layers and rigid bedrock condition, and also by applying an advanced constitutive model for simulating the behavior of jet-grout columns. The soil profile consists of a 10-m loose sand layer overlain and underlain by a 5-m dense sand layer. The acceleration time recorded during the Loma Prieta earthquake in 1989 is used as the input motion. The results show that the seismic load is decreased or may increase as a result of ground improvement. In addition, it is shown that by applying an advan...