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Field studies on dynamic properties of reinforced earth
Abstract
The concept of reinforced earth has not become popular in the case of foundations for buildings. Presumably, the practical difficulties in application and the exorbitant cost have outweighed the beneficial aspects of ‘Reinforced Earth’ in such applications. Block foundations which are usually provided for machines to take care of the dynamic loads are small and compact and the improvement of the base with reinforcements should not be a difficult or impractical proposition. In this investigation, the feasibility of improving the dynamic properties of soil b ase by applying high modulus materials, such as steel wires and low modulus materials as geotextiles, and a combination of both have been studied in a standard forced vertical block resonance test. The feasibility and the supremacy of the ‘Reinforced Earth’ with the reinforced bases of (i) mild steel frame stiffened with high tensile wires (ii) sand coated geotextiles with the inclusion of a thin layer of frictional sand and (iii) sand coated geotextiles stiffened with welded mesh, have been brought out.
... Due to rapid urbanization, machine foundations are forcibly located near residential areas, causing a displeasing environment through machineinduced vibrations. Such unfavorable vibrations adversely affect adjacent structures, nearby sensitive equipment and residents [1] but can be controlled by enhancing stiffness, damping potential, and elastic properties of the soil-foundation system [2][3][4][5][6][7]. Various reinforcement techniques for the foundation bed using high tensile wires, geosynthetics, bamboo grids, fiber, and rubber sheets, were adopted to enhance the dynamic properties of the soil [2][3][4][5][6][7][8][9][10][11][12][13][14][15]. ...
... Such unfavorable vibrations adversely affect adjacent structures, nearby sensitive equipment and residents [1] but can be controlled by enhancing stiffness, damping potential, and elastic properties of the soil-foundation system [2][3][4][5][6][7]. Various reinforcement techniques for the foundation bed using high tensile wires, geosynthetics, bamboo grids, fiber, and rubber sheets, were adopted to enhance the dynamic properties of the soil [2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Recently, geogrid in controlling machine-induced vibrations has drawn much interest from researchers. ...
... It can be seen from Figs. 6 and 7, that the inclusion of the geogrid layer leads to a considerable reduction in z r but enhancement in f mr compared to the UR. Similar responses were also observed by Boominathan et al. [2], Sreedhar and Abhishek [6], Venkateswarlu et al. [10], and Venkateswarlu and Hegde [13]. The reduction in z r may be attributed to the improvement in the soil strength facilitated by open confinement and lateral resistance mechanism offered by the geogrid reinforcement [7,10]. ...
This paper explains the behavior of harmonically loaded machine foundations supported by geogrid-reinforced soil beds using multi-model approaches, such as experimental, numerical, analytical, and artificial neural network (ANN) modeling techniques. Field block vibration tests are performed on a foundation bed measuring 1.47 m × 1.47 m × 0.65 m, prepared on the soil at IIT Kanpur, India [N26° 30′ 59.0892″ (latitude), E80° 13′ 51.6888″ (longitude)]. Two different reinforced cement concrete (RCC) footings of sizes 0.55 m × 0.55 m × 0.2 m and 0.65 m × 0.65 m × 0.2 m are employed in this investigation. The tests are performed at three different eccentric force settings considering three testbeds: unreinforced, single-layer and double-layer geogrid reinforced beds. Geogrid layers reduce resonant amplitude and dynamic shear strain while simultaneously improving resonant frequency, system characteristics and dynamic soil properties. Further, the experimental results are compared with those obtained from the finite element and mass-spring-dashpot analysis. The displacement amplitude of footings is also predicted at different frequencies using ANN modelling to endorse the authenticity of the study. Encouraging agreements can be observed among various modeling approaches considered in this study.
... Saride and Dutta (2016) suggested that stabilization is an option for sustainable, safe, and economical method to enrich the dynamic properties of a foundation bed. The studies conducted by Boominathan et al. (1991) and Haldar and Sivakumar Babu (2009) suggested that the foundation bed reinforced with metallic strips improves the dynamic performance of the foundation bed. Nowadays, the utilization of geosynthetics has drawn the attention of practitioners for strengthening the foundation beds. ...
... Identical nature of the dynamic response was observed from both the pits. Boominathan et al. (1991) studied the dynamic response of the foundation bed by considering the test pit size 3 times the width of the model footing. Thus, the dimensions of the test pit equal to 3.3 times the width of the concrete block were considered in the present study. ...
... Improvement in soil strength due to the open confinement and lateral resistance provided by the geogrid reinforcement might be the reason for the increase in the resonant frequency of the system. The improvement in the natural frequency of the system in the presence of reinforcement was also reported by Boominathan et al. (1991), and Venkateswarlu and Hegde (2019). Figure 9 shows the variation of displacement amplitude with the frequency for different reinforced conditions. ...
The study discusses the potential use of geosynthetics in isolating the ground vibration emanated from the vertical mode dynamic excitation. A field study was conducted to investigate the screening efficacy of reinforced foundation beds. In the field study, vibration was generated using a mechanical oscillator. Four different cases, namely, unreinforced, single layer geogrid, two layers of geogrid, and geocell reinforced cases were considered. The isolation efficacy was studied in terms of peak particle velocity and amplitude reduction ratio. The resonance response of different reinforced conditions was studied by varying the dynamic force, and frequency of the excitation. The effectiveness of the reinforced soil system was examined by comparing the performance of the reinforced system with the unreinforced system. From the field test results, a significant reduction in ground vibration was observed in the presence of geosynthetics. Maximum reduction was observed in the case of geocell reinforced condition as compared to other cases. In the presence of geocell, peak particle velocity and resonant amplitude were reduced by 48% and 61% respectively, as compared to the unreinforced condition. Similarly, 98% improvement in the stiffness of the foundation bed was observed in the presence of geocells. Further, the dynamic response obtained from the field study was compared with the mass spring dashpot analogy. The dynamic response predicted from the analytical study has shown reasonable agreement with the field test results. From the analytical comparison, 2.6 times improvement in the damping ratio of the foundation bed was noticed due to the inclusion of geocell reinforcement.
... Since 1950's, significant research had been carried out on the soil-foundation system under machine-induced dynamic loading. The vertical vibration response of foundation resting on layered/reinforced ground was investigated experimentally to examine the effect of embedment depth, effect of saturation and effect of reinforcement through both laboratory model tests (Baidya and Krishna 2001;Mandal and Baidya 2004;Samal 2011;Khati et al. 2012;Clement et al. 2015) in-situ tests (Boominathan et al. 1991;Baidya and Rathi 2004;Baidya and Mandal 2006;. Major observations were made from these studies: (1) the layer thickness and position of layer significantly affected the dynamic response of the soil-foundation system, (2) stiffness and damping of the soil-foundation system increased with increasing the embedment depth, degree of saturation of sand and footing base area and (3) ground improvement by reinforcement also significantly increased the dynamic properties of the sand and hence, shifted the natural frequency and reduced the peak amplitude. ...
... However, it has been noticed that the use of natural fiber as reinforcing material under cyclic and dynamic loading is limited (Kirar et al. 2012;Maheshwari et al. 2012). Lab and field studies on large-scale model testing for assessing the dynamic response of reinforced soil through block vibration test (BVT) are scanty (Boominathan et al. 1991;Rangwala et al. 2010;Samal 2011;Khati et al. 2012;Clement et al. 2015). These authors had used geosynthetics (geotextiles and geogrids), polypropylene fibers and mild steel frame as reinforcement. ...
... This confirms that the natural frequencies of identically same model foundation mass are almost same even though the gradation characteristics of sands are different. Field tests carried out on in-situ blocks resting/embedded on/in unreinforced and reinforced conditions also reported natural frequencies in the range of 21.5-45 Hz (Boominathan et al. 1991;Baidya and Rathi 2004;Baidya and Mandal 2006). This proves that the scaling adopted in the present study is capable of simulating in-situ foundation behavior under dynamic loading. ...
Free vibration tests were conducted on scaled model footing resting on unreinforced and hair fiber-reinforced sand to determine the dynamic characteristics of the soil-foundation system. The sand was reinforced with the random mixing of unsorted human hair fibers collected from barber shops and compacted to a relative density (RD) of 80% in the model test tank. The percentage of fiber inclusion was varied up to 1.0% by dry weight of sand. The reinforced sand was prepared with an initial moisture content of about 2–3% to obtain the consistent uniform mixing. The sand bed was filled in eight layers of 10 cm each in loose condition. Each layer was compacted using a calibrated plate vibrator to achieve the desired relative density before filling the next layer. The free vibration tests were conducted in model test tank by varying the depth of fiber reinforcement (dr) and the width of the fiber reinforcement (wr) for different percentage of fiber inclusions, viz., 0.5%, 0.75%, and 1.0%. The results demonstrated that addition of even 0.5% human hair fiber with the sand can help in shifting the natural frequency of the soil-foundation system.
... The limited literature is available to understand the behavior of geosynthetics reinforced soil under machine induced vibration. Boominathan et al. (1991) studied the effectiveness of reinforced earth under the machine foundation through a series of field resonance tests. The tests were conducted over the foundation beds reinforced with different types of reinforcement materials. ...
... The unreinforced and geogrid reinforced conditions were prepared in the test pit having the dimensions of 2 m 9 2 m 9 1.2 m. To avoid the effect of the boundary on displacement amplitude of a system, the length and width of the bed were selected as 3.3 times the width of concrete block (Raman 1975;Boominathan et al. 1991). The soil available in the campus of IIT Patna was used for the preparation of foundation bed. ...
... Thus, the maximum increase in the resonant frequency of the foundation bed was observed in the case of 0.3B as compared to the 0.45B. Several researchers were made similar observations (Boominathan et al. 1991;Sreedhar and Abhishek 2016). Rib width (MD 9 XMD) mm 3. 3 Similarly, the effect of the eccentric angle on the resonance parameters (resonant amplitude and resonant frequency) of both conditions were investigated. ...
This paper describes the application of artificial neural network (ANN) and genetic programming (GP) methods in predicting the dynamic response of geogrid reinforced machine foundation bed. The dataset used in both models was determined through field bock resonance tests. A series of field tests were conducted over the unreinforced and geogrid reinforced foundation beds. The dynamic response was studied in terms of displacement—frequency variation. The response of both unreinforced and reinforced conditions was studied under six different dynamic force levels. From the experimental results, the significant improvement in the machine foundation performance was observed in the presence of geogrid reinforcement. The formulations for predicting displacement amplitude were developed using ANN and GP. In the formulation, depth of placement of geogrid, eccentric angle, the natural frequency of foundation soil system, damping ratio, shear strain, shear modulus and the operating frequency of a machine were considered as input variables. Primarily, the statistical performance of the models was compared through different performance indices. In addition, different algorithms were described to identify the ranking of influencing parameters, which affect the dynamic response of a geogrid reinforced bed. From the analysis, the resonant parameters predicted from the models have shown good agreement with the field test results. The operating frequency was found to be the most influencing parameter for determining the displacement amplitude of the machine foundation bed. Further, the performance of the GP model was found more accurate for predicting the response of a system than the ANN model.
... The response of neighboring structures and equipment depends on the dynamic characteristics of the foundation soil, along with the distance from the vibration source (Moghaddas Tafreshi et al. 2022). Enhancing the dynamic characteristics of the foundation soil through various reinforcement methods, such as the use of materials like high tensile wire, bamboo grid, fiber, rubber sheets, rubber soil mixtures, geotextile, geocell, and geogrid, mitigates machineinduced vibration and its transmission effectively (Boominathan et al. 1991;Santhakumar et al. 2001;Haldar and Sivakumar Babu 2009;Clement et al. 2015;Samal et al. 2016;Sreedhar and Abhishek 2016;Venkateswarlu and Hegde 2017;Venkateswarlu et al. 2018;Dhanya et al. 2019;Hegde and Venkateswarlu 2019;Li et al. 2020;Venkateswarlu and Hegde 2020a, b;Zakeri et al. 2021;Hasthi et al. 2022;Venkateswarlu and Hegde 2023;Kuvat et al. 2024). Applying the geogrid has drawn significant attention in recent years as a remedy for machine-induced vibrations (Clement et al. 2015;Samal et al. 2016;Sreedhar and Abhishek 2016;Venkateswarlu et al. 2018;Venkateswarlu and Hegde 2020b). ...
... Hence, this study explores the attenuation response of unreinforced and geogrid-reinforced foundation beds and the effectiveness of the geogrid in controlling vibration propagation. Additionally, many of the existing studies (Boominathan et al. 1991;Santhakumar et al. 2001;Clement et al. 2015;Samal et al. 2016;Sreedhar and Abhishek 2016;Venkateswarlu et al. 2018;Dhanya et al. 2019;Venkateswarlu and Hegde 2020b) have focused on the dynamic response of geogrid-reinforced cohesionless foundation beds experimentally and numerically, leaving the response of geogrid-reinforced cohesive soils for isolated and interacting machine foundations unexplored. Hence, this study develops a 3D FE model to effectively capture the resonant amplitude (z r ) and resonant frequency (f mr ) of active and passive footings on unreinforced and geogrid-reinforced foundation beds. ...
The current study encompasses experimental and numerical investigations on the response of closely placed machine foundations resting on unreinforced and geogrid-reinforced soil beds. Large-scale field block vibration tests are performed on isolated and closely spaced block footings resting on prepared foundation beds at IIT Kanpur, India. The dynamic interaction between machine foundations is explored by considering various combinations of footings, in which one footing (active footing) is dynamically loaded, while the other (passive footing) is loaded statically. The tests involve three eccentric force settings for four distinct footing combinations at different clear spacings and reinforcement conditions. Steady-state vibrational responses are recorded for both active and passive footings. The experimental outcomes indicate that incorporating the geogrid causes a reduction in the resonant displacement amplitude and an improvement in the resonant frequency of both active and passive footings. For active footings, the resonant displacement amplitude decreases by 27%, while the resonant frequency increases by 21% in the presence of the geogrid. In contrast, for passive footings, the presence of the geogrid leads to a decrease in the resonant displacement amplitude by 21% and an increase in the resonant frequency by 1.2 times. The current investigation also presents the attenuation response of unreinforced and reinforced soil beds. The geogrid mitigates vibration propagation efficiently by reducing ground-borne vibrations. Including the geogrid in the foundation bed reduces ground vibrations by 39% at a distance of 0.6 m from the vibration source. A 3D finite-element (FE) model is developed for the numerical analysis. The established FE model captures the dynamic interference effect and the attenuation response under different bed conditions. A comparative study between the experimental and the numerical results demonstrates a promising level of agreement, affirming the efficacy of the developed numerical model.
... Very limited literature is available to understand the behavior of geosynthetics reinforced soil under machine foundations. Boominathan et al. (1991) have conducted the block resonance tests to understand the dynamic response of reinforced earth under vertical mode of vibrations. Geotextile and geogrid made up of high tensile wire grid have been used as a reinforcement material in this investigation. ...
... In addition, the provision of geogrid reinforcement slightly improved the natural frequency of the foundation soil system. Boominathan et al. (1991) and Sreedhar and Abhishek (2016) have reported the improvement in natural frequency of the system in the presence of reinforcement. Figure 8.11d shows the dynamic response of a two-layer geogrid reinforced soil system. From the figure, it is observed that the rate of reduction in displacement amplitude is high as compared to the single geogrid reinforced condition. ...
The present chapter describes the results of large-scale field vibration tests and cyclic plate load tests conducted on geosynthetics reinforced soil beds. A series of vertical mode block resonance tests are conducted over a rigid concrete footing resting on different reinforced soil conditions. The tests are performed in a test pit of size 2 m × 2 m × 0.5 m using a concrete footing of size 0.6 m × 0.6 m × 0.5 m. Four different conditions, namely unreinforced, single-layer geogrid reinforced, two-layer geogrid reinforced and geocell reinforced conditions were considered. The tests are performed under six different dynamic force levels using a Lazen-type mechanical oscillator. In total, 38 number of field tests are conducted. The dynamic response is studied in terms of reduction in resonant amplitude, peak particle velocity (PPV) and improvement in dynamic properties of the soil. Experimental results revealed that the displacement amplitude of vibration significantly reduced in the presence of geosynthetics. The maximum reduction is observed in the presence of geocell reinforcement as compared to other conditions. In the presence of geocell reinforcement, the resonant amplitude is decreased by 61% and the natural frequency of the soil system is increased by 1.38 times as compared to the unreinforced condition. In addition, the geocell reinforcement found to reduce the PPV by 48% at a distance of 0.5 m from the footing face. The elastic uniform compression of the foundation bed is improved by 91% in the presence of geocell reinforcement. From the cyclic plate load test results, four times improvement in natural frequency of the foundation soil system and 92% reduction in amplitude of the vibration were observed by the combined utilization of geocell and geogrid.
... The study of Hegde and Sitharam (2016) reported the efficacy of the geogrid and geocell in improving the dynamic properties of a soft clay bed. Various studies described the behavior of geogrid and geotextile reinforced soil in controlling the amplitude of machine induced vibration (Boominathan et al. 1991;Haldar and Sivakumar Babu 2009;Heidari and El Naggar 2010;Sreedhar and Abhishek 2016;Clement et al. 2015). Very few studies have examined the isolation behavior of geocell-reinforced beds supporting the machine foundations. ...
... The increase in stiffness of the foundation bed in the presence of geocell was the reason for the significant reduction in resonant amplitude of a system. Several researchers have made a similar observation (Boominathan et al. 1991;Mandal et al. 2012;Gao et al. 2017;Venkateswarlu et al. 2018a). ...
This paper investigates the isolation efficacy of geocell-reinforced foundation beds infilled with different materials through a series of block resonance tests. The geocell made with a novel polymeric alloy (NPA) was used in the experimental investigation. In total, five different cases — namely, unreinforced, geocell-reinforced silty sand, geocell-reinforced sand, geocell-reinforced slag, and geocell-reinforced aggregate — were considered. Presence of the geocell has resulted in improvement of screening efficacy of the foundation bed regardless of the infill material. The displacement amplitude of the geocell-reinforced bed cases was reduced by 68%, 64%, 61%, and 59%, respectively, for aggregate, slag, sand, and silty sand infill cases as compared to the unreinforced condition. Maximum isolation efficiency was observed in the presence of aggregate, among the four different infill materials. In the presence of aggregate infill, the shear modulus of the foundation bed was improved by 150%. Similarly, the peak particle velocity and peak acceleration were reduced by 57% and 48%, respectively. Further, the efficacy of mass spring dashpot (MSD) analogy was studied in predicting the frequency–displacement response of different reinforced cases. From the analytical study, a significant improvement in damping ratio of the foundation bed was observed in the presence of geocell reinforcement.
... However, very limited investigation has been carried out to understand the probable benefits of geosynthetics in enriching the performance of machine foundation. Boominathan et al. [28] investigated the effectiveness of the reinforced earth under the machine vibrations. The study was carried out by performing a series of field block resonance tests over the reinforced soil bases with different types of planar reinforcements. ...
... Further, IS 5249 [77] recommends that the ratio between the width of the test pit to the width of the machine foundation is three for conducting the block vibration test. Boominathan et al. [28] studied the dynamic response of foundation bed by considering the test pit size 3 times the width of the machine foundation. Hence, in the present study, the width of the foundation bed was considered equal to the 3.3 times the width of machine foundation. ...
This paper investigates numerically the potential use of cellular confinement systems in isolating the machine induced vibrations. The numerical analysis was carried out using the three dimensional explicit finite difference package FLAC3D. Primarily, the numerical model was validated with the results of field resonance tests, performed on the foundation beds reinforced with and without cellular confinement systems. The 3D cellular confinement was simulated using two techniques, namely, Equivalent Composite Approach (ECA), and Honeycomb Shape Approach (HSA). The isolation efficiency of the confined cell was determined in terms of the reduction in displacement amplitude, peak particle velocity, and the improvement in elasticity of the foundation bed. From the results, 56% reduction in displacement amplitude was observed in the presence of geocell reinforcement. Similarly, 42% change of resonant frequency was observed as compared to the unreinforced condition. The elasticity of the foundation bed was improved by 102% with the provisions of geocell. Further, it was noticed that the modelling of geocell through the HSA approach provided the accurate prediction of the experimental results. With the help of HSA technique, the effect of confinement area and the height of geocell in reducing the amplitude of vibration was investigated. Further, the parametric study was conducted to investigate the effect of different geocell properties on the dynamic behaviour of reinforced foundation bed. The parametric study results revealed that the geocell modulus and the interface friction angle directly influence the performance of geocell reinforced bed under dynamic loading condition.
... However, limited studies have been performed to understand the performance of geosynthetics under machine foundations. Boominathan et al. (1991) performed forced block resonance tests on reinforced silty sand beds. Test results revealed that the increment in coefficient of elastic uniform compression and shear modulus in the presence of high tensile wire grid. ...
... The provision of geogrid alters the tensile strength and natural frequency of the foundation soil, might be the reason for the decrease in displacement amplitude. The similar pattern was observed in experimental study results of many researchers (e.g., Boominathan et al. 1991, Sreedhar and Abhishek 2016and Kirar et al. 2016). Figure 7 Variation of displacement amplitude with geogrid location Figure 8 represents the variation in displacement amplitude of geocell reinforced foundation bed. ...
The foundation beds are often subjected to dynamic loads due to many circumstances, such as earthquakes, traffic loads, and the machine vibrations in the case of the machine foundations. Excessive vibrations caused by the dynamic sources can lead to the structural damage of the foundation soil. Over the years, geosynthetics have been effectively used in reducing the settlement of the foundations under static loads. However, the performance of geosynthetics is not fully analyzed under the dynamic loads. In the present study, the numerical analyses have been carried out to understand the performance of the machine foundations resting on the geocell reinforced beds. The analyses were carried out by using finite element software PLAXIS 2D. The hypothetical case of the circular machine foundation of 1 m diameter resting on the saturated silty sand was analyzed. Mohr-Coulomb failure criteria was used to simulate the behavior of the soil. Initially, the numerical model was validated with the existing results reported in the literature. The validated numerical model was further used to investigate the performance of the machine foundations. Three different cases, namely, unreinforced, geogrid reinforced and geocell reinforced were considered. The response of all the cases was studied by varying the frequency of dynamic excitation and maintaining the constant force amplitude. The depth of the placement of the geocell and geogrid was also varied. At the optimum location of geocell, 61% reduction in the displacement amplitude was observed as compared to unreinforced foundation bed. Similarly, as compared to geogrid, more than 50% reduction in the displacement was observed in the presence of geocell. In addition, 40% reduction in peak particle velocity was observed in the presence of geocell at the center of the footing. The resonant frequency was found to vary with the reinforcement system. Furthermore, 163% increase in the damping ratio of the soil was observed in the presence of geocell. In this way, the study highlights the possible new applications of geocell in supporting the machine foundations.
... Very limited literature is available to understand the behavior of geosynthetics reinforced soil under machine foundations. Boominathan et al. (1991) has conducted the block resonance tests to understand the dynamic response of reinforced earth under vertical mode of vibrations. Geotextile, and geogrid made up of high tensile wire grid has been used as a reinforcement material in this investigation. ...
... In addition, the provision of geogrid reinforcement slightly improved the natural frequency of the foundation soil system. Boominathan et al. (1991), and Sreedhar and Abhishek (2016) have reported the improvement in natural frequency of the system in the presence of reinforcement. Fig. 8d shows the dynamic response of a two layer geogrid reinforced soil system. ...
The manuscript describes the results of large scale field tests and numerical studies conducted on geosynthetics reinforced soil beds supporting model machine foundation. A series of vertical mode block resonance tests are conducted over a rigid concrete footing resting on different reinforced soil conditions. The tests are performed in a test pit of size 2 m × 2 m × 0.5 m using a concrete footing of size 0.6 m × 0.6 m × 0.5 m. Four different conditions, namely, unreinforced, single layer geogrid reinforced, two layer geogrid reinforced and geocell reinforced conditions were considered. The tests are performed under six different dynamic force levels using a Lazen type mechanical oscillator. In total, 38 number of field tests are conducted. The dynamic response is studied in terms of reduction in resonant amplitude, peak particle velocity (PPV) and improvement in dynamic properties of the soil. Experimental results revealed that the displacement amplitude of vibration significantly reduced in the presence of geosynthetics. The maximum reduction is observed in the presence of geocell reinforcement as compared to the other conditions. In the presence of geocell reinforcement, resonant amplitude is decreased by 61% and the natural frequency of the soil system is increased by 1.38 times as compared to the unreinforced condition. In addition, the geocell reinforcement found to reduce the PPV by 48% at a distance of 0.5 m from the footing face. The elastic uniform compression of the foundation bed is improved by 91% in the presence of geocell reinforcement. Further, the experimental results are validated with the numerical studies conducted by using finite difference package FLAC3D. The encouraging agreement in the dynamic behavior of reinforced soil is observed between the numerical and experimental studies. The numerical results revealed that the lateral spreading of vibrations is significantly controlled in the presence of geocell reinforcement.
... Ground improvement enhances the strength of soil and hence limits the dynamic parameters within the permissible range. Significant works had been conducted on the soil-foundation system (Layered/reinforced soil) subjected to machine-induced dynamic loads to investigate the effects of various parameters such as embedment depth, saturation, reinforcement through model tests (Mandal & Baidya 2004;Samal 2011;Khati et al. 2012;Clement et al. 2015) and in-situ tests (Boominathan et al. 1991). ...
... Ground improvement using different reinforcing materials (metal strips, geosynthetics or fibers) had been successfully implemented in different applications under static loading. However, it has been noticed that the use of fibers and geosynthetics as reinforcing material with the soil under machine foundations is not explored much (Boominathan et al. 1991;Khati et al. 2010;Samal 2011;Clement et al. 2015). ...
The free vibration tests were conducted on model footing resting on unreinforced and reinforced. The sand was reinforced with the human hair fibers and geogrids (PET and HDPE). The fiber inclusion was considered as 0.5% by dry weight of sand. The sand bed was filled in 8 layers, and each layer was compacted using a calibrated plate vibrator to achieve the desired relative density (80%). The free vibration tests were conducted in model test tank by varying the depth of reinforcement (dr) by keeping the width of reinforcement (wr) as constant. The results indicate that the hair fiber reinforcement and geogrid reinforcement could improve the natural frequency of the soil-foundation system. Damping is found to reduce with the inclusion of both reinforcing materials.
... Comparing to the studies performed in static loading, less investigations have been carried out for cyclic loading, especially on randomly distributed fiber reinforcement. Among such studies are Boominathan et al [8], Krishnaswamy and Isaac [9], and Vercueil et al [10] which mostly concentrate on evaluation of the dynamic behavior of soils reinforced with plane elements using cyclic triaxial test, torsion shear test, and resonant column test. Other studies such as Noorany and Uzdavines [11], Maher and Woods [12], Feng and Sutter [13], Li and Ding [14], and Boominathan and Hari [15] were focused on dynamic behavior of soils with randomly distributed fiber reinforcement. ...
... The histories of pore pressure at the top and bottom point of the sample, axial displacement, shear strain, and deviatoric stress as well as the stress path were then obtained. The test results performed on a sample reinforced by carpet strips with side ratio of 1 and mixture ratio of 0.5 percent at the confining stress of 100kPa after the 10 th loading step are presented in Figures (6) to (8). ...
... Besides, high interparticle friction and rubber particle deformation in the sand-rubber skeleton enhances the frictional and hysteresis damping, respectively [18]. In the latter case, at higher amplitudes of acceleration and subsequent vibration displacement, the high shear stiffness along with lateral resistance mechanism induced by the confinement effect of geogrid reinforcement limits horizontal acceleration amplitude [102]. Furthermore, the geogrid reinforcement was found to improve the natural frequency of the GSI bed, in line with the findings of Sreedhar & Abhishek [103] and Venkateswarlu et al. [104]. ...
In the present study, a geotechnical seismic isolation (GSI) bed, composed of geosynthetic-reinforced sand–rubber tire shred mixture layer between the base of the building foundation and the supporting soil medium, is considered to mitigate ground vibrations. The index and engineering properties including dynamic properties of sand–rubber tire shred mixtures are carried out to assess their suitability for seismic base isolation of buildings. In addition to that, the liquefaction resistance of sand rubber mixtures is also evaluated. Further, laboratory-based model experiments and Finite Element (FE) modeling was carried out for footing resting on geogrid-reinforced GSI layer under static loading. Further, 2D seismic response of a typical building on GSI was also carried out using finite element code ABAQUS. Finally, results of a series of field experiments conducted to study the response of model footing resting on the geogrid-reinforced GSI bed subjected to horizontal ground vibration are presented. Further, a 3D finite element (FE) model of the field study was developed in the time-domain to simulate and investigate the response of geogrid-reinforced GSI bed on a multi-layered soil system for different surface wave characteristics. In general, it was found that GSI with geogrid reinforcement is found to be effective in the mitigation of ground vibrations due to earthquakes and other source of vibration.
... Besides, high interparticle friction and rubber particle deformation in the sand-rubber skeleton enhances the frictional and hysteresis damping respectively (Feng and Sutter 2000). In the latter case, at higher amplitudes of acceleration and subsequent vibration displacement, the high shear stiffness along with the lateral resistance mechanism induced by the confinement effect of geogrid reinforcement limits horizontal acceleration amplitude (Boominathan et al. 1991). Furthermore, the geogrid reinforcement was found to improve the natural frequency of the GSI bed, in line with the findings of Sreedhar and Abhishek (2016) and . ...
... Thus, maintaining the foundation bed behaviour closer to the elastic state reduce the effect of vibrations. In this context, a few researchers have studied the behaviour of reinforced soil beds under vibration loading conditions [2,3]. In modern times, geosynthetics are widely used to reinforce soil foundations [4][5][6]. ...
The reliable estimation of displacement amplitude is the prime factor for the design of geo-structures supporting the vibration loads. Currently, very subtle knowledge is available to compute the displacement amplitude of footing resting on the geocell-reinforced bed subjected to vibration loading. The advent of artificial intelligence modelling has antiquated many traditional approaches. Thus, in the present study, a novel hybrid paradigm has been developed by combining the artificial neural network (ANN) with dragonfly optimizer (DFO), abbreviated as ANN-DFO. To train and test the model, the reliable database was developed by conducting extensive field vibration tests. To establish the specific prediction target for the proposed model, displacement amplitude (da) was considered as an output index. A combination of parameters involving properties of foundation bed, geocell reinforcement, and dynamic excitation has been considered as input variables. Along with the standalone ANN model, the predictive veracity of the ANN-DFO was also compared with three other robust machine learning models, namely, Gaussian process regression (GPR), random forest (RF), and M-5 rules. Primarily, the forecasting ability of the developed models was assessed based on rigorous statistical criteria and a multi-criteria approach. Moreover, the model is also validated against the entirely new independent data which is not part of the original dataset. From the results, ANN-DFO model has shown a superior performance in predicting the displacement amplitude of footing resting on geocell-reinforced beds as compared to the other benchmark models. Finally, the strength of input variables on the estimation of displacement amplitude was highlighted using the sensitivity analysis.
... It includes rows of solid piles, pile barriers, open and infilled trench barrier systems (Dasgupta et al. 1990;Al-Hussaini and Ahmad 1996;Adam and Von Estorff 2005;Gao et al. 2006;Alzawi and El Naggar 2011;Huang and Shi 2013;Esmaeili et al. 2014;Bose et al. 2018;Meng and Shi 2018 Accepted manuscript doi: 10.1680/jgein.21.00050 implementation becomes a challenging task in urban regions due to soil instability, ground subsidence, groundwater conditions, and underground lifelines. In such circumstances, the concept of reinforced earth is preferred to strengthen the foundation bed under vibration loads (Boominathan et al. 1991;and Heidari and El Naggar 2010). Among the reinforcement products, geocell was found to offer superior performance in improving the stiffness of the foundation beds (Hegde 2017). ...
The manuscript is aimed to provide numerous insights into the behavior of the geocell reinforced bed subjected to a vibration load. Vibration propagation mechanism, displacement, and stress response of geocell reinforcement have been described. Two different cases, namely, unreinforced and geocell-reinforced beds subjected to a vertical mode dynamic excitation have been analyzed using the finite-difference package FLAC 3D . Initially, the developed numerical model was validated with the results of field vibration test. Results revealed that the inclusion of the geocell reinforcement in the foundation bed significantly improves vibration isolation efficacy. The foundation bed strain due to vibration loading was reduced by 67% due to the provision of geocell reinforcement. Based on the observed wave propagation behavior of the geocell reinforced bed, a mechanism was proposed to quantify the diffraction angle and the dispersion distance of induced vibration. The diffraction angle was found to vary between 50° to 63° in the presence of a geocell mattress. The dynamic stress factor calculated based on the hoop stress theory was found to vary between 1.5 to 2 for geocell with different infill materials. Further, parametric analysis was performed to understand the effect of geocell geometry on the peak particle velocity (PPV) response of the reinforced bed.
... Further, the concept of reinforced earth has attained significant importance in improving the behavior of several civil engineering applications [15][16][17][18][19][20]. Saride and Dutta [21] reported the potential use of fly ash in enriching the behavior of expansive clay beds supporting the machine foundation. ...
This manuscript evaluates the effect of various influencing factors on the vibration mitigation efficiency of geocell-reinforced foundation beds. Parameters investigated include the width of geocell, depth of placement of geocell below the footing, depth of embedment of footing, infill materials, and the dynamic force level of the excitation. The effect of aforesaid parameters was studied by performing field vibration tests over the reinforced test beds of 3.6 m × 3.6 m × 1.2 m. To understand the vibration isolation efficacy, different vibration indicators, viz., displacement amplitude, peak particle velocity (PPV), and peak acceleration were evaluated. From the results, reinforcing the soil bed with geocell was found to be a worthwhile approach to control the vibration parameters. For achieving the maximum isolation, the optimum width and depth of placement of geocell were found to be 5B and 0.1B respectively. At its optimum width and depth of placement, the peak particle velocity was reduced by 50%. Similarly, it was observed that the 53% drop in the peak displacement amplitude of the foundation bed. Vibration parameters in the geocell reinforced case were found attenuated with the increase in footing embedment and modulus of infill material. On the other hand, the vibration parameters of the unreinforced and geocell reinforced cases were amplified distinctly due to the increase in dynamic excitation.
... It is therefore more common that fibrous reinforcement, distributed evenly throughout the construction material, is used to stabilise SBCMs, and such reinforcement can be divided into either 'natural' or 'synthetic' fibres. Examples of 'natural' fibres used and investigated in SBCMs include wool (Aymerich et al., 2012;Readle et al., 2015), hemp (Aymerich et al., 2016;Dugdale, 1960), seaweed (Achenza and Fenu, 2006) and straw (Clementi et al., 2008;Quagliarini and Lenci, 2010;Schroeder, 2011;Serrano et al., 2012), while 'synthetic' fibres include plastic (Binici et al., 2005), nylon (Kumar and Tabor, 2003), fibreglass (Consoli et al., 1998) and steel fibre (Boominathan et al., 1991). ...
Soil-based construction materials (SBCMs) are formed of a mixture of gravel, sand and clay
which, when mixed with water, may be used for construction. They are an environmentally-
friendly alternative to more traditional construction materials such as concrete and fired brick.SBCMs commonly incorporate foreign material into the soil to enhance the material properties. As awareness and use of SBCMs increase, new methods of reinforcement must be discovered to reduce the reliance on more environmentally harmful resources as a stabiliser (such as cement) to strengthen the material.
In this thesis, waste wool fibres from a carpet manufacture are investigated as a potential
alternative fibrous reinforcement in rammed earth (RE), and its effect on the behaviour of
stabilised and unstabilised RE is assessed. Compressive tests, shear tests and wedge splitting tests are performed to study the effect of fibrous (wool) and chemical (cement) stabilisation on RE, and recommendations on further use of these materials are made. Tests are also performed to investigate the shrinkage of different clays (bentonite and kaolinite) used in RE when mixed with sand or wool, in order to determine the effects of these materials on shrinkage behaviour.
Finally, advice is provided regarding the use of fibrous reinforcement in SBCMs, which is
applicable to both the SBCM industry and research, and new and pre-existing research areas are identified to prompt further study.
... However, practical implementation of such measures is a challenging task in urban areas due to soil instability, ground subsidence, underground lifelines, and cost. Alternatively, the concept of reinforced earth was suggested as an economical and adaptable approach to modify the soil response under dynamic situations (Boominathan et al. 1991). The evolution of this method introduced different reinforcement products, each trying to serve single or multiple functions. ...
This study describes the influence of various factors on the dynamic response of geocell reinforced beds subjected to machine induced vibration. A series of field vibration tests were conducted on two different foundation beds, namely, unreinforced and geocell reinforced. The studied factors include depth of placement of geocell, the width of geocell, and infill materials. Four different geo-materials were used to quantify the effect of infill material on geocell performance. From the results, the optimum width and depth of placement of the geocells for the maximum improvement in the performance were observed as 5B and 0.1B respectively. At the optimum width and depth of placement, a 49% reduction in peak particle velocity (PPV) of the foundation bed was observed. In addition, the peak displacement amplitude of vibration was decreased with the increase in the angle of shearing resistance (φ) of infill material.
... Currently, the reinforced earth technique being popularly used for strengthening the subgrade in order to support the static and cyclic loads (Hegde, 2017). Boominathan et al. (1991) and Haldar and Sivakumar Babu (2009) studied the potential benefits of this method in reducing the vibration induced by industrial machines. In addition, the use of geosynthetics was well-studied for strengthening the track performance (Biabani and Indraratna, 2015;Biabani et al., 2016;Nimbalkar and Indraratna, 2016). ...
This paper describes the potential use of geocell reinforcement in mitigating the traffic
induced vibration. The vibration caused by the vehicular movement was simulated over
the unreinforced and geocell reinforced sections using a mechanical oscillator. The
displacement amplitude and peak particle velocity were measured to understand the
vibration mitigation efficacy of geocell. The effect of depth of placement of geocell
on the mitigation of vibration parameters was studied. The inclusion of geocell was
found effective in reducing the induced vibration based on the experimental results.
The vibration mitigation efficacy of geocell was improved significantly at the shallow
depth of placement of geocell mattress. The improvement in elasticity of the subgrade
was observed maximum when the geocell was placed at a depth of 0.1B from the
ground surface. Further, analytical and numerical approaches were used to predict the
displacement amplitude vs. frequency response of reinforced soil sections. FLAC3D was
used for performing the numerical investigation. The geocell was modeled according to
its honeycomb shape to acquire the accurate response of geocell reinforced section.
Whereas, mass spring dashpot analogy was followed for the analytical evaluation. In
overall, the amplitude response predicted from the numerical and analytical studies were
found to be in good agreement with the experimental results.
... Limited studies have been conducted on the performance of reinforced foundation bed to support the machine foundation. The study of Boominathan et al. (1991) revealed that the role of reinforced earth was effective in controlling the machine vibrations. The soil reinforced with high tensile wire grid found to improve the shear modulus by 60%. ...
The present study investigates the efficacy of geosynthetics in improving the performance of machine foundation. A series of block resonance tests were conducted over the soil beds reinforced with the different type of geosynthetics. Three different cases, namely, unreinforced, geogrid reinforced, and geocell reinforced cases were considered. The experimental results have shown that the performance of geocell is more effective than geogrid and unreinforced conditions. In the presence of geocell, the displacement amplitude and peak particle velocity were reduced by 53% and 46% respectively, as compared to the unreinforced condition. Similarly, the maximum improvement in resonant frequency of the unreinforced soil bed was observed in the presence of geocell reinforcement. Further, the resonant frequency obtained from the field study was compared with the analytical solution derived from mass spring dashpot model. The resonant frequency obtained from the analytical solution has shown good agreement with the frequency obtained from the experimental study.
... So far, the limited work has been conducted on the application of geosynthetics in the field of machine foundation. Boominathan et al. (1991) conducted block resonance tests to investigate the dynamic properties of geosynthetic reinforced soil. Test results revealed that the significant improvement in elastic compression and reduction in amplitude was observed in the presence of high tensile wire grid. ...
... Trafiğin oluşturduğu dinamik yüklemelere maruz yol inşaatlarõnda taban zemini ve yol üst yapõsõnõ statik yüklere göre tasarlamak çok doğru bir yaklaşõm olmamaktadõr. Bu nedenle, bir çok araştõrmacõ, gerçekleştirdikleri çalõşmalarda etkiyen dinamik yükleri daha gerçekçi benzetebilmek için farklõ deney yöntemleri [9][10][11][12][13][14][15][16] ve farklõ teorik modeller [17][18][19] kullanmõşlardõr. Bu doğrultuda, bazõ araştõrmacõlar yol ve demiryolu taban zeminlerindeki güçlendirmelerin tekrar yükler altõndaki mukavemete etkisini incelemişlerdir [20][21][22]. ...
SUMMARY Recently, high quality geosynthetic materials will be highlighted, especially the use of the reinforcement function of geosynthetics in geotechnical engineering practice, such as improvement of soft ground, stabilization of slopes, and construction of road and railway embankments etc. under static and especially dynamic loading. However, the advantageous application of geosynthetic reinforcements requires a better understanding of the mechanical behavior of reinforced soil on traffic induced vibrations. The objective of this study is to present the effect of reinforcement on the behavior uniform sand by reinforcing with random distributed geotextiles. In this context, a series of cyclic torsional shear test was performed on saturated sand sample reinforced with geotextiles. Consequently, it was observed that reinforcement is significantly effective on the improvement of undrained cyclic behavior of sands.
... Many investigations have also been carrie out to study the effect of embedment on the dynamic properties of soils [Savinov, (1955); Barkan, (1962); Novak et al., (1970) ;Chae, (1971); Stoke et al., (1974); Saran et al., (1979) and Vijayvargiya (1980)]. A few attempts have also been made to study the embement effect and dynamic response of soil reinforced with geogrids [Sharma, (1997) ;Samal, (2009) and Khati (2009)]. Hence, there is a need to study the behaviour of embedded machine foundation system resting on reinforced soil subjected to dynamic loads. ...
One of the most governing factors in the design of the foundation supporting the vibration sources is to reduce the amplitude of vibration. Vibration generated from industrial machinery is frequency dependant, and frequency has a significant influence on these design factors. Therefore, this manuscript describes the influence of frequency of loading on the vibration mitigation efficacy and the behaviour of geocell reinforced bed using the experimental and numerical studies. As part of the experimental study, a series of field vibration tests have been performed over the unreinforced and geocell-reinforced soil beds by varying the frequency of loading between 15 and 45 Hz. Using field tests, different vibration isolation parameters namely, velocity reduction ratio (VRR), vibration mitigation efficiency and attenuation coefficient have been studied. Numerical analysis has been conducted using FLAC3D to demonstrate the variation of VRR with respect to some of the key parameters namely, footing shape, geocell area, and relative density of infill. From the experimental results, vibration mitigation efficiency of geocell reinforced beds corresponding to distinct frequencies of loading i.e., 15 Hz, 25 Hz, and 45 Hz was observed as 39%, 43%, and 49%, respectively. The attenuation coefficient of a geocell reinforced bed was found to increase with the increase in frequency. Use of geocell reinforcement, notably minimized the strain generated over the foundation bed. However, the strain corresponding to the unreinforced and geocell-reinforced beds was increased with the increase in frequency of loading. VRR was found to decrease with the increase in geocell area and relative density of the infill material.
The fundamental aim in the proper design of machine foundations is to limit the response amplitude by preventing resonance in all vibration modes. The effects of static and dynamic forces and embedment depths for foundation-induced vertical vibration have been examined, experimentally and analytically using the Cone model. Therefore, various vibration indicators such as displacement amplitude, resonance frequency and complex dynamic stiffness were evaluated. Finally, the statistical properties, Quantile-Quantile plots, and Root-Mean-Square Error values were used to gain confidence in applying the Cone model for predicting the soil bed dynamic behaviour. Per the results, it was observed that embedment increases resonance frequency, natural frequency ratio and damping ratio while the maximum resonant amplitude reduces as the embedment depth increases. Given the findings, due to the increasing dynamic force, a drop in resonance frequency and a rise in peak displacement amplitude of the foundation bed were observed. On the other hand, resonance frequency and amplitude are attenuated with an increase in static force level. Further, the complex dynamic stiffnesses predicted by the Cone model shows good agreement with that obtained experimentally. Thus, whenever feasible, the convenient and relatively accurate Cone model can be performed for assessing foundation vibration in practical engineering projects.
The isolation of foundation systems from the ground vibrations has been one of the prime interests of geotechnical engineers. Over the years, different methods have been adopted to isolate the foundation systems from ground vibrations. The latest trend is to use the barrier systems made from the geosynthetics in such applications. An attempt has been made in this study to quantify the performance of the barriers created using geosynthetics in mitigating the vibrations. For the study purpose, a field vibration test was performed on the three different reinforced barrier systems prepared in a test pit of size 3.6 m × 3.6 m × 1.2 m. It includes unreinforced, geogrid, and geocell reinforced barriers. To generate the ground vibration, dynamic excitation of varying magnitude was applied using the mechanical oscillator supported on a concrete block. The isolation descriptors, namely amplitude attenuation factor, degree of efficiency, and attenuation coefficient, were evaluated to highlight the vibration isolation potential of each barrier system. From the field test results, the inclusion of the geosynthetics was found to enhance the isolation effectiveness of the barrier system significantly. Maximum improvement in isolation parameters was observed in the case of a geocell barrier as compared to other cases. In the geocell barrier condition, more than 52% increase in the degree of efficiency was observed as compared to the unreinforced barrier. Isolation efficacy of the geocell barrier system was further improved by infilling the geocell pockets with the geomaterial having a higher friction angle. Also, the geocell barrier exhibited the maximum value of the attenuation coefficient as compared to other cases.
The reuse of Computer Numerical Control (CNC) milling waste spirals is becoming a challenging task for numerous countries because of the annual increase in steel production integrated with the CNC machines. This paper presents the results of a study of some geotechnical properties of a low plasticity clay (CL) mixed with steel CNC milling waste spirals. The spirals had been first coated with zinc (galvanization) in order to decrease the corrosion rate, and then mixed with the CL at different ratios (5%, 10%, 15%, 20%, and 25% by dry weight). The response of the mixtures has been investigated using an intensive series of laboratory experiments including compaction, permeability, consolidation, unconfined compressive strength (UCS), and California bearing ratio (CBR) tests. The test results indicated a considerable decrease in optimum moisture content (wopt), and an increase in maximum dry unit weight (γDmax) with an increase in the amount of waste spirals in the mixtures. A decrease of about 34% in coefficient of permeability (k) was observed from a 25% addition of waste spirals in the soil. The consolidation tests indicated various levels of decrease in the swelling index (cs), and compression index (cc) values as a result of the addition of the waste spirals. It was also observed that the highest CBR value of 11.22% was obtained for a mixture with 20% waste, whilst the maximum UCS value of 390.11 kPa was achieved for a mixture with 15% waste.
The behavior of the machine foundation resting on the geosynthetic reinforced soil bed is not well understood yet. The present study investigates the efficacy of geosynthetics reinforcement in supporting the machine foundations. 3D numerical studies have been performed using the explicit finite difference package FLAC3D. The behaviour of a square footing, 0.6 m wide and 0.5 m deep resting on a non-homogeneous foundation bed has been analysed. Three different cases, namely, unreinforced, geogrid and geocell reinforced conditions were considered. The analysis was carried out by varying the frequency of the excitation. The depth of placement of geogrid and geocell was varied. From the results, the opti-mum depth of placement of geogrid and geocell was found to be 0.4B and 0.1B respectively from the ground surface. Similarly, the optimum width of placement of geocell and geogrid was found to be 4B. In overall, the performance of geocell was found to be better than other conditions. In the presence of geo-cell, displacement amplitude and peak particle velocity were reduced by 44% and 42% respectively as compared to the unreinforced condition. Further, the geocell reinforcement improved the stiffness as well as the resonant frequency by 1.8 and 1.3 times as compared to unreinforced condition.
Improving ash pond areas of thermal power plants for further construction of civil engineering structures in earthquake prone areas is a challenging task. Keeping this in view, studies on dynamic response of pond ash reinforced with geogrids were undertaken. The efficacy of using geogrid reinforcement was experimentally investigated by conducting block resonance tests in the field (ash pond areas of a particular thermal power plant of India). The resonant frequencies and maximum amplitudes of vibrations were recorded to evaluate the dynamic elastic constants and damping ratio. Test results indicate that reinforcing pond ash with the geogrid has a decreasing effect on the stiffness of pond ash as well as the magnitude of amplitude of vibration. The results of the experiments are of considerable practical significance and especially useful while designing structures or foundations on pond ash deposits where the natural frequency of the soil foundation system may be close to the operating frequency of the machine or structure and the maximum amplitude has the possibility of exceeding the permissible limits.
Soil reinforcement is defined as a technique to improve the engineering characteristics of soil. In this way, using natural fibers to reinforce soil is an old and ancient idea. Consequently, randomly distributed fiber-reinforced soils have recently attracted increasing attention in geotechnical engineering for the second time. The main aim of this paper, therefore, is to review the history, benefits, applications; and possible executive problems of using different types of natural and/or synthetic fibers in soil reinforcement through reference to published scientific data. As well, predictive models used for short fiber soil composite will be discussed. On other words, this paper is going to investigate why, how, when; and which fibers have been used in soil reinforcement projects.
Fibre from the New Zealand flax plant, Phormium tenax, or Harakeke as it is otherwise known in Maori, has been used to reinforce soil–cement composites in an attempt to improve the strength and ductility of the composite material. Previous investigations have found the interfacial bond strength between the harakeke fibre and the soil–cement matrix to be an important factor for the strength of the composite. In an effort to improve the interfacial bond strength, an enamel paint coating has been applied to the fibre surface. Fibre lengths of 70 and 85 mm have been investigated along with fibre content levels of 0.6% and 0.8% measured as a percentage of the dry mass of the soil in the composite. Significant improvement in the ductility of the soil–cement composite has been realised with the addition of the harakeke fibre-reinforcement. It has been found that the specific make-up of the composite with regard to fibre length and content is not critical for the achievement of ductility improvement. Instead, these parameters were found to be controlled more by manufacturing issues such as the workability of the composite. It was found that 85 mm represented an upper limit on fibre length for the manual mixing technique adopted, while a maximum fibre content level of 0.8% was achieved. In order to reduce manufacturing difficulties, different mixing techniques were studied. A successful tumble mixing technique has been identified which is able to improve composite uniformity and the ease of manufacture. Based on the similarity of results for the two fibre content levels investigated, it is recommended that a level of 0.6% be adopted as this both improves the ease of manufacture and minimises the amount of fibre required. When the fibre content level was dropped below 0.6%, it was found that the material exhibited a more brittle failure behaviour.
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