- Open Access
Experimental study on mitigation of liquefaction-induced vertical ground displacement by using gravel and geosynthetics
© The Author(s). 2018
- Received: 29 August 2018
- Accepted: 26 November 2018
- Published: 4 December 2018
Earthquakes in liquefaction-prone areas are frequently followed by the settlement of surface structures due to subsoil liquefaction. This paper aims to study the influence of geosynthetics along with gravel usage to reduce the vertical soil displacement caused by liquefaction using a shake table equipment. This influence is analyzed by means of measuring soil acceleration, pore water pressures and vertical soil deformation due to the shaking process.
Results of a series of 1-g shaking table tests which have been conducted in different initial relative densities which are 50% (loose sand conditions) and 90% (dense sand conditions) to evaluate the performance of proposed mitigation against settlement problem are presented. It is found that ground settlement reduced around 11.4 mm for loose sand conditions, from 20.9 mm in the case with no countermeasure (Case 1) to 9.5 mm in the Case reinforced with gravel and geosynthetics Type II (Case 4). Correspondingly, for dense sand states, the settlement decreased by about 1.8 mm, from 5.6 mm in the Case 1 to 3.8 mm in Case 4. Moreover, a differential settlement between loose sand and dense sand conditions decreased as well, around 9.6 mm, from 15.3 mm in the Case 1 to 5.7 mm in Case 4.
By conducted a series of shake table tests, it is confirmed that the vertical ground displacement decreased by the use of geosynthetics and gravel up to 54% and 32% for loose sand and dense sand states, respectively. Furthermore, test results also show that there is a decrease in the differential settlement between loose sand and dense sand conditions, around 62%.
- Vertical displacement
- Differential settlement
- Relative density
- Shaking table test
Liquefaction is one of the phenomena which occur in the saturated loose sand layer during an earthquake. It takes place when the pore water pressure reaches a particular value which is close to the total stress of soil. One of the consequences that can occur is structures built on top or within the liquefied ground may fail due to ground settlement.
Landfilled ground occasionally liquefies due to a large-scale earthquake and triggers deformations on the ground surface and undermine construction lying on it, for example, the roads (Takahashi et al. 2015). This phenomenon occurred because the liquefied layer is having low strength when shocked with large amplitude seismic waves, caused large movements to the road surface, and as a result, deformation of the road surface took place. Nevertheless, even though the road surface was composed of asphalt and roadbed and had high-strength if the ground under the road surface is liquefied, the deformation will occur.
Many types of research have been carried out to investigate the ground displacement due to liquefaction phenomenon. For example, Ueng et al. (2010) presented that significant volume changes occur only when there is liquefaction of sand. Otherwise, the settlement is tiny. Among the variety of liquefaction countermeasure methods proposed, the use of gravel, geosynthetics, or geosynthetics in conjunction with gravel attracted some attention due to their effectiveness and relatively low cost. This method is thought to be a good technique to mitigate liquefiable soil problems. For instance, as presented by Murakami et al. (2010), a combination of geosynthetics and gravel to restrain liquefaction in embankments, focused on the vertical displacement of the embankments. The result showed that the settlement of the embankments decreased by nearly 35% by using gravel and geosynthetics. They concluded that the use of geosynthetics sandwiched between gravel would have high resistance to bending deformation due to the overburden load of the embankment. Even though this method does not overcome the occurrence of liquefaction completely, it does alleviate the excessive deformation such as settlement and lateral movement. Correspondingly, Noorzad and Amini (2014) pointed out that the fiber attachments considerably enhanced liquefaction resistance of sand specimens. Upon raising the fiber content and fiber length, the number of loading cycles leading to liquefaction enlarged.
Harmoniously, some other research also showed corresponding results, for example by use gravel presented by Orense et al. (2003), Morikawa et al. (2014), and Chang et al. (2014), and geosynthetics utilized reported by Vercuil et al. (1997), and Boominathan and Hari (2002).
Research related to the use of gravel combined with geosynthetics in order to mitigate ground deformation triggered by liquefaction is poorly investigated. This proposed mitigation method is expected to be widely used to overcome ground settlement due to liquefaction since it has the following advantages; 1) more economical compared to other methods such as vibration or sand piling. According to the Japanese Geotechnical Society (JGS) Kanto branch, ground reinforcement by using the banded geosynthetics type Paralink 300 L, the cost is around 1250 JPY (12 USD)/m2, whereas by using static clamping sand piling method about 20,000–30,000 JPY (180–270 USD)/m2 and by vibration type SCP method approximately 10,000 JPY (90 USD)/m2. 2) more workable, due to this method is simpler to be executed. 3) lower impact on the surrounding environment, because of vibration and noise caused by the use of heavy equipment during the installing process is less than other methods. 4) high strength and durability; Geosynthetics are material which provide high tensile strength and high durability due to its resistance to heat, weather, and chemical effects.
This paper highlights on studying the performance of the gravel along with geosynthetics to reduce liquefaction-induced vertical ground displacement by conducting a series of shaking table tests. The effectiveness of the gravel and geosynthetics was evaluated through the settlement occurred at the ground surface.
Shaking table test
Index properties of the materials used
Silica sand No. 7
Crushed stone No. 5
Geosynthetic Type I
Geosynthetic Type II
Density, ρ, g/cm3
Mean grain size, D50, mm
Relative density, Dr, %
50 & 90
Tensile strength, T, kN/m
Tensile stiffness, EA, kN/m
Tokyo Sokki Kenkyujo
Water pressure meter
-50 ~ + 50 kPa
150 mm/5.9 in
Tokyo Sokki Kenkyujo
Input harmonic wave used were as follows: frequency 5 Hz, a target maximum input acceleration of around 80 cm/s2, and a shaking duration time of 15 s.
Ground amplification test
To determine the impact of gravel and geosynthetic usage on ground acceleration, in the loose and dense sand conditions, a series of additional tests were performed. The results of this test will be analyzed and will be determined by changes in the ratio of amplification factors on each test. The ratio of the amplification factor is the ratio between the amplitude acceleration measured at the ground surface divided by the amplitude of the input acceleration on each test performed. In this test, only two cases observed, namely Case 1 and Case 4. Case 4 was chosen to represent the ground with the reinforced material (Cases 2, 3 and 4). It is thought that these three cases will result in similar results in this ground amplification test.
Pull out test
The test tank used in the pull-out test is built from galvanized steel and acrylic with inner dimensions: 0.8 m long, 0.6 m wide and 0.6 m high. The geosynthetics and sand used are the same as those used in the shake table test. Tensile force, displacements and normal stress were observed.
A summary of the data resulted in pull-out test, ground amplification test, and primary data measured during the shaking table test such as excess pore water pressure, acceleration, and settlement of ground surface are presented and discussed.
Pore water pressure
Generally, the results obtained show an insignificant difference in all cases, both for P1 and P2. As can be seen in Fig. 7, for water pressure meter placed in the loose sand zone (P1), although the maximum PWPR obtained is around 1 for Case 2, but the maximum value in Cases 1 and 3 is also immensely close to 1, around 0.97, which indicate that liquefaction occurred. In Case 4, the maximum PWPR is only slightly lower and showed a faster water pressure dissipation, compared to other cases. Correspondingly, for the dense sand state (P2), the maximum PWPR acquired is almost similar for all cases of about 0.4, even though the highest PWPR in Case 4 is little higher compared to other cases. These results signify that no liquefaction occurred in this zone.
According to the results, it can be said that the effect of the use of gravel and geosynthetics on pore water pressure is insignificant in these experiments. Since the main purpose of pore water pressure measurement is to determine the occurrence of liquefaction in the sand layer, therefore the influence of the use of gravel and geosynthetics on pore water pressure is not a major concern.
Vertical ground displacement
The coherence of the gravel layer with its high permeability and high tensile strength provided by geosynthetics were considered as the main reason for this good result. Since the tension generated in the geosynthetics restrain the deformation of the gravel layer and integrally perform like a rigid plate with high permeability, this reinforcement could reduce the settlement that occurred on the ground surface. Since the tensile strength and the tensile stiffness of geosynthetics Type II that used in Case 4 is higher compared to type I, this type of geosynthetics could restrain the deformation of the gravel and sand better than Type I, resulting in lower ground vertical displacement compared to geosynthetics Type I that used in Case 3.
Based on the results obtained from laboratory testing, this proposed mitigation can be applied to overcome the liquefaction-induced ground settlement and the resulting damage, such as the impassable roads due to differential settlement appeared caused by the subsoil layer liquefy. This will result in substantial losses if this damage occurs on vital roads. Moreover, tilted houses and building also could be appeared due to liquefaction, for instance as happened in Kumamoto earthquake 2016, Japan, where it was reported that many residential houses and buildings were tilted due to liquefaction (Setiawan et al., 2017). The use of gravel and geosynthetics in those examples mentioned above will be able to lower the settlement and the related-damages caused by liquefaction.
The effectiveness of gravel along with geosynthetics remediation to restrain the liquefaction-induced vertical ground displacement had been measured by conducting a series of shaking table tests. According to the results acquired from the tests carried out, the following conclusions are obtained. It is found that the use of gravel and geosynthetics effectively reduce the vertical ground displacement of liquefiable soil due to the permeability of the gravel and tension strength of the geosynthetics. The conjunction of these two reinforcing materials resulted in a permeable layer which behaves like a rigid plate.
The results showed that by using this proposed mitigation, the settlement of the ground surface decreased by around 54% in the liquefiable zone and up to 32% in the non-liquefiable zone. It is also observed that the differential settlement between liquefiable sand and non-liquefiable in the same condition decreased about 62%, from 15.3 mm in no countermeasure condition to 5.7 mm when model improved with gravel and geosynthetics Type II. In the future, gravel in conjunction with geosynthetics could be recommended and becomes an established liquefaction countermeasure mitigation due to its aforementioned advantages and effectivity to reduce the liquefaction-induced ground vertical displacement.
The first author obtained a scholarship from The Directorate General of The Ministry of Research, Technology and Higher Education (DG-RTHE) of the Republic of Indonesia as a doctoral student at Kanazawa University, Japan.
Availability of data and materials
All data generated or analyzed during this study are included in this published article (and its supplementary information files).
HS, YS, WS, HK, and MM participated in the laboratory shaking table tests. HS and WS prepared the data analysis. HS and MM drafted the manuscript. All authors have read and approved the final manuscript.
The authors declare that they have no competing interests.
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