Journal of Applied Engineering and Technological Science Vol 6.
2025: 1397-1411
AN EMPIRICAL STUDY FOR ESTIMATING ULTIMATE BEARING
CAPACITY OF CONCRETE SMALL-PILE CLUSTER IN SOFT CLAYS
Suyuti Suyuti1*.
Mukhlis Muslimin2 Department of Civil Engineering.
Universitas Khairun.
Indonesia1 Department of Mechanical Engineering.
Universitas Khairun.
Indonesia2 suyuti@unkhair.
Received: 01 April 2024.
Revised: 25 February 2025.
Accepted: 18 March 2025
*Corresponding Author
ABSTRACT
Soft subgrades with shear strength, cu of 10 kPa to 25 kPa are given low bearing capacity and high Local government has been built infrastructure of embankment such unpaved road on the soft subgrade by using timber and bamboo materials .
alled AuCerucukA.
are very familiar for Indonesian local people.
By developing load capacity of floating pile type, bamboo pile cluster was applied for Tol road in North the Java Island.
However, bamboo material limited of life construction inside the soft ground, and exploitation of timber pile was violated environmental issue.
Therefore, this research method is developed a new geometrical small - cluster pile by using concrete from local material or Igneus stone such as gravel and sand produced in quarry Ternate Island.
Ultimate bearing capacity of single small cluster pile installation modelled in soft subgrade tank.
Then, observed by several block concretes and it is presented by empirical formulae.
Finally, the ultimate load capacity of small-pile cluster in soft subgrade is obtained Qu of 15.
92 kN and 19.
79 kN for observation and calculation, respectively.
Rearrange of piles can be increased load capacity of small-cluster pile in soft subgrade as spacing single pile by spacing 5Deq to 3Deq.
Mostly load capacity of small-pile clusters should be calculated by using empirical method to provide bearing capacity based on geotechnical rule with laboratory and field soil investigation data and load standard for unpaved roads.
Keywords: Empirical Study.
Load Capacity.
Small-Pile Cluster.
Soft Clay.
Introduction Situation of lowland deposit of soft soil layers covered about 30 percents in Indonesia, it is included soft soil, soft clay and peat soil (Buana et al.
, 2.
These produces seriously problems soft subgrades of road embankment again saturated condition, consolidation process and big compressible layers (PUPR, 1999.
PUPR 2002.
Terzaghi et al.
, 1.
In fact, the soft subgrade given low bearing capacity and large settlement under load pressures of static and Recently the problem of small pile materials such as bamboo and timber pile are limited life construction beneath soft ground, and also timber pile damaged environmental issue.
Local engineers and government have to make a robust foundation of road construction on weak foundation.
By considering high intensity loads, a foundation structure must be satisfied design stability rule.
Consequently, stability criteria of embankment on soft subgrades are often considered by soil stabilization and piling method, and its soft ground for reinforcing chemical and mechanical.
By ensuing procedure construction step of embankment on soft soil for road, public work services were explained such as .
Clearing and cutting top soil, .
installed pile into soft ground, .
layed geotextile, .
spread and compacted granular material or cement-soil, and .
Filling up soil for road embankment (PUPR, 1999.
PUPR 2002.
PUPR
This guideline procedural is not explained the stability criterion design in detailed foundation by using piles.
In scientific report, the capacity of soft soil reinforced by timber piles as called in Indonesian AuCerucukAy (Roosseno, 1.
By experimental method of timber pile installed beneath a granular layer with polyfelt sheets as mattress for building foundation on the very soft soil .
oil mechanics of consistency cu of 25kN/m.
located at Semarang, it gives settlement as recorded about 25 centimeters.
By comparing ratio of load pressure p of 4,700 kg/m 2 .
r 46 kN/m.
to the settlement above, there was found bearing capacity of foundation up to two times by cu of 50 kN/m2.
But this scientific is too difficult to understand, because there are not presented mechanism of pile installation effect by mathematical formula based on physical Suyuti & Muslimin A Vol 6.
2025: 1397-1411 The mechanism of mechanical reinforcement used geotextile and timber piles on soft ground, they were explained settlement subtraction again the settlement due to embankment with timber pile installation to deformation on piles alone.
This timber pile installation was applied to construct soil embankment with floating pile system.
Mathematical equations prepared explanation based on geotechnical engineering rules, which used single timber pile (PWRC, 2.
By investigation performances capacity of bamboo material, they were reported uses bamboo for soft subgrade as foundation in mattress and pile cluster installation in worked trial embankment construction unity.
The trial embankment for Tol road in North Jakarta on the soft soil reinforced by bamboo cluster, those trials were reported by settlement plates for 98 days, which were placed by crossing beneath embankment.
The real settlements were recorded and compared with Finite Element (FE) Ae Method by consolidation effect and water process dissipation under loading pressure of embankment (Irsyam et al.
, 2008.
PUPR, 2005.
Sandyutama et al.
, 2015.
Y Daryanto et al.
, 1.
Satibi .
presented design criterion of behavior of soil embankment on the floating piles with cap system using FE-Method, which used concrete size pile d of 20 centimeters.
The piling into soft ground installed by length variation L of 20 up to 100 centimeters, soft soil layer H down to 20 meters, and effective bulk density ' of 7 kN/m 3.
Loading pressure of soil embankment constructed H b of 1 meter up to 4 meters with bulk density b of 18 kN/m3.
In simulations are used constitutive models to calculate deformation ground surface due to load of embankment.
A concept block behavior was effective to estimate heigh of embankment on floating pile of soft soil (Ghalesari et al.
, 2.
Structure performance of timber pile within the soft ground, several researchers were reported such as determination method of the oedometer direct permeability.
The multi- layers analysis includes any variation of consolidation parameters with several depths.
The consolidation parameters, settlement and pore water pressure analyses were simulated by using case histories two test fills on soft clays, which are used empirical relation in graphs of the soil plasticity index and ratio of undrained shear strength to effective overburden of subsoil, it can be produced soil stresses at the tip pile (AM.
Mesri, 1.
Field and laboratory test results presented to describe disturbance of timber pile driving into soft clays, glacial and lake soil deposit (Cummings et al.
, 1.
Relation of between soil cohesion with vane shear test results determined into load and settlement of pile driving alone 23 meters into saturated soft clay with plasticity index PI of 22% (Seed & Reese, 1.
They were monitored the settlement due to loading tests during 33 days, and given increment from 2.
2 kN to 4.
44 kN.
Axial pile capacity in clay soil, which reported the effect of pile length of penetration on developing shaft friction pile in clays (Al-Gharbawi et al.
, 2024.
Azzouz et al.
, 1990.
Gavin et al.
, 2010.
Seed & Reese, 1.
Practically, the use the small-pile clusters to become effective to increase bearing capacity of floating pile type again decreasing water content due to consolidation process at the surrounding pile installation.
The decreasing water content to be changed undrained shear strength su or undrained cohesive soil cu.
The factual, bearing capacity of pile in the soft clay can be considered mainly the influence of soil cohesion at along till tip of pile and circumference of timber single pile as well as skin friction of pile (Burland, 1973.
Carter, 1981.
Tomlinson, 1957.
Tomlinson, 1971.
Seed & Reese, 1.
Moreover, a potential area of increasing skin friction capacity developed by approaching method for river dike on soft soil using bamboo piles.
Where results were validated by trial embankment data on soft soil of using timber piles beneath mattress by spacing 5d, diameter 10cm, and length 3 meters.
The mattress was applied with soil cement wet mixing by empirical equations of friction capacity.
A foundation system on very soft clay must be satisfied by stability and settlement criterion as referred the theoretical profile for embankment performance, which are using several treatments such mechanical improvement (Almeida & Marques, 2013.
Elaarabi & Soorkty, 2014.
Zolotuchin et al.
, 2.
The bearing capacity performance of small-pile within soft clays depends on excess pressure of water dissipation due to consolidation.
Whatever, the Suyuti & Muslimin A Vol 6.
2025: 1397-1411 soil permeability of clay layer is usually too small.
The gaps can be summarized that resiliency of bamboo inside the soft clay is very limited for long life embankment construction, and again the environment issue.
In reality, a bamboo pile installation as foundation is to damaged range during long time inside soft ground.
The other hand, an engineer and government have to make an innovation structure of pile for road embankment, which is using local material for pile innovation.
Therefore, this study focused load capacity performance of concrete of small pile with cluster in soft clays, which used material local as solution alternative for bamboo and timber By piling small-pile cluster into soft clay, a treatment foundation of mechanically soil improvement system can be provided.
Literature Review In order to improve soft subgrades for supporting unpaved road with behind rear P, this research focused on three parts of application of full reinforcement method for increasing ultimate bearing capacity such as .
Soft subgrade alone, .
foundation mattress with geotextile, and .
mini-pile installation.
The illustration of unpaved road is followed standard design as below (Giroud & Noiray, 1981.
Milligan et al.
, 1989.
Lyons & Fannin, 2006.
Mulungye et al.
Unpaved pb Mattress Geotextile Pile cluster Soft subgrade:
cu, sat, i Deq Detailed Hard layer Fig.
Schematics of Unpaved Road on Soft Subgrade Reinforced by Pile Cluster Mechanism load pressures pb o rested by reinforcement system is formed as .
where ptr, pm, and puv are load pressures due to tires truck, mattress and unpaved layer Figure 1 shows Firstly, deposited alluvial of soft subgrades such as soft soil, peat soft The soil properties of consistency concerned by less than 12.
5 kN/m2 and 25 kN/m2 for very soft soil and soft.
There are reported investigation data results soil data, reported planning projects for new airport runway 2,500 meters and 45 meters in width in North Maluku (Jewell.
Ikhwan et al.
, 2022.
Lambe & Witmann, 1.
Mathematic equations for predicting ultimate bearing of soft soil subgrade with piling small-pile cluster for embankment.
So, the ultimate bearing capacity of soft soil with small-pile cluster of precast concrete .
may predict as (Miki, 1996.
Koerner et al.
, 1987.
Suyuti et al.
This research focused clay subgrades as original foundation, the ultimate stress of clay Suyuti & Muslimin A Vol 6.
2025: 1397-1411 subgrade can be delivered by several theoretical such (VesiN, 1973.
Kenny & Andrawes, 1997.
Terzaghi et al.
, 1.
In intermediate cases in which cu O 0, q O 0, and O 0, ultimate bearing capacity for strip footing considered by soil sharing strength of the overburden is written as .
Shearing bearing factors of the overburden of mattress depth D m for Df/B O 1.
0 are defined as (VesiN, 1.
In case general shearing failure, bearing factors of subsoil are predicted as .
From equation of .
, the ultimate stress of soft subgrade alone with cohesion c u O 0 for a foundation strip footing is formed as .
where cu is the soil cohesion undrained .
N/m.
Nc is bearing capacity factor, cd is the compressible factor .
= 0.
Secondly, many soil unpaved constructed on soft subgrades used geosynthetic as geotextile, previously researches reported to increase bearing capacity of soft soil with tensile forces, to anticipate soil materials fall down into soft ground, and to ensure any access pore water due to consolidation.
The reported originally several researches of geotechnical reinforcement system (Davis & Booker, 1973.
Miki, 1996.
Jewell, 1988.
PWRC, 2000.
Suyuti et al.
, 2.
where Tgt is the tensile strength of geotextile layer, ir is the friction of the geotextile and mattress layer.
B is the width of unpaved construction road.
Thirdly, to perform a good capacity of unpaved road on the soft subgrades, previous results for ultimate bearing capacity of pile cluster are presented.
Several researchers presented timber single capacity in clays.
In reported, ultimate load capacity Qu during 800 hours was given load 23.
35 kN.
Micro-single pile dimension of 15 centimeters in square by 4, 5 and 9 meters embedded in very soft soil in Kalimantan, they found ultimate load capacity Q u of 34.
kN (Sandyutama et al.
, 2015.
Seed & Reese, 1957.
Yudiawati, 2.
By using loading step with concrete blocks on the small-pile concrete installation in soft soil, the ultimate load (Q.
can be observed by using Figure 2 (Reznik, 1.
Suyuti & Muslimin A Vol 6.
2025: 1397-1411 Loads.
Q Elastic Plastic Data Deformation.
S Fig.
Mechanism prediction data of load and deformation data set Notes: Line of graph 0A: elastic area.
Line B: plastic area.
Point-U: Intersection line for ultimate load.
Figure 2 shown the ultimate bearing capacity of point load (Q .
may be predicted from the observation data.
The following steps are plotting observation data, forming graph with axisload and ordinate-deformation, making tangent as elastic line .
oint 0 Ae to A), making tangent as plastic line B, from point intersection and it is to continue and take liner line parallel with ordinate Y or deformation (S), and reading the load intensity (Q .
Theoretical ultimate load capacity of pile embedded into soil clays Q u is (Tomlinson.
Tomlinson, 1.
where C is the circumference of pile.
L is the length of pile, ca is the adhesion between pile and soil.
N c is the bearing capacity factor.
Ab is the area of base pile, cb is the adhesion at base of pile.
By addressing plasticity index PI to the ratio of cu/p'c, there are any increasing parabolic due to intensity values of PI.
Ratio of .
u/p'.
may express in linear equation as (AM.
Mesri.
AW.
Skempton, 1.
Then, cohesion undrained during and after piling into soft clay where PI is the plasticity index of soft subgrades unit percent, c u is the cohesion undrained, and p'c is the overburden pressure of sub soil.
Allowable load of piling in soft clays presented by adhesion parameters ca, diameter d and length of pile L, excess pore pressure should change an increasing adhesion between pile and clays ca.
Therefore, adhesion factor of pile and clay layer was verified field test data as (Flaate.
Gavin et al.
, 2010.
Carter, 1981.
Kolk & Van Der Velde, 1.
for O 1.
Where L is the length pile embedded, z is any depth of soil layer.
D is the diameter of pile cluster (D OO 2.
(Suyuti et al.
, 2.
, d is diameter of single pile.
The research results reported potential developed area intensity of skin friction of piles with cluster, which was piling small-pile cluster for trial embankments by using timber and bamboo (Irsyam et al.
, 2008.
Suyuti et al.
, 2019.
Ready & Nurtjahjaningtyas, 2020.
Sandyutama et al.
, 2015.
Suyuti et al.
, 2.
Then, time factor for consolidation around pile suggested as Suyuti & Muslimin A Vol 6.
2025: 1397-1411
and coefficient of consolidation cv is written as .
where LL is the liquid limit in percents, t is the consolidation time.
Research Methods Outline research method, the steps of prototype small-pile cluster process of precast concrete can be explained in figure 3 flow chart as below:
Literature Design model test Select Laboratory Experimental Calculate Load Fig.
Flow Chart of Construction Research Design model test Illustration of the installation small-pile cluster in the soft soil tank.
The static loads are applied five blocks for each day.
Then, a surveyor takes deformation due elastic and plastic for condition loads as shown in figure 4 (Sabaruddin et al.
, 2.
Static Block concretes mall pile Small-pile Wall oft soil tank Soft soil Top view Cross section Fig.
Illustration of Experimental Study Mathematic equations for predicting ultimate bearing of soft soil subgrade with piling small-pile cluster for embankment, it is expressed in figure 6 below.
Small-pile cluster installation should be placed by square pattern by spacing of pile (S .
= 3Deq 7Deq, where Deq = Oo3d 2.
= diameter of regularly pil.
To keep soft subgrades on saturated condition, these piles are installed on soft soil with water level QWT equal to GS.
here GS = ground surface.
GWT = ground water tabl.
(Miki.
Irsyam et al.
, 2008.
PWRC, 2.
Selecting and laboratory tests Prepared local material sampling to produce precast small-pile cluster by using manual gravel at Takome and sand at Kalumata as local site in Ternate as shown in figure 5 below:
Suyuti & Muslimin A Vol 6.
2025: 1397-1411 Sampling materials Check concrete consistency Measure bulk density Measure load compressive strength Fig.
Job Mix Design Formula for Producing Concrete Figure 5 shows laboratory test processing, from sampling material concrete to make mix design, and gives proportional of job mix design per cubic of concrete was given cement of 370 kg, water of 185 kg, sand of 509 kg, and gravel 1,135 kg.
This procedure mix design for normal concrete quality was followed National Standard of Indonesia no.
SNI .
2000 (BSN,
The result of three cubes for compression test are shown in figure 5.
Experimental study Precast concrete of small-pile cluster process, it is produced prototype 3d .
iameter d of 10c.
as shown in figure 6 below.
Figure 6 shows that precast concrete of small-pile cluster process with quality compressive strength of 20 MPa, it was produced prototype 3d .
ith single diameter .
of 10 Fabrication process of small-pile Installation illustration Suyuti & Muslimin A Vol 6.
2025: 1397-1411 Remove small- pile cluster Measure circumference Fig.
Schematics of Installation Process For Small-Pile Cluster Experimental Step Process In these simulations are conducted by several lengths of pile, diameter pile, spacing of piles and etc.
Also in reinforcing, it is giving 8mm for main bars and 6mm with space of 125mm for shear bar in figure 7.
The experimental step to observe an ultimate bearing capacity of single small-pile cluster modelled in the soft soil such as .
install small-pile cluster concrete in soft soil with length (L) of 100cm, it becomes 3 times of single diameter .
of 10 cm, .
Put layer local material to separate load, .
Put five concrete blocks step by step, a block concrete keeping 24 hours in figure 7, .
Observe deformation with 3.
points, and .
Calculate ultimate bearing capacity of soft subgrade with reinforcement q r as shown in figure 1 (PUPR, 1999.
PUPR,
In normally preparation for unpaved road on soft soil layers.
It is to make easy installation of small-pile cluster is tapered at tip on soft soil layer.
The soft soil tank was setting up saturated condition with heigh of 200 cm, width of 150 cm and length of 200 cm as shown in Figure 7.
Install small-pile cluster Observe deformation due to loads Suyuti & Muslimin A Vol 6.
2025: 1397-1411 Complete step of static loading with Removed the concrete blocks Fig.
Schematics of Experimental For Small-Pile Cluster in Soft Soil Tank Results and Discussions This section, analyses are applying soil properties in model full scale of soft soil tank such as undrained cohesion .
, internal friction .
and bulk density ().
Concrete precast small-pile can be observed as shown in figure 3.
Then, it is made simulation for several variations of soft soil properties and small-pile dimension.
Soil Properties dan small-pile Data Soil properties data in soft soil tank with area of 130 cm by 200 cm in heigh 130 cm.
It is due to pile installation in clays, recently soil properties are listed in Table 1.
Table 1 - Soft subgrades tank for observation (Suyuti et al.
, 2.
Items Unit Result Undrained cohesion, cu kN/m2 Bulk density, kN/m3 Internal friction, i Plasticity Index.
PI Empirical Simulations In these simulations are conducted by several lengths of pile, diameter pile Dimension of concrete precast data was observed such diameter of single pile .
of 10 cm, length L of 100 cm, diameter equivalent Deq of 2.
5d of 25 cm in width B of 1.
0 meter.
Experimental Results In order to observe an ultimate bearing capacity of soft clay with small-pile cluster installation, an experimental is conducted several block concretes and deformations.
The data set results as listed Table 2.
Block load .
Table 2 - Experimental result of loads and deformations Deformation records, i.
Static pressure load .
Point-1 Point-2 Point-3 Average Table 3 can be seen that loading five steps, it is plotting with five steps.
The results of recording deformation are plotting in curve loading and deformation as shown in Figure 8.
Then, figure 8 seen that ultimate load on soft clay with mini-pile cluster gives qu of 203 kN/m2.
Suyuti & Muslimin A Vol 6.
2025: 1397-1411 Fig.
Expression of The Ultimate Bearing Capacity For Small-Pile Cluster in Soft Clay Simulation Results In order to observe an ultimate bearing capacity of soft clay with small-pile cluster installation, simulation results for three variations of pile spacing s of 3 Deq and 5Deq as well as with low plasticity index PI of 10% are shown in Figures 9 and 10 as below.
Length of pile (L) = 100cm Length of pile (L) = 150cm Fig .
Simulation Results of Ultimate Bearing Capacity and Diameter Equivalent for Spacing Pile s of 3Deq Length of pile (L) = 100cm Length of pile (L) = 150cm Fig.
Simulation Results of Ultimate Bearing Capacity and Diameter Equivalent for Spacing Pile s = 5Deq Figures 9 and 10 shown the ultimate bearing capacity of mini-pile cluster in soft clays for plasticity index PI is about 5 percents.
Table 3 - Comparison Results Data and Calculation Method of Load Capacity Suyuti & Muslimin A Vol 6.
2025: 1397-1411
Data Location Material Venice Concrete Pile dimension Dia .
Ternate Concrete Hamilton
Pentre NGI
Concrete Concrete Banjarmasin
Mare Island
Mare Island
Ditto
Grimsby Ditto
San
Fransisco
Ditto
Gothenburg
Ditto
Ditto
Ratio
L/D
Ratio cu/p'0 Alfa Load capacity Calc Obs Concrete Timber Timber Timber Timber Timber Still pile Ditto Ditto Ditto Ditto Remark Kolk & Der Velde.
Recently Kolk & Der Velde.
Yudiawati.
Tomlinson.
Load capacities in Table 3 shown us that to find the solution of local material for smallpile cluster as solution, results of previously research in relevant in recently this research were Then, load capacities Qus above, it can be validated by observation this study results.
The implication of calculation and observation can be applied for supporting unpaved road.
This research is given load capacity Qu of 19.
79 kN and 15.
92 kN for calculation and observation The comparison results of calculation and observation as novelty of this study are inside the fifteen cases are presented in figure 11.
Data no.
Calculation.
Qu .
N) Observation.
Qu .
N) Fig.
Comparison Results of Calculation and Observation for Load Capacity of Single Pile Based on comparison data of several studies above, the piling installation was affected to increase load bearing capacity of soft subgrade for unpaved road.
Generally, these matters can be influenced by soil stresses at surrounding tip piles as shown in figure 12.
Suyuti & Muslimin A Vol 6.
2025: 1397-1411 Deq Deq Pile cluster Zone-1 Pile cluster Sp-y Zone-3 2Deq 2Deq Zone-2 Deq Soil Sp-x Tip .
Layout pile installation Soil stresses at surrounding tip pile Fig.
Illustration of State of the Clay Surrounding Small- Pile Clusters The generalization of use small- pile cluster was installed easily in soft subgrade by placing square pattern with spacing Sp-x and Sp-y for axis, and ordinate.
Then due to consolidation process, parameter of cohesion cu of soil elasticity can be changed.
The load capacity of shaft resistance of between piles and soil for reinforcing soft ground with single and group pile method can be increased to support unpaved roads.
Conclusions In natural condition, based on simulation result seen that low soil consistency, it can be decreased the ultimate bearing capacity of pile in the soft clays.
The evidence, when the spacing of piles made dense from spacing of 5D eq to 3Deq, then the ultimate bearing capacity of minipile in soft clays is increased about 65 percents.
Plasticity index, soil cohesion, effective pressure as well as pile dimensions are affecting into parameter of empirical calculation for determining ultimate load capacity of cluster pile Q u in soft ground.
In experimental, single small-pile cluster installed in soft clays, the loaded by concrete blocks as static loading and observe the elastic deformation during 24 hours, load capacity of small-pile cluster in soft clays Qu can be increased due to consolidation effect and shaft friction of pile that is correlating to the parameter of soil properties-mechanically and dimension of pile.
Finally, phenomenon of small-pile clusters of concrete local materials should be effectively used by longer spacing of small size in the soft clays for unpaved road based on geotechnical rule.
It is can be as alternatively bamboo or wooden pile to improve soft subgrade for constructing long life.
It can be applied by local engineer and government for unpaved road.
Acknowledgement Grateful acknowledgement to the ministry of education, culture, research and technology for supporting funding of prototype products in year 2023.
Also, thanks to the laboratory of Civil engineering program.
Engineering faculty of Universitas Khairun.
References