Permeable Interlocking Concrete Pavements: A Sustainable Solution for Urban and Industrial Water Management

Abstract

Anthropization has significantly altered the natural water cycle by increasing impermeable surfaces, reducing evapotranspiration, and limiting groundwater recharge. Permeable Interlocking Concrete Pavements (PICPs) have emerged as a permeable pavement, effectively reducing runoff and improving water quality. This study investigates the base depth for PICPs regarding the strength and permeability. This study examines the hydraulic and structural performance of Permeable Interlocking Concrete Pavements (PICPs) for urban and industrial applications by evaluating the effects of subgrade conditions, traffic loads, and material properties. Using DesignPave and PermPave software, the optimal base layer thickness is determined to prevent rutting while ensuring effective stormwater infiltration beneath 110 mm-thick concrete pavers placed on a 30 mm-thick bedding course. The required base thickness for urban pavements ranges from 100 mm to 395 mm, whereas for industrial pavements, it varies between 580 mm and 1760 mm, depending on subgrade permeability, traffic volume, and loading conditions. The findings demonstrate that PICPs serve as a viable and environmentally sustainable alternative to conventional impermeable pavements, offering significant hydrological and ecological benefits.

1. Introduction

Over the past few decades, anthropogenic activities have significantly altered the natural water cycle [1]. The expansion of impermeable surfaces has led to a reduction in evapotranspiration, surface and deep infiltration, and groundwater recharge, while simultaneously increasing runoff volumes [2]. Recent studies indicate that only 20% of urban surfaces remain permeable [3]. Under these conditions, an average of 55% of total precipitation is converted to runoff, while only 15% infiltrates into the subsurface [3]. The road network in urban areas plays a significant role in water management. Increasing impermeable surfaces can have significant environmental and infrastructural consequences, including the intensification of flood waves that overwhelm sewer systems and cause abrupt changes in watercourse flows [4]. This hydraulic overload can also lead to treatment plants’ malfunctioning, reducing their wastewater management efficiency [5]. Additionally, impermeable surfaces contribute to the deterioration of runoff water quality by collecting and transporting pollutants during short, intense rain events [6]. The disruption of the hydrological cycle is another critical impact, as reduced groundwater recharge in highly impermeable areas limits water availability for natural ecosystems and human use [7]. Furthermore, the expansion of impermeable surfaces exacerbates the urban heat island effect, increasing surface temperatures and worsening climate-related challenges in cities [8].

As a key component of sustainable urban drainage solutions (SuDS), they efficiently manage surface water by intercepting runoff, reducing its volume, and facilitating water treatment before returning to the environment [9]. Permeable pavements can be classified as either continuous or modular [10]. Continuous permeable pavements, such as gravel pavements, consist of a layer of gravel or crushed stone that enables water infiltration through intergranular voids. These pavements are primarily suitable for pedestrian traffic and generally offer a lower level of service [11]. Typically composed of aggregates ranging from 6 to 20 mm in size, they feature void ratios of up to 20%. To achieve a smooth surface with a runoff coefficient between 0.30 and 0.50, these layers are compacted using rollers to a thickness of 4–8 cm [1]. Their structural and functional performance depends on the geotechnical properties of the underlying layer [12]. Permeable concrete pavements, designed with a high void content (15–25%), allow water to percolate through their structure [13]. These pavements typically consist of an 8–10 cm-thick draining layer placed over a granular subbase [14]. They are suitable for vehicular and pedestrian traffic, provided the subgrade is not water-sensitive. On the other hand, modular permeable pavements utilize monolithic concrete pavers with open joints, enabling water to infiltrate through the surface layer and reach the deeper structural layers. Modular pavements can be classified into three main types based on the type of paver used [9]. Compact concrete pavers create tightly jointed pavements where the gaps are filled with crushed gravel without fines. These pavers are laid on a bedding layer of similar material, approximately 3 cm thick, which rests on a base layer with a low fines content, ensuring structural stability and durability. Concrete pavers with wide joints form grid pavements designed for areas with low-intensity vehicular traffic. These pavers, typically polygonal in shape, are laid on sand, with their wide joints filled with aggregates or topsoil and grass, allowing for effective water drainage. Lastly, permeable pavers facilitate water infiltration through their structure. Similarly to concrete grids, they consist of plastic grids filled with organic soil and grass, with green coverage exceeding 90%. Due to their composition, they are best suited for medium to light load applications, such as parking lots, where they provide an eco-friendly and permeable surface.

Whatever the pavement type, water can either infiltrate directly into the subgrade or be directed into the sewer system [15]. The first scenario (Figure 1a) is preferable in areas where stormwater contamination is minimal, allowing for natural infiltration. Conversely, the second approach (Figure 1b) is necessary where stormwater treatment is required due to the potential presence of sediments, fertilizers, bacteria, heavy metals, fuels, and lubricants [16].

The system in Figure 1a effectively removes pollutants from surface runoff without requiring pipes and channels, resulting in cost savings in infrastructure construction [17]. Recent studies indicate that permeable concrete pavements can remove 60–95% of sediments and 70–90% of hydrocarbons from stormwater, managing small lubricant spills (e.g., in parking lots and yards) throughout their service life [18]. In contrast, the system in Figure 1b incorporates drainage pipes to collect hydrocarbons and heavy metals for subsequent treatment [16], leading to increased construction and maintenance costs. In Italy, such drainage approaches are recommended for residential areas [19]. Furthermore, regional regulations permit the processing and storage of inert or natural materials in permeable areas without requiring a dedicated water collection system [20]. Additionally, new construction and redevelopment projects must ensure a minimum of 30% open and permeable surface area for residential and mixed-use developments, and 15% for industrial zones [21].

Permeable Interlocking Concrete Pavements (PICPs) combine the technical and environmental benefits of concrete, making them suitable for surfaces with a maximum speed limit of 50 km/h under medium to heavy traffic conditions [22]. Consequently, they are widely used in parking lots [23], low-speed roads [24], pedestrian pathways [1], and roadside shoulders [20]. Freshly installed block pavements typically exhibit a permeability of approximately 4000 mm/h [25], which decreases over time. However, studies suggest that even as permeability declines, it remains sufficient to handle rainfall intensities effectively [26]. The infiltration rate is regulated by the joint width, which generally does not exceed 1 cm. Key factors influencing the mechanical performance of permeable pavements include the shape, thickness, and laying pattern of the pavers [27]. Regardless of the adopted laying configuration, vertical loads and horizontal forces induced by braking, steering, and vehicle acceleration contribute to pavement displacements [28].

In this study, PICPs for urban streets and industrial yards are hydraulically and structurally sized using the software tools DesignPave v2.0 and PermPave v1.0. PermPave is primarily a hydraulic design tool used to evaluate the runoff control and infiltration capacity of permeable pavements. It determines the required base thickness to store and infiltrate stormwater, ensuring compliance with sustainable drainage criteria. DesignPave is a mechanistic pavement design software that integrates hydraulic and structural considerations to determine the optimal pavement layer thicknesses based on traffic loads, material properties, and subgrade conditions. The designed PICPs consist of concrete pavers on granular bedding sand layer and base layer, by varying subgrade properties, traffic conditions, and mechanical performances of the materials (Figure 2).

The pavers used in monolithic concrete block permeable pavements form tight-jointed pavements filled with crushed aggregate without fines and are laid on a bedding layer of the same material about 3 cm thick, spread over a base layer with low fine content.

2. Materials and Methods

In this study, the permeable pavement is composed of the following:

• Subgrade: This is the in situ soil whose properties determine the feasible type of permeable pavement cross-section and the required thickness to withstand traffic loads and manage stormwater;
• Permeable base course: This layer is composed of a compacted, unbound, 12.5–25 mm particle size, openly graded, crushed, and angular material, providing the primary load-bearing and water storage function. The material should meet [29], or for industrial pavements [30]. The Young’s modulus (E) describes the subgrade load-bearing capacity. The permeability of the base granular materials refers to the material compacted to at least 98% of the modified Proctor density;
• Bedding layer: This layer is composed of a 20–40 mm thick layer compliant with ASTM No. 8 for urban roads or [29] for industrial pavements. It consists of small-sized, crushed 2–5 mm stones with an open gradation;
• Joint filling aggregate: A uniform aggregate fills the joints between the pavers, enhancing load distribution. This material complies with ASTM No. 8 and 9 for urban pavements or ASTM C144 [31] for industrial pavements;
• Monolithic concrete pavers to permit the rapid infiltration of rainfall.

The hydraulic efficiency of permeable pavement systems is influenced by the materials used to construct base layers and joint fillings. Additionally, joint width, which typically ranges from 3 mm to 10 mm, plays a crucial role in determining the mechanical properties of the pavement.

The software tools to assess the hydraulic performance of these pavements and integrate water management strategies into the design process (Figure 3) are DesignPave v2.0 and PermPave [32].

These tools enable precise evaluation of permeability, infiltration capacity, and overall system performance under varying hydrological conditions.

The hydraulic design complies with the PermPave Runoff Control, which manages runoff from the pavement surface by infiltrating it into the ground and/or storing it within the pavement [33]. The model assumes that all stormwater infiltrates through the permeable pavement and into the subgrade, considering a full infiltration scenario with no external drainage system unless otherwise specified.

Table 1. Outlet flow and rainfall input data for PermPave analysis.

Variable (Acronym)	Value	Unit
Runoff coefficient [26] (φ)	0.3	-
Annual exceedance probability (AEP)	5	%
Rainfall duration (d)	30	min
Rainfall height	51.2	mm
Average rainfall intensity (i)	80	mm/h

summarizes the outlet flow and rainfall data for a 20-year return period with a 30 min storm duration, based on meteorological data from Milan, Italy [34].

This study investigates the performance of PICPs under urban traffic conditions [35], including passenger vehicles, trucks, and buses, as well as industrial pavements subjected to forklifts, straddle carriers, transtainers, and heavy off-road vehicles. Forklifts and cranes were selected due to their frequent use in logistics centers, ports, and industrial facilities. These conditions provide a rigorous test case for evaluating PICP durability under industrial traffic. Additionally, the inclusion of straddle carriers, transtainers, and other heavy off-road vehicles ensures a comprehensive assessment of PICP applications in industrial environments. PICPs with pavers featuring narrow-joint openings are deemed suitable for all traffic types, including heavy vehicles. The pavers used in this study have thickness of 110 mm, and the assumed surface infiltration rate is 9.0 × 10⁻⁵ m/s [32]. This value after 10-year service life was chosen based on the default value recommended by PermPave, as it provides a conservative estimate compared to the initial value 5.0 × 10⁻⁴ m/s. This ensures a cautious approach to permeability loss over time due to potential clogging. Industrial sites generally present a higher risk of hydrocarbon and heavy metal accumulation, which can accelerate infiltration reduction over time. However, the conservative permeability value (9.0 × 10⁻⁵ m/s), recommended by PermPave, already accounts for long-term clogging effects, ensuring a sufficient safety margin for both urban and industrial applications.

Three load-bearing capacity values have been considered by combining data from [36] and the PermPave manual. Specifically, the subgrade Young’s modulus values in

Table 2. Subgrade properties.

Young’s Modulus (MPa)	Soil Classification [37]	Hydraulic Conductivity (m/s)
150	SW	2.5 × 10−4
90	SM	2.5 × 10−6
30	SC	5.0 × 10−7

correspond to well-graded sand, gravelly sand with little or no fines (SW), silty sand, sand–silt mixtures (SM), and clayey sand, sand–clay mixtures (SC) [37], which have decreasing load-bearing capacity and permeability. All subgrade materials have a Poisson coefficient equal to 0.4, as per standard pavement design practices.

The values in Table 2 were chosen based on field data and existing literature to represent real-world urban and industrial conditions. The base course is a permeable graded material with a 15% effective void ratio, a permeability of 5.0 × 10⁻⁴ m/s, and a minimum thickness of 100 mm. All base materials have a Poisson coefficient equal to 0.35.

The result provided by PermPave for a typical full infiltration section is the thickness of the base layer. By varying the subgrade hydraulic conductivity (Table 2), the base thickness adjusts accordingly (

Table 3. Minimum base thickness according to the hydraulic criteria.

Subgrade	Minimum Base Thickness (mm)
SW	100
SM	240
SC	270

). The model determines the minimum required base thickness to store and infiltrate rainfall, ensuring that surface runoff is minimized.

The results from the Runoff Control model reveal a decreasing trend in base thickness as subgrade permeability increases (Figure 4).

When subgrade permeability exceeds 2.0 × 10⁻⁵ m/s, the base thickness stabilizes at a minimum of 100 mm, indicating that further increases in permeability have a negligible effect on the hydraulic performance of the pavement system.

The PermPave calculation utilizes ten hydrographs to determine the minimum base thickness required for runoff control [33]. In this study, the total catchment area does not receive contributions from surrounding areas, with no contributions from adjacent impermeable surfaces [38]. The DesignPave software [32] was employed to verify the base thickness determined from PermPave. DesignPave is a mechanistic design software that integrates hydraulic and structural performance considerations for permeable pavements. It models load distribution, calculates base thickness, and ensures that pavements can withstand traffic-induced stresses while maintaining infiltration capacity. The software accounts for key factors such as material properties, subgrade conditions, and traffic loads to ensure compliance with local and international design standards. Operational loads are transferred to the subgrade using a piecewise linear stress distribution (Figure 5a). DesignPave employs the Method of Equivalent Thickness (MET) to compute the required base thickness. MET converts a multilayer system into a homogeneous system with an equivalent modulus (Figure 5b) [39]. This approach facilitates a more accurate assessment of pavement performance under varying load and environmental conditions, optimizing the design for urban and industrial applications.

For each layer within the road pavement structure, this method enables the determination of the corresponding thickness, provided that the material properties of the layer conform to the assumed homogeneous half-space model (Equation (1)) [39].

$$h_{eq1}=f{h}_1{\left({\displaystyle \frac{E_1}{E_m}}\right)}^{0.33}\sqrt[3]{{\displaystyle \frac{1-{\nu }_m^2}{1-{\nu }_1^2}}}$$

(1)

where f is a coefficient equal to 0.8, ν_m is the Poisson’s ratio of the homogeneous half-space, E_m is the Young’s modulus of the homogeneous half-space in MPa, h₁ is the layer thickness, ν₁ is the Poisson’s ratio of the layer, E₁ is the Young’s modulus of the layer in MPa, h_eq1 is the layer thickness in the homogeneous half-space, and n is equal to 0.80.

For PICPs, MET determines the equivalent thicknesses of the permeable blocks, bedding layer, and base in relation to the subgrade [39]. This approach results in a pavement structure with mechanical properties equivalent to those of the subgrade and the computed layer thicknesses. Since the system is considered homogeneous, axial (σ_z), tangential (σ_t), and radial (σ_r) stresses can be determined using Boussinesq’s theory (Equations (2) and (3)).

$${\sigma }_z=p\left[{\displaystyle \frac{z^3}{{\left(a^2+z^2\right)}^{\frac{3}{2}}}}-1\right],$$

(2)

$${\sigma }_r={\sigma }_t={\displaystyle \frac{p}{2}}\left[{\displaystyle \frac{2z(1+{\nu }_m)}{{\left(a^2+z^2\right)}^{\frac{1}{2}}}}-{\displaystyle \frac{z^3}{{\left(a^2+z^2\right)}^{\frac{3}{2}}}}-(1+2{\nu }_m)\right]$$

(3)

where p is the inflation pressure (800 kPa), a is the contact area (0.15 m), and z is the depth.

The vertical deformation at the interface with the subgrade (ε_z) depends on the subgrade modulus (E_subgrade), ν_m, σ_z, σ_t, and σ_r according to Equation (4).

$${\epsilon }_z={\displaystyle \frac{1}{E_{subgrade}}}\left[{\sigma }_z-{\nu }_m({\sigma }_r+{\sigma }_t)\right],$$

(4)

The elastic deformation (ε_z) is used to estimate the allowable number of passes (N) that a pavement can withstand before developing unacceptable rutting. The Edwards and Valkering criterion [40] was adopted in this study (Equation (5)).

$$N={\left({\displaystyle \frac{2.8·{10}^{-2}}{{\epsilon }_z}}\right)}^{\left(\frac{1}{0.25}\right)}$$

(5)

For urban pavements, traffic is modeled through the equivalent standard single axle load (ESA) [41]. Therefore, the number of repetitions (N) related to the standard axle causing the same damage is given by Equation (6):

$$N={\left({\displaystyle \frac{W}{ESA}}\right)}^4\times N_a$$

(6)

where N_a is the number of repetitions of the axle load, W is the axle load, and ESA is a Single axle with dual tyres (SADT) with a total load of 80 kN.

The urban traffic complies with that proposed by DesignPave and consists of single axle with single wheel (SAST), single axle with dual wheels (SADT), tandem axle with single wheel (TAST), tandem axle with dual wheels (TADT), and triple axle with dual wheels (TRDT). Three project traffic values have been considered for the designed road pavement: 400,000 (low traffic), 1,500,000 (moderate traffic), and 4,000,000 (high traffic) passes of commercial vehicles. Those traffic assumptions comply with the Italian reference standard for pavement design [36].

DesignPave computes axle loads for industrial applications based on vehicle geometry and container weight. The industrial vehicles considered in this study include the following:

• Front forklift: A two-axle vehicle with the majority of the load carried by the front axle. For load repetition calculations, only the twin front axle is considered, as it experiences the highest load;
• Side forklift: It consists of two axle groups, each containing one or two axles. Since one side bears most of the load, only the wheels on the lifting side are included in the load repetition analysis;
• Gantry crane: Comprising two groups of axles, each with two single-wheel axles. As front and rear wheels may carry different loads, both wheels on each side are considered for repetition calculations;
• Central forklift with two steering tandem axles;
• Mobile crane: A two-axle vehicle where the front axle, equipped with twin wheels, bears the highest load. Consequently, the wheels on the front axle are used for load repetition calculations in pavement design.

All selected vehicles conform to those modeled in DesignPave. The study considers total vehicle passes of 100,000, 250,000, and 500,000 over a 20-year service life, representing low, moderate, and high traffic conditions typical in industrial environments such as logistics centers and warehouses. These values are derived from real-world operational scenarios. Dynamic load effects induced by braking, cornering, and acceleration are considered according to [32]. Furthermore, industrial vehicle traffic and container loads affect the design [32] and flatness [42] of permeable industrial pavements. This study includes 6 m and 12 m containers with a critical load of 21,000 kg. For industrial pavement customization [33], the design methodology incorporates Miner’s rule to assess unbound base course material performance [43]. Specifically, Miner’s law is applied to verify that the allowable number of passes (N) exceeds the expected number of passes (n) for each wheel load of the industrial vehicles, ensuring pavement durability and structural integrity.

3. Results and Discussion

This section presents the results of the base layer thicknesses for urban and industrial pavements. These results are categorized using an alphanumeric code (ij), where i represents the Young’s modulus of the base layer (ranging between 1 and 10, corresponding to values between 271 and 573 MPa), and j denotes the pavement type (U for urban pavement sand I for industrial pavements) (

Table 4. Sheet organization for urban and industrial pavements.

Base Young’s Modulus (MPa)	Urban Pavement	Industrial Pavement
271	1U	1I
341	2U	2I
373	3U	3I
405	4U	4I
435	5U	5I
464	6U	6I
492	7U	7I
520	8U	8I
547	9U	9I
573	10U	10I

). Twenty catalog sheets have been developed, each containing nine results based on three traffic volume levels and three subgrade-bearing capacity values. For urban pavements, base layer thickness is influenced by both hydraulic and structural conditions. In contrast, for industrial pavements, only traffic conditions determine the required base thickness. A detailed analysis is provided, exploring variations in subgrade bearing capacities and traffic load scenarios, and comparing the outputs of PermPave and DesignPave to highlight their differences.

3.1. Urban PICPs Design

Figure 6 and Figure 7 represent 1U and 1I sheets, respectively.

For the sake of brevity, additional catalog sheets are provided in Appendix A (Figure A1, Figure A2, Figure A3, Figure A4, Figure A5, Figure A6, Figure A7, Figure A8, Figure A9, Figure A10, Figure A11, Figure A12, Figure A13, Figure A14, Figure A15, Figure A16, Figure A17 and Figure A18). The designed base thickness is the maximum value obtained from PermPave and DesignPave calculations, ensuring compliance with hydraulic and structural requirements. A results comparison is provided in

Table 5. Urban results comparison.

				400,000 Passes		1,500,000 Passes		4,000,000 Passes
	Subgrade	Base
	v [-] 0.4	v [-] 0.35
Sheet	E	E	PermPave Thickness	DesignPave Thickness	Design Thickness	DesignPave Thickness	Design Thickness	DesignPave Thickness	Design Thickness
[-]	[MPa]	[MPa]	[mm]	[mm]	[mm]	[mm]	[mm]	[mm]	[mm]
1U	30	271	270	235	270	315	315	395	395
2U		341		215	270	295	295	365	365
3U		373		210	270	285	285	355	355
4U		405		205	270	275	275	345	345
5U		435		200	270	270	270	335	335
6U		464		195	270	265	270	330	330
7U		492		190	270	260	270	325	325
8U		520		185	270	255	270	320	320
9U		547		180	270	250	270	315	315
10U		573		180	270	245	270	310	310
1U	90	271	240	140	240	205	240	270	270
2U		341		125	240	190	240	250	250
3U		373		120	240	185	240	240	240
4U		405		115	240	180	240	235	240
5U		435		115	240	175	240	230	240
6U		464		110	240	170	240	225	240
7U		492		110	240	165	240	220	240
8U		520		105	240	165	240	215	240
9U		547		105	240	160	240	215	240
10U		573		100	240	160	240	210	240
1U	150	271	100	100	100	155	155	215	215
2U		341		100	100	140	140	195	195
3U		373		100	100	135	135	190	190
4U		405		100	100	135	135	185	185
5U		435		100	100	130	130	180	180
6U		464		100	100	125	125	180	180
7U		492		100	100	125	125	175	175
8U		520		100	100	120	120	170	170
9U		547		100	100	120	120	170	170
10U		573		100	100	120	120	165	165

Note: the results from PermPave are blue and those from DesignPave are green.

.

In Table 5, the wide range of base thickness values for urban pavements (100 mm to 395 mm) primarily depends on three key factors: subgrade bearing capacity, traffic intensity, and hydraulic performance requirements.

• Subgrade Bearing Capacity: The ability of the subgrade to support loads significantly affects the base thickness. Pavements on low-strength subgrades (E_subgrade = 30 MPa) require a thicker base to distribute loads effectively, while high-strength subgrades (E_subgrade = 150 MPa) can support thinner base layers.
• Traffic Intensity: The number of commercial vehicle passes directly impacts the required base thickness. Under low traffic conditions (400,000 vehicle passes), the base layer thickness is primarily dictated by hydraulic performance rather than structural strength, often resulting in a minimum thickness of 100 mm. However, as traffic volume increases (up to 4,000,000 vehicle passes), the base should be thickened to 395 mm to accommodate repeated load cycles.
• Hydraulic Performance Requirements: The PermPave model dictates the minimum base thickness required to store and infiltrate stormwater. For subgrades with low permeability (SC, 5.0 × 10⁻⁷ m/s), the base needs to be thicker to compensate for the slow infiltration rate. In contrast, for high-permeability subgrades (SW, 2.5 × 10⁻⁴ m/s), a thinner base is enough, as stormwater infiltrates more efficiently.

These factors interact, meaning that for high-traffic roads built on low-permeability, weak subgrades, the base thickness approaches the upper limit (395 mm). Conversely, for low-traffic roads with well-draining, strong subgrades, the minimum required base thickness of 100 mm is adequate.

3.2. Industrial PICPs Design

For industrial pavements, the base thickness varies between 580 mm and 1760 mm (

Table 6. Industrial results comparison.

				100,000 Passes		250,000 Passes		400,000 Passes
	Subgrade	Base
	v [-] 0.4	v [-] 0.35
Sheet	E	E	PermPave Thickness	DesignPave Thickness	Design Thickness	DesignPave Thickness	Design Thickness	DesignPave Thickness	Design Thickness
[-]	[MPa]	[MPa]	[mm]	[mm]	[mm]	[mm]	[mm]	[mm]	[mm]
1I	30	271	270	1380	1380	1585	1585	1760	1760
2I		341		1280	1280	1470	1470	1630	1630
3I		373		1240	1240	1430	1430	1585	1585
4I		405		1210	1210	1390	1390	1540	1540
5I		435		1180	1180	1360	1360	1505	1505
6I		464		1155	1155	1330	1330	1475	1475
7I		492		1135	1135	1305	1305	1445	1445
8I		520		1115	1115	1280	1280	1420	1420
9I		547		1095	1095	1260	1260	1395	1395
10I		573		1080	1080	1240	1240	1375	1375
1I	90	271	240	915	915	1070	1070	1205	1205
2I		341		845	845	995	995	1115	1115
3I		373		820	820	965	965	1085	1085
4I		405		800	800	940	940	1055	1055
5I		435		780	780	915	915	1030	1030
6I		464		765	765	900	900	1010	1010
7I		492		750	750	880	880	990	990
8I		520		735	735	865	865	970	970
9I		547		725	725	850	850	955	955
10I		573		715	715	840	840	940	940
1I	150	271	100	740	740	885	885	1010	1010
2I		341		690	690	825	825	935	935
3I		373		670	670	800	800	905	905
4I		405		650	650	775	775	885	885
5I		435		635	635	760	760	860	860
6I		464		620	620	745	745	845	845
7I		492		610	610	730	730	830	830
8I		520		600	600	715	715	815	815
9I		547		590	590	705	705	800	800
10I		573		580	580	695	695	790	790

).

The results in Table 6 derive just from traffic conditions, as the thicknesses required from hydraulic performances are insufficient. Specifically, subgrades with low bearing capacity (E equal to 30 MPa) are not suitable for permeable industrial pavements due to the excessive base thickness required to support structural loads.

3.3. Discussion

The integration of traffic-induced stress, cumulative damage assessment, material degradation, and permeability loss into the modeling process ensures that the recommended base thicknesses are designed to maintain structural and hydraulic performance throughout the pavement’s service life.

These findings highlight that while initial design calculations provide a reliable estimate of base thickness, long-term performance considerations must be integrated into maintenance planning. Future studies could further refine pavement durability modeling by incorporating real-world wear data and site-specific material aging trends. The results confirm that the required base thickness for urban pavements highly depends on structural and hydraulic factors. While structural loads (traffic) play a pivotal role in high-traffic scenarios, hydraulic performance requirements control the base thickness for low-traffic scenarios, particularly in areas with low-permeability subgrades. The overestimation of base thickness by PermPave for high-strength subgrades suggests that while the model ensures effective stormwater infiltration, it may lead to unnecessarily thick base layers in cases where structural integrity is already assured. This highlights an important practical implication: for projects with high-strength subgrades (E ≥ 150 MPa), using only PermPave may lead to excessive material usage. Instead, a combined approach using both PermPave and DesignPave can optimize base thickness by ensuring both hydraulic and structural performance while minimizing material costs and environmental impact. The 150 MPa Young’s modulus threshold represents a critical point beyond which subgrade stiffness no longer influences base thickness requirements in permeable pavement design. This finding is essential for urban planners and pavement designers, as it suggests that the areas with well-draining soils and moderate traffic can optimize pavement design by using thinner base layers, reducing material costs and environmental impact.

4. Conclusions

Flood waves, water quality deterioration due to pollutants on pavements, disruption of the hydrological cycle, and increased surface temperatures caused by the Urban Heat Island (UHI) effect are some undesirable consequences of surface impermeabilization. This study investigated PICPs composed of concrete pavers with open joints that facilitate infiltration. These openings allow rainwater to enter a permeable base layer, which supports the pavers while providing runoff storage and treatment. Specifically, 110 mm pavers placed on 30 mm bedding sand achieve a surface infiltration rate of 9.0 × 10⁻⁵ m/s. The base layer consists of compacted, unbound crushed material (12.5–25 mm) with a 15% effective void ratio, a permeability of 5.0 × 10⁻⁴ m/s, a Young’s modulus ranging from 271 to 573 MPa, a Poisson ratio of 0.35, and a minimum thickness of 100 mm. Three subgrade types (i.e., SW, SM, and SC) were evaluated, representing decreasing load-bearing capacities and hydraulic conductivities of 2.5 × 10⁻⁴ m/s, 2.5 × 10⁻⁶ m/s, and 5.0 × 10⁻⁷ m/s, respectively. The hydraulic and structural performance of PICPs was assessed using PermPave and DesignPave software.

The findings demonstrate that permeable pavements are a viable alternative to conventional impermeable surfaces in urban and industrial settings. The geometric and mechanical properties of the concrete pavers and bedding layer have minimal impact on the required base thickness. Instead, the base layer thickness is primarily affected by subgrade type, permeability, number of vehicle passes, and the Young’s modulus of the base layer. For industrial pavements, additional factors such as the number and type of vehicles and dynamic loading effects further influence the required base thickness, leading to greater thicknesses compared to urban pavements under similar hydraulic and mechanical subgrade conditions.