{"id":101994,"date":"2026-06-29T13:27:53","date_gmt":"2026-06-29T13:27:53","guid":{"rendered":"https:\/\/geostru.ai\/en\/products\/rpd\/"},"modified":"2026-07-02T15:57:36","modified_gmt":"2026-07-02T15:57:36","slug":"rpd","status":"publish","type":"page","link":"https:\/\/geostru.ai\/ro\/products\/rpd\/","title":{"rendered":"RPD NX"},"content":{"rendered":"
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RPD NX<\/h1>\n<\/div><\/div>\n

Web-based design and verification of road pavements \u2014 the AASHTO 1993 empirical method, the Ivanov rational (deflection) method and the Westergaard rational (rigid multilayer-plate) method, side by side, with a real-time 2D type-section, a 3D model of the package and a built-in AI assistant. Opens in any browser \u2014 no installs, no hardware keys.<\/p>\n<\/div><\/div>\n<\/div>\n<\/div>\n<\/div>\n\n

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RPD NX<\/div><\/div>\n<\/div>\n<\/div>\n<\/div>\n\n
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What it does<\/h2>\n<\/div><\/div>\n

RPD NX takes a road pavement from traffic and subgrade all the way to a fully verified, reinforced package \u2014 three design methods, real-time drawings and traceable normative reports, entirely in the browser.<\/p>\n<\/div><\/div>\n

Three design methods<\/strong> \u2014 AASHTO 1993 empirical (Structural Number), Ivanov rational (maximum deflection) and Westergaard rational (multilayer plate for rigid pavements), computed side by side.<\/p>\n<\/div><\/div>\n

Design traffic in equivalent standard axles<\/strong> \u2014 average daily traffic, growth rate, commercial share and lane distribution converted to 8.2-tonne ESALs with the fourth-power damage law and the road-type spectrum.<\/p>\n<\/div><\/div>\n

Layered pavement package<\/strong> \u2014 per-layer thickness and material coefficients for wear, binder, base and subbase courses, with each layer switchable in and out of the check.<\/p>\n<\/div><\/div>\n

Real-time 2D & 3D<\/strong> \u2014 a type-section that redraws as you type and a navigable 3D model of the pavement package.<\/p>\n<\/div><\/div>\n

Reports and cloud projects<\/strong> \u2014 Word and PDF calculation reports, SVG type-sections and .rpdnx<\/em> projects saved to GeoDropbox, available in seven languages.<\/p>\n<\/div><\/div>\n<\/div>\n<\/div>\n<\/div>\n\n

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The three design methods<\/h2>\n<\/div><\/div>\n

AASHTO 1993 \u2014 empirical method<\/h3>\n<\/div><\/div>\n

Sizes the pavement by its Structural Number and checks the standard 8.2-tonne axles the structure can carry against those that will actually transit the design lane over its service life.<\/p>\n<\/div><\/div>\n

Structural Number<\/strong> \u2014 SN = \u03a3 a\u1d62 \u00b7 m\u1d62 \u00b7 D\u1d62, from each layer thickness D\u1d62 with its structural coefficient a\u1d62 and drainage coefficient m\u1d62.<\/p>\n<\/div><\/div>\n

Safety factor<\/strong> \u2014 FS = N\u2088.\u2082,lim \/ N\u2088.\u2082,calc, verified when FS > 1.<\/p>\n<\/div><\/div>\n

Reliability-driven<\/strong> \u2014 reliability R and its normal deviate Z_R, overall standard deviation S\u2080, serviceability loss \u0394PSI and subgrade resilient modulus M_R.<\/p>\n<\/div><\/div>\n

Ivanov \u2014 rational method (maximum deflection)<\/h3>\n<\/div><\/div>\n

An elastic (Boussinesq) approach for flexible pavements that limits the surface deflection produced by the design wheel load.<\/p>\n<\/div><\/div>\n

Equivalent elastic modulus<\/strong> \u2014 built up from the subgrade (E\u2080 = 65 \u00b7 CBR^0.65) through each active layer to a single E_eq.<\/p>\n<\/div><\/div>\n

Admissible deflection<\/strong> \u2014 f_adm = 0.17 \u2212 0.026 \u00b7 log\u2081\u2080(N), from the end-of-life daily standard axles N.<\/p>\n<\/div><\/div>\n

Safety factor<\/strong> \u2014 FS = f_adm \/ f_d, with the calculated deflection f_d = p \u00b7 Dp \/ E_eq from tyre pressure p and footprint Dp.<\/p>\n<\/div><\/div>\n

Westergaard \u2014 rational method (rigid pavements)<\/h3>\n<\/div><\/div>\n

Models a rigid (concrete) pavement as a multilayer plate on elastic soil, solved with a double Fourier series, to check the maximum slab deflection.<\/p>\n<\/div><\/div>\n

Per-layer stiffness<\/strong> \u2014 elastic modulus E, thickness and Poisson ratio for each layer, with the \u03b1K coefficient linking modulus to the reaction modulus (K = E \/ \u03b1K).<\/p>\n<\/div><\/div>\n

Subgrade reaction<\/strong> \u2014 the reaction modulus K closes the model; deflection is verified at the surface layer.<\/p>\n<\/div><\/div>\n

Safety factor<\/strong> \u2014 FS = f_adm \/ f_d, verified when FS \u2265 1.<\/p>\n<\/div><\/div>\n<\/div>\n<\/div>\n<\/div>\n\n

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How it works<\/h2>\n<\/div><\/div>\n

A guided flow takes you from project setup to an exported report in eight steps.<\/p>\n<\/div><\/div>\n

1 \u00b7 General data<\/strong> \u2014 project description, road type (which sets the traffic spectrum), design life and reliability\/serviceability parameters.<\/p>\n<\/div><\/div>\n

2 \u00b7 Geometry & preview<\/strong> \u2014 lanes, widths, shoulders and slopes, with the cross-section drawn in real time in 2D and 3D.<\/p>\n<\/div><\/div>\n

3 \u00b7 Pavement stratigraphy<\/strong> \u2014 layer thicknesses and coefficients for wear, binder, base and subbase courses; toggle layers and add geogrid reinforcement.<\/p>\n<\/div><\/div>\n

4 \u00b7 Subgrade & traffic<\/strong> \u2014 subgrade CBR or resilient modulus, average daily traffic (TGM), growth rate and commercial-vehicle share.<\/p>\n<\/div><\/div>\n

5 \u00b7 Calculation method<\/strong> \u2014 choose AASHTO 1993, Ivanov or Westergaard.<\/p>\n<\/div><\/div>\n

6 \u00b7 Results<\/strong> \u2014 safety factor, Structural Number, allowable axles and pass\/fail, computed automatically.<\/p>\n<\/div><\/div>\n

7 \u00b7 Meet verification<\/strong> \u2014 when FS < 1, clickable suggestions (thicker layers or a geogrid with a given TBR) that recalculate instantly; when over-designed, an optimisation card proposes trimming material.<\/p>\n<\/div><\/div>\n

8 \u00b7 Export<\/strong> \u2014 Word\/PDF reports, SVG sections and .rpdnx<\/em> cloud projects.<\/p>\n<\/div><\/div>\n<\/div>\n<\/div>\n<\/div>\n\n

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Inputs and outputs<\/h2>\n<\/div><\/div>\n

What you enter<\/h3>\n<\/div><\/div>\n

Road type and traffic<\/strong> \u2014 TGM, growth rate, commercial-vehicle and design-lane shares, trajectory dispersion; standard deviation S\u2080 for AASHTO.<\/p>\n<\/div><\/div>\n

Design targets<\/strong> \u2014 service life, reliability R, initial and final PSI.<\/p>\n<\/div><\/div>\n

Subgrade<\/strong> \u2014 CBR, resilient modulus M_R or reaction modulus K.<\/p>\n<\/div><\/div>\n

Layers<\/strong> \u2014 per-layer thickness and, by method, structural coefficient a and drainage m, elastic modulus E, Poisson ratio and \u03b1K.<\/p>\n<\/div><\/div>\n

Wheel load<\/strong> \u2014 tyre inflation pressure and contact footprint.<\/p>\n<\/div><\/div>\n

What you get<\/h3>\n<\/div><\/div>\n

Verification<\/strong> \u2014 safety factor and pass\/fail for the chosen method.<\/p>\n<\/div><\/div>\n

Design quantities<\/strong> \u2014 Structural Number, allowable standard axles (N\u2088.\u2082,lim), admissible and calculated deflections, equivalent modulus.<\/p>\n<\/div><\/div>\n

Drawings<\/strong> \u2014 real-time 2D type-section and navigable 3D package model.<\/p>\n<\/div><\/div>\n

Deliverables<\/strong> \u2014 Word\/PDF report, SVG section and .rpdnx<\/em> cloud project, in seven languages.<\/p>\n<\/div><\/div>\n<\/div>\n<\/div>\n<\/div>\n\n

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Reinforcement, AI and optimisation<\/h2>\n<\/div><\/div>\n

Bituminous geogrids<\/strong> \u2014 add a geogrid interlayer and apply its Traffic Benefit Ratio (TBR) to raise the allowable traffic, straight from the manufacturer's data sheet.<\/p>\n<\/div><\/div>\n

Auto-solver<\/strong> \u2014 when a check fails, RPD NX solves for the layer thicknesses or reinforcement needed and offers them as one-click, instantly-recalculated proposals.<\/p>\n<\/div><\/div>\n

Optimisation<\/strong> \u2014 when a package passes with margin, it suggests trimming thickness while staying compliant, saving material.<\/p>\n<\/div><\/div>\n

Built-in Gemini assistant<\/strong> \u2014 an optional AI layer explains every parameter and result, identifies the governing method and proposes motivated changes to layers and materials.<\/p>\n<\/div><\/div>\n<\/div>\n<\/div>\n<\/div>\n\n

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Who it's for<\/h2>\n<\/div><\/div>\n

Road and infrastructure engineers \u00b7 Pavement designers \u00b7 Geotechnical engineers \u00b7 Public-works technicians \u00b7 Consultants. RPD NX is for anyone who today sizes road pavements with spreadsheets or desktop tools and wants a single web environment that goes from traffic and subgrade to a fully verified, reinforced package with traceable normative output.<\/p>\n<\/div><\/div>\n<\/div>\n<\/div>\n<\/div>\n\n

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Why it's different<\/h2>\n<\/div><\/div>\n

Runs directly in the browser \u2014 no installation, no hardware key, always up to date.<\/p>\n<\/div><\/div>\n

Three established methods \u2014 AASHTO 1993, Ivanov and Westergaard \u2014 in one place, side by side.<\/p>\n<\/div><\/div>\n

Faithful to the originals and aligned with the Italian CNR pavement catalogue; every formula and coefficient transcribed verbatim.<\/p>\n<\/div><\/div>\n

Real-time 2D type-section and 3D package model as you design.<\/p>\n<\/div><\/div>\n

Built-in AI that explains results and proposes compliant, motivated changes.<\/p>\n<\/div><\/div>\n

Traceable Word\/PDF reports and cloud projects, in seven languages.<\/p>\n<\/div><\/div>\n<\/div>\n<\/div>\n<\/div>\n\n

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Frequently asked questions<\/h2>\n<\/div><\/div>\n

Are AASHTO 1993, Ivanov and Westergaard still current?<\/strong>
Yes. They are classic, consolidated methods that remain the standard professional reference and underpin the Italian CNR pavement catalogue.<\/p>\n<\/div><\/div>\n

Why is the reliability deviate Z_R negative?<\/strong>
That is correct: Z_R is the standard-normal deviate for reliability R and is negative for R > 50% (for example \u22121.282 at 90%), which makes higher-reliability designs more conservative.<\/p>\n<\/div><\/div>\n

Where is the Calculate button?<\/strong>
There isn't one. Results are computed automatically when you open the Results tab, and only when the inputs have changed.<\/p>\n<\/div><\/div>\n

What happens if a check fails (FS < 1)?<\/strong>
A \u201chow to meet verification\u201d card appears with clickable proposals \u2014 thicker layers or a geogrid with a given TBR \u2014 that recalculate instantly.<\/p>\n<\/div><\/div>\n

What is a geogrid's TBR?<\/strong>
The Traffic Benefit Ratio multiplies the allowable axles gained from a bituminous geogrid; use the value from the manufacturer's technical sheet.<\/p>\n<\/div><\/div>\n

What units does the Structural Number use?<\/strong>
SN is shown in inches (with the centimetre equivalent); you enter layer thicknesses in centimetres.<\/p>\n<\/div><\/div>\n<\/div>\n<\/div>\n<\/div>\n\n

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Ready to start with RPD NX?<\/h2>\n<\/div><\/div>\n

Choose your plan and start using RPD NX today. Runs in the browser, always up to date, no installation required.<\/p>\n<\/div><\/div>\n\n\n<\/div>\n<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"","protected":false},"author":0,"featured_media":0,"parent":101181,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_ai_seo_pilot_schema_type":"auto","footnotes":""},"class_list":["post-101994","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/geostru.ai\/ro\/wp-json\/wp\/v2\/pages\/101994","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/geostru.ai\/ro\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/geostru.ai\/ro\/wp-json\/wp\/v2\/types\/page"}],"replies":[{"embeddable":true,"href":"https:\/\/geostru.ai\/ro\/wp-json\/wp\/v2\/comments?post=101994"}],"version-history":[{"count":2,"href":"https:\/\/geostru.ai\/ro\/wp-json\/wp\/v2\/pages\/101994\/revisions"}],"predecessor-version":[{"id":102027,"href":"https:\/\/geostru.ai\/ro\/wp-json\/wp\/v2\/pages\/101994\/revisions\/102027"}],"up":[{"embeddable":true,"href":"https:\/\/geostru.ai\/ro\/wp-json\/wp\/v2\/pages\/101181"}],"wp:attachment":[{"href":"https:\/\/geostru.ai\/ro\/wp-json\/wp\/v2\/media?parent=101994"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}