Outcome
This project developed an adjustment of cone penetration test (CPT) based classification chart to account for organic clays and peat. Furthermore, new CPT-based correlations are developed for geotechnical parameters of organic soils. Moreover, we developed a new model based on critical state soil mechanics, linking the effective strength parameters to undrained strength parameters, following existing approaches for slope instability analysis. Finally, we carried out a back analysis study of the Eemdijk full-scale dike failure test, consisting of three tests: (1) a ground dike, (2) a sheet pile reinforced dike and (3) pull-over tests on sheet pile panels. The interpretation of the test measurements provided valuable insights into the sheet pile performance to extreme loading conditions and beyond failure.
Eemdijk full-scale test; dike with sheet pile reinforcement after to failure. Photo by Arny Lengkeek https://www.instagram.com/eemdijk_damwandproef/
Motivation and practical challenge
As a geotechnical engineer with over 20 years of practical experience on hydraulic and geotechnical projects in the Netherlands and abroad, my motivation is related to better combining the theory with engineering and practice for dikes. Therefore, this project builds upon the current slope stability assessment approaches of dikes with sheet pile reinforcement and my experience in soil parameter determination, constitutive models and soil structure-interaction. This knowledge comes together in interpreting the soil investigation tests and related parameters, which are input for the advanced finite element method (FEM) models used for the stability, the strength of the sheet pile and the deformation assessment. Moreover, the Eemdijk full-scale test was a unique experiment that allowed me to validate analytical models’ performance in the dike engineering practice.
Research challenge
This project answers the following research question: How does a dike reinforced by a sheet pile stability wall perform under high water conditions, and how can this be modelled? Subquestions are divided into two categories. The first category applies to parameter determination for dikes in general, and the second category to the Eemdijk experiment (“Eemdijk damwandproef”) focuses on dikes reinforced by sheet piles.
Innovative components
In The Netherlands and other deltas globally, very soft and highly organic soils are omnipresent. With the adjustment of the CPT-based classification these organic soils are better classified. Futhermore, new CPT-based correlation are developed, for example, the soil unit weight for soils, ranging from sands to peat. A new theoretical model (CSR model) was developed, implementing the limit equilibrium method (LEM) on slope stability analysis. The new relationship obtains the undrained shear strength based on effective strength and stiffness parameters. Finally, regarding the “Eemdijk damwandproef”, two parallel 60m long full-scale test dikes of which one was reinforced with a sheet pile were loaded until failure with:
- Sheet pile pullover tests consisting of 4 sheet pile configurations in length and width.
- Ground dike stability test where the water level in the sand core of the dike is step-wised increased by infiltration.
- Sheet pile dike stability test to create a realistic load scenario and failure mechanism.
Components of the research relating the new methods and the Eemdiijk full-scale test including and illustration and photo impressions during and after the test. Source: Illustration and after test photo by POV macrostabiliteit. During test photo is by Arny Lengkeek.
Relevant for whom and where?
Engineers who design dikes with structural inclusions, such as sheet piles, with finite element method (FEM) models. Engineers who use CPTs for parameter determination of soft organic soils for civil engineering projects in general.
The components of this research are developed for a range of typical dike sections for the Dutch riverine area, and for a case study of a full-scale test embankment in Eemdijk.
Progress and practical application
This project developed improved CPT-based classification and correlations for the organic soils, directly applicable for Dutch dike engineering projects. The correlations are based on statistical methods and include the confidence interval.
The new developed CSR model to obtain the undrained shear strength strikes a balance between the current practice using the empirical Stress History and Normalised Soil Engineering Properties (SHANSEP) equation and the theoretical elaboration of undrained shear strength based on critical state soil mechanics. The CSR model allows for a variable spacing ratio that can be fitted to laboratory test data. The CSR model can be implemented in LEM, where it can be used for stability analysis.
The Eemdijk full-scale test gave insight into the soil-structure interaction of the structurally reinforced dike on soft soil, loaded by high water and uplift conditions. The capacity of sheet piles complies with the Eurocode and even shows robustness after failure for a less conservative approach than in the current guidelines. The sheet piles contribute to the dike’s water-retaining capacity after structural failure and prevent breaching. For a detailed description of each finding, please check the related outputs.
Recommendations for practice
- Consider using the updated CPT based classification given its improvements compared to previous methods for the sedimentary deposits found in The Netherlands.
- Consider using the new CSR model to compare effective strength and undrained strength parameters and reduce uncertainties in parameter determination and stability analysis.
- The back-analysis of the Eemdijk confirms that despite the complex soil-structure interaction, the FEM models perform well. The strength and deformations are underestimated due to anisotropy and 3D effects. The reduction of stiffness parameters is not required for advanced models as the reduction in strength parameters already covers this.
Last modified: 12/01/2022
Contributing researchers
Arny Lengkeek
Delft University of Technology
User group
Project outputs
Application of geo-statistics and pairwise established CPT-based correlations for line infrastructure
A method to use CPT and laboratory tests to calculate characteristic values, on the basis of pairwise established CPT-based correlations. We illustrate the method in six cases accounting for regional and local variations, failure extent and availability of local CPTs.
22/11/2021
Bevat: Conference proceedings
Eemdijk full-scale field test programme: ground dike and sheet pile dike failure test
Two similar test dikes were constructed at full scale (5m high, 25m wide, 60m long) to gain better understanding of the failure mechanism and deformations for both dikes, one of which served as a reference for the dike that had an 18m long sheet pile wall was installed.
01/09/2019
Bevat: Conference proceedings
Eemdijk full-scale field test programme: sheet pile pullover tests
The full-scale pullover tests consisted of 4 sheet pile configurations to gain more insight in the soil-structure interaction and the structural behavior of sheet piles beyond maximum bending capacity.
01/09/2019
Bevat: Conference proceedings
Impact of the Eemdijk full-scale test programme
This paper describes the rationale behind the test setup and operation of the test programme in relation to the current design codes and guidelines. First the set of knowledge questions to be resolved is considered. These questions gave direction to the type of failure tests, the required instrumentation and the impact of conclusions.
01/09/2019
Bevat: Conference proceedings
CPT based unit weight estimation extended to soft organic soils and peat
A new correlation is proposed that can be used to estimate the saturated soil unit weight from sands to highly organic soils. Our proposal outperforms other considered correlations. The variation in the estimation is however still considerable and comparable to earlier studies.
21/06/2018
Bevat: Conference proceedings
Events
14/06/2021
Reflection: Macro stability - better parameters or models or do we need to reinforce the dikes?
Macro instability of the inner slope is an important failure mechanism that has a large influence on the costs of dike reinforcements and their impacts on the landscape. There are various uncertainties considering the strength parameters and models. There seem to be various options when a dike does not meet the standards: better parameter estimation, better models, or realize a conservative and expansive reinforcement. Which options could we explore to deal with macro instability in an efficient manner?
News
Cross-Project Macro Stability Exploration (in Dutch)
22/11/2021
Within the total tasking of the Flood Protection Programme, the failure mechanism macro stability is the most important cost item for dike sections that...
Eemdijk test: dike with sheet piles has collapsed (in Dutch)!
21/03/2018
The test dike with sheet piles collapsed on March 17 around 4 pm. The results of this trial will be used by all dike...
