Projektname: BioSolidEncap

Projektkennzeichen: ZF 401 681 0Rh7

Projektverantwortlicher: Prof. Dr.-Ing. Frank Wuttke

Projektbeginn: 01.04.2018 Projektende: 31.06.2021

Mitarbeiter: Shadi Zeinali,

M.Sc., Zarghaam

Rizvi, Dr.-Ing.

HiWi:

Thema: Effect of bacterial-treatment on mechanical properties of soils

Projektbeschreibung:

The research project aim is to do a systematic experimental investigation of controlled

biomineralization for the simple, inexpensive and permanent stabilization of heaps and tailing

slopes, so that potentially dangerous situations can be avoided or reduced, and to improve

knowledge transfer and cooperation between science and industry.

In this regard, the project BioSolidEncap is divided into three subsections. The work packages

1-5 are the experimental and numerical developments, the next two packages 6-7 deal with

optimization of the developed models and large-scale implementation challenges and the final

three work packages 8-10 are related to product development and market suitability, which in

title consist of: WP 1: Preparatory work

WP 2: Experimental work on microbacterially modified and controlled mechanical

parameter changes

WP 3: Numerical developments for mapping discrete pore network models based on

lattice element models

WP 4: Numerical developments for the coupling of discrete pore network models with

continuum models

WP 5: Validation of Numerical Developments by Experimental Experiments

WP 6: Application of Field Stabilization and Simulation Methods

WP 7: Correction of numerical developments based on field and laboratory studies

WP 8: Derivation of simplified recommendations for practical use

Ergebnisse: Work Package 1: Three sites are identified with the help of the project partner near Köln for

collection of the heap and tailing materials for cementation trails. The standard geotechnical

laboratory tests are performed on the field samples and sand types. Sieve analysis of analysis are

depicted in Figures 1 and 2. Effect of size distribution on biocementation and mechanical

properties of samples has been studied. Samples treated from a new synthesized bacterium from

project partner, Sansatec Co., will be received to do tests on them, too.

Figure 1- Sieve analysis of the studied Sands for MICP

Figure 2- Sieve analysis of the studied tailing materials for MICP

Work Package 2: The calcite precipitation and the location and amount of active bonds are

analyzed with SEM and XCT and the results are presented for the standard sand. The similar

procedure is ongoing for characterization of the field soil with similar technique. Preliminary

probability test on a few samples has been done by previous colleague, which its sample

preparation took 2 weeks (Figure 3 to 7). Due to time-limit of the project, the set up and bacterial

medium has been modified and boosted to some extent, and will be used for column injection.

The Triaxial and other mechanical tests will be performed in the coming months to define the

failure criteria of the numerical model which is so far considered based on educational guess.

The following main results can be summarized for the experimental section up to now:

Figure 3- The MICP setup for the laboratory-scale test. a) inline cylinders to generate four samples in one trail

run. b) section of a biocemented sand column

Figure 4-: The split test to estimate the tensile strength. a) The bio cemented sample b) sample under a

compression testing machine c) formation of the failure surface.

Figure 5- The splitting test. a) The change in cohesion value computed for a different combination of processes. b)

behaviour of the material during the splitting test. The resulting in brittle behaviour.

Figure 6- Change in the permeability of sand with MICP treatment over time

In-situ water content and density of “Heinrich-Robert” and “Scholven” sites were measured as

it is shown in Table 1. Table 1- In-situ water content and density of field materials

H. Robert B. Scholven

Water content [%] 12.2 10.17

Density of the sample [g/cc] 1.99 1.73

Oedometer biotreated samples from field samples were prepared by the project partner, and the

result of this test was not successful due to the schrinkage that has happened to the bacterially

treated field soil. Hence, the sample lost its cohesion to the steel ring of the Oedometer device

(Fig. 7).

Figure 7-surface of Heinrich-Robert soil sample and the leakage issue

Splitting tensile strength test has been done on 110 small cylindrical samples. Samples from 3

types of sand (Hagebaumart, Strandsand, Fine quartz sand) were biotreated by the partner. Sieve

analysis of studied sands and tested samples are shown in figure 1, 9. Split test was carried out

on biocemented sands and Density before and after biotreatment, carbonate percentage and

Tensile strength have been monitored. As shown in figure 8 to 12, a relationship between tensile

strength and cementation percentage has been detected, which in general the Tensile strength is

increased by the cementation increase. But not in all cementation levels and soil types, increasing

cementation level led to more Tensile strength. Tensile strength of the Hagebaumart line is,

however, higher than two other sands, Impact of the coefficient of uniformity, the angularity of

the soil particles, and effective cementation distribution (contact) in the soil matrix should not

be also neglected.

(a)

(b)

(c)

(d)

Figure 8- extruded Strandsand sample (a,b), adjusted sample into the UL-25 compressing device (c,d)

(a)

(b)

Figure 9- Cracked samples in the UL25 compression device (a, b)

(a)

(b)

Figure 10- Strandsand results (a,b)

(a)

(b)

Figure 11- Hagebaumart sand results (a,b)

(a)

(b)

Figure 12- Fine Quartz sand results (a,b)

Bacterially treated column samples are being produced with a two-step injection process with

sand, and the hydraulic conductivity test and mechanical tests will be done on the treated

samples. Due to time-limit of the project, the set up and bacterial medium has been modified and

boosted to some extent based on an in medium precipitation test, and will be used for column

injection. Factors considered in the column experiment work plan are pictured in Figure 14.

Figure 13- Factors considered in designing the column experiment plan

Clear evidence of bond-forming calcite and surface deposited calcite and active bond deposits

of calcites have been shown in Figures 14 and 15, and a back-calculation is performed with

image analysis. Only about 8-11% deposited calcite results in bond strengthening and thus

processes to improve the numbers of the active bond calcite are ongoing with different

techniques. Plus, as shown in figure 16, once a critical density has reached, the strength of the

sample start decreasing even with more amount of calcite precipitation. The observation is in

match with micro characterization. Mathematical analyses are going to quantify and formulate a

simple equation to find the critical density and calcite content.

Figure 14- XCT of Biocemented sand, the grey areas show the quartz sand grain and the bright white spots shows

the formation of the Calcite cement on the surface and among the grain boundaries.

Figure 15- A 3D planar cut to identify the active and redundant calcite bonds

Figure 16- A 3D plot of increase in strength with amount of calcite precipitation and density. After reaching a

critical density the strength depreciates even with more calcite bonds.

Work Package 3: The lattice element method is developed, and the behavior of bio-cemented

material is studied with superior crack and failure modelling parameters (Figure 17-19). The

Finite Element Model is in progress for failure study of tailing dam with commercial software

Plaxis 2D.

Mechanical Lattice Model

Figure 17- Meso-scale representation of bio-cemented sand a initial state with sand grains and voids b deformed

state in which failure of neighbouring lattice elements produces the crack propagation by activating embedded

discontinuities

a)

b)

Figure 18- Three different medium meshes (3200 cells) of the similar porosity value. The brown elements are the

grains, and grey elements are the voids or cemented voids. B) the failure pattern of samples under uniaxial

compression with 10% of cementation.

Figure 19- mesh sensitivity test for 8.24% cementation with different meshes a) macroscopic curves; failed

elements in b) coarse mesh (800 cells), c) medium mesh (3200 cells), d) fine mesh (7200 cells)

Hydraulic Conductivity model

A conceptualises porous materials at mesoscale by pore lattice element method is developed to

model as the first step to model the change in the hydraulic conductivity. The generation of

granular assembly is done with the Poisson random lattice generation scheme. The pores are the

inscribed circles or spheres in the Voronoi cells (Fig 12a), and later the cells are connected with

throats of different radius following the first approximation random distribution. (Fig 12b)

The lattice model is capable of considering the shapes of pores and connections and is applied

to predict experimentally measured permeability of sand. The model with refined mesh

converges to the effective value of the experimental result. (Fig 12 c)

Figure 20-: (a) Voronoi cells (b) inscribed circle, connecting throats (c) Computed hydraulic conductivity

Figure 21-: The Numerical simulation of flow in the porous granular media with the rectangular geometry of

250000 seed points.(a)Generation of porous media with segregated Poisson Voronoi scheme with (grains)red and

(voids)blue (b) the pore network with the inscribed spheres to generate the pores of the pore network model. (c)

distribution of pressure in the pores with an applied pressure of 1 Pa at the top (red) and 0 Pa at the bottom (blue).

Work Package 4: For large scale implementation the feasibility study will be performed on the

calibrated and developed model with Plaxis 2D. A large-scale bacterial injection on a Dike is

also going to be done with the help of our Partner.

Work Package 5: The process will be followed and is coupled with WP 4

Work Package 6: The field implementation process involves material testing and evaluation of

effective physical parameters. Using these parameters from laboratory test, the FEM model in

Plaxis will allow accurate modelling of tailing dam failure. The process is in progress for model

development and experimental test are almost completed.

Work Package 7: The model calibration process is in progress as explained in WP 3-6.

Work Package 8 & 9: The recommendations related to the simplified application of technology

for practical use and characterisation of the market size and target group will be identified once

the laboratory, field and numerical modelling results are available.

Datum, Ort: 22.02.2021