A.F. van Tol

Analytical Model for Fracture Grouting in Sand

A conceptual, analytical model has been developed to describe the fracture grouting process in sand. The objective of the model is to improve understanding about this process in sand and to model propagation of the fractures. The results can be used to assess the parameters that control the fracture process. It is assumed that the complicated shape of a fracture in sand can be simplified to a geometrical shape (such as a tube or a plane) as a first approximation. Filtration of the grout appears to have a significant influence on the fracture shape when grout is injected into permeable subsoil such as sand. By assuming a pressure at which a fracture starts and a minimum pressure for propagation, it appeared possible to calculate the width-to-length ratio of the fracture independent of other soil properties. Quantification of the flow inside a fracture and the filtration processes resulted in a model that has been used to study differences in fracturing behavior in model tests and field tests on fracture grouting in sand. It was concluded that the width-to-length ratio of the fractures in a permeable soil decreases if the injection pressure of the grout or the permeability of the grout cake is decreased.

Relation of Enzymatic Reaction Rate and Hydrophobicity of the Solvent

Abstract Solvent effects on enzymatic reaction rates have been modelled according to the transition state theory. It is argued that the chemical activities of the reaction components must be kept constant in order to evaluate solvent effects on catalytic activity. Preliminary experimental results show similar trends for condensation and hydrolytic reaction rates. A simple method for the determination of water activity is discussed.

Investigation of Soil-Arching Development in Dense Sand by 2D Model Tests

A trapdoor system has frequently been used to study soil arching and its development in recent years. The load transfer in the fill of piled embankments is very similar to a trapdoor system with multiple trapdoors. There are multiple arching models described in different standards and guidelines for piled embankments that can be subdivided into three archingmodel families. To study the soil-arching type and its development, a series of model tests with sand fills were carried out in a two-dimensional (2D) multi-trapdoor test setup. The tests considered four factors—the fill height, trapdoor width, pile width, and grain size of the sand—with four values for each factor. Triangular slip surfaces were found at very small deformations using the particle image velocimetry (PIV) technique. These surfaces evolved in ways that could be related to the three types of stress-distribution ratio curves, with development patterns similar to the arching families of piled embankments: (1) the rigidmodel family, (2) the equal-settlement-plane-model family, and (3) the limit-equilibriummodel family. The limit-equilibrium-model family occurred in tests with narrow trapdoor widths.

Validating and Improving Models for Vibratory Installation of Steel Sheet Piles with Field Observations

Vibratory driving is the most common installation technique for steel sheet pile walls. In practice, the assessment of the feasibility of this installation process is mainly based on rules of thumb, on numerical and empirical models or on experts opinions. In order to improve these prediction methods and formulas, 252 observations from the Dutch engineering practice have been compared with six different types of models. This comparison has been carried out applying the receiver operating characteristic (ROC) curve technique, which is new in geotechnical engineering. This paper introduces the ROC-curve technique to estimate mainly the quality of a model and to be able to optimize parameters and variables in the model. 252 field observations were used to re-examine prediction methods for the minimum required vibration force and to prove the ROC method works. The paper shows this technique is suitable for three purposes: (1) determining the quality of a model, (2) objectively comparing several models to each other, given certain assumptions and (3) for optimizing thresholds within a model. The model with added professionals’ experience proves to perform equally well as the numerical model Hypervib-I.

Kinetic Resolution of Racemic Glycidyl Esters with Porcine Pancreatic Lipase: A Major Effect of Ping-Pong Kinetics

Abstract In the kinetic resolution of chiral glycidyl esters with porcine pancreatic lipase, PPL, the ratio of V S /[S] over V R /[R] was found to decrease strongly with increasing degree of conversion (ξ). This finding could not be rationalized on the basis of current models for enzymatic enantioselectivity. The importance of enzyme mechanism, partitioning of esters in a two-phase organic/aqueous-solvent system and the adsorption of PPL at an interface were evaluated. A major effect could be attributed to the ping-pong kinetic mechanism of PPL-catalysis. Different enantioselectivities of PPL acting in the aqueous phase and at the ester-water interface were observed.

Mechanisms of hydraulic fracturing in clay, sand and rock

Hydraulic fracturing is studied, mainly in the context of compen- sation grouting. It appeared that different from hydraulic fracturing in rock and clay, the flow from the fracture to the surrounding subsoil cannot be neglected. Due to this flow there is a minimum thickness over length ratio of a fracture in sand, which is a function of drainage of fracture fluid ant the percentage of solid material in the fracture fluid. A description will be given as well as experimental results confirming the theory developed. The neccessary injection pressure and the shape of the fracture, depends on the properties of the injection fluid, the permeability of the surrounding soil material and the discharge rate during injection. A consequence is that the grout bodies made in compensation grouting differ from what is usually assumed