The Environmental Effect Of Diaphragm Wall Panel Construction

Diaphragm wall has been widely used in engineering practice due to its own advantages, such as basement construction of high buildings, subway station construction, pier building, shore protection engineering, cut-off wall, retaining wall etc. Since the beginning of the20th century, diaphragm wall technology has made considerable progress and development in the aspect of wall geometry, usage range, construction technology, construction equipment, design theory etc. However, the environmental influence of diaphragm wall construction did not get enough attention by far. The first step of diaphragm wall construction is slurry trench opening. The soil stress and displacement around the hole must be rearranged throughout the whole construction process. Some existing methods may provide efficient ways to analyze the stability of slurry trench in uniform ground, but they may not be suitable for the layered soil structures. The earth pressure rearrangement around the wall panel due to wall construction has been neglected. The excavation simulation based on the earth pressure rearrangement has not caught researcher’s eyes, either. The ground movement influencing on the neighboring buildings and underground utilities due to the opening process has not been quantitative. Therefore, on the basis of reviews of the potential environmental detriment due to diaphragm wall construction, the specified works in this paper are listed as follows:1. The stability estimation methods for slurry trench is classified with respect to the mechanical fundamental, Rankine and Coulomb Theory. The Horizontal Slice Method is presented in this paper to validly analyze the stability of slurry trench in layered ground. The typical two-dimensional failure model is investigated, being divided into slices. From the force equilibrium of each slice and force and moment equilibrium of each slice, the3M and4M equations models are established respectively. The3M model is verified to be accurate, reliable and necessary and the weakness of4M model is discussed. Finally, an example problem is provided to illustrate variations of the factor of stability and critical failure plane angle with the length of the groundwater table, surcharge loading, slurry height and slurry unit weight. The horizontal slice force to vertical slice force ratio is defined to investigate the development of the horizontal slice force.2. The construction of10adjacent panels of a diaphragm wall of an ultra deep excavation in Wuhan city is modelled by a three dimensional FDM code. The construction procedure consists of the excavation supported by bentonite slurry, fresh concrete pouring, and the hardening of the concrete. The results of the numerical computation show good agreement with the field test data. The construction process of a full oscillating sequence discovers the development and causes of the stress rearrangement by the construction of the diaphragm wall. Base on the diaphragm wall construction process, a symmetrical part with five panels is chosen to model the step-wise excavation in two different types, namely the conventional model which neglects the construction process of diaphragm wall and the proposed model which considers the construction process of diaphragm wall. The numerical results including horizontal wall deflections, surface ground settlement and strut forces of the two model types are compared. It is shown that the construction of diaphragm wall has an significant impact on the deep excavation of pit computation and can not been neglected.3. An analytical solution for horizontal stress and displacement distribution due to diaphragm wall construction is derived based on the complex variables theory. The2-D plane stress assumption is verified by comparing computing results from3-D model. Base on the plane stress assumption, a conformal transformation function that maps the area outside a rectangular hole onto the region inside a unit circle is derived and used to obtain a horizontal stress and displacement solution. The solution is verified by comparing the numerical results. By performing s parametric study, a simplified equation of calculating the horizontal displacement at the midpoints at the face of the diaphragm wall is proposed. Finally, the solution is testified in practice.4. The causes and characteristics of surface settlements due to deep excavation and diaphragm wall construction are discussed and compared. Considering the special characteristics of Wuhan binary structural stratum, numerical simulations are conducted and parameter study on surface ground settlement induced by diaphragm wall construction is accomplished. An experienced formula taking soil elastic modulus, lateral earth pressure and slurry unit weight into account is established based on and Peck’s theory and considerable numerical tests. Finally, the proposed approximate is used in an example and the formula is verified to be useful and practical.5. An object oriented graphical user interface diaphragm wall procedure is design and developed. It consists of the stability estimation of slurry trench, the analytical horizontal stress and displacement solution due to the diaphragm wall construction, and the prediction of surface ground settlement due to the diaphragm wall construction in Wuhan binary structural stratum.