Underwater construction of diaphragm walls and basement pdf
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- Diaphragm walls: Construction and Design
- Underwater construction of diaphragm walls and basement ppt
- Diaphragm walls: Construction and Design
- Underwater Construction Of Diaphragm Walls And Basement Pdf
Diaphragm walls: Construction and Design
Dewatering using the dewatering systems composed of diaphragm walls and pumping wells is commonly adopted for deep excavations that are undertaken in deep aquifers. However, dewatering can sometimes induce environmental problems, especially when diaphragm walls cannot effectively cut off the aquifers.
The shaft excavation with the depth of All these results are lesser than that predicted by empirical methods, which also confirmed the applicability of this innovative excavation. Thus, this innovative solution can be applicable to other deep excavations that are undertaken in ultrathick aquifers, especially for the excavation of coarse sediments with high permeability.
With the development of urban infrastructure, a growing number of deep excavation projects have appeared in China [ 1 — 5 ]. In many cases, deep excavation constructions are inevitably built below the water table in urban environments, especially in the coastal regions of China. As a result, dewatering is usually essential to be carried out prior to the excavation to ensure dry and workable conditions inside the excavation and to prevent the excavation bottom uplift or liquefaction when a deep excavation is undertaken in aquifers [ 6 — 8 ].
In general, there are thick aquifers in coastal regions of China, which are composed of sand, gravel, and silt of Quaternary deposits. In this situation, groundwater control is considerably difficult for deep excavations due to the high permeability of soils and heavily thick aquifers [ 9 — 11 ]. Thus, underground enclosures low-permeability barriers are commonly used for deep excavations in the presence of groundwater, such as deep cement mixing DCM columns, diaphragm walls, and jet grouting columns [ 12 — 15 ].
These underground enclosures are conducted to retain the surrounding soils as well as to prevent lateral groundwater from flooding into the excavations. So far, many researchers have focused on the issue related to the environmental effect caused by dewatering and excavation during deep excavations [ 16 — 20 ]. Pujades et al. Generally, when low-permeability barriers are embedded into the impermeable layers, the aquifers will be completely cut off by these enclosed barriers.
Under these conditions, dewatering inside an excavation just lowers the groundwater level, and it cannot cause groundwater drawdown outside the barrier. However, the deeper the excavation depth of the foundation pit, the deeper the depth of underground enclosures required, which thus renders more challenging and uneconomical. In fact, it is unrealistic to employ those completely enclosing barriers for a deep excavation that are undertaken in ultrathick aquifers, and on the contrary, the partially penetrating curtains are the most widely used for deep excavations.
Wang et al. Wu et al. As a result, the partial penetrating curtains produce positive effect in reducing the groundwater drawdown and water inflow from outside the excavation. Despite many obvious advantages of partial penetrating curtains, it is not without its problem. In such a case that a deep excavation was undertaken in ultrathick aquifers with high permeability, a combination of partial penetrating curtains and pumping wells may not be able to lower the groundwater level inside the excavation and simultaneously minimize the effect of dewatering on the surrounding buildings outside the excavation.
Thus, other groundwater control scenarios should be developed for a deep excavation when undertaken in ultrathick aquifers. Currently, dewatering was usually performed prior to the excavation when deep excavations undertaken below the water table, whereas few deep excavations that were conducted using the underwater excavation technique have appeared in the literature.
The objective of this study is to present an innovative excavation combining dewatering excavation and underwater excavation without drainage, which is employed for deep excavation of a shaft excavation that is undertaken in ultrathick aquifer in Fuzhou, China. The In this paper, first, the site characterization and pumping test are introduced.
Then, the novel excavation and construction method for the deep shaft excavation is proposed. The effect of the innovative excavation on the soil deformation outside the excavation was analyzed through numerical simulation. Finally, the excavation performance of the deep shaft excavation that was undertaken in the ultrathick aquifer was investigated through real-monitoring data obtained from the field, in order to confirm the applicability of this innovative technique.
This case history can provide meaningful references and insights into other projects involving deep excavations that are undertaken in ultrathick aquifers. The innovative solution can also be an alternative for the excavations that are undertaken in deep aquifers when groundwater control is difficult for deep excavations.
The investigated project is an air shaft of Metro line 2, located on the east side of Wulongjiang Wetland Park in Fuzhou, China. Due to the proximity of critical infrastructures, such as flood protection dike, the 3rd ring expressway, a gas station, and several underground service pipes, the surrounding environment of the air shaft is complex, which therefore brings some difficulties and challenges to the construction of the air shaft. The internal length of the air shaft along the subway tunnel alignment is The cut and cover method is adopted in the air shaft excavation.
The layout of the air shaft is presented in Figures 1 a and 1 b. The geology of the study site was characterized by means of borehole drilling. Nevertheless, the silty clay layer may have discontinuities, and as a result, gravel soil is directly connected to the sand layer. The depth of the miscellaneous fill layer is from 1.
A layer of plain fill underlies the miscellaneous fill layer with the depth of 6. There is a medium-coarse sand layer with the thickness of The next layer is a thin layer of silty clay with the thickness of 0.
There is a gravel soil layer with the thickness of The typical geology profile is displayed in Figure 1 c. The groundwater at the site consists of unconfined water and bedrock fissure water. The piezometric head of unconfined water is 3. Moreover, due to the site adjacent to Wulongjiang River, the groundwater is closely connected with the Wulongjiang River. That brings much challenge to groundwater control for the air shaft excavation. The watertightness assessment test WAT is considered as one of the most convincing means to verify this.
Thus, the WAT was carried out prior to the excavation to verify the feasibility of the dewatering system. Since the air shaft has a small area of The layout of pumping tests is shown in Figure 2. The pumping test was started on May 10, , and lasted for hours 50 for pumping and 50 for recovery. Well Y4 was used as a pumping well, and wells Y1 and Y5 as observation wells inside the enclosures.
Figures 3 a and 3 b display the time-history curves of the pumping rate of pumping well and the variation of drawdown measured in different observation wells during the pumping test, respectively.
Instead, the drawdown of observation wells changed rapidly. As the drawdown inside the enclosures increased, the pumping rate of the pumping well gradually decreased. After hour pumping test, the water levels of observation wells Y1 and Y5 were Both of them were below the bottom of the Phase I excavation The water level outside the excavation did not change significantly during the whole pumping test but changed regularly with the tidal effects.
The water level inside the enclosures recovered slowly when the pumping was stopped, which increased by only 9. Simultaneously, the water level inside the enclosure dropped quickly but recovered slowly.
The phreatic water level outside the enclosure did not change during the pumping test less than 0. This implied there was much challenge in lowering the water level inside to ensure dry and workable conditions for the whole excavation of the air shaft. Groundwater level inside the enclosures needs to be lowered below the excavation bottom to provide dry and workable conditions for the excavation. Nevertheless, the watertightness assessment test has proved that the success of lowering the water level inside below the excavation bottom at the depth of Since the hydraulic conductivity of gravels at the lower part of the excavation zone is rather large and groundwater recharge comes from the Wulongjiang River rapidly, it is quite difficult to successfully lower the groundwater level below the excavation bottom at the depth of Considering such various factors as the geology with high permeability, high head water, the deep excavation close to the Wulongjiang River, critical infrastructures, and underground pipelines surrounding the air shaft, there is a great deal of risk and challenge for the dewatering and excavation.
Furthermore, even though groundwater level inside the excavation was able to be lowered below the excavation bottom, it may cause potential hazard e.
Defects in these enclosure structures are frequent, which can even result in soil being dragged towards the deep excavation and sink holes at the ground surface [ 19 — 21 ]. In view of the abovementioned risk for the air shaft excavation, an innovative scenario for the air shaft excavation of The construction procedure of the air shaft, as presented in Figure 4 , included the following: a dewatering and Braced excavations up to the depth of The coupled hydromechanical numerical model was conducted using the finite difference program to investigate the feasibility of this innovative scenario combining dewatering excavation and underwater excavation without drainage.
Simultaneously, the effect of the deep excavation on the soil deformation outside the excavation was predicted in advance. The governing differential equations characterizing the hydromechanical response of porous materials in FLAC 3D are presented as follows [ 25 ].
For a homogeneous, isotropic solid, and constant fluid density, it is presented as where is the specific discharge vector; k is the tensor of absolute mobility coefficient of the medium; is the relative mobility coefficient and related to saturation s , , and which is zero and one for zero and full saturation, respectively; is the fluid pressure; is the fluid density; and is the gravity vector.
For small deformations, the fluid mass balance can be described as where is the volumetric fluid source intensity, is the variation of fluid content of variation of fluid volume per unit volume of porous material due to diffusive fluid mass transport, and t is the time. The balance of momentum is given in the following form: where is the bulk density and in which is the density of the dry matrix, is the fluid density, n is the porosity, and s is the saturation.
Changes in the variation of fluid content are closely related to variation in saturation s , pore pressure , and mechanical volumetric strain. The equation describing the response of pore fluid is given as where and are the Biot modulus and Biot coefficient, respectively. The equation describing the constitutive response of the porous solid is formulated as where is the corotational stress rate, H is the functional form of the constitutive law, is a history parameter, is the Kronecker delta, and is the strain rate.
In particular, the elastic relations which relate effective stresses to strains are small strain where the superscript 0 refers to the initial state, is the strain, and K and G are the bulk and shear moduli of the drained elastic solid, respectively. The relation between strain rate and velocity gradient is given as. The top surface of the numerical model was free in all directions.
The bottom part of the numerical model was fixed, so there were neither horizontal nor vertical movements. Additionally, no horizontal movement was allowed on x - z planes or y - z planes at the boundaries of the hydromechanical numerical model. In the numerical model, both soils and enclosure structures diaphragm walls were modelled by the solid elements, and the struts are modelled by beam elements. A linear elastic-plastic constitutive model described by using the Mohr-Coulomb strength criterion was used to simulate the behavior of soils.
Table 1 lists the calculated parameters of soils from laboratory tests. Soil-structure interaction was modelled by interfaces on both sides of walls. Interfaces in FLAC3D are one sided, and the constitutive model is also described by a linear Coulomb shear-strength criterion. The necessary input parameters of interfaces on both sides of walls in the modelling are the normal stiffness k n , shear stiffness k s , cohesive strength c s , and frictional strength f s.
The normal stiffness k n is consistent with the shear stiffness k s , determined by using the following equation [ 25 ]: where and are bulk and shear modulus, respectively, and is the smallest width of an adjacent zone to the interfaces in the normal direction. When there is a great difference in the stiffness of the two materials on both sides of the interface, K and G are determined from the softer material, and the interface stiffness is 10 times larger than the softer-side stiffness [ 25 ].
Excavation and support of the air shaft are a dynamic process, and the influence of groundwater seepage is taken into account in numerical simulations. The coupled hydromechanical simulations mainly focused on the deformation behavior of the retaining structures and surrounding soil during deep excavation.
The depth of each excavation was 2.
Underwater construction of diaphragm walls and basement ppt
Dewatering using the dewatering systems composed of diaphragm walls and pumping wells is commonly adopted for deep excavations that are undertaken in deep aquifers. However, dewatering can sometimes induce environmental problems, especially when diaphragm walls cannot effectively cut off the aquifers. The shaft excavation with the depth of All these results are lesser than that predicted by empirical methods, which also confirmed the applicability of this innovative excavation. Thus, this innovative solution can be applicable to other deep excavations that are undertaken in ultrathick aquifers, especially for the excavation of coarse sediments with high permeability. With the development of urban infrastructure, a growing number of deep excavation projects have appeared in China [ 1 — 5 ]. In many cases, deep excavation constructions are inevitably built below the water table in urban environments, especially in the coastal regions of China.
Diaphragm walls: Construction and Design
The walls act as cut off wall or serve as a structural member. Excavated trench creates a form for the wall. The trench is filled with bentonite slurry continuously circulated at all times.
Underwater Construction Of Diaphragm Walls And Basement Pdf
The present invention relates to a kind of construction of continuous concrete wall technology, particularly relate to a kind of construction method of underground continuous wall under Red Sandstone cobble geological conditions. The Lanzhou engineering is the landmark of Lanzhou and even whole the Northwest, and main building height m is the Northwest's first high building. Engineering is positioned at the busiest section, urban centre, and the contiguous major urban arterial highway of periphery and many buildings residence building have many municipal pipelines under the road, and the surrounding enviroment protection is had relatively high expectations. Project first phase foundation ditch area is about m2, and foundation ditch periphery linear meter is m, and underground four layers, cutting depth is the darkest to be
Due to the nature of concrete and reinforced concrete, structures are built divided into sections by forming joints, namely three types — construction joints, movement joints and connection joints. The key function of joint sealing is to minimize water ingress and create a secure waterproofing barrier. The seal must be capable of accommodating the anticipated joint opening and closing due to static reasons or temperature changes. Joint sealing solutions are recommended for use in all kinds of construction and joints for waterproofing. Construction joints are designed to split areas of the structure into separate concrete sections for work scheduling reasons, or as a structural measure to transfer load, for example. The reinforcement in construction joints is therefore continuous through the joint.
The underground diaphragm wall construction method in the red sandstone Download PDF Find Prior Art Similar 3) underwater concrete construction and bottom land slip casting basement excavation abstract,description 2
PARSONS BRINCKERHOFF GENERAL GUIDELINES FOR DESIGN …
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