JPH02140318A - Settlement adjustment construction with water storage tank and water stop wall - Google Patents

Abstract

PURPOSE:To decrease consolidation reduction and cope with the liquefaction of a sand layer by providing water storage tanks and water stop walls around structures, forming gravel drains, and raising or lowering the ground water level than the ordinary water surface. CONSTITUTION:Large water storage tanks 3 and 13 are provided around structures 2 and 12, and water stop walls 5 and 15 reaching clay layers 4 and 14 are separately formed on the whole periphery. Gravel drains 8 and 18 packed with crushed stones or the like are formed below structure batholithes 6 and 16 and between outer peripheries 7 and 17 and the water stop walls 5 and 15. When the structure 2 is a medium scale and the consolidation settlement is large, water is fed in the gravel drain 8 from the water storage tank 3, the ground water level 10 is raised from the ordinary water surface 9, and the consolidation settlement of the clay layer 4 continued below a sand layer 11 is decreased. When the structure is a small scale, the structure batholith 16 is further dug to form a deep well 19, underground water is drawn up by an underwater pump 20, and the ground water level 22 is lowered than the ordinary water surface 23 to cope with the liquefaction of a sand layer 24.

Description

[Detailed description of the invention] [Industrial field of application] Blocking off groundwater in the surrounding ground of a structure with a water-stopping wall I~, if consolidation settlement is expected to be large, water is removed between the structure and the water-stopping wall. By supplying water, the groundwater level is raised above the normal water level to reduce consolidation settlement of the clay layer, and for structures where the majority of the parts are underground, the groundwater level is always lowered below the normal water level using deep wells placed in advance. This invention relates to a subsidence adjustment construction method using a water storage tank and a water-stop wall that are adapted to cope with the liquefaction of a sand layer.

[Conventional technology]

Traditionally, waterfront areas (Waterfront areas)
.

In cases where the supporting layer is at a depth of more than several tens of meters, such as in the case of ground located in a large area, pile foundations become difficult, so floating foundations may be considered as an alternative. For the foundations of structures built on ground where the soil layer near the ground surface is composed of sand and a clay layer below it, liquefaction of the sand layer during an earthquake and consolidation settlement of the clay layer, as in the Niigata Earthquake, can occur. That was the problem.

[Problem that the invention seeks to solve]

When the supporting layer is more than several tens of meters deep, such as in waterfront areas, floating foundations are used.
ng foundation) is used, but
For the foundations of structures built on ground where the soil layer near the ground surface is composed of sand and a clay layer below it, liquefaction of the sand layer during an earthquake, as in the Niigata Earthquake, and consolidation settlement of the clay layer can occur. This invention attempts to solve the problem of increasing size.

[Means for Solving the Problems] This invention provides a large water tank around the structure when the supporting layer is at a depth of more than several tens of meters, such as in the ground in a waterfront area, and the clay is poured in advance. Water cutoff walls that reach the layer cut off groundwater in the surrounding ground of the structure, and gravel drains filled with crushed stone or gravel are installed between the base of the structure, the outer periphery of the structure, and the water cutoff wall, and are used for medium-sized structures. In case,
If consolidation settlement is predicted to be large, supply water from the water tank to the gravel drain to raise the groundwater level above the normal water level to reduce consolidation settlement of the clay layer below the sand layer, or to reduce the consolidation settlement of the clay layer below the sand layer. Alternatively, for structures that are mostly underground, we dig deeper than the base of the structure to form multiple deep wells, and pump groundwater from the deep wells to constantly lower the groundwater level below the normal water level to create a sand layer. This problem was solved by dealing with liquefaction.

[For production]

A large water storage tank is installed around the structure built on the ground in the waterfront area, and a water stop wall that reaches the clay layer is used to cut off groundwater in the surrounding ground of the structure, and the bottom wall of the structure and the outer periphery of the structure are also installed. In the case of medium-sized structures, compaction settlement of the clay layer can be achieved by filling crushed stone or gravel between the cutoff wall and forming a gravel drain, or by digging deeper than the base of the structure to form multiple deep wells. If it is predicted that the water level will be large, water will be supplied from the water storage tank to the gravel drain to raise the groundwater level above the normal water level to reduce consolidation settlement of the clay layer below the sand layer. The effective load does not change even if the groundwater rises and falls, but the boundary conditions (values) of the clay layer change, and the partial pressure increases or decreases as the partial pressure increases or enters a hysteresis process. It is something to do.

The rise and fall of the groundwater level does not affect the loads involved in the subsidence of structures, but it does change the consolidation conditions of the clay layer. If the sand layer is predicted to liquefy for a small-scale structure or a structure that is mostly underground, groundwater is pumped up from a deep well dug deeper than the base of the structure to keep the groundwater level below the normal water level. It is possible to deal with liquefaction by At this time, the amount of settlement increases as the water pressure decreases due to the drop in the groundwater level, resulting in an increase in effective stress, which causes the clay to expand, and is further affected by the structural load, so the amount of consolidation and settlement increases. , groundwater is reduced or the overburden pressure increases, making it possible to cope with liquefaction during earthquakes.

〔Example〕

waterfront area
If the support layer is at a depth of more than several tens of meters, such as the ground 1 in the structure 2, a large water tank 3 (resevoi
r), and separately, a water stop wall 5 reaching the clay layer 4 is formed in advance around the entire periphery of the structure 2, and the water stop wall 5 is used to prevent the structure 2 from forming.
A gravel drain 8 is constructed by blocking groundwater in the surrounding ground and filling crushed stone or gravel between the lower surface of the structure base 6, the outer periphery 7 of the structure 2, and the water stop wall 5.
If the structure 2 is medium-sized and consolidation settlement is predicted to be large, water is supplied from the water tank 3 into the gravel drain 8 to lower the groundwater level 1 below the normal water level 9.
0 to reduce the consolidation settlement of the clay layer 4 that continues below the sand layer 11. In the case of Figure 2, the structure 12
If the structure 12 is small-scale or mostly underground, a large water tank 13 is installed around the structure 12, and a separate tank 13 is installed around the structure 12.
A water stop wall 15 that reaches the clay layer 14 is formed in advance around the entire periphery of the structure 12, and the water cutoff wall 15 blocks groundwater in the surrounding ground of the structure 12.
A gravel drain 18 filled with crushed stones or gravel is formed between the outer periphery 17 of the structure and the water stop wall 15, and the structure bottom plate 16 is
On the lower surface of the structure 12, a deep well 19 is dug deeper than the structure bottom a16 of the structure 12.
), and a submersible pump 2 is installed in each of the deep wells 19.
0 is interpolated and the pumping pipe 2 of each submersible pump 20 is
1 to the water storage tank 13. The submersible pump 20 is operated to pump up groundwater to constantly lower the groundwater level 22 below the normal water level 23 to cope with the liquefaction of the sand layer 24.

〔effect〕

Existing technology can be used as is, and its effectiveness is supported by soil mechanics.

[Brief explanation of the drawing]

1 and 2 are longitudinal sectional views of the embodiment, FIG. 1 is a longitudinal sectional view of the equipment when raising the water level, and FIG. 2 is a longitudinal sectional view of the equipment when lowering the water level. License applicant: Toda Construction Co., Ltd.

Claims (2)

[Claims] (1) If the supporting layer is at a depth of more than several tens of meters, such as in the ground in a waterfront area, a large water tank should be installed around the structure, and a water stop wall that reaches the clay layer should be installed around the structure in advance. In the case of medium-sized structures, consolidation settlement is expected to be large by blocking groundwater in the ground and installing gravel drains filled with crushed stone or gravel between the base of the structure, the outer periphery of the structure, and water-stop walls. In this case, water is supplied from the water tank into the gravel drain to raise the groundwater level above the normal water level, thereby reducing consolidation settlement of the clay layer below the sand layer. Subsidence adjustment method. (2) When the supporting layer is at a depth of more than several tens of meters, such as in the ground in a waterfront area, a large water tank is installed around the structure, and a water stop wall that reaches the clay layer is placed around the structure in advance. We cut off the groundwater in the ground, install gravel drains filled with crushed stone and gravel between the structure's base, the outer periphery of the structure, and the water-stop wall, and drill deeper than the structure's base to form multiple deep wells. A subsidence adjustment method using a water storage tank and a water stop wall, which is characterized by pumping up groundwater from the deep well and constantly lowering the groundwater level below the normal water level to cope with liquefaction of the sand layer.