A kind of stepped support method for foundation pit in soft soil

Abstract

The invention discloses a stepped supporting method for a soft soil foundation pit. The method is characterized by comprising the steps that a, original ground natural unprotected open cut excavationis performed to from a first-stage platform, and first-stage steel sheet piles are vertically inserted in the circumferential direction of the foundation pit on the first-stage platform; b, inward excavation is performed continuously from the inner side faces of the first-stage steel sheet piles to form a construction platform, and a stirring pile drilling machine is controlled to construct stirring piles on the construction platform in a mode that the upper portion is hollow and the lower portion is solid; c, whole excavation is carried out from the outside to the inside in sequence on the construction platform, so that the hollow portions above the solid portions of all stages of the stirring piles are excavated to form the platforms, and the steel sheet piles are vertically inserted inthe positions, close to the solid piles, of the outer sides of all the platforms until excavation is performed to be flush with the elevation of the foundation pit. The stepped supporting method for the soft soil foundation pit has the advantages that firstly excavation is carried out to form the construction platform, the construction platform and the stirring piles of which the lower portions have hollow portions make the effective pile length can reach a deeper soft soil treatment range, and the requirements for stable supporting of the 10-meter-deep foundation pit are achieved.

Description

technical field [0001] The invention relates to foundation pit construction, in particular to a step-type support method for weak soil foundation pits. Background technique [0002] Weak foundation refers to the foundation mainly composed of silt, silty soil, flush filling soil, miscellaneous filling soil or other highly compressive soil layers. The cohesion and internal friction angle of this kind of soft soil foundation are small, allowing the excavation slope to be relatively gentle. [0003] Cement mixing pile refers to an effective form of soft foundation treatment. It is a main agent that uses cement as a curing agent. The cement is sprayed into the soil by a mixing pile machine and fully stirred to make a series of physical and chemical reactions between the cement and the soil. , to harden the soft soil and improve the strength of the foundation. [0004] For weak soil foundation pits, vertical support technology is not limited by site conditions, and the amount of...

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Problems solved by technology

[0004] For weak soil foundation pits, vertical support technology is not limited by site conditions, and the amount of excavation is small, which is the most ideal support method. However, due to the structural requirements of steel sheet piles, the height of the protruding support part is limited to ≤ 1 / of the overall height 3. The length of the general steel sheet pile is only about 15m, which cannot be applied to foundation pits as deep as 10m, and the construction requirements are high and the cost is high; the difficulty of slope excavation is low, the cost is low, and the site is limited. Therefore, using agitation Pile reinforcement of soft soil can increase the excavation slope ratio and reasonably control the support cost, but there are still some limitations in the use of this method

[0005] In the prior art, because it is often affected by the surrounding buildings, the excavation area of ​​the foundation pit is limited, and it is impossible to form a large-scale excavation with a relatively gentle slope according to the bearing capacity of the soft soil itself. The Chinese invention patent application with the publication number CN108035359 A is disclosed A method for excavating a side slope is disclosed, the steps are: 1) using cement mixing piles to process the ground to be excavated; 2) excavating the foundation and the cement mixing piles together after the age of the cement mixing piles is over, form a slope

This method can indeed break through the allowable excavation slope ratio limit of soft soil foundation, but has the following defects: 1. This method still belongs to slope method excavation in essence, and the mixing pile above the excavation slope line needs to be excavated. If only As a temporary support measure, the economy is poor. 2. Due to the construction technology of the cement mixing pile, the effective length of the pile is only about 10m, and the bottom of the anti-sliding pile of the mixing pile group needs to enter at least 2m below the sliding arc. If the soft soil layer The distribution is deep, and this method cannot be used; 3. The reinforcement capacity of cement mixing piles is limited, and it cannot be used in deep foundation pits with extremely narrow excavation areas

[0007] However, during the construction of the mixing piles, near the inner platform of the Dongjing River embankment, it was found that the emergency flood control stones distributed many years ago were distributed in a large area within a depth range of 5-6m below the ground, such as figure 1 As shown, it is difficult to continue the construction of the mixing pile according to the original plan, and the original design support section is difficult to form within this range, and the construction support cannot be carried out

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