Test Research On Bearing Capacity Characteristics Of Rigid Pile Composite Foundation On The Highly Weathered Rock

The rigid pile composite foundation include high-strength pile, soil and cushion. Most domestic engineerings are of this type when the top of the rigid pile of composite foundation is able to pierce the cushion and the bottom of pile can pierce the soil under load. However, in some areas with shallow-buried rock, when the bearing capacity and deformation of natural foundation can not meet the requirements, it is considered that using the craft of rigid pile composite foundation is appropriate for ground treatment of buildings. The rigid pile falls on the highly weathered rock strata and the rock strata provides end-bearing resistance. By setting reasonable layer of cushion, it can enable rigid pile and soil share building load together. Because of the lack of model test datas and engineering supports, the bearing mechanism and design calculation methods of composite foundation need to be studied.To explore for the bearing capacity characters of the rigid pile composite foundation that the pile-end falls on the highly weathered rock, the article studies on the mechanism of cushion deformation and the relationship between cushion thickness and rigid pile composite foundation based on the indoor model test and outdoor model test. And combined with pratical engineerings, the article study the applicability of the rigid pile composite foundation that the pile-end falls on the highly weathered rock.The main research results are as follows through the test and data analysis.(1) According to the test, the amount of cushion-piercing deformation increase with the increase of cushion thickness in the same condition of pile diameter and load.And the amount of cushion-piercing deformation increase with the decrease of pile diameter in the same condition of cushion thickness and load.(2) According to the test, the thickness of cushion is closely related to the load sharing ratio, stress and bearing capacity mobilized extent of rigid pile and soil. With the increase of cushion thickness, the load sharing ratio and stress of pile in composite foundation decrease. On the opposite, load sharing ratio and stress of soil increase.(3) The rigid pile and soil could constitute composite foundation when the bottom of rigid pile falls on the highly weathered rock. The bearing capacity of the rigid pile composite foundation can be calculated with the formula (7.1.5-2) in 《Technical code for ground treatment of building》(JGJ79-2012)(4) According to the tests, the cushion thickness of rigid pile composite foundation is recommended to adopt (0.4～0.6) D+s and "s"represents the deformation of rigid pile composite foundation of buildings at bearing capacity value. In applications, the cushion thickness is recommended to adopt (0.5～0.75) D.(5) The strength of rigid pile whose body materials is commercial concrete should satisfy the following requirements. And "fcu,k" represents compressive strength standard value of concrete cubes.(6) According to the tests, the deformation of rigid pile composite foundation can be calculated with following formula.And "Ps" represents additional pressure of soil sharing on the base at quasi-permanent combination.