Study On Failure Mode Of Typical Soil-rock Foundation Pit In Jinan And The Support Structure Selection

Based on geological conditions of Jinan,this paper uses plaxis software to analysis failure mode of typical soil-rock foundation pit,research the deformation and force law of composite soil nail wall with micro pile.The main conclusions are as follows:1、Failure modeThe soil and fully weathered rock slope can be regarded as the whole soil layer,The failure mode is the circular sliding surface.For soil,fully weathered rock and strongly weathered rock slope,when slope ratio is larger than 1:0.8,circular sliding failure of soil layer,fully weathered rock stratum and partial strong weathered rock stratum will appear.When the slope ratio is less than 1:0.8,circular sliding failure of soil layer,fully weathered rock stratum will appear and the bottom end of the failure surface is tangent to the interface of the strongly weathered rock stratum with no damage occurs in.For soil,fully weathered rock,strongly weathered rock and medium weathered rock slope,when slope ratio is larger than 1:0.8,circular sliding failure of soil layer,fully weathered rock stratum and partial strong weathered rock stratum will appear.When the slope ratio is less than 1:0.8,circular sliding failure of soil layer,fully weathered rock stratum will appear and the bottom end of the failure surface is tangent to the interface of the strongly weathered rock stratum.The medium weathered rock stratum is always free of damage.2、Compared with pile-anchor support structure,composite soil nail wall with micro pile has smaller pile diameter,higher strength and smaller pile spacing.The deformation control effect is slightly weaker than that of the pile-anchor supporting structure,but its internal force control effect is better.The peak value of internal force occurs when excavating to the middle weathered rock interface while the peak value of deformation occurs when excavating to the bottom of the foundation pit The failure surface is a circular sliding surface in the soil layer and gravel layer The bottom end of failure surface is tangent to the medium weathered rock interface.3、End-suspended pile strctureThe peak value of internal force and deformation occurs when excavating to the middle weathered rock interface.The failure surface is a circular sliding surface in the soil layer,and the bottom end of it is tangent to the soil rock interface.The medium weathered rock stratum is always free of damage.End-suspended pile with embedded depth 1.5m and rock shoulder width 0.5-1m is the construction which is conducive to the internal force and displacement control.